Patent Publication Number: US-11642141-B2

Title: Devices and methods for performing knee arthroplasty

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application is a divisional of U.S. patent application Ser. No. 16/251,636, filed Jan. 18, 2019, entitled DEVICES AND METHODS FOR PERFORMING KNEE ARTHROPLASTY, which application is a continuation of U.S. patent application Ser. No. 13/661,636, filed Oct. 26, 2012, now U.S. Pat. No. 10,201,356, entitled Devices and Methods for Performing Knee Arthroplasty, which claims the benefit of U.S. Provisional Patent Application Ser. No. 61/552,321, filed Oct. 27, 2011, the contents of each application incorporated herein by reference in their entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to surgical devices and methods, and more particularly relates to orthopaedic devices and methods for performing knee arthroplasty. 
     BACKGROUND 
     Total knee arthroplasty procedures often require the sacrifice of the anterior cruciate ligament (ACL) and/or the posterior cruciate ligament (PCL). As such, total knee prostheses often include structures and mechanisms that attempt to provide the same or similar functions provided by the ACL and PCL. However, these conventional total knee prostheses may not fully replicate the normal proprioception, kinematics, and/or biomechanical functions provided by natural ligaments. Bicruciate retaining knee replacements have been used in the past, but were associated with problems of knee stiffness and implant failure that were likely attributable to inadequate implant design, instrumentation, and/or implantation technique. Accordingly, there is a desire in some cases to preserve functioning cruciate ligaments in young and active patients who require knee joint replacement, to maintain a natural feeling, and normal biomechanical function and performance of the knee after total knee replacement. There is also a desire for more efficient and accurate devices and methods for preparing femurs and tibias for bicruciate retaining implants (i.e., ACL and PCL preserving implants), as well as other types of knee implants, since many knee procedures (especially, but not limited to, bicruciate retaining procedures) often utilize devices and methods that are less than ideal. 
     Thus, there remains a need to provide improved devices and methods for performing knee arthroplasty. The present invention satisfies this need and provides other benefits and advantages in a novel and unobvious manner. 
     SUMMARY 
     While the actual nature of the invention covered herein can only be determined with reference to the claims appended hereto, certain forms of the invention that are characteristic of the embodiments disclosed herein are described briefly as follows. 
     Devices and methods for performing knee arthroplasty procedures are provided, including device and methods used in association with total knee arthroplasty (TKA) procedures and techniques including, for example, procedures and techniques such as bicruciate retaining arthroplasty, as well as other procedures and techniques described herein. 
     In one form of the invention, instrumentation is provided for resection of the proximal tibia. The instrumentation includes a mounting base adapted for coupling to the proximal tibia, a cutting guide extending laterally from the mounting base and including a lateral guide channel arranged along a cutting plane and dimensioned to guide a cutting device generally along the cutting plane to form a resection cut in the proximal tibia, and an elongate pin interconnected with a mounting portion of the instrument and dimensioned for receipt within an opening in the proximal tibia, the elongate pin positioned adjacent the lateral guide channel within the cutting plane to thereby limit lateral displacement of the cutting device within the lateral guide channel along the cutting plane. 
     In another form of the invention, instrumentation is provided for resection of the proximal tibia. The instrumentation includes a cutting device, a mount device configured for attachment to the proximal tibia and including a generally planar reference member extending along a reference plane, a mounting base releasably lockable to the planar reference member of the mount device, a cutting guide extending laterally from the mounting base and including a lateral guide channel arranged along a cutting plane and dimensioned to guide the cutting device generally along the cutting plane to form a resection cut in the proximal tibia, and an elongate pin pivotally connected to either the mounting base or the cutting guide and configured for pivotal movement generally along the cutting plane, the elongate pin dimensioned for receipt within an opening in the proximal tibia, the elongate pin positioned adjacent the lateral guide channel within the cutting plane to thereby limit lateral displacement of the cutting device within the lateral guide channel along the cutting plane. 
     In another form of the invention, a method is provided for resection of the proximal tibia. The method includes the steps of providing an instrument including a cutting guide and an elongate pin, the cutting guide defining a lateral guide channel extending along a cutting plane, the elongate pin interconnected with a mounting portion of the instrument and positioned adjacent the lateral guide channel within the cutting plane, inserting the elongate pin into an opening in the proximal tibia, mounting the instrument to the proximal tibia, guiding a cutting device through the lateral guide channel generally along the cutting plane to form a resection cut in the proximal tibia, and limiting displacement of the cutting device within the lateral guide channel laterally beyond the elongate pin to control a lateral depth of the resection cut in the proximal tibia. 
     It is one object of the present invention to provide improved orthopaedic devices and methods for performing knee arthroplasty. Further embodiments, forms, features, aspects, benefits, objects, and advantages of the present invention will become apparent from the detailed description and figures provided herewith. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    illustrates a distal portion of a femur bone. 
         FIG.  2    illustrates a proximal portion of a tibia bone. 
         FIG.  3    illustrates a resected distal portion of a femur bone. 
         FIG.  4    illustrates a femoral trial component attached to the resected distal portion of the femur bone of  FIG.  3   . 
         FIG.  5    illustrates a datum block according to one form of the invention, as shown in relation to the proximal tibia. 
         FIG.  6 A  illustrates a left side view of the datum block of  FIG.  5   . 
         FIG.  6 B  illustrates a right side view of the datum block of  FIG.  5   . 
         FIG.  6 C  illustrates an anterior end view of the datum block of  FIG.  5   . 
         FIG.  6 D  illustrates a bottom view of the datum block of  FIG.  5   . 
         FIG.  6 E  illustrates a top view of the datum block of  FIG.  5   . 
         FIG.  6 F  illustrates a posterior end view of the datum block of  FIG.  5   . 
         FIG.  7 A  illustrates an unlocked configuration of the datum block of  FIG.  5   . 
         FIG.  7 B  illustrates a locked configuration of the datum block of  FIG.  5   . 
         FIG.  8 A  illustrates one embodiment of a locking mechanism used in association with the datum block of  FIG.  7 A , as shown in an unlocked configuration. 
         FIG.  8 B  illustrates the locking mechanism of  FIG.  8 A , as shown in a locked configuration. 
         FIG.  9    illustrates the datum block of  FIG.  5    provisionally attached to the proximal tibia by a provisional attachment pin. 
         FIG.  10    illustrates the datum block of  FIG.  5    terminally attached to the proximal tibia by terminal attachment pins. 
         FIG.  11    illustrates a depth stylus according to one form of the invention, as shown attached to the datum block of  FIG.  5    in relation to the proximal tibia. 
         FIG.  12    illustrates a perspective view of the depth stylus of  FIG.  11   . 
         FIG.  13 A  illustrates a left side view of the depth stylus of  FIG.  11   . 
         FIG.  13 B  illustrates a right side view of the depth stylus of  FIG.  11   . 
         FIG.  13 C  illustrates a bottom view of the depth stylus of  FIG.  11   . 
         FIG.  13 D  illustrates an anterior end view of the depth stylus of  FIG.  11   . 
         FIG.  14    illustrates one embodiment of an adjustment mechanism used in association with the depth stylus of  FIG.  11   . 
         FIG.  15    illustrates a second operational position of the depth stylus of  FIG.  11   . 
         FIG.  16 A  illustrates an alternative operational configuration of the depth stylus of  FIG.  11   , as shown in a first operational position in relation to the proximal tibia. 
         FIG.  16 B  illustrates an alternative operational configuration of the depth stylus of  FIG.  11   , as shown in a second operational position in relation to the proximal tibia. 
         FIG.  17 A  illustrates an eminence stylus according to one form of the invention, as shown attached to the datum block of  FIG.  5    in relation to the proximal tibia. 
         FIG.  17 B  illustrates an eminence stylus according to another form of the invention, as shown attached to the proximal tibia. 
         FIG.  18 A  illustrates a left side view of the eminence stylus of  FIG.  17 A . 
         FIG.  18 B  illustrates a right side view of the eminence stylus of  FIG.  17 A . 
         FIG.  18 C  illustrates an anterior end view of the eminence stylus of  FIG.  17 A . 
         FIG.  18 D  illustrates a top view of the eminence stylus of  FIG.  17 A . 
         FIG.  18 E  illustrates a bottom view of the eminence stylus of  FIG.  17 A . 
         FIG.  18 F  illustrates a posterior end view of the eminence stylus of  FIG.  17 A . 
         FIG.  19 A  illustrates a perspective view of the eminence stylus of  FIG.  17 A  in a first operational position. 
         FIG.  19 B  illustrates a perspective view of the eminence stylus of  FIG.  17 A  in a second operational position. 
         FIG.  19 C  illustrates a perspective view of the eminence stylus of  FIG.  17 A  in a third operational position. 
         FIG.  19 D  illustrates a top view of the first operational position of the eminence stylus of  FIG.  19 A . 
         FIG.  19 E  illustrates a top view of the second operational position of the eminence stylus of  FIG.  19 B . 
         FIG.  20 A  illustrates the eminence stylus of  FIG.  17 A  in relation to the datum block of  FIG.  5    in preparation for medial resection of the proximal tibia. 
         FIG.  20 B  illustrates the eminence stylus of  FIG.  17 A  locked to the datum block of  FIG.  5    and pinned to the proximal tibia in relation to the medially resected proximal tibia. 
         FIG.  20 C  illustrates the datum block of  FIG.  5    in relation to the medially resected proximal tibia with the eminence stylus of  FIG.  17 A  removed from the datum block. 
         FIG.  21 A  illustrates an anterior end view of an eminence stylus according to another form of the invention. 
         FIG.  21 B  illustrates a top view of the eminence stylus of  FIG.  21 A . 
         FIG.  22    illustrates the eminence stylus of  FIGS.  21 A and  21 B  locked to the datum block of  FIG.  5   . 
         FIG.  23    illustrates a graduated tibial pin according to one form of the invention. 
         FIG.  24 A  illustrates the graduated tibial pin of  FIG.  23   , as shown relative to the eminence stylus of  FIG.  17 A  locked to the datum block of  FIG.  5   , all shown in relation to the proximal tibia. 
         FIG.  24 B  illustrates the graduated tibial pin of  FIG.  23   , as shown engaged with the eminence stylus and anchored in the proximal tibia. 
         FIG.  24 C  illustrates the graduated tibial pin of  FIG.  23   , as shown engaged with the eminence stylus and anchored in the proximal tibia in relation to the medially resected proximal tibia. 
         FIG.  25 A  illustrates a superior view of  FIG.  24 A . 
         FIG.  25 B  illustrates a superior view of  FIG.  24 B . 
         FIG.  25 C  illustrates a superior view of  FIG.  24 C . 
         FIG.  26    illustrates a lateral cut guide according to one form of the invention, as shown attached to the datum block of  FIG.  5   . 
         FIG.  27    illustrates a perspective view of the lateral cut guide of  FIG.  26   . 
         FIG.  28 A  illustrates a top view of the lateral cut guide of  FIG.  27   . 
         FIG.  28 B  illustrates an anterior view of the lateral cut guide of  FIG.  27   . 
         FIG.  29 A  illustrates a superior view of  FIG.  26   . 
         FIG.  29 B  illustrates a superior view of  FIG.  26    following lateral resection of the proximal tibia and removal of the lateral bone fragment. 
         FIG.  30    illustrates a saw capture block according to one form of the invention, as shown attached to the datum block of  FIG.  5   . 
         FIG.  31    illustrates a perspective view of the saw capture block of  FIG.  30   . 
         FIG.  32 A  illustrates an anterior end view of the saw capture block of  FIG.  31   . 
         FIG.  32 B  illustrates a bottom view of the saw capture block of  FIG.  31   . 
         FIG.  33 A  illustrates a left side view of  FIG.  30   . 
         FIG.  33 B  illustrates a top view of  FIG.  30   . 
         FIG.  33 C  illustrates an anterior end view of  FIG.  30   . 
         FIG.  34    illustrates a recut block according to one form of the invention, as shown terminally attached to the proximal tibia by terminal attachment pins in relation to the medially resected proximal tibia. 
         FIG.  35    illustrates a side view of  FIG.  34   . 
         FIG.  36 A  illustrates a left side view of the recut block of  FIG.  34   . 
         FIG.  36 B  illustrates a right side view of the recut block of  FIG.  34   . 
         FIG.  36 C  illustrates an anterior end view of the recut block of  FIG.  34   . 
         FIG.  36 D  illustrates a bottom view of the recut block of  FIG.  34   . 
         FIG.  36 E  illustrates a top view of the recut block of  FIG.  34   . 
         FIG.  36 F  illustrates a posterior end view of the recut block of  FIG.  34   . 
         FIG.  37 A  illustrates an unlocked configuration of the recut block of  FIG.  34   . 
         FIG.  37 B  illustrates a locked configuration of the recut block of  FIG.  34   . 
         FIG.  38 A  illustrates one embodiment of a locking mechanism used in association with the recut block of  FIG.  37 A , as shown in an unlocked configuration. 
         FIG.  38 B  illustrates the locking mechanism of  FIG.  38 A , as shown in a locked configuration. 
         FIG.  39 A  illustrates one embodiment of a threaded member used in association with the locking mechanism of  FIGS.  38 A and  38 B . 
         FIG.  39 B  illustrates one embodiment of a gripper member used in association with the locking mechanism of  FIGS.  38 A and  38 B . 
         FIG.  39 C  illustrates a bottom view the locking mechanism of  FIGS.  38 A and  38 B . 
         FIG.  39 D  illustrates an end view the locking mechanism of  FIGS.  38 A and  38 B . 
         FIG.  40    illustrates a tibia size gauge according to one form of the invention, as shown relative to the datum block of  FIG.  5    and the eminence stylus of  FIG.  17 A , all shown in relation to the proximal tibia. 
         FIG.  41 A  illustrates a first operational position of the tibia size gauge of  FIG.  40   , as shown in relation to the eminence stylus and the unresected medial region of the proximal tibia. 
         FIG.  41 B  illustrates the tibia size gauge of  FIG.  40   , as shown in relation to a medial portion of a tibial baseplate. 
         FIG.  41 C  illustrates the tibial baseplate of  FIG.  41 B  engaged to the resected proximal tibia. 
         FIG.  42 A  illustrates a second operational position of the tibia size gauge of  FIG.  40   , as shown in relation to the eminence stylus and the unresected lateral region of the proximal tibia. 
         FIG.  42 B  illustrates the tibia size gauge of  FIG.  40   , as shown in relation to a lateral portion of a tibial baseplate. 
         FIG.  42 C  illustrates the tibial baseplate of  FIG.  42 B  engaged to the resected proximal tibia. 
         FIG.  43    illustrates a tibia size gauge according to another form of the invention, including a gauge pointer engaged with another embodiment of an eminence stylus locked to the datum block of  FIG.  5    in relation to the proximal tibia. 
         FIG.  44 A  illustrates a perspective view of the gauge pointer of  FIG.  43   . 
         FIG.  44 B  illustrates a perspective view of the eminence stylus of  FIG.  43   . 
         FIG.  45 A  illustrates an anterior end view of the tibia size gauge of  FIG.  43   . 
         FIG.  45 B  illustrates a top view of the tibia size gauge of  FIG.  43   , as shown in relation to the proximal tibia. 
         FIG.  46    illustrates a tibia rotation gauge according to one form of the invention. 
         FIG.  47 A  illustrates the eminence stylus of  FIG.  17 A  attached to the datum block of  FIG.  5   , as shown in a first misaligned rotational orientation relative to the proximal tibia. 
         FIG.  47 B  illustrates the eminence stylus of  FIG.  17 A  attached to the datum block of  FIG.  5   , as shown in a second misaligned rotational orientation relative to the proximal tibia. 
         FIG.  48    illustrates the tibia rotation gauge of  FIG.  46    engaged with the eminence stylus and the anterior surface of the proximal tibia to correct the misaligned rotational orientations shown in  FIGS.  47 A and  47 B . 
         FIG.  49    illustrates the tibia rotation gauge of  FIG.  46    engaged with the anterior surface of the proximal tibia to correct the misaligned rotational orientations shown in  FIGS.  47 A and  47 B . 
         FIG.  50    illustrates the tibia rotation gauge of  FIG.  46    engaged with an anterior surface of a tibial baseplate. 
         FIG.  51    illustrates a schematic illustration of the tibia rotation gauge of  FIG.  46    engaged with an anterior surface of a set of tibial baseplates having varying sizes. 
         FIG.  52    illustrates a perspective view of a tibia insert trial according to one form of the invention. 
         FIG.  53    illustrates an exploded view of the tibia insert trial of  FIG.  52   . 
         FIG.  54    illustrates a bottom view of the main body component of the tibia insert trial of  FIG.  52   . 
         FIG.  55 A  illustrates a femoral trial component attached to the resected distal femur in relation to the medially resected proximal tibia. 
         FIG.  55 B  illustrates a femoral trial component attached to the resected distal femur in relation to the medially and laterally resected proximal tibia. 
         FIG.  56 A  illustrates a first operational position of the tibia insert trial of  FIG.  52    inserted between the femoral trial component and the medially resected proximal tibia of  FIG.  55 A . 
         FIG.  56 B  illustrates a second operational position of the tibia insert trial of  FIG.  52    inserted between the femoral trial component and the medially and laterally resected proximal tibia of  FIG.  55 B . 
         FIG.  57    illustrates a perspective view of a tibia size template according to one form of the invention. 
         FIG.  58 A  illustrates a superior view of the tibia size template of  FIG.  57   . 
         FIG.  58 B  illustrates an inferior view of the tibia size template of  FIG.  57   . 
         FIG.  59 A  illustrates a first operational position of the tibia size template of  FIG.  57   , as shown in relation to the medially resected proximal tibia. 
         FIG.  59 B  illustrates a second operational position of the tibia size template of  FIG.  57   , as shown in relation to the medially and laterally resected proximal tibia. 
         FIG.  60 A  illustrates a superior view of  FIG.  59 A . 
         FIG.  60 B  illustrates a superior view of  FIG.  59 B . 
         FIG.  61 A  illustrates a perspective view of an anterior chisel according to one form of the invention. 
         FIG.  61 B  illustrates another perspective view of the anterior chisel of  FIG.  61 A . 
         FIG.  62 A  illustrates the anterior chisel shown in  FIG.  61 A  in relation to the medially and laterally resected proximal tibia. 
         FIG.  62 B  illustrates the anterior chisel shown in  FIG.  61 B  in relation to the medially and laterally resected proximal tibia. 
         FIG.  63 A  illustrates a left side view of  FIG.  62 A . 
         FIG.  63 B  illustrates a left side view of  FIG.  62 B . 
         FIG.  64 A  illustrates a perspective view of the proximal tibia following formation of a vertical cut into the tibial eminence resulting from the cutting step shown in  FIGS.  62 A and  63 A . 
         FIG.  64 B  illustrates a perspective view of the proximal tibia following formation of a horizontal cut into the tibial eminence resulting from the cutting step shown in  FIGS.  62 B and  63 B . 
         FIG.  64 C  illustrates a perspective view of the proximal tibia following formation of the vertical and horizontal cuts into the tibial eminence and removal of the superior/anterior portion of the tibial eminence. 
         FIG.  65    illustrates a perspective view of a keel cavity formation instrument according to one form of the invention. 
         FIG.  66    illustrates an exploded view of the keel cavity formation instrument of  FIG.  65   . 
         FIG.  67    illustrates a left side view of the keel cavity formation instrument of  FIG.  65   . 
         FIG.  68    illustrates a tibial baseplate trial for use in association with the keel cavity formation instrument of  FIG.  65   , as shown engaged with the medially and laterally resected proximal tibia and with the superior/anterior portion of the tibial eminence removed from the proximal tibia. 
         FIG.  69    illustrates the keel cavity formation instrument of  FIG.  65    engaged with the tibial baseplate trial of  FIG.  68    in relation to the distal femur and the proximal tibia. 
         FIG.  70 A  illustrates a first operational position of the keel cavity formation instrument of  FIG.  65    for forming medial and lateral keel slots in the medially and laterally resected surfaces of the proximal tibia. 
         FIG.  70 B  illustrates a second operational position of the keel cavity formation instrument of  FIG.  65    for forming an anterior keel slot in the anterior resected surface of the proximal tibia. 
         FIG.  70 C  illustrates a third operational position of the keel cavity formation instrument of  FIG.  65    for forming clearance openings in the proximal tibia at locations between the medial and lateral keel slots and the anterior keel slot. 
         FIG.  71 A  illustrates a superior view of the proximal tibia following formation of the medial and lateral keel slots in the medially and laterally resected surfaces of the proximal tibia. 
         FIG.  71 B  illustrates a superior view of the proximal tibia following formation of the anterior keel slot in the anterior resected surface of the proximal tibia. 
         FIG.  71 C  illustrates a superior view of the proximal tibia following formation of the clearance openings in the proximal tibia at locations between the medial and lateral keel slots and the anterior keel slot. 
         FIG.  72 A  illustrates a perspective view of an anterior tibial gauge according to one form of the invention. 
         FIG.  72 B  illustrates another perspective view of the anterior tibial gauge of  FIG.  72 A . 
         FIG.  73 A  illustrates a perspective view of a tibial baseplate trial according to one form of the invention engaged with the resected proximal tibia. 
         FIG.  73 B  is a superior view of  FIG.  73 A . 
         FIG.  74 A  illustrates a perspective view of the anterior tibial gauge of  FIG.  72 A  engaged with the tibial baseplate trial of  FIG.  73 A  in relation to the resected tibial eminence of the proximal tibia. 
         FIG.  74 B  is a superior view of  FIG.  74 A . 
     
    
    
     DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS 
     For the purpose of promoting an understanding of the principles of the present invention, reference will now be made to the embodiments illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is hereby intended. Any alterations and further modifications in the described embodiments, and any further applications of the principles of the invention as described herein are contemplated as would normally occur to one skilled in the art to which the invention relates. 
     The following descriptions and illustrations of non-limiting embodiments of the present invention are exemplary in nature, it being understood that the descriptions and illustrations related thereto are in no way intended to limit the inventions disclosed herein and/or their applications and uses. Certain features and details associated with other embodiments of devices and methods that may be used in association with the present invention are found in commonly owned U.S. patent application Ser. No. 12/790,137 filed on May 28, 2010, which claims the benefit of U.S. Provisional Patent Application Ser. No. 61/182,435 filed May 29, 2009 and U.S. Provisional Patent Application Ser. No. 61/299,835 filed Jan. 29, 2010, the contents of each application incorporated herein by reference in their entirety. 
     In total knee arthroplasty procedures, various devices and methods are used in the preparation of a distal portion of a femur for receipt of a femoral implant, and in the preparation of a proximal portion of a tibia for receipt of a tibial implant. The primary focus of this application is on devices and methods used in the preparation of the proximal tibia. However, other devices and methods used in the preparation of a distal femur which may also be used in association with the present invention are found in U.S. patent application Ser. No. 12/790,137, the contents of which have been incorporated herein by reference in their entirety. 
     There is a strong relationship between femoral attachment locations of soft tissues and the articulation between the tibia and the femur. As a general matter, it can be shown that for knee implant designs relying more on contrived means of kinematic control and stability rather than on the native soft tissue structures, kinematic patient outcomes are less sensitive to mismatch between, for instance, the inferior/superior position of the native femoral articular surfaces and the implanted femoral articular surfaces, although such mismatches can still be significant in some instances. However, when more native structures are preserved in order to provide kinematic control and stability (e.g., with bi-cruciate retaining implants), the preservation of the femoral joint line can sometimes become more important to patient outcome. 
     Currently, the common practice is to favor resection of the distal femur to the level of the trochlea, rather than by measuring a resection depth from the medial femoral condyle. However, it may be preferable in at least some cases to utilize methods and apparatus that counteract any tendency to resect the distal femur at a level other than the thickness of the distal femoral implant. For example, it may be preferable to resect an amount equivalent to the thickness of the distal femoral implant as measured from the distal medial (and/or lateral) condyle, which may better account for the mesial attachment sites on the femur of the posterior and/or anterior cruciate ligaments. It may also be preferable in at least some cases to utilize methods and apparatus that allow for early trialing and assessment of extension space and laxity. 
     Some methodologies associated with total knee arthroplasty procedures also reduce complications by not solving for femoral and tibial degrees of freedom simultaneously, but instead preparing the femur first and then subsequently preparing the tibia. By completing all of the femoral resections prior to the tibial resections, the surgeon is provided with a fixed set of values from which he or she can determine the remaining tibial degrees of freedom. Another benefit of preparing the femur first provided by some of the methodologies associated with total knee arthroplasty procedures is that they ensure proper kinematics. For proper kinematics, the femoral implant should generally conform to and articulate with the native anatomy well (e.g., natural soft tissues and native tibial cartilage). By separating the femoral resection steps from the tibial resection steps, the surgeon has no other input variables with which to make femoral resection decisions other than input variables provided by the native femoral anatomy. A further benefit of preparing the distal femur before the proximal tibia is that a surgeon still has the flexibility of performing a posterior stabilized, cruciate retaining surgery or a bicruciate retaining surgery with little or no time penalty or bone loss, even after the femoral side has been prepared. Many of the devices and methods described below, however, are not limited to only femur first techniques, or techniques that achieve all of the above benefits. 
     The following description and figures set forth a total knee arthroplasty procedure including preparation of the distal portion of the femur first, followed by subsequent preparation of the proximal portion of the tibia. By way of example, a distal portion  10  of the femur is shown in  FIG.  1   , and a proximal portion  12  of the tibia is shown in  FIG.  2    illustrating the tibial eminence region  14 , the medial tibial plateau region  16   a , and the lateral tibial plateau region  16   b , each shown prior to preparation for receipt of femoral and tibial implant components. 
     As should be appreciated, the distal femur  10  may be prepared using various cutting instruments, trials, and other devices, examples of which are disclosed in U.S. patent application Ser. No. 12/790,137, the contents of which have been incorporated herein by reference in their entirety. One example of a prepared distal femur  10  is illustrated in  FIG.  3   . Additionally,  FIG.  4    illustrates one embodiment of a femoral trial component  18  that may be attached to the prepared distal femur  10  prior to preparation of the proximal tibia  12 . However, it should be understood that the shape and configuration of the prepared distal femur  10  and the femoral trial component  18  are exemplary in nature and do not limit the scope of the invention. 
     Following preparation of the distal femur  10 , the proximal tibia  12  is prepared using the following devices and methods according to various embodiments of the present invention. However, it should be understood that the devices and methods of the present invention may be used in total knee arthroplasty procedures including simultaneous or alternating preparation of the distal femur  10  and the proximal tibia  12 , or in total knee arthroplasty procedures where preparation of the proximal tibia  12  occurs first followed by preparation of the distal femur  10 . 
     One problem faced when performing bicruciate-retaining TKA procedures that is of potential significance to at least some of the embodiments described herein is the complexity of the tibial resections. This complexity stems from at least two factors relating to the preservation of the cruciate ligaments. 
     A first factor is that there are more important degrees of freedom relating to bicruciate-retaining arthroplasty procedures than is apparent for typical posterior-stabilized or PCL-retaining arthroplasty procedures. For instance, in total knee arthroplasty, objects such as resection guides and other instrumentation in three-dimensional space have six degrees of freedom, including three translational degrees of freedom and three rotational degrees of freedom. At least four additional variables or “forms” may also apply in TKA procedures, including femoral implant size, tibial implant size, tibial insert thickness, and tibial insert articular shape. For a posterior-stabilized or cruciate-retaining arthroplasty procedure, only three degrees of freedom (one translational and two rotational) are usually considered important. For many, although not necessarily all, bicruciate-retaining arthroplasty procedures, there are at least three additional degrees of freedom which are considered important (i.e., one translational, one rotational, and one “form”). These three additional degrees of freedom arise due to constraints imposed by preservation of the tibial eminence to which the cruciate ligaments are attached. 
     A second factor of potential relevance is that bicruciate retaining knee arthroplasty requires precise surgical techniques. The trade off with a bicruciate-retaining technique is that of an increased risk of mechanical complications such as stiffness, instability, fracture or implant loosening due to the complexity of the surgery, in exchange for increased postoperative patient mobility and function. A bicruciate retaining technique therefore requires more decisions to fix additional degrees of freedom, as well as a greater degree of decision accuracy in order to mitigate the increased risks as compared to conventional posterior stabilized or posterior cruciate retaining total knee arthroplasty procedures. 
     Properly controlling and managing the abovementioned degrees of freedom and other factors during surgery is one of the keys to a clinically and commercially successful bicruciate retaining arthroplasty. Clinical success often depends on the ability of a surgeon to accurately and properly implant a well-designed prosthesis in order to achieve the advantages provided by the well-designed prosthesis. Commercial success often depends on the ability of the surgeon to accurately and properly implant a well-designed prosthesis with confidence, reproducibility and speed. Some, although not necessarily all, of the embodiments described herein address these concerns. 
     Of all knee arthroplasty procedures, the risks associated with tibial resection degrees of freedom (i.e., varus/valgus angle, posterior slope angle, and resection depth) are greater for bicruciate-retaining arthroplasty procedures than for posterior-stabilized or posterior cruciate-retaining procedures. This is because varus/valgus angle, posterior slope angle, and resection depth directly affect the operation of the cruciates in guiding proprioceptive joint motion. Moreover, the risks associated with the additional degrees of freedom specific to bicruciate retaining arthroplasty (particularly internal/external rotation angle and medial/lateral position of the tibial plateau and eminence resections) can include severe penalties for error, including but not limited to compromised structural integrity of the tibial eminence, compromised joint motion, and/or compromised cortical rim coverage. Errors associated with any of the five degrees of freedom associated with a bicruciate retaining procedure may present a surgeon with complex judgment decisions (i.e., to favor achieving the best possible cortical coverage over providing maximum preservation of the tibial eminence and its anterior and posterior cruciate ligament attachment sites). Such judgment decisions may include, for instance, whether or not to re-cut a bone to correct a perceived error, or to simply let the error remain. Re-cutting decisions contribute to an increase in both time and complexity, and may subsequently increase the likelihood of propagating further errors. 
     Embodiments of the bicruciate retaining total knee arthroplasty techniques and instrumentation described herein present surgeons with a truly complex surgery in a simplified format through thoughtful organization, reduction, and readily accessible information. As will be discussed herein, these embodiments may provide, at least in part, improved devices and methods for preparing a proximal tibia during total knee arthroplasty procedures. The devices and methodologies described below can be generally divided into three stages including: controlling degrees of freedom, making resections, and performing finishing steps. 
     As will be discussed in greater detail below, controlling degrees of freedom can include one or more of the steps of: roughly setting tibial resection depth, setting a neutral (or reference) varus/valgus angle for the medial and lateral tibial plateau resections, setting a neutral (or reference) posterior slope for the medial and lateral tibial plateau resections, fine-tuning the posterior slope angle and/or varus/valgus angle for the medial and lateral tibial plateau resections, setting medial-lateral positioning of the medial and lateral eminence bone cuts, setting an internal-external rotation angle for the medial and lateral eminence bone cuts (if desirable), determining an appropriately-sized tibial eminence width (related to implant size), and fine tuning the depth for both the medial and lateral tibial plateau resections. As will also be discussed in greater detail below, making resections can generally include one or more of the steps of making a medial tibial plateau resection, making medial and lateral tibial eminence bone cuts, performing a medial plateau balance check, performing a lateral tibial plateau resection, assessing fit of the implant to bone, and performing a trial reduction to assess range of motion, joint stability, and soft tissue tension. Additionally, finishing steps can generally include one or more of the steps of making an anterior eminence bone cut and an anterior tibial plateau resection to remove an anterior block portion of the tibial eminence, removing bone at eminence corners, assessing fit of the implant to bone, punching one or more keel cavities or openings into the cancellous bone of the proximal tibia, and implanting a tibial component. Various devices and instruments for performing these steps and procedures will now be discussed in detail below. 
     A. Datum Block 
     Referring to  FIG.  5   , show therein is a datum or alignment block  100  according to one form of the present invention, as shown in relation to the proximal tibia  12 . The datum block  100  can be used as a fundamental instrument to provide a neutral/reference tibial foundation to which other devices or instruments may be engaged to and referenced from. The datum block  100  generally includes a main body  102  configured for attachment to the proximal tibia  12 , a reference bench or table  104  extending from the main body  102  and configured for removable attachment of various devices/instruments to the datum block  100 , and a locking or pinch force mechanism  106  associated with the main body  102  and configured to removably lock other devices/instruments to the datum block  100 . 
     As shown in  FIG.  5   , in the illustrated embodiment, the datum block  100  is configured to engage and support an extramedullary alignment rod or “up rod”  108  having a central longitudinal axis L. In one embodiment, one end of the alignment rod  108  is removably attached to the main body  102  of the datum block  100 . However, other embodiments are also contemplated wherein an end of the alignment rod  108  is removably or permanently attached to the main body  102  or other portions of the datum block  100 . In still other embodiments, the opposite end of the alignment rod  108  may be removably attached to a mounting device associated with the patient&#39;s ankle to provide additional support and alignment capabilities. As should be appreciated, the alignment rod  108  may be aligned with axes and/or other features associated with the proximal tibia  12  to correspondingly align the datum block  100  (and other devices and instruments attached to the datum block  100 ) with such axes/features and/or other anatomic structures. For example, in some cases it may be desirable to roughly align the central longitudinal axis L of the alignment rod  108  along the anatomic and/or mechanical axis  13  of the tibia (in one or both of the sagittal and coronal planes) at the tubercle of the proximal tibia  12 , while offsetting the datum block  100  from the tubercle of the proximal tibia  12 . Other alignment techniques and procedures are also contemplated as falling within the scope of the present invention, many of which would occur to one having ordinary skill in the art. In the illustrated embodiment, the alignment rod  108  has a non-circular transverse cross section, and more specifically has at least one flat section for constraining rotation. However, in other embodiments, the alignment rod  108  may be provided with other suitable shapes and configurations, including a circular transverse cross section. 
     Referring collectively to  FIGS.  6 A- 6 F  in combination with  FIG.  5   , shown therein are further details associated with the datum block  100 . In the illustrated embodiment, the main body  102  of the datum block  100  includes a superior portion  110  and an inferior portion  130 . In one embodiment, the superior and inferior portions  110 ,  130  are formed unitarily with one another to define a single-piece monolithic structure. However, in other embodiments, the superior and inferior portions  110 ,  130  may be formed separately and coupled together to define an integrated multi-piece structure. 
     In the illustrated embodiment, the superior portion  110  of the main body  102  of the datum block  100  defines a substantially flat/planar superior surface  112 , a groove or indicia  114  extending along the planar superior surface  112  in an anterior-posterior direction, and a cavity  116  ( FIGS.  5  and  6 D ) extending through the superior portion  110  from the planar superior surface  112  in a superior-inferior direction. In one embodiment, the groove/indicia  114  is generally aligned with the central longitudinal axis L of the alignment rod  108  and provides a visual indication or marker that may be aligned with the center of the proximal tibia  12  (i.e., alignable with the center of the tibial eminence  14 ) to roughly locate the datum block  100  in the appropriate position and orientation relative to the proximal tibia  12 . The superior portion  110  of the main body  102  further defines an elongate pin-receiving slot  120  extending therethrough in an anterior-posterior direction and having a slot length/extending generally in a superior-inferior direction and a slot width w extending in a medial-lateral direction. The superior portion  110  also defines a plurality of pin-receiving openings  122  extending therethrough generally in an anterior-posterior direction. As will be discussed in further detail below, the elongate slot  120  is sized and configured for receipt of a provisional attachment pin or fastener  190  configured to provisionally attach the datum block  100  to the proximal tibia  12 , and the openings  122  are each sized and configured for receipt of a terminal attachment pin or fastener  196  configured to terminally attach the datum block  100  to the proximal tibia  12 . 
     In the illustrated embodiment, the inferior portion  130  of the main body  102  of the datum block  100  defines a first passage  132  extending partially therethrough from an inferior surface in an inferior-superior direction and having an inner cross section corresponding to the outer cross section of the alignment rod  108  ( FIG.  6 D ). The inferior portion  130  of the main body  102  further defines a second passage  134  extending partially therethrough from an anterior end surface in an anterior-posterior direction and communicating with the first passage  132  ( FIGS.  5  and  6 C ). As illustrated in  FIG.  6 D , the first passage  132  is sized and configured to receive an end portion of the alignment rod  108  therein. As illustrated in  FIG.  6 C , the second passage  134  is at least partially threaded and is configured for threaded engagement with a set screw or fastener  136  having an end portion that engages the alignment rod  108  to retain the alignment rod  108  within the first passage  132 . As further illustrated in  FIG.  6 D , the inferior portion  130  of the main body  102  also defines a visualization opening  138  positioned adjacent the first passage  132  and communicating with the second passage  134  to provide access to the second passage  134  and visualization of the set screw  136 . As also illustrated in  FIG.  6 D , the inferior portion  130  of the main body  102  also defines an aperture  140  positioned adjacent the anterior surface of the inferior portion  130  and sized and configured for receipt of a retention pin  142  that serves to prevent the set screw  136  from backing entirely out of the second passage  134 . As illustrated in  FIG.  6 B , a posteriorly-facing surface of the inferior portion  130  of the main body  102  defines a radially contoured groove  144  extending along a generally uniform radius relative to a central pivot axis C and terminating at an end surface  146 , the purpose of which will be discussed below. 
     As indicated above, the datum block  100  includes a reference bench or table  104  extending from the main body  102  and configured for removable attachment of various devices/instruments to the datum block  100 . In the illustrated embodiment, the reference bench  104  is formed unitarily with the superior portion  110  of the main body  102  to define a single-piece monolithic structure. However, in other embodiments, the reference bench  104  may be formed separately from the main body  102  and coupled to the superior portion  110  to define an integrated multi-piece structure. As shown in  FIG.  6 B , in the illustrated embodiment, the reference bench  104  has a non-rectangular trapezoidal-shaped configuration defining a narrowing or tapered width extending away from the main body  102  in a medial-lateral direction. However, other suitable shapes and configurations of the reference bench  104  are also contemplated as falling within the scope of the present invention. 
     As shown in  FIGS.  6 A- 6 C , the reference bench  104  defines a substantially flat/planar superior surface  150  and a substantially flat/planar inferior surface  152 , with the planar superior and inferior surfaces  150 ,  152  preferably arranged generally parallel with one another, although non-parallel arrangements of the planar superior and inferior surfaces  150 ,  152  are also contemplated. Additionally, the planar inferior surface  152  of the reference bench  104  is positioned opposite the planar superior surface  112  of the main body  102  to thereby define a space or gap  154  therebetween ( FIGS.  6 A- 6 C ) sized and configured for receipt of plate-like portions of other devices and instruments to be connected with the datum block  100 , details of which will be set forth below. In the illustrated embodiment, the planar inferior surface  152  of the reference bench  104  is preferably arranged generally parallel with the planar superior surface  112  of the main body  102 , although non-parallel arrangements of the opposing surfaces are also contemplated. In the illustrated embodiment, the reference bench  104  also defines a groove or indicia  156  extending along the planar superior surface  150  in an anterior-posterior direction. The groove/indicia  156  is preferably arranged generally parallel with the groove/indicia  114  extending along the planar superior surface  112  of the main body  102 . In one embodiment, the groove/indicia  156  provides a general visual indication or marker of the location of the vertical cut associated with the medial resection of the proximal tibia  12 . 
     As indicated above, the datum block  100  includes a locking or pinch force mechanism  106  associated with the main body  102  that is configured to removably lock various devices/instruments to the datum block  100 . Referring to  FIGS.  7 A and  7 B , illustrated therein are unlocked and locked configurations of the datum block  100 , respectively. Additionally, referring to  FIGS.  8 A and  8 B , illustrated therein are corresponding unlocked and locked configurations of the locking mechanism  106 , respectively. 
     In the illustrated embodiment, the locking mechanism  106  generally includes a lever arm or actuator member  160  pivotally attached to the inferior portion  130  of the datum block  100 , and a gripper or actuated member  180  positioned within the cavity  116  in the superior portion  110  of the datum block  100  and movably engaged with a proximal end portion of the lever arm  160 . As will be discussed in further detail below, pivotal movement of the lever arm  160  in the direction of arrow P correspondingly displaces the gripper member  180  in an inferior-superior direction in the direction of arrow A to correspondingly compress the gripper member  180  against a plate-like portion of a device/instrument positioned within the space or gap  154  defined between the planar inferior surface  152  of the reference bench  104  and the planar superior surface  112  of the main body  102  of the datum block  100  to thereby capture the plate-like portion within the space  154  and retain the device/instrument in a fixed position and orientation relative to the datum block  100 . The locking or pinch force mechanism  106  thereby serves to maintain the position and angular alignment/orientation of various devices/instruments with respect to the datum block  100 . 
     In the illustrated embodiment of the locking or pinch force mechanism  106 , the lever arm  160  has a generally rectangular bar-like configuration that generally includes an inferior portion  162  and a superior portion  164  that are connected to one another via a flexible hinge portion  163  which permits the superior portion  164  to be displaced toward/away from the inferior portion  162  to correspondingly vary a gap G between the inferior and superior portions  162 ,  164 . The inferior portion  162  of the lever arm  160  is pivotally attached to the inferior portion  130  of the datum block  100  via a pivot pin  166  to thereby allow for pivotal movement of the lever arm  160  relative to the datum block  100  about a central pivot axis C. The inferior portion  162  of the lever arm  160  is also provided with a stop member or pin  167  posteriorly offset from the pivot pin  166  and configured to limit pivotal movement of the lever arm  160  away from the main body  102  of the datum block  100 . As the lever arm  160  is pivoted about the pivot pin  166  away from the main body  102 , the stop member  167  is displaced along the radially contoured groove  144  defined by the posteriorly-facing surface of the inferior portion  130  of the main body  102  ( FIG.  6 B ) until the stop member  167  is engaged against the end surface  146  of the groove  144 , thereby preventing further pivotal movement of the lever arm  160  away from the main body  102 . Additionally, the inferior portion  162  of the lever arm  160  defines a passage  168  ( FIG.  6 D ) anteriorly offset from the pivot pin  166  and extending through the inferior portion  162  in an inferior-superior direction. The passage  168  is at least partially threaded and is configured for threading engagement with an adjustment bolt  170  having a threaded shank portion  170   a  and a proximal end  170   b  defining a series of radially-extending notches or splined grooves  171 . The inferior portion  162  of the lever arm  160  further includes a retaining pin  172  that at least partially extends into the passage  168  to prevent the adjustment bolt  170  from backing entirely out of the passage  168 . 
     The superior portion  164  of the lever arm  160  includes a proximal end portion having a cam structure  174  that defines a superior cam surface  176  that extends along an asymmetrical curve or contour relative to the central pivot axis C. The superior portion  164  further defines a spline or V-shaped projection  178  extending from an inferior surface thereof that is sized and configured for engagement within one of the radially-extending notches or splined grooves  171  defined by the proximal end  170   b  of the adjustment bolt  170 . As should be appreciated, tightening the adjustment bolt  170  into the passage  168  in the lever arm  160  forces the superior portion  164  of the lever arm  160  away from the inferior portion  162  to widen the gap G therebetween, which in turn displaces the superior cam surface  176  of the cam structure  174  away from the central pivot axis C. Additionally, engagement of the spline or V-shaped projection  178  of the lever arm  160  within one of the radially-extending notches or splined grooves  171  defined by the proximal end of the adjustment bolt  170  prevents the adjustment bolt  170  from loosening and backing out of the passage  168  in the lever arm  160 . 
     Referring to  FIGS.  8 A and  8 B , in the illustrated embodiment of the locking or pinch force mechanism  106 , the gripper or actuated member  180  is provided as a two-piece component including a superior component  182  and an inferior component  186 . In the illustrated embodiment, the superior component  182  is permitted to translate in an inferior-superior direction generally along the arrow A, and the inferior component  186  is also permitted to translate in an inferior-superior direction generally along the arrow A as well as in an anterior-posterior direction relative to the superior component  182  generally along arrow B. The superior component  182  may be provided with a generally circular configuration sized for displacement within the cavity  116  in the main body  102  of the datum block  100  generally along the arrow A. The superior component  182  also defines a superior gripping surface  184   a  that may be compressed against plate-like portions of devices/instruments positioned within the space or gap  154  defined between the reference bench  104  and the main body  102  of the datum block  100 , and further defines a substantially flat/planar inferior surface  184   b . The inferior component  186  may also be provided with a generally circular configuration sized for displacement within the cavity  116  in the main body  102  of the datum block  100  in the inferior-superior direction generally along arrow A and in the anterior-posterior direction generally along the arrow B. The inferior component  186  defines a substantially flat/planar superior surface  188   a  configured for sliding engagement with the substantially flat/planar inferior surface  184   b  of the superior component  182 , and further defines an inferior bearing surface  188   b  configured for sliding engagement with the superior cam surface  176  defined by the superior portion  164  of the lever arm  160 . In the illustrated embodiment, the inferior bearing surface  188   b  defines a curved contour extending along a generally uniform/constant radius. However, other suitable shapes and configurations of the inferior bearing surface  188   b  are also contemplated. 
     As set forth above,  FIGS.  7 A / 7 B and  FIGS.  8 A / 8 B illustrate unlocked and locked configurations of the datum block  100  and the locking or pinch force mechanism  106 . In the unlocked configuration, a plate-like portion of a device/instrument may be positioned within the space or gap  154  defined between the planar inferior surface  152  of the reference bench  104  and the planar superior surface  112  defined by the main body  102  of the datum block  100 . The datum block  100  and the locking mechanism  106  are then transitioned from the unlocked configuration illustrated in  FIGS.  7 A and  8 A  to the locked configuration illustrated in  FIGS.  7 B and  8 B  by pivoting the lever arm  160  about the central pivot axis C in a superior direction along arrow P. As should be appreciated, pivoting of the lever arm  160  along arrow P causes the superior cam surface  176  defined by the superior portion  164  of the lever arm  160  to slidably engage the inferior bearing surface  188   b  defined by the inferior component  186  of the gripper member  180 , which in turn displaces the inferior component  186  generally along arrow A as well generally along arrow B. The inferior component  186  in turn forces the superior component  182  of the gripper member  180  in an inferior-superior direction generally along arrow A and compresses the superior gripping surface  184   a  of the superior component  182  into compressed engagement against a plate-like portion of a device/instrument positioned within the space  154  defined between the reference bench  104  and the main body  102  of the datum block  100  to thereby lock the device/instrument in a select position and orientation relative to the datum block  100 . 
     As should be appreciated, the compression or clamping force exerted by the superior component  182  onto the plate-like portion of the device/instrument positioned within the space  154  may be adjusted or calibrated to satisfy particular clamping/locking requirements. Specifically, the compression or clamping force may be adjusted via tightening or loosening of the adjustment bolt  170 . For example, tightening of the adjustment bolt  170  forces the superior portion  164  of the lever arm  160  away from the inferior portion  162  to widen the gap G therebetween, which in turn displaces the superior cam surface  176  of the cam structure  174  away from the central pivot axis C to thereby increase the compression or clamping force exerted by the superior component  182  of the gripper member  180  onto the plate-like portion of the device/instrument positioned within the space or gap  154  defined by the datum block  100 . Additionally, loosening of the adjustment bolt  170  allows the superior portion  164  of the lever arm  160  to be displaced toward the inferior portion  162  to reduce the gap G therebetween, which in turn displaces the superior cam surface  176  of the cam structure  174  toward from the central pivot axis C to thereby decrease the compression or clamping force exerted by the superior component  182  of the gripper member  180  onto the plate-like portion of the device/instrument positioned within the space or gap  154  in the datum block  100 . 
     As should be appreciated, the locking or pinch force mechanism  106  may be transitioned from the unlocked configurations illustrated in  FIGS.  7 A and  8 A  to the locked configurations illustrated in  FIGS.  7 B and  8 B  (and vice-versa) without the need for separate driver instruments or locking tools (e.g., a hex driver or a wrench). Additionally, the clamping or compression force exerted by the locking or pinch force mechanism  106  may be easily adjusted via a single adjustment mechanism (i.e., tightening or loosening of the adjustment bolt  170 ). Although a particular type and configuration of the locking or pinch force mechanism  106  has been illustrated and described herein for use in association with the datum block  100 , it should be understood that other types and configurations of locking/pinching mechanisms or other compression structures/devices are also contemplated for use in association with the present invention in addition to or in lieu of the locking or pinch force mechanism  106 . 
     Referring to  FIG.  9   , the datum block  100  is provisionally attached to the proximal tibia  12  by a provisional attachment pin or fastener  190  extending through the elongate slot  120  in the main body  102  of the datum block  100 . The provisional attachment pin  190  may include a threaded distal end portion (not shown) for anchoring in bone tissue, and a proximal head portion  192  having drive features that facilitate driving of the provisional attachment pin  190  into tibial bone. In the illustrated embodiment, the drive features may include providing the proximal head portion  192  with a non-circular transverse cross section including, for example, one or more flattened regions. Additionally, the proximal head portion  192  may be provided with an enlarged annular region or ring  194  having a transverse cross section sized larger than the slot width w of the elongate slot  120 . The enlarged portion  194  of the head  192  thereby serves to retain the datum block  100  on the provisional attachment pin  190  to prevent the datum block  100  from becoming disengaged from the provisional attachment pin  190 . However, because of the elongate slot  120 , the datum block  100  is permitted to translate along the provisional attachment pin  190  in a superior-inferior direction (i.e., to adjust resection depth), rotate about the provisional attachment pin  190  in a medial-lateral direction (i.e., to adjust the varus-valgus angle), rotate about the provisional attachment pin  190  in an anterior-posterior direction (i.e., to adjust the posterior slope angle), and translate along the provisional attachment pin  190  in an anterior-posterior direction (as limited by engagement of the enlarged head portion  194  against the anterior surface of the main body  102  of the datum block  100 ). As should be appreciated, placement of the provisional attachment pin  190  within the elongate slot  120  in the main body  102  of the datum block  100  provides fine-tuning capability as to adjustment of the particular position and orientation of the datum block  100  relative to the proximal tibia  12  prior to terminal/final attachment to the proximal tibia  12 . 
     Referring to  FIG.  10   , once the datum block  100  is positioned in the appropriate superior/inferior position along the proximal tibia  12  and is rotated to the appropriate medial-lateral angle and anterior-posterior angle, the datum block  100  may be terminally attached to the proximal tibia  12  by a pair of terminal attachment pins or fasteners  196   a ,  196   b  extending through respective ones of the pin-receiving openings  122  in the main body  102  of the datum block  100 . The terminal attachment pins  196   a ,  196   b  may include a threaded distal end portion (not shown) for anchoring in bone tissue, and a proximal head portion  198  having features that facilitate driving of the terminal attachment pins  196   a ,  196   b  into tibial bone. In the illustrated embodiment, the drive features include providing the proximal head portion  198  with a non-circular transverse cross section including, for example, one or more flattened regions. As shown in  FIG.  10   , the pin-receiving openings  122  and the terminal attachment pins  196   a ,  196   b  are oriented at an oblique angle relative to the elongate slot  120  and the provisional attachment pin  190 . As a result, the datum block  100  is retained in position relative to the proximal tibia  12  without having to tighten the enlarged region  104  of the proximal head portion  192  of the provisional attachment pin  190  against the main body  102  of the datum block  100  and/or without having to engage a further attachment pin to the datum block  100  at an oblique angle relative to the terminal attachment pins  196   a ,  196   b.    
     B. Depth Stylus 
     Referring to  FIG.  11   , shown therein is a depth stylus  200  according to one form of the present invention, as attached to the datum block  100  in relation to the proximal tibia  12 . As will be discussed in greater detail below, the depth stylus  200  can be used as a multi-functional measurement instrument to take pre-resection measurements and post-resection measurements to verify and confirm the proper depth of the medial and lateral plateau resection cuts. 
     The depth stylus  200  generally includes a base portion or mounting block  202  configured for attachment to the datum block  100 , an articulating pointer or stylus rod  204  configured to articulate relative to the mounting block  202  and to engage a superior surface of the proximal tibia  12  for measurement relative to a reference plane, and an actuation or adjustment mechanism  206  engaged with the mounting block  202  and the stylus rod  204  to move the stylus rod  204  toward and away from the mounting block  202  in an inferior-superior direction to correspondingly adjust the vertical position of the stylus rod  204  relative to the reference plane, or vice-versa (i.e., to correspondingly adjust the position of the reference plane relative to the stylus rod  204 ). Further elements and features associated with the components of the depth stylus  200  will be set forth in greater detail below with particular reference to  FIGS.  12 - 14   . 
     In the illustrated embodiment, the mounting block  202  is a single-piece monolithic structure including a mounting portion  210  and a connector portion  220 . In one embodiment, the mounting portion  210  is divided into superior and inferior portions  212 ,  214 , respectively, that are separated from one another by a slot  216 . The superior mounting portion  212  has a plate-like configuration defining substantially flat/planar superior and inferior surfaces  217   a ,  217   b , respectively. The inferior mounting portion  214  also has a plate-like configuration defining substantially flat/planar superior and inferior surfaces  218   a ,  218   b , respectively. The slot  216  defined between the superior and inferior mounting portions  212 ,  214  has a slot width w that is sized for receipt of the reference bench  104  of the datum block  100  therein. Once the depth stylus  200  is positioned in a desired position and orientation relative to the reference bench  104  of the datum block  100 , the locking or pinch force mechanism  106  is actuated to lock the depth stylus  200  in a select position and orientation relative to the datum block  100 . Actuation of the locking or pinch force mechanism  106  correspondingly compresses the planar superior surface  218   a  of the plate-like mounting portion  214  against the planar inferior surface  152  of the reference bench  104  to thereby capture/lock the plate-like mounting portion  214  within the space  154  defined between the main body  102  and the reference bench  104  of the datum block  100 , which in turn retains the depth stylus  200  in a fixed position relative to the datum block  100 . As should be appreciated, locking of the depth stylus  200  in a fixed inferior-superior position relative to the datum block  100  stabilizes the depth stylus  200  during measurements, which in turn removes an element of toggle/tolerance between the depth stylus  200  and the datum block  100  to thereby improve the accuracy of the measurements taken with the depth stylus  200 . 
     In one embodiment, the connector portion  220  of the mounting block  202  serves to interconnect the stylus rod  204  with the adjustment mechanism  206 . Specifically, the connector portion  220  defines a first passage  222  extending laterally therethrough, and a second passage  224  extending therethrough in a superior-inferior direction and arranged generally perpendicular to the first passage  222 . Although the axial centerlines of the first and second passages  222 ,  224  are offset from one another, the passages  222 ,  224  are positioned in communication with one another. As will be discussed below, the passages  222 ,  224  are sized and configured to house components of the stylus rod  204  and the adjustment mechanism  206 . The connector portion  220  further defines a third passage  226  extending therethrough in a direction generally parallel with the second passage  224  and intersecting the first transverse passage  222 . The third passage  226  provides visualization of and/or access to internal components housed within the connector portion  220  of the mounting block  202 . As shown in  FIGS.  11  and  13 D , an anterior surface of the connector portion  220  defines a reference or measurement marker  228 , the purpose of which will be discussed below. 
     In the illustrated embodiment, the stylus rod  204  generally includes a mounting base portion  230  and a rod portion  240 , each extending generally along a longitudinal axis L. In one embodiment, the base portion  230  has a generally rectangular bar-like configuration and defines an axial opening (not shown) extending therethrough generally along the longitudinal axis L for receipt of the rod portion  240 . The base portion  230  also defines a spacer or stem  232  extending transversely therefrom which is sized and configured for slidable receipt within the superior-inferior passage  224  in the connector portion  220  of the mounting block  202 . As shown in  FIGS.  13 A and  13 B , a reference pin or marker  234  extends from an inferior surface of the base portion  230  in a superior-inferior direction and is positioned adjacent the distal end of the base portion  230 . Additionally, the base portion  230  further defines a series of opening or slots  236  extending therethrough in a superior-inferior direction. 
     In the illustrated embodiment, the rod portion  240  of the stylus rod  204  generally includes an elongate rod portion  242 , a handle or grip portion  244  attached to the proximal end of the elongate rod portion  242 , and a pointer or reference bar  246  extending from a distal end of the elongate rod portion  242 . In the illustrated embodiment, the elongate rod portion  242  and the proximal handle portion  244  each have a generally circular outer cross section, and one side of the elongate rod portion  242  is provided with a flattened or truncated surface  243  which serves to stabilize the rotational position of the elongate rod portion  242  relative to the mounting base portion  230 . However, it should be understood that other shapes and configurations of the elongate rod portion  242  and the proximal handle portion  244  are also contemplated. In one embodiment, the distal pointer  246  extends from the elongate rod portion  242  at an angle θ relative to the longitudinal axis L. In one specific embodiment, the angle θ is approximately 35°. However, other angles θ are also contemplated. Additionally, the thickness of the distal pointer  246  inwardly tapers along its length to a reduced cross section adjacent its distal end to thereby define a relatively pointed distal end surface  248  to improve the accuracy of the depth stylus  200 . 
     Referring to  FIG.  14   , shown therein is one embodiment of the adjustment mechanism  206  which, as indicated above, serves to displace the stylus rod  204  toward and away from the mounting block  202  in an inferior-superior direction to correspondingly adjust the position of the stylus rod  204  relative to a reference plane, or vice-versa. In the illustrated embodiment, the adjustment mechanism  206  generally includes a rotational actuator or drive member  250  and a linear actuator or plunger member  270 . The rotational actuator  250  includes a thumb wheel or knob grip  252 , a stem or shaft  254  extending axially from the thumb wheel  252  and arranged along a rotational axis R, and a pinion gear  256  coupled to the shaft  254  and defining a series of gear teeth  258 . The thumb wheel  252  includes a number of scalloped or recessed regions  260  that facilitate manual rotation of the thumb wheel  252  about the rotational axis R by a user. The thumb wheel  252  also includes numerals or other indicia/markings  262  positioned uniformly about an outer circumferential surface of the thumb wheel  252 , the purpose of which will be discussed below. As should be appreciated, the shaft  254  is rotationally mounted within the transverse passage  222  extending through the connector portion  220  of the mounting block  202  to allow rotational movement of the shaft  254  and the pinion gear  256  about the rotational axis R upon exertion of a rotational force or torque onto the thumb wheel  252 . The thumb wheel  252  may also be provided with one or more projections or detents  264  extending laterally from an inner side surface of the thumb wheel  252  which are positionable within recesses or grooves (not shown) formed in an adjacent side surface of the mounting block  202  to provide a certain degree of resistance to rotational movement of the drive member  250  to allow incremental rotational movement of the drive member  250  relative to the mounting block  202 . 
     In the illustrated embodiment, the plunger member  270  of the adjustment mechanism  206  includes an actuated shaft or rack  272  extending generally along a displacement axis D and defining a series of notches or gear teeth  274  positioned along its length. The plunger member  270  further defines an enlarged head or guiding portion  276  positioned adjacent an inferior end of the rack  272  which is sized and configured for slidable displacement within the inferior portion of the passage  224  in the connector portion  220  of the mounting block  202 . In one embodiment, the enlarged head  276  has a generally circular outer cross section corresponding to the circular inner cross section of the inferior portion of the passage  224 , and also defines a series of scallops or recesses  278  formed along the outer circumferential surface of the enlarged head  276  to promote sliding engagement of the enlarged head  276  along the inferior portion of the passage  224 . As should be appreciated, exertion of a rotational force or torque onto the thumb wheel  252  rotates the shaft  254  and the pinion gear  256  about the rotational axis R, which in turn intermeshes the gear teeth  258  of the pinion gear  256  with the notches/teeth  274  on the rack  272  to correspondingly displace the plunger member  270  along a displacement axis D, which thereby results in displacement of the stylus rod  204  toward and away from the mounting block  202  (or vice-versa) to correspondingly adjust the inferior-superior position of the stylus rod  204  relative to a reference plane. 
     Referring once again to  FIG.  11   , once the depth stylus  200  is locked in position relative to the datum block  100 , the stylus rod  204  can be rotationally displaced relative to the mounting block  202  about the displacement axis D, and the rod portion  240  of the stylus rod  204  can be axially displaced along the longitudinal axis L relative to the base portion  230  to correspondingly position the distal end surface  248  of the pointer  246  at an infinite number of positions along the outer surface of the proximal tibia  12 . Additionally, the inferior-superior position of the stylus rod  204  along the displacement axis D can also be adjusted relative to the mounting block  202  by turning the thumb wheel  252  in a clock-wise or counter clock-wise direction. As should be appreciated, the position of the distal end surface  248  of the pointer  246  can therefore be adjusted in three dimensions for positioning at any point along the outer surface of the proximal tibia  12 . 
     Once the distal end surface  248  of the pointer  246  is positioned in abutment against a selected point P 1  along the outer surface of the proximal tibia  12  (e.g., along the medial tibial plateau  16   a ), the user can determine/measure the distance of the selected point P 1  relative to a reference plane in an inferior-superior direction. In one embodiment, the reference plane comprises the plane formed by the superior surface  150  of the reference bench  104  of the datum block  100 . However, it should be understood that the depth stylus  200  may be configured to determine/measure the distance of selected points along the proximal tibia  12  in an inferior-superior direction relative to other reference planes. As will be discussed in further detail below, the plane defined by the superior surface  150  of the reference bench  104  defines the cutting plane along which horizontal medial and lateral resection cuts C HM , C VM  ( FIGS.  20 B and  20 C ) will be formed during resection of the medial and lateral tibial plateau regions  16   a ,  16   b . Additionally, as shown in  FIG.  11    and as set forth above, the datum block  100  may be provisionally attached to the proximal tibia  12  by the provisional attachment pin  190  extending through the elongate slot  120  in the main body  102  of the datum block  100 . Because the datum block  100  is not yet terminally attached to the proximal tibia  12  (i.e., is not securely attached to the proximal tibia by the terminal attachment pins  196 ), the datum block  100  is permitted to translate in a superior-inferior direction via sliding engagement of the provisional attachment pin  190  along the length of the elongate slot  120 , which in turn correspondingly adjusts the plane defined by the superior surface  150  of the reference bench  104  and the proposed/intended resection depth of the horizontal medial and lateral resection cuts C HM , C VM . 
     As should be appreciated, with the distal end surface  248  of the pointer  246  positioned in abutment against the selected point P 1  along the outer surface of the proximal tibia  12 , the superior-inferior position of the datum block  100  may be adjusted via rotating the thumb wheel  252  in a clockwise or counter-clockwise direction, which in turn adjusts the superior-inferior position of the reference/cutting plane defined by the reference bench  104  on the datum block  100  to a desired resection depth (i.e., to a desired position for subsequent formation of the horizontal medial and lateral resection cuts C HM , C VM ). As shown in  FIG.  11   , the inferior-superior distance from the selected point P 1  in contact with the distal end surface  248  of the pointer  246  relative to the reference/cutting plane (i.e., the proposed/intended resection depth) is determined by observing which of the reference numerals  262  on the thumb wheel  252  is aligned with the reference marker  228  on the anterior surface of the mounting block  202  (i.e., reference numeral “9” in the illustrated embodiment). As should be appreciated, further adjustment or fine-tuning of the position of the reference/cutting plane defined by the datum block  100  (i.e., the proposed/intended resection depth) can be made by incrementally turning the thumb wheel  252  until a desired position of the reference/cutting plane (i.e., the resection depth) is achieved. At this point, the superior-inferior position of the datum block  100  (and the desired resection depth) may be fixed by driving one or more of the terminal attachment pins  196  through corresponding pin-receiving openings  122  in the datum block  100 . 
     In one embodiment, the distal end surface  248  of the pointer  246  may initially be positioned and held in abutment against the selected point P 1  along the outer surface of the proximal tibia  12 , followed by rotation of the thumb wheel  252  to correspondingly adjust the superior-inferior position of the datum block  100  and the reference/cutting plane defined by the reference bench  104  until a desired resection level has been achieved (as indicated by the reference numerals  262  on the thumb wheel  252  aligned with the reference marker  228  on the mounting block  202 ). However, in another embodiment, the resection depth may be initially set by aligning the appropriate reference numeral  262  on the thumb wheel  252  with the reference marker  228 , followed by adjustment of the superior-inferior position of the datum block  100  until the distal end surface  248  of the pointer  246  is positioned in abutment against the selected point P 1  along the outer surface of the proximal tibia  12 . 
     In addition to using the depth stylus  200  to position the datum block  100  at a desired superior-inferior position and the reference/cutting plane at a desired resection depth, it should be understood that the depth stylus  200  may be used at any time in a knee arthroplasty procedure to measure and check/verify the superior/inferior position of the reference/cutting plane relative to any reference point on the proximal tibia  12  by positioning the distal end surface  248  of the pointer  246  in abutment against the reference point (i.e., via rotational/translational positional adjustment of the stylus rod  204  and inferior-superior positional adjustment via rotation of the thumb wheel  252 ) and observing which of the reference numerals  262  on the thumb wheel  252  is aligned with the reference marker  228  on the mounting block  202 . 
     Referring to  FIG.  15   , shown therein is another operational position of the stylus rod  204  wherein the distal end surface  248  of the pointer  246  is positioned in contact with another selected point P 2  along the proximal tibia  12  (e.g., along the lateral tibial plateau  16   b ) to determine the distance of the selected point P 2  from the reference plane in an inferior-superior direction. Once again, the inferior-superior distance of the selected point P 2  in contact with the distal end surface  248  of the pointer  246  relative to the reference plane (i.e., the plane formed by the superior surface  150  of the reference bench  104  of the datum block  100 ) may be determined by observing which of the reference numerals  262  is aligned with the reference marker  228  (i.e., reference numeral “12” in the illustrated embodiment). 
     Referring now to  FIGS.  16 A and  16 B , shown therein is an alternative operational configuration of the depth stylus  200 . In this alternative operational configuration, the depth stylus  200  may be removed/detached from the datum block  100  (via de-actuation of the pinch force mechanism  106 ) and used as a hand-held caliper-type instrument. This alternative operational configuration of the depth stylus  200  may be particularly useful, for example, in providing measurements of a resected bone fragment F removed/resected from proximal tibia  12 . However, it should be understood that in this alternative operational configuration, the depth stylus  200  may be used to provide measurements of other structures as well including, for example, attached bone portions of the distal femur  10  or the proximal tibia  12  (i.e., the tibial eminence following resection), femoral or tibial bone implant components, or other structures of devices that require measurement. 
     As shown in  FIG.  16 A , in the alternative operational configuration of the depth stylus  200 , the rod portion  240  of the stylus rod  204  may be retracted into the base portion  130  and rotated 180° about the longitudinal axis L relative to the base portion  230  to position the distal pointer  246  in a refracted position and in an upwardly extending orientation to avoid interference with the bone fragment F (or another structure or device) being measured. The bone fragment F may be inserted into the open space between the planar superior surface  217   a  of the mounting block  202  and the reference pin  234 , with the reference pin  234  positioned directly above a selected point P 3  along the bone fragment F to be measured. As shown in  FIG.  16 B , the inferior-superior position of the stylus rod  204  may then be adjusted relative to the mounting block  202  along the displacement axis D by turning the thumb wheel  252  until the distal end surface of the reference pin  234  is positioned in contact with the selected point P 3  along the bone fragment F, and the opposite surface of the bone fragment F (i.e., the planar surface of the bone fragment F) is slightly compressed into contact with the planar superior surface  217   a  of the mounting block  202 . The measured distance between the selected point P 3  and the opposite surface of the bone fragment F (i.e., the thickness of the bone fragment F) is determined by observing which of the reference numerals  262  on the thumb wheel  252  is aligned with the reference marker  228  on the anterior surface of the mounting block  202  (i.e., reference numeral “9” in the illustrated embodiment). 
     C. Eminence Stylus 
     Referring to  FIG.  17 A , shown therein is an eminence stylus  300  according to one form of the present invention, as attached to the datum block  100  in relation to the proximal tibia  12 . As will be discussed in greater detail below, the eminence stylus  300  includes alignment features that serve to align the eminence stylus  300  relative to anatomic features of the proximal tibia  12  and/or the distal femur  10 , and also includes guide or capture features that serve to guide an oscillating or reciprocating saw or another type of cutting instrument along various cutting planes to form multiple resection cuts in the proximal tibia  12 . 
     The eminence stylus  300  generally includes a base portion or body  302  configured for attachment to the datum block  100 , a carriage  304  movably attached to the base portion  302  and configured for linear displacement along a longitudinal displacement axis L arranged in a generally anterior-posterior direction, and a pair of articulating arms or indicator members  306   a ,  306   b  pivotally attached to the carriage  304  and configured for pivotal displacement about a pivot axis P arranged generally perpendicular to the longitudinal displacement axis L. Further elements and features associated with the eminence stylus  300  will be set forth in greater detail below. 
     Referring to  FIG.  17 B , shown therein is an eminence stylus  300   a  according to another form of the present invention, as attached to the proximal tibia  12 . In many respects, the eminence stylus  300   a  is configured similar to the eminence stylus  300  illustrated and described above. However, the eminence stylus  300   a  includes other elements, features and operational characteristics not found in the eminence stylus  300 , the details of which will be described below. 
     It should be understood that like elements and features associated with the eminence stylus  300  and the eminence stylus  300   a  are referred to using the same reference numbers. Similar to the eminence stylus  300 , the eminence stylus  300   a  generally includes a base portion or body  302 , a carriage  304  movably attached to the base portion  302  and configured for linear displacement along a longitudinal displacement axis L arranged in a generally anterior-posterior direction, and a pair of articulating arms or indicator members  306   a ,  306   b  pivotally attached to the carriage  304  and configured for pivotal displacement about a pivot axis P arranged generally perpendicular to the longitudinal displacement axis L and the anatomic axis  13  of the tibia. Further details associated with the elements and features of the base portion  302 , the carriage  304  and the indicator members  306   a ,  306   b  of the eminence stylus  300   a  need not be discussed herein, it being understood that these elements and features may be configured identical to like components of the eminence stylus  300 . However, in other embodiments, the base portion  302 , the carriage  304  and/or the indicator members  306   a ,  306   b  of the eminence stylus  300   a  may be configured different from those of the eminence stylus  300 . Unlike the eminence stylus  300  which is configured for releasable attachment to the datum block  100  or a similar instrument or device, the eminence stylus  300   a  is configured for attachment directly to the proximal tibia  12 . Specifically, in the illustrated embodiment, the eminence stylus  300   a  includes a mounting block  380  defining at least one pin-receiving opening  382  extending therethrough in an anterior-posterior direction, and with one or more attachment pins  196   a ,  196   b  positioned within and extending through the opening  382  to operatively attach the eminence stylus  300   a  to the proximal tibia  12 . Further elements and features associated with the eminence stylus  300   a  will be set forth in greater detail below. 
     Referring collectively to  18 A- 18 F, in the illustrated embodiment of the eminence stylus  300  shown in  FIG.  17 A , the base portion  302  is a single-piece monolithic structure and generally includes a base plate  310 , a pair of medial and lateral cutting guide flanges  312   a ,  312   b  extending from the base plate  310  in an inferior-superior direction and spaced apart to define an open inner region or yoke therebetween, an inferior mounting flange  314  extending from the base plate  310  in a medial-lateral direction, and a superior cutting guide flange  316  extending from the base plate  310  in a medial-lateral direction and superiorly offset from the inferior mounting flange  314  so as to define a slot  318  therebetween. Although the base portion  302  has been illustrated and described as being formed as a single-piece monolithic structure, in other embodiments, various pieces/elements of the base portion  302  may be formed separately from one another and integrated into a multi-piece assembly. 
     In one embodiment, the base plate  310  has a generally planar configuration and a generally rectangular shape. However, other shapes and configurations are also contemplated. The base plate  310  defines a pair of circular pin receiving openings  320   a ,  320   b  extending entirely through the base plate  310  and aligned generally along the longitudinal axis L in an anterior-posterior direction, and with the openings  320   a ,  320   b  arranged symmetrical on opposite sides of the longitudinal axis L. Additionally, the base plate  310  includes a rectangular-shaped guide notch or channel  322  ( FIGS.  18 C and  18 F ) formed in the superior surface of the base plate  310  and aligned generally along the longitudinal axis L in an anterior-posterior direction. The guide channel  322  is sized and configured to receive an inferior portion of the carriage  304  therein so as to aid in guidably displacing the carriage  304  linearly along the longitudinal axis L ( FIGS.  19 A and  19 B ). The base plate  310  also defines a threaded aperture  324  ( FIG.  18 E ) extending through the base plate  310  in an inferior-superior direction and aligned generally with the longitudinal axis L, and further defines a pair of threaded apertures  326   a ,  326   b  extending at least partially through the base plate  310  in an inferior-superior direction and arranged symmetrically on opposite sides of the longitudinal axis L. The threaded apertures  326   a ,  326   b  are configured to threadingly receive a pair of fasteners or set screws  328   a ,  328   b.    
     As indicated above, the medial and lateral cutting guide flanges  312   a ,  312   b  extend from the base plate  310  in an inferior-superior direction and are spaced apart to define an open inner region or yoke therebetween. In the illustrated embodiment, the medial and lateral cutting guide flanges  312   a ,  312   b  each have a triangular-shaped configuration. However, other shapes and configurations of the medial and lateral cutting guide flanges  312   a ,  312   b  are also contemplated. Additionally, the medial and lateral cutting guide flanges  312   a ,  312   b  define substantially flat/planar inner surfaces  330   a ,  330   b , respectively, arranged generally parallel with one another and facing the open inner region. The planar inner surfaces  330   a ,  330   b  are preferably generally aligned with the central axes of the pin receiving openings  320   a ,  320   b , respectively. As will be discussed in further detail below, the substantially flat/planar inner surfaces  330   a ,  330   b  of the medial and lateral cutting guide flanges  312   a ,  312   b  cooperate with adjacent surfaces of the indicator members  306   a ,  306   b  to form medial and lateral cutting guides or channels configured to guide an oscillating or reciprocating saw (or another type of cutting instrument) to form vertical cuts associated with the medial and lateral resection of the proximal tibia  12 . 
     As also indicated above, the inferior mounting flange  314  and the superior cutting guide flange  316  each extend from the base plate  310  in a medial-lateral direction and are offset from one another in an inferior-superior direction to define a slot  318  therebetween. In one embodiment, the inferior mounting flange  314  has a generally rectangular configuration and the superior cutting guide flange  316  has a generally trapezoidal-shaped configuration. However, other suitable shapes and configurations are also contemplated. In the illustrated embodiment, the inferior mounting flange  314  has a plate-like configuration defining substantially flat/planar superior and inferior surfaces  340 ,  342 , respectively. Similarly, the superior cutting guide flange  316  likewise defines substantially flat/planar superior and inferior surfaces  344 ,  346 , respectively. The slot  318  defined between the inferior mounting flange  314  and the superior cutting guide flange  316  has a slot width w that is sized for receipt of the reference bench  104  of the datum block  100  therein. As illustrated in  FIG.  17 A , once the eminence stylus  300  is positioned in a desired position and orientation relative to the reference bench  104  of the datum block  100 , the locking or pinch force mechanism  106  of the datum block  100  is actuated to compress the superior surface  340  of the inferior mounting flange  314  against the inferior surface  152  of the reference bench  104  to thereby lock the eminence stylus  300  in a select position and orientation relative to the datum block  100 . 
     As will be set forth in detail below, the substantially flat/planar inferior surface  346  defined by the superior cutting guide flange  316  of the eminence stylus  300  forms a superior boundary of a cutting guide. In one embodiment, the substantially flat/planar inferior surface  346  is preferably generally aligned with the central axis of the pin receiving opening  320   a  ( FIG.  18 C ). As illustrated in  FIG.  20 A , the substantially flat/planar inferior surface  346  of the superior cutting guide flange  316  is aligned substantially parallel with and offset from the substantially flat/planar superior surface  150  of the reference bench  104  of the datum block  100  to thereby form a medial cutting guide or channel  348  defined between the adjacent inferior and superior surfaces  346 ,  150 . In one embodiment, the planar superior surface  150  defined by the reference bench  104  is aligned generally tangent with the diameter of the medial pin receiving opening  320   a . As should be appreciated, the medial cutting guide  348  preferably defines a channel width sized in relatively close tolerance with the cutting blade thickness of an oscillating or reciprocating saw (or another cutting device) to form a smooth and accurate medial resection cut in the proximal tibia  12 , further details of which will be set forth below. 
     In the illustrated embodiment, the carriage  304  has a generally U-shaped configuration including a base wall  350  defining a substantially flat/planar superior surface, and a pair of side walls  352   a ,  352   b  extending from the base wall  350  in an inferior-superior direction and defining substantially flat/planar inner side surfaces and substantially flat/planar outer side surfaces. The carriage  304  may also be provided with an end wall  354  to provide further structural support and rigidity to the carriage  304 . Additionally, the carriage  304  may be provided with a pair of projections or detents  353   a ,  353   b  extending laterally outward from outer surfaces of the side walls  352   a ,  352   b , respectively, the purpose of which will be discussed below. The carriage  304  also defines an elongate slot  356  having a length extending generally along the longitudinal axis L. The carriage  304  further includes a pin or fastener  358  ( FIGS.  18 D and  18 F ) including a threaded shank portion  358   a  and an enlarged head portion  358   b . The threaded shank portion  358   a  extends through the elongate slot  356  and is threaded into the threaded aperture  324  in the base plate  310  ( FIG.  18 E ). In one embodiment, the enlarged head portion  358   b  has a generally circular outer cross section that is positioned in relatively close tolerance and sliding engagement with the substantially flat/planar inner side surfaces of the side walls  352   a ,  352   b  of the carriage  304  ( FIGS.  18 D and  18 F ). As should be appreciated, the fastener  358  serves to retain the carriage  304  on the base portion  302  to prevent unintended or inadvertent removal of the carriage  304 . However, as will be discussed in greater detail below, the carriage  304  may be axially displaced relative to the base portion  302  along the longitudinal axis L to provide a degree of adjustability to the eminence stylus  300 . Additionally, as shown in  FIG.  18 C , an inferior region of the base wall  350  and/or the side walls  352   a ,  352   b  is recessed into the guide channel  322  formed along the superior surface of the base plate  310  to facilitate guiding displacement of the carriage  304  along the longitudinal axis L. 
     In the illustrated embodiment, the articulating arms or indicator members  306   a ,  306   b  each include a mounting plate portion  360  and an elongate blade portion  362 . As should be appreciated, the mounting plate portion  360  and the blade portion  362  of the indicator members  306   a ,  306   b  cooperate to define substantially flat/planar outer side surface  364   a ,  364   b , respectively. As shown in  FIGS.  18 C and  18 D , the flat/planar outer side surface  364   a ,  364   b  of the indicator members  306   a ,  306   b  are aligned substantially parallel with and offset from the respective flat/planar inner side surfaces  330   a ,  330   b  of the medial and lateral cutting guide flanges  312   a ,  312   b  to thereby form a medial cutting guide or channel  366   a  defined between the adjacent side surfaces  330   a ,  364   a , and a lateral cutting guide or channel  366   b  defined between the adjacent side surfaces  330   b ,  364   b . As should be appreciated, the medial and lateral cutting guides  366   a ,  366   b  preferably define a channel width sized in relatively close tolerance with the cutting blade thickness of an oscillating or reciprocating saw (or another cutting device) to form smooth and accurate resection cuts in the proximal tibia  12 , further details of which will be set forth below. 
     The mounting plate portions  360  of the indicator members  306   a ,  306   b  are pivotally attached to the side walls  352   a ,  352   b  of the carriage  304  via one or more pivot pins  370  ( FIG.  19 B ) to allow for pivotal movement of the indicator members  306   a ,  306   b  about the pivot axis P from a substantially horizontal orientation ( FIG.  19 B ) to a substantially vertical orientation ( FIG.  19 C ). The ends or heads of the pivot pins  370  are flush with or recessed slightly below the flat/planar outer side surface  364   a ,  364   b  of the indicator members  306   a ,  306   b  to provide a substantially smooth and uninterrupted cutting guide surface. The inner surfaces of the mounting portions  360  of the indicator members  306   a ,  306   b  each define a series of recesses or grooves  372  ( 18 F and  19 C) that are sized to receive the detents  353   a ,  353   b  to thereby provide a certain degree of resistance to pivotal movement of the indicator members  306   a ,  306   b  about the pivot axis P to allow for incremental pivotal movement of the indicator members  306   a ,  306   b  relative to the carriage  304 . The indicator members  306   a ,  306   b  may therefore be provisionally maintained in a select pivotal position via positioning of the detents  353   a ,  353   b  in select ones of the recesses/grooves  366 . In one embodiment, the portion of the mounting plate  360  positioned adjacent the pivot axis P has a somewhat greater thickness compared to the elongate blade portion  362  to provide the indicator members  306   a ,  306   b  with greater rigidity and structural integrity. Additionally, each of the elongate blade portions  362  preferably defines substantially flat/planar upper and lower edges  374   a ,  374   b  and a rounded distal end surface  376 . 
     Although a particular shape and configuration of the indicator members  306   a ,  306   b  has been illustrated and described herein, it should be understood that other suitable shapes and configurations are also contemplated. Additionally, although the indicator members  306   a ,  306   b  have been illustrated as pivoting simultaneously with one another about the pivot axis P relative to the carriage  304 , it should be understood that the indicator members  306   a ,  306   b  may pivot independent from one another about the pivot axis P (i.e., the indicator members  306   a ,  306   b  may be positioned at different angular orientations relative to one another). Furthermore, in the illustrated embodiment of the eminence stylus  300 , the indicator members  306   a ,  306   b  pivot about the pivot axis P along travel planes that are substantially parallel to one another. However, in other embodiments, the eminence stylus  300  may be configured such that the indicator members  306   a ,  306   b  pivot about the pivot axis P along travel planes that are not parallel to one another (i.e., are arranged oblique to one another). 
     Referring now to  FIGS.  19 A- 19 E , the carriage  304  may be axially displaced relative to the base portion  302  along the longitudinal axis L between a first fully extended posterior-most position ( FIGS.  19 A and  19 D ) and a second fully retracted anterior-most position ( 19 B and  19 E). The eminence stylus  300  is therefore capable of translating the carriage  304  (and the indicator members  306   a ,  306   b  attached to the carriage  304 ) toward and away from the proximal tibia  12  (or distal femur  10 ) in an anterior-posterior direction along the longitudinal axis L ( FIG.  17 A ). As should be appreciated, axial displacement of the carriage  304  relative to the base portion  302  is limited by abutment of the threaded shank portion  358   a  of the fastener  358  against the end surfaces of the elongate slot  356  (i.e., axial displacement of the carriage  304  is limited by the length of the elongate slot  356 ). Additionally, it should also be appreciated that the ability to translate the carriage  304  (and the indicator members  306   a ,  306   b  attached to the carriage  304 ) along the longitudinal axis L may more easily accommodate for different sizes of knees (e.g., varying sizes of the distal femur  10  and the proximal tibia  12 ). Furthermore, the ability to translate the carriage  304  along the longitudinal axis L to the fully retracted anterior-most position ( FIGS.  19 B and  19 E ) allows the indicator members  306   a ,  306   b  to clear the distal femur  10  for pivotal displacement about the pivot axis P to their vertical orientation ( FIG.  19 C ) which may be used to check alignment with the anterior region of the distal femur  10 . As should be further appreciated, sliding displacement of the enlarged head portion  358   b  along the inner guide surfaces of the side walls  352   a ,  352   b  and/or sliding displacement of the inferior region of the base wall  350  along the guide channel  322  formed in the base plate  310  facilitate smooth and uninhibited guiding displacement of the carriage  304  generally along the longitudinal axis L as the carriage  304  is moved axially relative to the base portion  302 . 
     Referring to  FIGS.  20 A- 20 C , some of the operational characteristics associated with the eminence stylus  300  according to embodiments of the invention will now be discussed. The eminence stylus  300  is initially provisionally attached to the datum block  100  by positioning the inferior mounting flange  314  of the eminence stylus  300  into the slot or channel  154  defined between the reference bench  104  and the main body  102  of the datum block  100 . In this provisional attachment arrangement, the position and orientation of the eminence stylus  300  may be adjusted relative to the datum block  100  and various anatomic features associated with the proximal tibia  12  and the distal femur  10 . In some embodiments, the indicator members  306   a ,  306   b  may be used to provide visual indicators to aid in adjusting the eminence stylus  300  to the desired position and orientation. For example, the longitudinal axis L and the space between the indicator members  306   a ,  306   b  might be centrally positioned and generally aligned with the anatomic axis  13  of the tibia, and the central plane extending between the space between the indicator members  306   a ,  306   b  might be arranged generally coplanar with the central plane of the tibia  12 . Other alignment techniques and procedures used by those of skill in the art are generally known and need not be discussed in detail herein. 
     As illustrated in  FIG.  20 A , after the eminence stylus  300  is positioned in a desired position and orientation relative to the proximal tibia  12 , the locking or pinch force mechanism  106  of the datum block  100  is actuated to compress the superior surface  340  of the inferior mounting flange  314  against the inferior surface  152  of the reference bench  104  to thereby lock the eminence stylus  300  in the selected position and orientation. However, as should be appreciated, if further adjustment to the position/orientation of the eminence stylus  300  becomes necessary or is desired, the locking or pinch force mechanism  106  of the datum block  100  can simply be deactuated/unlocked to provide further adjustment opportunity (i.e., by pivoting the lever arm  160  of the locking mechanism  106  in a downward direction). 
     Referring to  FIG.  20 B , once the eminence stylus  300  is locked in position relative to the datum block  100 , a graduated tibial pin  390  according to one form of the invention is inserted into the medial pin receiving opening  320   a  in the eminence stylus  300  and anchored to the proximal tibia  12 . A second graduated tibial pin  390  may likewise be inserted into the lateral pin receiving opening  320   b  and anchored to the proximal tibia  12 . Further details regarding the graduated tibial pin  390  and a technique for installation/use of the graduated tibial pin  390  according to one form of the invention will be set forth in detail below. As should be appreciated, the graduated tibial pin  390  provides further stabilization and support to the eminence stylus  300  to prevent unintended/unintentional movement of the eminence stylus  300  relative to the proximal tibia  12  (and the datum block  100 ) during formation of the resection cuts. Additionally, the graduated tibial pin  390  also serves as a guard or stop during formation of the tibial resection cuts to control the depth of the cuts and to prevent overcutting or notching which might otherwise compromise the strength and integrity of the tibial eminence  14 . 
     Once the graduated tibial pin  390  is inserted into the medial pin receiving opening  320   a  and anchored to the proximal tibia  12 , an oscillating or reciprocating saw (or another cutting device) is inserted into and displaced along the medial cutting guide  348  defined between the inferior surface  346  of the superior cutting guide flange  316  (on the eminence stylus  300 ) and the superior surface  150  of the reference bench  104  (on the datum block  100 ) to form a horizontal medial resection cut C HM . As indicated above, the graduated tibial pin  390  serves as a guard or stop to control the depth of the horizontal resection cut and to prevent overcutting or notching of the tibial eminence  14 . After formation of the horizontal medial resection cut C HM , the oscillating or reciprocating saw (or another cutting device) is inserted into and displaced along the medial cutting guide  366   a  defined between the adjacent flat/planar side surfaces defined by the medial cutting guide flange  312   a  and the medial indicator member  306   a  to form the vertical medial resection cut C VM  to complete the medial resection of the proximal tibia  12 . Once again, the graduated tibial pin  390  serves as a guard or stop to control the depth of the vertical resection cut and to prevent overcutting. 
     Following completion of the medial tibial resection, the graduated tibial pin  390  can be removed from the medial pin receiving opening  320   a  and inserted into the lateral pin receiving opening  320   b  of the eminence stylus  300  and anchored to the proximal tibia  12 . Alternatively, a second graduated tibial pin (not shown) may be inserted into the lateral pin receiving opening  320   b  and anchored to the proximal tibia  12 . The oscillating or reciprocating saw (or another cutting device) is then inserted into and displaced along the medial cutting guide  366   b  defined between the adjacent flat/planar side surfaces defined by the lateral cutting guide flange  312   b  and the lateral indicator member  306   b  to form a vertical lateral resection cut C VL  in the proximal tibia  12 . Once again, the graduated tibial pin  390  serves as a guard or stop to control the depth of the vertical resection cut and to prevent overcutting or notching. In one embodiment, a single-blade saw (or another type of cutting device) is used to form the vertical medial resection cut C VM  and vertical lateral resection cut C VL . However, in other embodiment, a dual-blade saw (or another type of cutting device) may be used to form the vertical medial resection cut C VM  and vertical lateral resection cut C VL  simultaneously. Examples of dual-blade saws suitable for use in association with the present invention are disclosed in U.S. patent application Ser. No. 12/790,137, the contents of which have been incorporated herein by reference in their entirety. 
     It should be appreciated that while the medial and lateral cutting guides  366   a ,  366   b  defined between the adjacent flat/planar side surfaces of the cutting guide flanges  312   a ,  312   b  and the mounting plate portions  360  of the medial and lateral indicator members  306   a ,  306   b  serve as the primary guide structures (a complete saw blade capture extending along both sides of the saw blade) for guiding the saw blade along a particular cutting plane (i.e., a vertical cutting plane), the elongate blade portions  362  of the indicator members  306   a ,  306   b  also serve as additional guide structures along regions of the proximal tibia  12  posterior to the cutting guides  366   a ,  366   b  during a cutting operation. In this manner, the elongate blade portions  362  of the indicator members  306   a ,  306   b  serve as an extension of the cutting guides  366   a ,  366   b  to guide/control the tip and distal portion of the saw blade and to control the path of the saw blade in locations posterior to the cutting guides  366   a ,  366   b , particularly when forming posterior portions of the vertical eminence resection cuts. Additionally, the elongate blade portions  362  of the indicator members  306   a ,  306   b  also serve as positive inner boundaries or stops to protect the bone intended for preservation (i.e., the unresected bone). It should also be appreciated that although the indicator members  306   a ,  306   b  are illustrated and described as being positioned medially or inwardly offset from the medial and lateral cutting guide flanges  312   a ,  312   b  to form inner boundaries or stops to control/guide the position of the saw blade, in other embodiments, the indicator members  306   a ,  306   b  may be positioned outward from the medial and lateral cutting guide flanges  312   a ,  312   b  to form outer boundaries or stops to control/guide the position of the saw blade. 
     As shown in  FIG.  20 C , following the formation of the horizontal medial resection cut C HM , the vertical medial resection cut C VM , and the vertical lateral resection cut C VL , the eminence stylus  300  may be removed from the datum block  100  to provide access to the medially resected tibia for inspection, trialing and/or measuring using the depth stylus  200  or other measuring instruments. If re-cutting of one or more of the resection cuts is required or desired, the eminence stylus  300  may be re-engaged with the datum block  100 , re-positioned/re-aligned with respect to the proximal tibia  12 , and re-locked to the datum block  100 . Alternatively, other devices/instruments may be used to recut or perform other cutting operations on the proximal tibia  12 , the details of which will be set forth below. As shown in  FIG.  20 C , due to the design and configuration of the datum block  100 , one potential benefit or advantage provided by the present invention is that the planar superior surface  150  of the datum block  100  is arranged co-planar with the horizontal medial resection cut C HM . Accordingly, the planar superior surface  150  of the datum block  100  and the horizontal medial resection cut C HM  extend along a single reference plane, which may be beneficial when engaging other devices or instruments to the datum block  100  and/or when performing other procedures or techniques on the proximal tibia  12 . 
     Although the formation of the horizontal and vertical resection cuts on the proximal tibia  12  have been illustrated and described as occurring in a particular order, it should be understood that other cutting sequences are also contemplated. Additionally, although formation of the vertical lateral resection cuts C VL  has been illustrated and described as occurring immediately after completion of the medial tibial resection, it should be understood that the eminence stylus  300  may be removed from the datum block  100  after completion of the medial tibial resection to provide access to the medially resected tibia for inspection, trialing and/or measuring to verify the accuracy of the medial resection cuts (i.e., position, depth, posterior slope angle, varus/valgus angle, etc.). In this manner, if the medial resection is found to be inaccurate and/or requires re-cutting, appropriate corrections/adjustments can be made prior to forming the lateral resection cuts. The eminence stylus  300  (or other devices or instruments) may be engaged with the datum block  100  and positioned/aligned with respect to the proximal tibia  12  prior to being locked to the datum block  100 , followed by re-cutting of the medial resections and/or formation of the vertical lateral resection cuts C VL . 
     Referring once again to  FIG.  17 B , shown therein is the eminence stylus  300   a  attached to the proximal tibia  12  by the attachment pins  196   a ,  196   b . In many respects, the eminence stylus  300   a  is configured similar to the eminence stylus  300 , generally including a base portion  302 , a carriage  304  movably attached to the base portion  302  and configured for linear displacement along the longitudinal displacement axis L, and a pair of indicator members  306   a ,  306   b  pivotally attached to the carriage  304  and configured for pivotal displacement about the pivot axis P. However, unlike the eminence stylus  300  which is configured for indirect coupling to the proximal tibia  12  by way of the datum block  100 , the eminence stylus  300   a  is configured for direct attachment to the proximal tibia  12 . 
     In the illustrated embodiment, the eminence stylus  300   a  includes a mounting block  380  defining at least one pin-receiving opening  382  extending therethrough in an anterior-posterior direction, and with one or more attachment pins  196   a ,  196   b  positioned within and extending through the pin-receiving opening  382  and anchored to tibial bone to operatively attach the eminence stylus  300   a  to the proximal tibia  12 . In one embodiment, the base portion  302  and the mounting block  380  are formed unitarily with one another to define a single-piece monolithic structure. However, in other embodiments, the base portion  302  and the mounting block  380  may be formed separately and coupled/interconnected together to define an integrated multi-piece structure. In one embodiment, the pin-receiving opening  382  is configured as an elongate slot having a slot length/extending generally in a medial-lateral direction and including inferior and superior surfaces  382   a ,  382   b  that are spaced apart to define a slot width w. The slot length/preferably extends across substantially an entire width of the mounting block  380 , and the slot width w is preferably sized in relatively close tolerance with the outer diameter of the attachment pins  196   a ,  196   b  to provide secure and stable engagement between the mounting block  380  of the eminence stylus  300   a  and the attachment pins  196   a ,  196   b . Although the pin-receiving opening  382  is illustrated and described as an elongate slot, it should be understood that other configurations of the pin-receiving opening  382  are also contemplated including, for example, a circular configuration. Additionally, although both of the attachment pins  196   a ,  196   b  are illustrated as extending through a single pin-receiving openings  382 , it should be understood that the mounting block  380  may be provided with any number of the pin-receiving openings  382 , including two or more pin-receiving opening  382  sized and configured for individual receipt of respective ones of the attachment pins  196   a ,  196   b.    
     In the illustrated embodiment, the eminence stylus  300   a  includes a superior cutting guide flange  384  configured similar to the superior cutting guide flange  316  of the eminence stylus  300 . The superior cutting guide flange  384  extends from the base portion  302  in a medial-lateral direction and is offset from a medial portion of the mounting block  380  in an inferior-superior direction to thereby define a cutting guide channel  386  therebetween. In one embodiment, the mounting block  380  has a generally rectangular transverse cross-section and the superior cutting guide flange  384  has a generally trapezoidal-shaped transverse cross-section. However, other suitable shapes and configurations are also contemplated. Additionally, in the illustrated embodiment, the mounting block  380  defines a substantially flat/planar superior surface  388   a  and the superior cutting guide flange  384  defines substantially flat/planar inferior surface  388   b , with the planar superior and inferior surfaces  388   a ,  388   b  offset from one another in an inferior-superior direction to define the cutting guide channel  386  therebetween. The cutting guide channel  386  is sized for receipt of a cutting device therein and is configured to guide the cutting device generally along a cutting plane in a medial-lateral direction to form a medial resection cut in the proximal tibia  12 . In this manner, the mounting block  380  and the cutting guide flange  384  cooperate to define a cutting guide that is sized in relatively close tolerance with the thickness of the cutting device (e.g., a cutting blade of an oscillating or reciprocating saw, or another type of cutting device) to form a smooth and accurate medial resection cut in the proximal tibia  12  generally along the cutting plane of the cutting guide channel  386 , further details of which have been set forth above with regard to the eminence stylus  300 . 
     Having described the structural features associated with the eminence stylus  300   a , reference will now be made to attachment of the eminence stylus  300   a  to the proximal tibia  12  according to one embodiment of the present invention. As discussed above in association with  FIG.  10   , once the datum block  100  is positioned in the appropriate superior/inferior position along the proximal tibia  12  and is rotated to the appropriate medial-lateral angle and anterior-posterior angle, the datum block  100  may be terminally attached to the proximal tibia  12  by a pair of terminal attachment pins  196   a ,  196   b  extending through respective ones of the pin-receiving openings  122  in the main body  102  of the datum block  100 . 
     In some instances, it may be desirable to interchange the datum block  100  with the eminence stylus  300   a  or another instrument or device. More specifically, it may be desirable to remove the datum block  100  from the attachment pins  196   a ,  196   b  and replace the datum block  100  with the eminence stylus  300   a  or other instruments or devices. Since the attachment pins  196   a ,  196   b  are preferably arranged generally parallel with one another, the datum block  100  can be easily detached from the proximal tibia  12  by simply sliding the datum block  100  off of the attachment pins  196   a ,  196   b  in an anterior direction. Once the datum block  100  is removed from the attachment pins  196   a ,  196   b , the eminence stylus  300   a  can be attached to the proximal tibia  12  using the same attachment pins  196   a ,  196   b  previously used to attach the datum block  100  to the proximal tibia  12  ( FIG.  10   ). Specifically, the proximal end portions of the attachment pins  196   a ,  196   b  extending from the proximal tibia  12  may be inserted into the elongate slot  382  in the mounting block  380 , and the eminence stylus  300   a  may be slid along the proximal end portions of the attachment pins  196   a ,  196   b  in an anterior-posterior direction and rotated about the pins  196   a ,  196   b  in a medial-lateral direction until the eminence stylus  300   a  is properly positioned and oriented relative to the proximal tibia  12 . In one embodiment, the eminence stylus  300   a  is slid along the proximal portions of the attachment pins  196   a ,  196   b  in an anterior-posterior direction until the eminence stylus  300   a  abuts an anterior aspect of the proximal tibia  12 . 
     As should be appreciated, since the eminence stylus  300   a  is attached to the proximal tibia  12  using the same attachment pins  196   a ,  196   b  that were used to attach the datum block  100  to the proximal tibia  12  (i.e., the attachment pins  196   a ,  196   b  remain anchored to the proximal tibia  12  after removal of the datum block  100 ), the position and orientation of the eminence stylus  300   a  relative to the proximal tibia  12  is advantageously based on the same points of reference used to set the position and orientation of the datum block  100 . Notably, removal of the attachment pins  196   a ,  196   b  from the proximal tibia  12  is not required to detach the datum block  100  from the proximal tibia  12  or to attach the eminence stylus  300   a  to the proximal tibia  12 . Additionally, it should be appreciated that the elongate pin-receiving slot  382  in the mounting block  380  of the eminence stylus  300   a  has the same relative position and orientation as corresponding pairs of the pin-receiving openings  122  in the datum block  100 . Therefore, the eminence stylus  300   a  may be interchanged with the datum block  100  using the same attachment pins  196   a ,  196   b  previously used to attach the datum block  100  to the proximal tibia  12 , and the eminence stylus  300   a  may take on the same position and orientation relative to the proximal tibia  12  as the datum block  100 . 
     In one embodiment, the eminence stylus  300   a  is arranged at a position and orientation on the proximal tibia  12  that corresponds to the prior position and orientation on the datum block  100 . In one specific embodiment, the planar superior surface  388   a  of the mounting block  380  of the eminence stylus  300   a  is arranged substantially parallel with the previously-positioned planar superior surface  150  of the reference bench  104  of the datum block  100 . In another specific embodiment, the planar superior surface  388   a  of the eminence stylus  300   a  is arranged substantially co-planar with the previously-positioned planar superior surface  150  of the datum block  100 . However, other embodiments are also contemplated wherein the planar superior surface  388   a  of the eminence stylus  300   a  may be arranged non-parallel with and/or non-coplanar with the previously-positioned planar superior surface  150  of the datum block  100 . As should be appreciated, the attachment pins  196   a ,  196   b  provide two reference points that define a datum plane or substantially planar datum joint that serves to attach the datum block  100  to the proximal tibia  12  in a select position and orientation corresponding to the previous position and orientation of the datum block  100 . 
     Additionally, in other embodiments of the invention, the eminence stylus  300   a  may include other structures/features that provide a neutral/reference tibial foundation to which other devices or instruments may be engaged to and referenced from. For example, in some embodiments, the eminence stylus  300   a  may be provided with a reference table configured similar to the reference bench  104  illustrated and described above with regard to the datum block  100  to provide a structure to which other instruments or devices may be lockingly engaged. Additionally, in some embodiments, the eminence stylus  300   a  may be provided with a lock mechanism similar to that of the locking mechanism  106  of the datum block  100  to selectively and releasably lock other instruments or devices to a reference bench of the eminence stylus  300   a.    
     Referring to  FIGS.  21 A and  21 B , shown therein is an eminence stylus  300 ′ according to another form of the present invention. Referring to  FIG.  22   , shown therein is the eminence stylus  300 ′ attached to the datum block  100  (which may in turn be anchored to the proximal tibia  12 ). The eminence stylus  300 ′ is configured identical to the eminence stylus  300  illustrated and described above with the exception of the additional elements and features described below. Like the eminence stylus  300 , the eminence stylus  300 ′ generally including a base portion or body  302 ′ configured for attachment to the datum block  100 , a carriage  304 ′ movably attached to the base portion  302 ′ and configured for linear displacement along a longitudinal displacement axis L, and a pair of articulating arms or indicator members  306   a ′,  306   b ′ pivotally attached to the carriage  304 ′ and configured for pivotal movement relative to the carriage  304 ′. The elements and features associated with these components need not be discussed herein, it being understood that the elements and features associated with the base portion  302 ′, the carriage  304 ′ and the indicator members  306   a ′,  306   b ′ are configured identical to like elements and features associated with the base portion  302 , the carriage  304  and the indicator members  306   a ,  306   b  of the eminence stylus  300 . 
     Unlike the eminence stylus  300  which cooperates with the datum block  100  to provide a single horizontal medial cutting guide  348  (as defined between the superior cutting guide flange  316  and the reference bench  104 ), as illustrated in  FIG.  22   , the eminence stylus  300 ′ provides both a horizontal medial cutting guide  348 ′ and a horizontal lateral cutting guide  380 ′. Specifically, like the horizontal medial cutting guide  348  associated with the eminence stylus  300 , the horizontal medial cutting guide  348 ′ is likewise defined between the inferior surface  346 ′ of the superior cutting guide flange  316 ′ and the superior surface  150  of the reference bench  104  ( FIG.  22   ). Additionally, the horizontal lateral cutting guide  380 ′ is defined between an inferior cutting guide flange  382 ′ and a superior cutting guide flange  384 ′, each extending laterally from the right hand side of the base plate  310 ′ in a medial-lateral direction. In one embodiment, the inferior and superior cutting guide flanges  382 ′,  384 ′ are formed unitarily with the base plate  310 ′ so as to define a single-piece monolithic structure. However, in other embodiments, one or both of the inferior and superior cutting guide flanges  382 ′,  384 ′ may be formed separately from the base plate  310 ′ and integrated with the base plate  310 ′ to define a multi-piece assembly. In the illustrated embodiment, the inferior and superior cutting guide flanges  382 ′,  384 ′ each have an irregular shape. However, other suitable shapes and configurations are also contemplated including, for example, rectangular or trapezoidal shapes. 
     In the illustrated embodiment, the inferior cutting guide flange  382 ′ defines a substantially flat/planar superior surface  386 ′, and the superior cutting guide flange  384 ′ similarly defines a substantially flat/planar inferior surface  388 ′. In one embodiment, the planar superior surface  386 ′ defined by the inferior cutting guide flange  382 ′ is generally tangent with the diameter of the lateral pin receiving opening  320   b ′, and is also arranged substantially co-planar with the superior surface  150 ′ defined by the reference bench  104  of the datum block  100  ( FIG.  22   ). The planar inferior surface  388 ′ of the superior cutting guide flange  384 ′ is arranged substantially co-planar with the inferior surface  346  defined by the superior cutting guide flange  316 ′ extending medially from the base plate  310 ′. Additionally, the planar superior surface  386 ′ of the inferior cutting guide flange  382 ′ is aligned substantially parallel with and offset from the planar inferior surface  388 ′ of the superior cutting guide flange  384 ′ to thereby form the lateral cutting guide or channel  380 ′. As should be appreciated, the lateral cutting guide  380 ′ preferably defines a channel width equal to the channel width of the medial cutting guide  348 ′, each being sized in relatively close tolerance with the cutting blade thickness of an oscillating or reciprocating saw (or another cutting device) to form smooth and accurate horizontal resection cuts in the proximal tibia  12 . 
     As should be appreciated, the eminence stylus  300 ′ may be used in the same manner as described above with regard to the eminence stylus  300  to form the horizontal medial resection cut C HM , the vertical medial resection cut C VM , and the vertical lateral resection cut C VL  ( FIGS.  20 A- 20 C ). However, the eminence stylus  300 ′ may also be used to form a horizontal lateral resection cut C HL  (shown as a dashed line in  FIG.  20 C ) to complete the lateral resection of the proximal tibia  12 . Specifically, with the graduated tibial pin  390  inserted into the lateral pin receiving opening  320   b ′ and anchored to the proximal tibia  12 , an oscillating or reciprocating saw (or another cutting device) may be inserted into and displaced along the horizontal lateral cutting guide  380 ′ defined between the inferior cutting guide flange  382 ′ and the superior cutting guide flange  384 ′ to thereby form the horizontal lateral resection cut C HL . As indicated above, the graduated tibial pin  390  serves as a guard or stop to control the depth of the horizontal resection cut and to prevent overcutting or notching of the tibial eminence  14  which might otherwise compromise the strength and integrity of the tibial eminence  14 . After formation of the final resection cut, the eminences stylus  300 ′ may be removed from the datum block  100 . As should be appreciated, the design of the eminence stylus  300 ′ allows for the formation of all necessary resection cuts to complete medial and lateral resection of the proximal tibia  12 . 
     D. Graduated Tibial Pin 
     Referring to  FIG.  23   , shown therein is a graduated tibial pin  390  according to one form of the present invention for use in association with the eminence stylus  300  or the eminence stylus  300 ′. As indicated above, the graduated tibial pin  390  provides further stabilization and support to the eminence stylus  300 ,  300 ′ to prevent unintended/unintentional movement of the eminence stylus  300  relative to the proximal tibia  12  (and the datum block  100 ), and also serves as a guard or stop during formation of the tibial resection cuts to control the depth of the cuts and to prevent overcutting or notching which might otherwise compromise the strength and integrity of the tibial eminence  14 . In the illustrated embodiment, the graduated tibial pin  390  is configured as an elongate rod extending along a longitudinal axis L and generally including a distal-most end  390   a , a distal bone engaging/anchoring portion  392 , a proximal head portion  394 , and a marked portion  396  including a series of markers or indicia  398  positioned generally along the proximal region of the pin  390 . 
     In one embodiment, the pin  390  has a substantially circular outer cross section. However, other embodiments are also contemplated wherein the graduated tibial pin  390  is provided with other cross-sectional shapes. In another embodiment, the distal bone engaging/anchoring portion  392  includes a drill flute  392   a  or another type of cutting feature to provide the pin  390  with self-drilling/self-cutting capabilities, and a thread cutting tap  392   b  or another type of thread forming feature to provide the pin  390  with self-tapping capabilities. The threads of the tap  392   b  also serve to anchor the pin  390  in bone tissue to prevent the pin  390  from pulling out of the bone. However, it should be understood that in other embodiments, the pin  390  may be provided with other types of anchor elements to retain the pin  390  in bone tissue, and need not necessarily include self-drilling/self-cutting/self-cutting capabilities. In the illustrated embodiment, the proximal head portion  394  is configured for coupling with a driver or another tool/instrument capable of exerting a rotational force or torque onto the pin  390  to drive the pin  390  into bone tissue. In one embodiment, the proximal head portion  394  is provided with one or more flattened or truncated regions  394   a  to facilitate the application of a rotational force or torque onto the proximal head  394 . However, other configurations are also contemplated including, for example, providing the proximal head  394  with a hexagonal configuration for mating engagement with a hex-driver. In one embodiment, the series of markers or indicia  398  along the marked portion  396  comprise a series of bands or lines having varying widths and/or a varying number of lines per band. However, other embodiments are also contemplated wherein the markers or indicia  398  may comprise numbers, letters, symbols, colors, or other readily identifiable indicia. 
     Referring now to  FIGS.  24 A- 24 C and  25 A- 25 C , shown therein is the graduated tibial pin  390  in relation to the proximal tibia  12  and the eminence stylus  300 . As shown in  FIGS.  24 A and  25 A , once the eminence stylus  300  is adjusted to a desired position and orientation relative to the proximal tibia  12  and locked to the datum block  100 , the graduated tibial pin  390  is positioned atop the proximal tibia  12  and adjacent the medial flange  312   a  of the eminence stylus  300 , with the longitudinal axis L of the pin  300  in general alignment with the indicator members  306   a ,  306   b  and substantially perpendicular or normal to the mechanical axis  13  of the tibia. The anterior-posterior position of the graduated tibial pin  390  is then adjusted until the distal-most end  390   a  of the pin  390  is positioned slightly anterior to the posterior surface of the proximal tibia  12 . The position of the distal-most end  390   a  of the pin  390  relative to the posterior surface of the proximal tibia  12  can be determined visually or manually by tactile touch. In this position/orientation of the pin  90 , an observation/notation is made as to which of the markers or indicia  398  along the marked portion  396  of the pin  390  is aligned with a particular reference location, which in the illustrated embodiment comprises the anterior end surface or edge defined by the medial flange  312   a  on the eminence stylus  300 . However, other reference locations are also contemplated. As shown in  FIGS.  24 A and  25 A , the indicia  398   a  is generally aligned with the anterior end surface of the medial flange  312   a.    
     Referring to  FIGS.  24 B and  25 B , the graduated tibial pin  390  is then inserted into the pin-receiving opening  320   a  in the eminence stylus  300  and is driven into the proximal tibia  12  until the noted indicia  398   a  is generally aligned with the anterior end surface of the medial flange  312   a . In this position, the graduated tibial pin  390  will be fully engaged/anchored within the proximal tibia  12  with the distal-most end  390   a  of the pin positioned slightly anterior to the posterior surface of the proximal tibia  12 . As should be appreciated, in this position, the graduated tibial pin  390  provides maximum protection against overcutting of the horizontal and vertical resection cuts, particularly along the posterior region of the proximal tibia, the likes of which might otherwise result in weakening of the remaining portion of the tibial eminence  14  and/or tibial condyles and potential fracturing of the same. However, the above-discussed procedure for inserting the graduated tibial pin  390  into the proximal tibia  12  ensures that the distal-most end  390   a  of the pin does not penetrate or puncture through the posterior surface of the proximal tibia  12 , thereby avoiding potential damage or trauma to soft tissue structures residing behind the posterior cortex which might otherwise be damaged by the distal-most end  390   a  of the pin  390  protruding through the posterior cortical wall. Accordingly, by controlling the insertion depth of the pin  390  into the proximal tibia  12 , the position of the distal-most end  390   a  of the pin  390  relative to the posterior cortical wall can be correspondingly controlled, thereby minimizing the risks associated with over-insertion of the pin  30  (i.e., puncturing the posterior cortical wall and potentially damaging adjacent soft tissue structures) and under-insertion of the pin  30  (i.e., leaving the posterior region of the proximal tibia  12  unprotected against overcutting of the horizontal and vertical resection cuts and potentially compromising the structural integrity of the unresected bone via posterior tibial notching). 
     Referring to  FIGS.  24 C and  25 C , illustrated therein is the proximal tibia  12  subsequent to formation of the horizontal and vertical medial resection cuts C HM , C VM  and removal of the medially resected bone fragment. As discussed above and as shown in  FIGS.  24 C and  25 C , the above-discussed procedure for inserting the graduated tibial pin  390  into the proximal tibia  12  ensures that the distal-most end  390   a  of the pin  390  is positioned proximately adjacent the posterior cortical wall W P  but does not penetrate or puncture through the posterior cortical wall W P , while at the same time providing maximum protection against overcutting of the horizontal and vertical medial resection cuts C HM , C VM . Although the above-discussed procedure for controlling the insertion depth of the graduated tibial pin  390  has been illustrated and described in association with medial resection of the proximal tibia  12 , it should be understood that the insertion procedure can likewise be used in association with lateral resection of the proximal tibia  12 . 
     E. Lateral Cut Guide 
     Referring to  FIG.  26   , shown therein is a lateral cut guide  400  according to one form of the present invention, as attached to the datum block  100  in relation to the proximal tibia  12 . As should be appreciated, the lateral cut guide  400  is attached to the datum block  100  via the locking or pinch force mechanism  106  of the datum block  100 , details of which have been set forth above. Although the lateral cut guide  400  is shown attached to and used in association with the datum block  100 , it should be understood that the lateral cut guide  400  may also be attached to and used in association with the recut block  600  (discussed below) or other devices or instruments. 
     As will be discussed in greater detail below, the lateral cut guide  400  includes guide or capture features that serve to guide an oscillating or reciprocating saw (or another type of cutting instrument) along a cutting plane to form a horizontal lateral resection cut C HL  ( FIG.  29 B ) in the proximal tibia  12 . As discussed above, the eminence stylus  300  may be used to form a horizontal medial resection cut C HM , a vertical medial resection cut C VM , and a vertical lateral resection cut C VL  ( FIGS.  26  and  29 A ). Upon removal of the eminence stylus  300  from the datum block  100  and attachment of the lateral cut guide  400  to the datum block  100 , the lateral cut guide  400  may be used to form the horizontal lateral resection cut C HL  ( FIG.  29 B ) to complete the lateral resection of the proximal tibia  12 . As also discussed above, the embodiment of the eminence stylus  300 ′ may alternatively be used to form each of the resection cuts to perform complete medial and lateral resection of the proximal tibia  12  via a single instrument (the eminence stylus  300 ′) attached to the datum block  100 . 
     Referring collectively to  FIGS.  27 ,  28 A and  28 B , in the illustrated embodiment, the lateral cut guide  400  generally includes a medial mounting portion  402 , a lateral guide portion  404 , and a tibial pin  406  attached to the mounting portion  402 . In one embodiment, the mounting portion  402  and the guide portion  404  are formed unitarily with one another to define a single-piece monolithic structure. However, in other embodiments, the mounting portion  402  and the guide portion  404  may be formed separately from one another and integrated together to form a multi-piece assembly. Additionally, in the illustrated embodiment, the tibial pin  406  is pivotally attached to the mounting portion  402  via a pivot pin or hinge  408  to allow articulating pivotal movement of the tibia pin  406  relative to the mounting portion  402  about the pivot axis P ( FIG.  28 A ). However, other embodiments are also contemplated wherein the tibial pin  406  is fixedly attached to the mounting portion  402 , or fixedly, pivotally and/or translatably attached to other portions of the lateral cut guide  400 . 
     In one embodiment, medial mounting portion  402  has a plate-like configuration and defines an elongate slot or channel  410  extending therethrough in an anterior-posterior direction to thereby define a superior mounting plate portion  412  and an inferior mount plate portion  414 , each having a substantially flat/planar configuration and a generally rectangular shape. The superior and inferior mounting plates  412 ,  414  are connected to one another via a medial wall  416 . The inferior mounting plate  412  defines substantially flat/planar superior and inferior surfaces  418 ,  420 , respectively. Additionally, the superior mounting plate  414  may also define substantially flat/planar superior and inferior surfaces. In one embodiment, the lateral guiding portion  404  includes superior and inferior guide plate portions or wings  422 ,  424  that extend from the superior and inferior mounting plates  412 ,  414 , respectively. The superior guide plate  422  defines a substantially flat/planar inferior surface  426 , and the inferior guide plate  422  defines a substantially flat/planar superior surface  428 . The planar inferior surface  426  of the superior guide plate  422  is aligned substantially parallel with and offset from the planar superior surface  428  of the inferior guide plate  422  to thereby form a lateral cutting guide or channel  430  defined between the adjacent inferior and superior planar surfaces  426 ,  428 . As should be appreciated, the lateral cutting guide channel  430  preferably defines a channel width sized in relatively close tolerance with the cutting blade thickness of an oscillating or reciprocating saw (or another cutting device) to form a smooth and accurate horizontal lateral resection cut along the proximal tibia  12 . The superior surface of the superior guide plate  422  and the inferior surface of the inferior guide plate  424  are tapered in a medial-lateral direction to provide increased visualization of the proximal tibia  12  during a cutting operation, but may alternatively be provided as flat/planar surfaces. Additionally, the lateral end portion of the cutting guide portion  404  preferably defines a concave region  405  that may serve as a soft tissue retractor to facilitate creation of space for entry of the sawblade into the lateral cutting guide channel  430  to avoid damage or trauma to the soft tissue. 
     The tibial pin  406  includes a base or mounting ring portion  440  ( FIG.  28 B ) configured for pivotal attachment to the mounting portion  402  (via passing the pivot pin  408  through an opening in the mounting ring  440 ), and also includes an elongate pin portion  442  extending from the mounting ring portion  440 . Since the tibial pin  406  is positively connected to the mounting portion  402 , the risk of losing, misplacing or dropping the tibial pin  406  is removed. In one embodiment, the elongate pin portion  442  has a generally circular or square-shaped outer cross section that is sized substantially equal to the outer cross section of the graduated tibial pin  390 . As will be discussed below, the elongate pin portion  442  is positionable in the lateral pin opening O L  ( FIG.  29 A ) previously formed in the proximal tibia  12  by the graduated tibial pin  390  that was inserted into the lateral pin-receiving opening  320   b  in the eminence stylus  300  and driven into the proximal tibia  12  prior to formation of the vertical lateral resection cut C VL  ( FIG.  20 C ). The elongate pin portion  442  is also provided with a tapered distal end  444  to facilitate insertion into the previously-formed lateral pin opening O L . 
     Referring collectively to  FIGS.  26 ,  29 A and  29 B , shown therein is the lateral cut guide  400  attached to the datum block  100  in relation to the proximal tibia  12 . Having described the structural features associated with the lateral cut guide  400 , some of the operational characteristics associated with the lateral cut guide  400  according to various embodiments of the present invention will now be discussed. 
     The lateral cut guide  400  is initially engaged to the datum block  100  by inserting the elongate pin portion  442  of the tibial pin  406  into the previously-formed lateral pin opening O L , and by positioning the inferior mounting plate  414  into the slot  154  defined between the reference bench  104  and the main body  102  of the datum block  100 . In this initial engagement arrangement, since the tibial pin  406  is pivotally attached to the medial mounting portion  402  and since the elongate pin portion  42  is able to slide along the lateral pin opening O L , the position and orientation of the lateral cut guide  400  may be easily adjusted relative to the datum block  100 . Additionally, pivotal attachment of the tibial pin  406  to the mounting portion  402  allows the pin  406  to be adjustably maneuvered to conform to varying pin opening orientations and/or tibial bone shapes. However, it should be noted that the particular position and orientation of the lateral cut guide  400  (other than the inferior-superior position) on the datum block is not critical to the success/accuracy of the cutting operation. Additionally, as shown in  FIGS.  29 A and  29 B , the shape/contour of the posterior region of the lateral guiding portion  404  is preferably configured to abut the anterior outer surface of the proximal tibia  12  when the lateral cut guide  400  is engaged to the datum block  100  to provide additional stabilization and support to the lateral cut guide  400  during a cutting operation to provide increased cutting accuracy. Additionally, as indicated above, the concave region  405  of the lateral guiding portion  404  is intended to serve as a soft tissue retractor to facilitate creation of space for entry of the sawblade into the lateral cutting guide channel  430  to avoid damage or trauma to the soft tissue. 
     Once the lateral cut guide  400  is positioned and oriented relative to the datum block  100 , the pinch force mechanism  106  may be actuated to lock the lateral cut guide  400  in a position relative to the datum block  100 . Actuation of the pinch force mechanism  106  correspondingly compresses the planar superior surface  418  of the inferior mounting plate  414  against the planar inferior surface  152  of the reference bench  104  to thereby capture/lock the lateral cut guide  400  to the datum block  100 , which in turn retains the lateral cut guide  400  in a fixed position and orientation relative to the datum block  100 . As should be appreciated, locking of the lateral cut guide  400  maintains the lateral cutting guide  430  in a fixed inferior-superior position relative to the datum block  100 , which in turn provides increased cutting accuracy. 
     After the lateral cut guide  400  is properly aligned and positioned relate to the datum block  100  and engaged with the datum block  100  via actuation of the pinch force mechanism  106 , an oscillating or reciprocating saw (or another cutting device) is inserted into and displaced along the lateral cutting guide  430  to form the horizontal lateral resection cut C HL  in the proximal tibia  12  ( FIG.  29 B ) to complete the lateral resection of the proximal tibia  12 . As should be appreciated, positioning of the elongate pin portion  442  of the tibial pin  406  into the previously-formed lateral pin opening O L  serves as a guard or stop to control the depth of the horizontal lateral resection cut C HL  and to prevent overcutting or notching of the tibial eminence  14  which might otherwise compromise the strength and integrity of the tibial eminence  14 . In addition to serving as a protective guard or stop, the tibial pin  406  also provides additional stabilization and support to the lateral cut guide  400  during the cutting operation to provide increased cutting accuracy. Although the illustrated embodiment of the elongate pin portion  442  does not extend across the entire anterior-posterior dimension of the proximal tibia  12 , it should be understood that other lengths of the elongate pin portion  442  may be used that extend across substantially the entire anterior-posterior dimension of the proximal tibia  12 . 
     As should be appreciated, the combined use of the eminence stylus  300  (described above) and the lateral cut guide  400  allows for the formation of all necessary resection cuts to complete medial and lateral resection of the proximal tibia  12 . As should also be appreciated, since the eminence stylus  300  and the lateral cut guide  400  are both locked to the datum block  100  in the same manner using a constant reference plane (i.e., by compressing a planar mounting plate against the inferior surface  152  of the reference bench  104 ), it is possible to ensure that the horizontal medial resection cut C HM  (formed via use of the eminence stylus  300 ) and the horizontal lateral resection cut C HL  (formed via use of the lateral cut guide  400 ) are co-planar to one another. 
     F. Saw Capture Block 
     Referring to  FIG.  30   , shown therein is a saw capture block  500  according to one form of the present invention, as attached to the datum block  100 . However, it should be understood that the saw capture block  500  may also be attached to and used in association with the recut block  600  (discussed below) or other devices or instruments. In the illustrated embodiment, the saw capture block  500  is attached to the datum block  100  via the locking or pinch force mechanism  106  of the datum block  100 , details of which have been set forth above. Additionally, although not illustrated in  FIG.  30   , it should be understood that the datum block  100  is initially attached to the proximal tibia  12  via the provisional attachment pin  190  and/or the terminal attachment pins  196  ( FIG.  10   ) prior to attachment of the saw capture block  500  to the datum block  100 . 
     The saw capture block  500  includes features that cooperate with features of the datum block  100  (or the recut block  600 ) to provide a saw capture or cutting guide channel that guides an oscillating or reciprocating saw (or another type of cutting instrument) along a cutting plane to form a horizontal resection cut in the proximal tibia  12 . In one embodiment, the saw capture block  500  may be used in association with the datum block  100  (or the recut block  600 ) to perform a total or full resection of the proximal tibia  12  (i.e., the complete removal of a proximal region of the proximal tibia  12  to form a planar resection cut extending entirely across the proximal tibia  12 ). For example, the saw capture block  500  may be particularly beneficial for use in association with CR (cruciate retaining) and PS (posteriorly stabilized) arthroplasty procedures, although use of the saw capture block  500  in association with other knee arthroplasty procedures is also contemplated. 
     Referring collectively to  FIGS.  31 ,  32 A and  32 B , in the illustrated embodiment, the saw capture block  500  is a single-piece monolithic structure including an inferior mounting portion  502  and a superior guide portion  504 . In one embodiment, the inferior mounting portion  502  and the superior guide portion  504  are formed as a single piece to provide the saw capture block  500  as a single-piece monolithic structure. However, in other embodiments, the inferior mounting portion  502  and the superior guide portion  504  may be formed separately from one another and integrated together to form a multi-piece saw capture block assembly. 
     In one embodiment, the inferior mounting portion  502  has a plate-like configuration defining substantially flat/planar superior and inferior surfaces  510 ,  512 , respectively. Additionally, in a further embodiment, the inferior mounting plate  502  has a trapezoidal shape and defines an outer perimeter sized and configured for general alignment with an outer perimeter of the superior portion  110  of the main body  102  of the datum block  100  ( FIG.  6 E ). As should be appreciated, alignment of the anterior region of the inferior mounting plate  502  with the anterior region of the superior portion  110  aids in proper alignment and positioning of the saw capture block  500  relative to the datum block  100  ( FIG.  30   ). However, other shapes and configurations of the inferior mounting plate  502  are also contemplated. Additionally, an alignment mark or line indicia  514  extending in a medial-lateral direction is defined along the superior surface  510  of the inferior mounting plate  502  ( FIG.  31   ) which may be aligned with the anterior edge of the reference bench  104  of the datum block  100  to further aid in alignment and positioning of the saw capture block  500  relative to the datum block  100  ( FIG.  30   ). 
     The inferior surface  512  of the inferior mounting plate  502  may be provided with a recess or indentation  516  ( FIG.  32 B ) that is generally alignable with the gripper member  180  associated with the pinch force mechanism  106  of the datum block  100  when the saw capture block  500  is positioned in general alignment on the datum block  100 . As should be appreciated, the recess  514  has an inner cross section that is sized somewhat larger than the outer cross section of the gripper member  180  such that when the pinch force mechanism  106  is partially actuated (i.e., positioning of the lever arm  160  at a pivotal location between the fully locked and fully unlocked positions), the gripper member  180  is partially received within the recess  516 , but is not compressed tightly against the mounting plate portion  502 . In this operational configuration the saw capture block  500  is provisionally retained on the datum block  100 , but is not securely locked to the datum block  100 . The saw capture block  500  is therefore permitted to rotate relative to the datum block  100  and translate relative to the datum block  100  within the confines of the recess  516  (i.e., translation is limited by abutment of the gripper member  180  against the inner parametrical surfaces  518  of the recess  516 ). Use of this provisionally retained configuration may be particularly beneficial during a cutting operation to allow a wider range of motion of the cutting instrument relative to the proximal tibia  12 , while still maintaining engagement of the saw capture block  500  with the datum block  100 . However, at any point in the cutting operation, the saw capture block  500  may be locked in position on the datum block  100  by fully actuating the pinch force mechanism  106  to lock the saw capture block  500  in position. 
     Additionally, it should be understood that in other embodiments, engagement between the saw capture block  500  and the datum block  100  is fully constrained and does not allow any relative movement between the saw capture block  500  and the datum block  100 . As should be appreciated, compressed engagement of the gripper member  180  against the mounting plate portion  502  via full actuation of the pinch force mechanism  106 , in combination with engagement between three mating surface pairs defined between the saw capture block  500  and the datum block  100 , fully and securely constrains the saw capture block  500  in position relative to the datum block  100 . As shown in  FIG.  33 C , in the illustrated embodiment, the three mating surface pairs between the saw capture block  500  and the datum block  100  include mating engagement of the inferior planar surface defined by mounting plate  502  of the saw capture block  500  with the superior planar surface defined by the superior portion  110  of the datum block  100 , mating engagement of the superior planar surface defined by the mounting plate  502  of the saw capture block  500  with the inferior planar surface defined by the reference table  104  of the datum block  100 , and mating engagement of the medially-facing edge of the mounting leg  522  ( FIG.  32 A ) of the saw capture block  500  with the laterally-facing edge defined by the reference table  104  of the datum block  100 . However, other mating surface pairs defined between the saw capture block  500  and the datum block  100  are also contemplated. 
     In one embodiment, the superior capture or guide portion  504  has a guide plate portion  520  and a mounting leg portion  522  extending between and interconnecting the guide plate portion  520  and the inferior mounting plate  502 . The guide plate portion  520  defines substantially flat/planar superior and inferior surfaces  524 ,  526 , respectively, and has a generally trapezoidal shape defining an outer perimeter sized and configured for general alignment with an outer perimeter of the reference bench  104  of the datum block  100  ( FIG.  6 E ). Alignment of the outer perimeter of the guide plate  520  with the outer perimeter of the reference bench  104  may further aid in proper alignment and positioning of the saw capture block  500  relative to the datum block  100  ( FIG.  30   ). However, other shapes and configurations of the guide plate  520  are also contemplated. The mounting leg  522  includes a spacer portion  522   a  attached to the inferior surface  526  of the guide plate  520 , and a base portion  522   b  that is attached to the superior surface  510  of the inferior mounting plate  502 . A guide slot  528  is defined between the inferior surface  526  of the guide plate  520  and a superior surface of the mounting leg base portion  522   b.    
     Referring collectively to  FIGS.  30  and  33 A- 33 C , shown therein is the saw capture block  500  attached to the datum block  100 . Having described the structural features associated with the saw capture block  500 , some of the operational characteristics associated with the saw capture block  500  according to various embodiments of the present invention will now be discussed. 
     The saw capture block  500  is initially engaged to the datum block  100  by positioning the inferior mounting plate  502  into the slot or channel  154  defined between the reference bench  104  and the main body  102  of the datum block  100 . In this initial engagement arrangement, the position and orientation of the saw capture block  500  may be adjusted relative to the datum block  100 . As indicated above, various features associated with the saw capture block  500  may be used to properly position and orient the saw capture block  500  relative to the datum block  100 . For example, alignment of the mark or line indicia  514  defined along the superior surface  510  of the inferior mounting plate  502  with the anterior edge of the bench  104  may aid in properly positioning and orienting the saw capture block  500  relative to the datum block  100 . Additionally, alignment of the anterior perimeter of the inferior mounting plate  502  with the anterior region of the superior portion  110  of the datum block  100 , as well as alignment of the outer perimeter of the guide plate  520  with the outer perimeter of the reference bench  104 , may further aid in properly positioning and orienting the saw capture block  500  relative to the datum block  100 . Once the saw capture block  500  is properly positioned and oriented relative to the datum block  100 , the pinch force mechanism  106  may be actuated to lock the saw capture block  500  in a position relative to the datum block  100 . Actuation of the pinch force mechanism  106  correspondingly compresses the planar superior surface  510  of the inferior mounting plate  502  against the planar inferior surface  152  of the reference bench  104  to thereby capture/lock the saw capture block  500  to the datum block  100 , which in turn retains the saw capture block  500  in a fixed position and orientation relative to the datum block  100 . As should be appreciated, locking of the saw capture block  500  in a fixed inferior-superior position relative to the datum block  100  provides a fixed saw capture guide between the saw capture block  500  and the datum block  100 . 
     As shown most clearly in  FIGS.  30  and  33 C , when the saw capture block  500  is engaged with the datum block  100 , the planar inferior surface  526  of the guide plate  520  is aligned substantially parallel with and offset from the planar superior surface  150  of the reference bench  104  to thereby form a medial-lateral cutting guide or channel  530  defined between the adjacent inferior and superior planar surfaces  526 ,  150 . As should be appreciated, the medial-lateral cutting guide  530  preferably defines a channel width sized in relatively close tolerance with the cutting blade thickness of an oscillating or reciprocating saw (or another cutting device) to form a smooth and accurate resection cut along the proximal tibia  12 . Additionally, the width of the guide slot  528  defined between the inferior surface  526  of the guide plate  520  and the superior surface of the mounting leg base portion  522   b  ( FIG.  32 A ) is equal to the distance separating the inferior and superior planar surfaces  526 ,  150  to thereby provide the medial-lateral cutting guide  530  with a uniform channel width entirely along the medial-lateral dimension of the saw capture block  500 . 
     After the saw capture block  500  is properly aligned and positioned relate to the datum block  100  and engaged with the datum block  100  via actuation of the pinch force mechanism  106 , an oscillating or reciprocating saw (or another cutting device) is inserted into and displaced along the medial-lateral cutting guide  530  to fully resect the proximal tibia  12 . As shown in  FIG.  33 C , the cutting guide  530  is open and unrestricted along the anterior and posterior sides and along the medial side of the cutting guide  530 . Additionally, as shown in  FIG.  33 A , the cutting guide  530  is open and unrestricted along the posterior region along the lateral side of the cutting guide  530 , with the anterior region along the lateral side being blocked by the mounting leg  522  of the saw capture block  500 . However, the open posterior region along the lateral side of the cutting guide  530  provides a pathway for the saw to fully resect the proximal tibia  12 . However, as indicated above, if additional access to the proximal tibia  12  is required, the pinch force mechanism  106  may be positioned in a partially actuated position wherein the saw capture block  500  is provisionally retained on the datum block  100 , but is permitted to rotate and translate (within a confined range) relative to the datum block  100  to allow for a wider range of motion of the saw or cutting instrument. Following resection of the proximal tibia  12 , the saw capture block  500  may be removed from the datum block  100  to allow for engagement of other devices and instruments to the datum block  100 . 
     G. Recut Block 
     Referring to  FIGS.  34  and  35   , shown therein is a recut block  600  according to one form of the present invention, as shown in relation to the proximal tibia  12 . In the illustrated embodiment, the recut block  600  is attached to the proximal tibia  12  using the terminal attachment pins  196   a ,  196   b  previously used to attach the datum block  100  to the proximal tibia  12  ( FIG.  10   ), the details of which will be set forth below. Accordingly, the position and orientation of the recut block  600  relative to the proximal tibia  12  is advantageously based on the same points of reference used to set the position and orientation of the datum block  100 . However, other techniques and devices for attaching the recut block  600  to the proximal tibia  12  are also contemplated. 
     As will also be set forth in greater detail below, the reference/resection plane (i.e., the planar superior surface of the reference bench) defined by the recut block  600  may be varied/angled relative to the horizontal reference/resection plane defined by the datum block  100 . Accordingly, should a change to the horizontal medial resection cut C HM  and/or the horizontal lateral resection cut C HL  be desired (i.e., a different posterior slope angle, varus-valgus angle, or both), the datum block  100  can be removed from the terminal attachment pins  196   a ,  196   b  and replaced with a recut block  600  defining the appropriate reference/resection plane to recut one or both of the horizontal resection cuts to the desired angle. As should be appreciated, a kit or set containing multiple recut blocks  600  defining different reference/resection planes (i.e., different posterior slope angles, varus-valgus angles, or both) can be provided to accommodate intra-operative changes/alterations to the horizontal medial resection cut C HM  and/or the horizontal lateral resection cut C HL . 
     Similar to the datum block  100 , the recut block  600  is used as a fundamental instrument to provide a neutral/reference tibial foundation to which other devices or instruments may be engaged to and referenced from. Additionally, the recut block  600  is designed to be substantially interchangeable with the datum block  100 . Accordingly, any device or instrument that is used in association with the datum block  100  may also be used in association with the recut block  600 . Therefore, if the datum block  100  is replaced with the recut block  600  to recut one or both of the horizontal resection cuts at a different angle, subsequent steps and techniques associated with the knee arthroplasty procedure which utilize other devices and instruments can be performed using the recut block  600 . 
     As indicated above, the recut block  600  is attached to the proximal tibia  12  using the terminal attachment pins  196   a ,  196   b  previously used to attach the datum block  100  to the proximal tibia  12  ( FIGS.  34  and  35   ). Notably, it is not necessary to remove the terminal attachment pins  196   a ,  196   b  from the proximal tibia  12  to detach the datum block  100  from the proximal tibia  12  or to attach the recut block  600  to the proximal tibia  12 . Instead, referring back to  FIG.  10   , the provisional attachment pin  190  is removed from the proximal tibia  12  and the datum block  100  is simply slipped off of the terminal attachment pins  196   a ,  196   b . Since the recut block  600  is interchangeable with the datum block  100 , the recut block  600  is slipped over the proximal heads  198  of the terminal attachment pins  196   a ,  196   b  (via the same pin-receiving openings that were used to attach the datum block  100  to the proximal tibia  12 ) and displaced along the pins  196   a ,  196   b  until positioned adjacent the proximal tibia  12 . Since the recut block  600  is attached to the proximal tibia  12  using the identical points of reference (the pins  196   a ,  196   b ) used to attach the datum block  100  to the proximal tibia  12 , the position and orientation of the recut block  600  relative to the proximal tibia  12  can be set to match that of the datum block  100  (with the exception of defining a different horizontal reference/resection plane). If desired, a third terminal attachment pin may be inserted into another of the pin-receiving openings and driven into the proximal tibia at an oblique angle relative to the pins  196   a ,  196   b  to retain the recut block  600  in position adjacent the proximal tibia  12 . Alternatively, a third terminal attachment pin having an enlarged head (like the provisional attachment pin  190 ) may be inserted into another of the pin-receiving openings and driven into the proximal tibia  12  until the enlarged head is compressed against the recut block  600  to retain the recut block  600  in position adjacent the proximal tibia  12 . 
     Referring collectively to  FIGS.  36 A- 36 F , shown therein are further details associated with the recut block  600 . The recut block  600  generally includes a main body  602  configured for attachment to the proximal tibia  12 , a reference bench or table  604  extending from the main body  602  and configured for removable attachment of various devices/instruments to the recut block  600 , and a locking mechanism  606  associated with the main body  602  and configured to removably lock the other devices/instruments to the recut block  600 . In the illustrated embodiment, the recut block  600  is not configured to engage and support an extramedullary alignment rod (such as the alignment rod  108  associated with the datum block  100 ). However, in other embodiments, the recut block  600  may be configured to engage and support an extramedullary alignment rod or other types of alignment devices. 
     In the illustrated embodiment, the main body  602  of the recut block  600  is configured as a single-piece monolithic connection block  610  defining a substantially flat/planar superior surface  612 , a laterally facing surface  614 , a cavity  616  ( FIG.  34   ) extending through the connection block  610  from the planar superior surface  612  in a superior-inferior direction, and a passage  618  ( FIG.  36 C ) extending through the connection block  610  in an anterior-posterior direction and transversely intersecting and positioned in communication with the cavity  616 . As will be discussed in greater detail below, the cavity  616  and the passage  618  serve to house components of the locking mechanism  606 . The connection block  610  has a generally rectangular shape configured similar to that of the superior portion  110  of the datum block  100 . However, other shapes and configuration are also contemplated. 
     The connection block  610  further defines a plurality of pin-receiving openings  622  extending therethrough generally in an anterior-posterior direction that are sized and configured for receipt of the terminal attachment pins  196   a ,  196   b  anchored to the proximal tibia  12  or for receipt of additional attachment pins. As should be appreciated, the pin-receiving openings  622  defined in the recut block  600  have the same relative position and orientation as the pin-receiving openings  122  defined in the datum block  100  such the recut block  600  may be interchanged with the datum block  100  using the same terminal attachment pins  196   a ,  196   b  previously used to attach the datum block  100  to the proximal tibia  12 . 
     As indicated above, the recut block  600  includes a reference bench or table  604  extending from the main body  602  and configured for removable attachment of various devices/instruments to the recut block  600 . In the illustrated embodiment, the reference bench  604  is formed unitarily with the main body  602  to define a single-piece monolithic structure. However, in other embodiments, the reference bench  604  may be formed separately from the main body  602  and coupled thereto to define an integrated multi-piece structure. As shown in  FIG.  36 E , the reference bench  604  has a non-rectangular trapezoidal shape configured similar to that of the reference bench  104  of the datum block  100 , defining a narrowing or tapered width extending away from the main body  602  in a medial-lateral direction. However, other suitable shapes and configurations of the reference bench  604  are also contemplated as falling within the scope of the present invention. 
     As shown in  FIGS.  36 A- 36 C , the reference bench  604  defines a substantially flat/planar superior surface  650  and a substantially flat/planar inferior surface  652 , with the planar superior and inferior surfaces  650 ,  652  preferably arranged generally parallel with one another, although non-parallel arrangements of the planar superior and inferior surfaces  650 ,  652  are also contemplated. Additionally, the planar inferior surface  652  of the reference bench  604  is positioned opposite the planar superior surface  612  of the connection block  610  to thereby define a space or gap  654  therebetween sized and configured for receipt of plate-like portions of other devices and instruments to be connected with the recut block  600 , details of which will be set forth below. In the illustrated embodiment, the planar inferior surface  652  of the reference bench  604  is preferably arranged generally parallel with the planar superior surface  612  of the connection block  610 , although non-parallel arrangements of the opposing superior and inferior surfaces are also contemplated. Additionally, although not specifically illustrated in the drawing figures, the reference bench  604  may be provided with a groove or indicia extending along the planar superior surface  650  in an anterior-posterior direction to provide a visual indication or marker corresponding to the location of the vertical medial resection C VM  of the proximal tibia  12  (i.e., similar to the groove/indicia  156  defined along the reference table  104  of the datum block  100 ). 
     As discussed above and as illustrated in  FIG.  36 A- 36 C , the recut block  600  defines a reference/resection plane P extending along the planar superior surface  650  of the reference bench  604 . As also discussed above, the reference/resection plane P of the recut block  600  may be varied/angled relative to the horizontal reference/resection plane of the datum block  100  (as defined along the planar superior surface  150  of the reference bench  104 ). Accordingly, should a change to the previously cut horizontal medial resection cut C HM  and/or the horizontal lateral resection cut C HL  (formed using the datum block  100 ) be desired (i.e., having a different posterior slope angle, varus-valgus angle, or both), the datum block  100  can be replaced with a recut block  600  defining the appropriate reference/resection plane P to recut one or both of the horizontal resection cuts to the desired angle. For example, as illustrated in  FIG.  36 A , the planar superior surface  650  of the recut block  600  may be provided with a reference/resection plane P having a posterior slope angle β that varies from the horizontal reference/resection plane of the datum block  100  within the range of +β to −β. Additionally, as illustrated in  FIG.  36 B , the planar superior surface  650  of the recut block  600  may be provided with a reference/resection plane P having a varus-valgus angle θ that varies from the horizontal reference/resection plane of the datum block  100  within the range of +θ to −θ. In other embodiments, the planar superior surface  650  of the recut block  600  may be provided with a reference/resection plane P having a varus-valgus angle θ and a posterior slope angle β that both vary from the horizontal reference/resection plane of the datum block  100 . 
     As also discussed above, a kit or set containing multiple recut blocks  600  defining varying reference/resection planes can be provided to accommodate intra-operative changes/alterations to the horizontal medial resection cut C HM  and/or the horizontal lateral resection cut C HL . For example, the kit may include multiple recut blocks  600  defining reference/resection planes P having a posterior slope angle β of +2°, +4°, +6°, −2°, −4°, −6°, etc., or any other posterior slope angle β that may be used in a knee arthroplasty procedure to form a horizontal medial resection cut C HM  and/or the horizontal lateral resection cut CH having a desired posterior slope angle. The kit may also include multiple recut blocks  600  defining reference/resection planes P having a varus-valgus angle θ of +2°, +4°, +6°, −2°, −4°, −6°, etc., or any other varus-valgus angle θ that may be used in a knee arthroplasty procedure to form a horizontal medial resection cut C HM  and/or the horizontal lateral resection cut CH having a desired varus-valgus angle. Additionally, providing the kit with further recut blocks  600  defining reference/resection planes P exhibiting other desired features and characteristics is also contemplated as falling within the scope of the present invention. 
     As indicated above, the recut block  600  includes a locking mechanism  606  associated with the main body  602  that is configured to removably lock various devices/instruments to the reference bench  604 . Referring to  FIGS.  37 A and  37 B , illustrated therein are unlocked and locked configurations of the recut block  600 , respectively. Additionally, referring to  FIGS.  38 A and  38 B , illustrated therein are corresponding unlocked and locked configurations of the locking mechanism  606 , respectively. 
     In the illustrated embodiment, the locking mechanism  606  generally includes a threaded member or bolt-type actuator member  660  threadedly engaged within the anterior-posterior passage  618  in the connection block  610  of the recut block  600 , and a gripper member or actuated member  680  positioned within the inferior-superior cavity  616  in the connection block  610  and movably engaged with the threaded member  660 , the details of which will be set forth below. The main body  602  of the recut block  600  includes additional elements and features associated with the locking mechanism  606 . For example, the connection block  610  defines a circular opening  624  ( FIG.  36 F ) extending through a posterior wall of the connection block  610  in communication and general alignment with the anterior-posterior passage  618  that is sized to receive a distal end portion of the threaded member  660  therein to thereby act as a bearing surface to provide additional support and stability to the locking mechanism  606 . Additionally, a retaining pin  626  ( FIGS.  36 D and  36 E ) at least partially extends into the anterior-posterior passage  618  to prevent the threaded member  660  from backing entirely out of the passage  618 . A visualization slot or window  628  ( FIG.  36 D ) also extends through the inferior surface of the connection block  610  in communication with the passage  618  to provide direct visualization of and access to the components of the locking mechanism  606 . 
     Referring specifically to  FIGS.  37 A / 37 B and  38 A/ 38 B, illustrated therein are unlocked and locked configurations of the recut block  600  and the locking mechanism  606 . In the unlocked configuration shown in  FIGS.  37 A / 38 A, a plate-like portion of a device/instrument may be positioned within the space or gap  654  defined between the planar inferior surface  652  of the reference bench  604  and the planar superior surface  612  of the connection block  610 . The recut block  600  and the locking mechanism may then be transitioned from the unlocked configuration illustrated in  FIGS.  37 A / 38 A to the locked configuration illustrated in  FIGS.  37 B / 38 B via actuation of the locking mechanism  606 . Actuation of the locking mechanism  606  is accomplished by rotating the threaded member  660  to threadingly displace the threaded member  660  along the anterior-posterior passage  618  in the direction of arrow A, which in turn displaces the gripper member  680  in an inferior-superior direction along the cavity  616  in the direction of arrow B, and correspondingly engages the gripper member  680  against the plate-like portion of the device/instrument positioned within the gap  654  and compresses the plate-like portion against the planar inferior surface  652  of the reference bench  604  to thereby retain the device/instrument in a fixed position and orientation relative to the recut block  600 . 
     Referring to  FIGS.  39 A- 39 D , shown therein are further details regarding the locking mechanism  606  including the threaded member  660  and the gripper member  680 . In the illustrated embodiment, the threaded member  660  generally includes a proximal head portion  662 , a threaded portion  664 , a tapered portion  666  and a distal stem portion  668 . The proximal head portion  662  includes one or more drive features  670  that facilitates receipt of a rotational force or torque onto the threaded member  660 . In one embodiment, the drive feature  670  comprises a hexagonal-shaped recess formed in the proximal head portion  662 . However, other types and configurations of suitable drive features are also contemplated. The threaded portion  664  includes external threads  672  that are configured for threading engagement with internal threads (not shown) formed along the anterior-posterior passage  618  in the connection block  610 . Additionally, the threaded portion  664  may be provided with an unthreaded portion  674  adjacent the location where the threaded member  660  engages the gripper member  680  to avoid interference between the external threads  672  and the gripper member  680 . The tapered portion  666  defines a tapered outer surface  676  that is inwardly tapered in a proximal-distal direction. The distal stem portion  668  includes a substantially smooth cylindrical-shaped shaft that extends through a guide channel formed in the gripper member  680  and which is positioned within the circular opening  624  ( FIG.  36 F ) extending through the posterior wall of the connection block  610  to thereby act as a bearing to provide additional support and stability to the locking mechanism  606 , and particularly to the threaded member  660 . Although a particular configuration of the threaded member  660  has been illustrated and described herein, other configurations of actuator members, including non-threaded actuator members, are also contemplated for use in association with the locking mechanism  606 . 
     In the illustrated embodiment, the gripper member  680  generally includes an inferior bearing portion  682  and a superior gripping portion  684 . The inferior bearing portion  682  includes a channel  686  extending therethrough in an anterior-posterior direction and which is sized to receive the tapered portion  666  and the distal stem portion  668  of the threaded member therein. The channel  686  is partially bound by one or more bearing surfaces  688  configured for sliding engagement with the tapered surface  676  of the threaded member  660 . The bearing surfaces  688  may be angled to define an inward taper extending in an anterior-to-posterior direction. However, non-tapered bearing surfaces  688  are also contemplated. Additionally the channel  686  narrows adjacent the posterior end of the gripper member  680  to define a guide slot  690  sized to received the distal stem portion  668  of the threaded member  660  therein to stabilize engagement between the gripper member  680  and the threaded member  660  and to allow the threaded member  660  to be linearly displaced along the channel  686 . The superior gripping portion  684  of the gripper member may be provided with a generally circular outer cross section sized for guiding displacement within the inferior-superior cavity  616  in the connection block  610  generally along the arrow B. The gripping portion  684  also includes a superior gripping surface  692  configured for compressed engagement against plate-like portions of devices/instruments positioned within the gap  654  defined between the reference bench  604  and the connection block  610  of the recut block  600 . 
     As indicated above, the recut block  600  and the locking mechanism are transitioned from the unlocked configuration illustrated in  FIGS.  37 A / 38 A to the locked configuration illustrated in  FIGS.  37 B / 38 B via actuation of the locking mechanism  606  which is accomplished by rotating the threaded member  660  using a hex driver or another type of driver instrument to threadingly displace the threaded member  600  along a threaded portion of the passage  618  in the connection block  610  in the direction of arrow A. Displacement of the threaded member  660  in the direction of arrow B slidably displaces the tapered surface  676  of the threaded member  660  along the bearing surfaces  688  of the gripper member  680 , which in turn displaces the gripper member  680  along the cavity  616  in the connection block  610  in the direction of arrow B. As should be appreciated, the sliding interaction between the tapered surface  676  and the bearing surfaces  688  converts linear displacement of the threaded member  660  in the direction of arrow A into liner displacement of the gripper member  680  in the direction of arrow B. Liner displacement of the gripper member  680  in the direction of arrow B in turn compresses a plate-like portion of device/instruments positioned within the gap  654  defined between the reference bench  604  and the connection block  610  against the planar inferior surface  652  of the reference bench  604  to thereby lock/retain the device/instrument in a fixed position and orientation relative to the recut block  600 . 
     As should be appreciated, the compression or clamping force exerted by the gripper member  680  onto the plate-like portion of the device/instrument positioned within the space  654  is controlled by incremental threading insertion or retraction of the threaded member  660  into and out of the passage  618  in the connection block  610 . Although the illustrated embodiment of the locking mechanism  606  uses a hex driver (not shown) to drive the threaded member  660  into and out of the passage  618 . However, other embodiments are also contemplated wherein the threaded member  660  may be rotated via a thumb wheel or a T-shaped handle that may be incorporated into the bolt-type actuator  660  to avoid the need for a separate driver instrument. Although a particular type and configuration of the locking mechanism  606  has been illustrated and described herein for use in association with the recut block  600 , it should be understood that other types and configurations of locking mechanisms or other compression structures/devices are also contemplated for use in association with the present invention in addition to or in lieu of the locking mechanism  606  including, for example, the pinch force mechanism  106  illustrated and described above with regard to the datum block  100 . 
     H. Tibia Size Gauge 
     Referring to  FIG.  40   , shown therein is a tibia size gauge  700  according to one form of the present invention. As will be discussed in greater detail below, the tibia size gauge  700  may be used to reference/measure medial and/or lateral aspects of the proximal tibia  12  along the tibial cortex (e.g., at the medial tibial cortex  12   MC  and/or at the lateral tibial cortex  12   LC ) at the proposed/intended level of the horizontal resection cuts. In this manner, the tibial baseplate implant I may be appropriately sized, and the resulting position of the tibial baseplate implant I ( FIGS.  41 C and  42 C ) may be appropriately centered on the resected proximal tibia  12  in a medial-lateral direction to minimize underhang/overhang of the baseplate implant I relative to the outer periphery of the resected proximal tibia  12 , which in turn results in a stronger and more secure and stable engagement of the tibial implant on the proximal tibia. 
     As shown in  FIG.  40   , the tibia size gauge  700  is used in association with the eminence stylus  300  attached to the datum block  100 , with the datum block  100  in turn pinned to the proximal tibia  12 , the details of which have been illustrated and described above. However, it should be appreciated that the tibia size gauge  700  may also be used in association other devices and instruments, including but not limited to the eminence stylus  300 ′ illustrated and described above. 
     The tibia size gauge  700  generally includes a scaled reference or datum plate  710  having a length extending generally along a longitudinal axis L, a first reference arm  720  extending axially from the scaled datum plate  710  and including a distal pointer  722  defining a distal end surface  724  configured for engagement with an outer surface of the proximal tibia  12 , and a second reference arm  730  transversely offset from the scaled plate  710  by a transversely extending spacer arm  740  and including a distal pointer  732  defining a distal end surface  734  configured for engagement with an outer surface of the proximal tibia  12 . In the illustrated embodiment, the tibia size gauge  700  is provided as a single-piece, substantially flat/planar plate having a generally uniform and relatively thin plate thickness t ( FIG.  40   ). However, other embodiments are also contemplated wherein the tibia size gauge  700  may take on other configurations and/or may be provided as multiple pieces or elements that are interconnected with one another to form the tibia size gauge  700 . Additionally, in the illustrated embodiment, the first and second reference arms  720 ,  730  are oriented at an oblique angle relative to the longitudinal axis L of the scaled datum plate  710 . However, in other embodiments, the first and second reference arms  720 ,  730  may be arranged generally parallel with the longitudinal axis L. Further, in the illustrated embodiment, the distal end surfaces  724 ,  734  of the distal pointers  722 ,  732  are curved or rounded to provide secure and stable engagement with an outer surface of the proximal tibia  12 . However, in other embodiments, the distal end surfaces  724 ,  734  may be provided with a pointed configuration or a blunt configuration. 
     In the illustrated embodiment, the scaled datum plate  710  is configured for positioning within the medial cutting guide  348  which, as discussed above in association with  FIGS.  20 A- 20 C , is used to form the medial horizontal resection cut C HM  in the proximal tibia  12 . As also discussed above, the medial cutting guide  348  is formed between the planar inferior surface  346  defined by the cutting guide flange  316  on the eminence stylus  300  and the planar superior surface  150  defined by the reference bench  104  on the datum block  100 . As should be appreciated, the superior-inferior location of the medial cutting guide  348  (which is dictated by the inferior-superior location of the datum block  100  on the proximal tibia  12 ) determines the level/location of the horizontal medial and lateral resection cuts C HM , C HL , and the internal-external angular orientation of the eminence stylus  300  dictates the internal-external angular orientation of the medial cutting guide  348  and the resulting orientation of the vertical medial and lateral resection cuts C VM , C VL . The thickness t ( FIG.  40   ) of the scaled datum plate  710  is preferably sized in relatively close tolerance with the width of the medial cutting guide  348  to maintain the scaled datum plate  710  in a substantially co-planar relationship with the cutting plane defined by the medial cutting guide  348  (i.e., the plane along which the horizontal medial resection cut C HM  is formed). 
     As shown in  FIG.  40   , the scaled datum plate  710  includes one or more measurement scales  712  that each include scaled measurement indicia  714  which serve to provide a visual indication as to the distances being measured by the tibia size gauge  700 . In the illustrated embodiment, the scaled measurement indicia  714  include a series of parallel lines  714   a  and a series of numbers  714   b  corresponding to the parallel lines  714   a . In one embodiment, the parallel lines  714   a  alternate between solid lines and dashed lines to aid in identifying/distinguishing which of the parallel lines  714   a  is aligned with a predetermined measurement reference feature, which is the present embodiment is the straight/planar medial edge  316   a  defined by the cutting guide flange  316  of the eminence stylus  300 . However, it should be understood that other measurement reference features are also contemplated. In a further embodiment, adjacent pairs of the numbers  714   b  are offset from one another in an axial direction (along the longitudinal axis) to aid in identifying/distinguishing which of the numbers  714   b  is associated with the line that is aligned with the predetermined reference feature. Although one particular embodiment of the scaled measurement indicia  714  has been illustrated and described herein, it should be understood that other suitable types and configurations of measurement indicia are also contemplated for use in association with the tibia size gauge  700 . 
     Additionally, in the illustrated embodiment, the tibia size gauge  700  is configured to provide measurements of medial and lateral aspects of the proximal tibia  12  (e.g., the medial tibial cortex  12   MC  and the lateral tibial cortex  12   LC ;  FIGS.  40   / 41 A/ 42 A). Additionally, the tibia size gauge  700  is configured to provide measurements associated with both the left knee and the right knee (i.e., the tibia size gauge  700  is configured to be ambidextrous). Accordingly, the illustrated embodiment of the scaled datum plate  710  is provided with four measurement scales  712   a ,  712   b ,  712   c  and  712   d  ( FIGS.  41 A / 42 A), with the measurement scale  712   a  associated with measurements of medial aspects of the left knee (“LM”), the measurement scale  712   b  associated with measurements of lateral aspects of the left knee (“LL”), the measurement scale  712   c  associated with measurements of medial aspects of the right knee (“RM”), and the measurement scale  712   d  associated with measurements of lateral aspects of the right knee (“RL”). However, it should be understood that the tibia size gauge  700  may be provided with any number of measurement scales  712  including, for example, a single measurement scale. 
     Referring now to  FIGS.  41 A- 41 C , shown there is a technique according to one form of the invention for using the tibia size gauge  700  to reference/measure medial aspects of the proximal tibia  12  along the tibial cortex (e.g., at the medial tibial cortex  12   MC ) at the proposed/intended level of the horizontal resection cuts to determine the appropriate size of the tibial baseplate implant I to be installed on the proximal tibia  12  subsequent to resection. As indicated above, the datum block  100  is initially pinned to the proximal tibia  12 , and the eminence stylus  300  is provisionally engaged to the datum block  100  and centered/aligned in relation to the proximal tibia  12  or other anatomic structures using the indicator members  306   a ,  306   b , the alignment rod  18  and/or other alignment structures or alignment techniques. Once the eminence stylus  300  is centered/aligned in relation to the proximal tibia  12 , the eminence stylus  300  is locked in position on the datum block  100  via the pinch lock mechanism  106 . As indicated above, the proposed/intended level of the horizontal resection cuts corresponds to the cutting plane defined by the medial cutting guide  348 . 
     The scaled datum plate  710  of the tibia size gauge  700  is positioned within the medial cutting guide  348 , with the measurement scale  712   a  associated with measurements of medial aspects of the left knee (i.e., “LM”) positioned adjacent the straight/planar medial edge  316   a  of the cutting guide flange  316 . The distal end surface  724  of the pointer  722  is then positioned in contact with the medial tibial cortex  12   MC  on the medial side of the proximal tibia  12 . While maintaining contact between the distal end surface  724  of the pointer  722  and the medial tibial cortex  12   MC , the user observes which of the parallel lines  714   a  on the measurement scale  712  is aligned with the straight/planar medial edge  316   a  of the cutting guide flange  316 . The tibia size gauge  700  may require a certain degree of internal-external rotation within the medial cutting guide  348  to obtain alignment between the appropriate line  714   a  and the straight/planar medial edge  316   a . In the illustrated embodiment, the number  714   b  corresponding to the line  714   a  aligned with the medial edge  316   a  relates to the size of the tibial baseplate implant I ( FIGS.  41 B and  41 C ) that would properly fit on the proximal tibia  12  subsequent to resection. As shown in  FIG.  41 A , the indicated size measurement is “4”, which corresponds to a size 4 tibial baseplate implant I to be installed on the proximal tibia  12  ( FIG.  41 B ). As shown in  FIG.  41 C , subsequent to resection and finishing of the proximal tibia  12 , the appropriately sized baseplate implant I is installed on the resected proximal tibia  12  wherein underhang/overhang of the baseplate implant I on the resected proximal tibia  12  is minimized relative to the peripheral outer boundary of the proximal tibia  12  due to the above-described implant sizing technique. 
     As discussed above, in the illustrated embodiment, the numbers  714   b  on the measurement scale  712  relate to the size of the tibial baseplate implant I. However, in other embodiments, the numbers  714   b  on the measurement scale  712  may relate to the actual linear distance between the medial tibial cortex  12   MC  in contact with the distal end surface  724  of the pointer  722  and the centerline of the eminence stylus  300  (i.e., the centerline between the indicator members  306   a ,  306   b ), which preferably corresponds to the anatomic medial-lateral center of the proximal tibia  12  at the proposed/intended level of resection. 
     In the measurement technique illustrated in  FIGS.  41 A- 41 C  and described above, the appropriate size of the tibial baseplate implant I to be installed on the proximal tibia  12  is determined by referencing/measuring medial aspects of the proximal tibia  12  along the tibial cortex (e.g., at medial tibial cortex  12   MC ) at the proposed/intended level of resection. However, referring to  FIGS.  42 A- 42 C , it should be understood that the appropriate size of the tibial baseplate implant I may also be determined by referencing/measuring lateral aspects of the proximal tibia  12  along the tibial cortex (e.g., at the lateral tibial cortex  12   LC ) at the proposed/intended level of resection. Specifically, once the eminence stylus  300  is centered/aligned in relation to the proximal tibia  12 , the scaled datum plate  710  of the tibia size gauge  700  is initially positioned within the medial cutting guide  348  with the second reference arm  730  extending along the lateral side of the proximal tibia  12  and with the distal end surface  734  of the pointer  732  positioned in contact with the lateral tibial cortex  12   LC . Additionally, the measurement scale  712   b  associated with measurements of lateral aspects of the left knee (i.e, “LL”) is positioned adjacent the straight/planar medial edge  316   a  of the cutting guide flange  316 . While maintaining contact between the distal end surface  734  of the pointer  732  and the lateral tibial cortex  12   LC , the user observes which of the parallel lines  714   a  on the measurement scale  712  is aligned with the straight/planar medial edge  316   a  of the cutting guide flange  316 . As shown in  FIG.  42 A , the indicated size measurement is once again indicated as “4”, which corresponds to the size of the tibial baseplate implant I to be installed on the proximal tibia  12  ( FIGS.  42 B / 42 C) following resection to minimize underhang/overhang of the baseplate implant I relative to the peripheral outer boundary of the proximal tibia  12  at the level of resection. 
     As indicated above, the tibia size gauge  700  is configured to be ambidextrous, meaning the tibia size gauge  700  may also be used to reference/measure medial and lateral aspects of the proximal tibia  12  associated with both the left knee and the right knee. As should be appreciated, when referencing/measuring medial and lateral aspects of the proximal tibia  12  associated with the left knee, the measurement scales  712   a ,  712   b  associated with measurements of medial aspects of the left knee (i.e, “LM”) and lateral aspects of the left knee (i.e., “LL”) are used. However, when referencing/measuring medial and lateral aspects of the proximal tibia  12  associated the right knee, the measurement scales  712   c ,  712   d  associated with measurements of medial aspects of the right knee (i.e., “RM”) and lateral aspects of the right knee (i.e., “RL”) are used. 
     Referring collectively to  FIGS.  41 A- 41 C  and  FIGS.  42 A- 42 C , a technique according to a further form of the invention may be used to ensure that the appropriately sized tibial baseplate implant I is centered on the resected proximal tibia  12  (i.e., the centerline C of the implant I is aligned with the true anatomic center of the proximal tibia  12  at the proposed/intended level of the horizontal resection cuts). Notably, determining the true anatomic center of the proximal tibia  12  at the proposed/intended level of resection may be used to ensure the correct position of the horizontal resection cuts (i.e., that the resection cuts are centered relative to the true anatomic center of the proximal tibia  12 ), which in turn dictates the ultimate position of the baseplate implant I on the proximal tibia  12 . The disclosed centering technique references/measures both medial and lateral aspects of the proximal tibia  12  along the tibial cortex (e.g., at the medial tibial cortex  12   MC  and at the lateral tibial cortex  12   LC ) at the proposed/intended level of resection, and uses the resulting measurements to determine the true anatomic center of the proximal tibia  12  at the proposed/intended level of resection, the details of which will be discussed below. 
     As discussed above and as shown in  FIG.  41 A , the tibia size gauge  700  is initially used to reference/measure the medial tibial cortex  12   MC  at the proposed/intended level of resection by observing which of the parallel lines  714   a  on the measurement scale  712   a  is aligned with the straight/planar medial edge  316   a  of the cutting guide flange  316 . As also discussed above and as shown in  FIG.  42 A , the tibia size gauge  700  may then be used to reference/measure the lateral tibial cortex  12   LC  at the proposed/intended level of resection by observing which of the parallel lines  714   a  on the measurement scale  712   b  is aligned with the straight/planar medial edge  316   a  of the cutting guide flange  316 . If the observed measurement associated with the referencing/measuring of the medial tibial cortex  12   MC  is equal to the observed measurement associated with the referencing/measuring of the lateral tibial cortex  12   LC , then the eminence stylus  300  is appropriately centered along the true anatomic center of the proximal tibia  12  at the proposed/intended level of resection, and the vertical resection cuts can then be made for receipt of the tibial baseplate implant I at the appropriately centered position on the resected proximal tibia  12 . 
     However, if the observed medial and lateral measurements are not equal to one another, then the medial-lateral position and/or the orientation of the eminence stylus  300  can be correspondingly adjusted based on the observed medial and lateral measurements to more closely align the eminence stylus  300  with the true anatomic center of the proximal tibia  12  at the proposed/intended level of resection. For example, if the observed medial measurement is “3” and the observed lateral measurement is “5”, then the eminence stylus  300  may be unlocked from the datum block  100  and the position of the eminence stylus  300  shifted in a lateral direction to more closely align the centerline of the eminence stylus  300  with the true anatomic center of the proximal tibia  12  at the proposed/intended level of resection. After the adjustment to the position of the eminence stylus  300  is made, further medial and lateral measurements are once again taken and compared with one another to determine if further adjustment to the position of the eminence stylus  300  is required, or whether the true anatomic center has been reached. 
     As should be appreciated, this iterative measurement process using the tibia size gauge  700  to reference/measure both medial and lateral aspects of the proximal tibia  12  along the tibial cortex at the proposed/intended level of resection results in more accurate centering of the eminence stylus  300  with the true anatomic center of the proximal tibia  12 . As should be further appreciated, centering of the eminence stylus  300  with the true anatomic center of the proximal tibia  12  results in the formation of correctly centered/positioned resection cuts, which in turn ensures that the centerline C of the implant I is properly aligned with the anatomic center of the proximal tibia  12  at the resection level to thereby minimize underhang/overhang of the implant I relative to the peripheral outer boundary of the proximal tibia  12  ( FIGS.  41 C / 42 C). 
     Referring to  FIGS.  43 - 45   , shown therein is a tibia size gauge  750  according to another form of the present invention. Similar to the tibia size gauge  700  illustrated and described above, the tibia size gauge  750  may be used to reference/measure medial aspects of the proximal tibia  12  along the tibial cortex (e.g., at the medial tibial cortex  12   MC ) at the proposed/intended level of the horizontal resection cuts to determine the appropriate size of the tibial baseplate implant I to be installed on the resected proximal tibia  12 . Additionally, the tibia size gauge  750  also includes features that serve to appropriately align/orient the resection cuts on the proximal tibia  12 , which in turn results in proper alignment of the baseplate implant I on the resected proximal tibia  12  to thereby minimize underhang/overhang of the baseplate implant I on the resected proximal tibia  12 . As should be appreciated, minimizing underhang/overhang of the baseplate implant I on the resected proximal tibia  12  tends to provide a stronger and more secure and stable engagement of the tibial implant on the proximal tibia  12 . 
     As shown in  FIG.  43   , the tibia size gauge  750  is used in association with an eminence stylus  300 ″ (which is a modified version of the eminence stylus  300 ) attached to the datum block  100 , with the datum block  100  in turn pinned to the proximal tibia  12 , the details of which have been illustrated and described above. In the illustrated embodiment, the tibia size gauge  750  generally includes the eminence stylus  300 ″ which defines a scaled datum plate  760 , and an indicator member  770  removably attached to the scaled datum plate  760 . The indicator member  770  includes structures and features that reference/engage medial and anterior aspects of the proximal tibia  12  and, in cooperation with the scaled datum plate  760 , provide a visual measurement indication as to the estimated/appropriate size of the tibial baseplate implant I to be installed on the proximal tibia  12  subsequent to resection. 
     As indicated above, the eminence stylus  300 ″ is a modified version of the eminence stylus  300  illustrated and described above, and is configured virtually identical to the eminence stylus  300  with the exception of defining a scaled datum plate  760 . More specifically, the eminence stylus  300 ″ generally includes a base portion or body  302 ″ configured for attachment to the datum block  100 , a carriage  304 ″ movably attached to the base portion  302 ″ and configured for linear displacement along a longitudinal displacement axis L arranged in a generally anterior-posterior direction, and a pair of articulating arms or indicator members  306   a ″,  306   b ″ pivotally attached to the carriage  304 ″ and configured for pivotal displacement relative to the carriage  304 ″. Additionally, the base portion  302 ″ generally includes a base plate  310 ″, an inferior mounting flange  314 ″ extending from the base plate  310 ″ in a medial-lateral direction, and a superior cutting guide flange  316 ″ extending from the base plate  310 ″ in a medial-lateral direction and superiorly offset from the inferior mounting flange  314 ″. The mounting flange  314 ″ may be compressed against an inferior surface of the reference bench  104  via actuation of the pinch force mechanism  106  to lock the eminence stylus  300 ″ in a select position and orientation relative to the datum block  100 . Additionally, a substantially flat/planar inferior surface defined by the cutting guide flange  316 ″ cooperates with a substantially flat/planar superior surface defined by the reference table  104  of the datum block  100  to thereby form a medial cutting guide or channel  348 ″ therebetween. It should be understood that the eminence stylus  300 ″ is configured substantially identical to the eminence stylus  300  and operates in a manner substantially identical to that of the eminence stylus  300 , with the exception of incorporation of the features associated with the scaled datum plate  760  onto the superior surface  344 ″ of the cutting guide flange  316 ″. 
     As illustrated most clearly in  FIGS.  45 A and  45 B , the scaled datum plate  760  includes a measurement scale  762  that includes scaled measurement indicia  764  which serve to provide a visual indication as to the distances being measured by the tibia size gauge  750 . In the illustrated embodiment, the scaled measurement indicia  764  include a series of parallel grooves  764   a  cut into the superior surface  344 ″ of the cutting guide flange  316 ″ and extending in an anterior-posterior direction, and numbers  764   b  corresponding to the grooves  764   a . In one embodiment, the grooves  764   a  are V-shaped and extend across the superior surface  344 ″ in an anterior-posterior direction. Although one particular embodiment of the scaled measurement indicia  764  has been illustrated and described herein, it should be understood that other suitable types and configurations of measurement indicia are also contemplated for use in association with the tibia size gauge  750 . 
     In the illustrated embodiment, the indicator member  770  extends along a longitudinal axis L and generally includes an inferior flat/planar plate  772  having a generally uniform and relatively thin plate thickness t ( FIG.  44 A ), and a superior flat/planar plate  774  offset from the inferior plate  772  to define a gap G therebetween. The superior plate  774  includes a tooth or projection  776  ( FIG.  45 A ) extending into the gap G toward the inferior plate  772  and configured for sliding engagement within and along individual ones of the parallel grooves  764   a  cut into the superior surface  344 ″ of the cutting guide flange  316 ″. In the illustrated embodiment, the tooth  776  has a V-shaped profile and is sized and shaped for sliding displacement along individual ones of the parallel V-shaped grooves  764   a  ( FIG.  45 A ). However, other suitable shapes and configurations of the tooth  776  and the grooves  764   a  are also contemplated. Additionally, the superior plate  774  is provided with a generally triangular-shaped outer profile defining an apex or arrowhead  778  at a distal end thereof. However, other suitable shapes and configurations of the superior plate  774  are also contemplated. The indicator member  770  further includes a first reference arm  780  extending axially from the inferior plate  772  and including a distal pointer  782  defining a distal end surface  784  configured for engagement with a medial aspect of the proximal tibia  12 , and a second reference arm  790  which also extends axially from the inferior plate  772  and including a distal pointer  792  defining a distal end surface  794  configured for engagement with an anterior aspect of the proximal tibia  12 . In the illustrated embodiment, the distal end surfaces  784 ,  794  of the distal pointers  782 ,  792  are curved or rounded to provide secure and stable engagement with the medial and anterior outer surfaces of the proximal tibia  12 . However, in other embodiments, the distal end surfaces  784 ,  794  may be provided with a pointed configuration or a blunt configuration. 
     As shown in  FIG.  43   , the indictor member  770  is attached to the scaled datum plate  760  (which corresponds to the cutting guide flange  316 ″ of the datum block  300 ″) by positioning the inferior plate  772  into the medial cutting guide  348 ″ (formed between the cutting guide flange  316 ″ and the reference bench  104  of the datum block  100 ), and by positioning the V-shaped tooth  776  defined by the superior plate  774  into one of the V-shaped grooves  764   a  defined along the scaled datum plate  760 . As should be appreciated, the superior-inferior location of the medial cutting guide  348 ″ determines the level/location of the resection cuts, and the inward-outward angular orientation of the eminence stylus  300 ″ dictates the inward-outward angular orientation of the medial cutting guide  348 ″ and the resulting orientation of the vertical eminence resection cut. 
     Referring now to  FIGS.  45 A and  45 B , shown there is a technique according to one form of the invention for using the tibia size gauge  750  to reference medial aspects of the proximal tibia  12  along the tibial cortex (e.g., at the medial tibial cortex  12   MC ) at the proposed/intended level of the horizontal resection cuts to determine the appropriate position and orientation (i.e., angular alignment) of the resection cuts to be formed in the proximal tibia  12  to receive the tibial baseplate implant I. As indicated above, the datum block  100  is initially pinned to the proximal tibia  12 . Based on an initial estimation of the size of the tibial baseplate implant I to be installed on the proximal tibia  12 , the indictor member  770  is attached to the scaled datum plate  760  by sliding the V-shaped tooth  776  of the indicator member  770  into the appropriate V-shaped groove  764   a  on the scaled datum plate  760 , and with the distal apex or arrowhead  778  of the indicator member  770  pointing to the estimated size of the tibial baseplate implant I. As shown in the exemplary embodiment illustrated in  FIG.  45 B , the estimated size of the tibial baseplate implant I to be installed on the proximal tibia  12  is set to a size of “3”. 
     With the indictor member  770  fully engaged/assembly on the scaled datum plate  760  of the eminence stylus  300 ″, the eminence stylus  300 ″ (with the indicator member  770  attached to the scaled datum plate  760  at the scale location corresponding to the estimated size of the implant I) is engaged to the reference bench  104  of the datum block  100  and is displaced in an anterior-posterior direction until the distal end surface  784  of the pointer  782  is positioned in contact with the medial tibial cortex  12   MC , and the distal end surface  794  of the pointer  792  associated with the second reference arm  790  is positioned in contact with the anterior tibial cortex  12   AC  of the proximal tibia  12 . Notably, these two points of contact between the indicator member  770  and the proximal tibia  12  at the level of resection serve to effectively center and align the eminence stylus  300 ″ relative to the proximal tibia  12  or other anatomic structures (e.g. cruciate ligaments). Proper centering/alignment of the eminence stylus  300 ″ may be checked/verified by observing the position/orientation of the indicator members  306   a ″,  306   b ″ relative to the proximal tibia  12  or other anatomic structures (e.g. cruciate ligaments). Although the illustrated embodiment establishes two points of contact between the tibia size gauge  750  and the proximal tibia  12 , it should be understood that three or more points of contact between the tibia size gauge  750  and the proximal tibia  12  may alternatively be established. 
     Once the eminence stylus  300 ″ (with the indictor member  770  attached thereto and positioned in contact with the medial and anterior aspects of the proximal tibia  12 ) is appropriately centered/aligned in relation to the proximal tibia  12 , the eminence stylus  300 ″ may be locked in position on the datum block  100  via actuation of the pinch lock mechanism  106 . At this point, the indictor member  770  may be removed from the eminence stylus  300 ″. Because proper centering/alignment of the eminence stylus  300 ″ relative to the proximal tibia  12  using the above-described centering/alignment technique results in formation of the resection cuts at the appropriate position and orientation, the tibial baseplate implant I will also be properly positioned/oriented on the resected proximal tibia  12 , whereby underhang/overhang of the baseplate implant I is thereby minimized relative to the peripheral outer boundary of the proximal tibia  12 . 
     As should be appreciated, the above-described technique for centering/aligning the eminence stylus  300 ″ relative to the proximal tibia  12  utilizes an initial estimation of the size of the tibial implant I to set the indictor member  770  at the appropriate location/position on the scaled datum plate  760 , and then displaces the eminence stylus  300 ″ (with the indictor member  770  engaged thereto) in an anterior-posterior direction to establish at least two points of contact with the proximal tibia  12  at the level of proposed/intended resection to center/align the eminence stylus  300 ″ relative to the proximal tibia  12 , the accuracy of which can be confirmed/verified via the indicator members  306   a ″,  306   b ″. However, other techniques for centering/aligning the eminence stylus  300 ″ relative to the proximal tibia  12  using the tibia size gauge  750 , as well as other uses of the tibia size gauge  750 , are also contemplated. 
     For example, in another form of the invention, the datum block  100  is initially pinned to the proximal tibia  12 , and the eminence stylus  300 ″ is provisionally engaged to the datum block  100  and generally centered/aligned in relation to the proximal tibia  12  or other anatomic structures using the indicator members  306   a ″,  306   b ″, the alignment rod  18  and/or other alignment structures or alignment techniques. Once the eminence stylus  300 ″ is generally centered/aligned in relation to the proximal tibia  12 , the eminence stylus  300 ″ may be provisionally locked in position on the datum block  100  via partial actuation of the pinch lock mechanism  106  (i.e., movement of the eminence stylus  300 ″ is resisted but not prevented). The distal end surface  784  of the pointer  782  is then be generally aligned with the medial tibial cortex  12   MC  on the medial side of the proximal tibia  12 , and the V-shaped tooth  776  defined by the superior plate  774  of the indicator member  770  is positioned in the appropriate V-shaped groove  764   a  defined along the scaled datum plate  760 . The V-shaped tooth  776  is then displaced along the V-shaped groove  764   a  by correspondingly displacing the indicator member  770  in an anterior-posterior direction until the distal end surface  784  of the pointer  782  is positioned in contact with the medial tibial cortex  12   MC , and the distal end surface  794  of the pointer  792  associated with the second reference arm  790  is positioned in contact with the anterior tibial cortex  12   AC  of the proximal tibia  12 . If the distal end surface  784  of the pointer  782  does not contact the medial tibial cortex  12   MC , the indicator member  770  is disengaged from the scaled datum plate  760  and repositioned on the scaled datum plate  760  with the V-shaped tooth  776  positioned in a different V-shaped groove  764   a  that provides contact of the distal end surface  784  of the pointer  782  with the medial tibial cortex  12   MC , and contact of the distal end surface  794  of the pointer  792  with the anterior tibial cortex  12   AC . Notably, these two (or more) points of contact between the indicator member  770  and the proximal tibia  12  further centers/aligns the eminence stylus  300 ″ to the appropriate position/orientation relative to the proximal tibia  12 . At this point, the eminence stylus  300 ″ may be fully locked in position on the datum block  100  via full actuation of the pinch lock mechanism  106 , followed by resection of the proximal tibia  12  using the techniques illustrated and described above. 
     Additionally, as shown in  FIG.  45 B , the user may observe which of the numbers  764   b  on the measurement scale  762  is aligned with the distal apex or arrowhead  778  defined by the indicator member  770 . In the illustrated embodiment, the number  764   b  aligned with the distal apex or arrowhead  778  relates to the size of the tibial baseplate implant I that would properly fit on the proximal tibia  12  subsequent to resection. As shown in  FIG.  45 B , the indicated size measurement is “3”, which corresponds to the appropriate size of the tibial baseplate implant I to be installed on the proximal tibia  12 . Subsequent to resection and finishing of the proximal tibia  12 , the appropriately sized baseplate implant I is installed on the resected proximal tibia  12  wherein underhang/overhang of the baseplate implant I on the resected proximal tibia  12  is minimized relative to the peripheral outer boundary of the proximal tibia  12  due to the above-described implant sizing and alignment techniques. 
     I. Tibia Rotation Gauge 
     Referring to  FIG.  46   , shown therein is a tibia rotation gauge  800  according to one form of the present invention. The tibia rotation gauge  800  may be used to align/orient the eminence stylus  300  to the appropriate angular orientation relative to the proximal tibia  12 , which in turn aligns/orients the resection cuts on the proximal tibia  12  to ensure proper alignment of the baseplate implant I on the resected proximal tibia  12  to thereby minimize underhang/overhang of the baseplate implant I on the resected proximal tibia  12 . As should be appreciated, minimizing underhang/overhang of the baseplate implant I on the resected proximal tibia  12  tends to provide a stronger and more secure and stable engagement of the tibial implant on the proximal tibia  12 . As will be discussed in greater detail below, the tibia rotation gauge  800  is engaged with the eminence stylus  300  and includes alignment features that engage anterior aspects of the proximal tibia  12  to adjust the angular position of the eminence stylus  300  to the appropriate orientation relative to the proximal tibia  12 . 
     As shown in  FIGS.  47 A,  47 B and  48   , the tibia rotation gauge  800  may be used in association with the eminence stylus  300  attached to the datum block  100 , with the datum block  100  in turn pinned to the proximal tibia  12 , the details of which have been illustrated and described above. However, it should be understood that the tibia rotation gauge  800  may also be used in association other devices and instruments, including but not limited to the eminence stylus  300 ′, the recut block  600 , the tibia size gauge  700 , and the tibia size gauge  750 . The tibia rotation gauge  800  may be particularly useful when used in association with the tibia size gauge  700  and/or the tibia size gauge  750  to align/orient the eminence stylus  300  to the appropriate orientation relative to the proximal tibia  12  prior to performing the sizing/centering techniques associated with the tibia size gauge  700  and the sizing/alignment techniques associated with the tibia size gauge  750 . 
     Referring once again to  FIG.  46   , in the illustrated embodiment, the tibia rotation gauge  800  extends along a longitudinal axis L and generally includes a base plate or handle portion  802 , a medial alignment leg  804   a  extending axially from the base plate  802  and including a distal alignment foot or flange  806   a  defining a distal end bone-contacting surface or edge  808   a  configured for engagement with the anterior outer surface of the proximal tibia  12 , and a lateral alignment leg  804   b  extending axially from the base plate  802  and including a distal alignment foot or flange  806   b  defining a distal end bone-contacting surface or edge  808   b  configured for engagement with the anterior outer surface of the proximal tibia  12 . The distal end bone-contacting surfaces or edges  808   a ,  808   b  are outwardly tapered at a taper angle θ relative to the longitudinal axis L. The taper angle θ is preferably set to generally match or conform to the contour or outer profile of the anterior outer surface of the proximal tibia  12 , and more specifically the anterior tibial cortex  12   AC , at the level of the horizontal resection cuts. In one embodiment, the taper angle θ falls within a range of about 30° to 90°. In another embodiment, the taper angle θ falls within a range of about 45° to 75°. In a further embodiment, the taper angle θ is set at approximately 60°. However, other taper angles θ are also contemplated. Additionally, in the illustrated embodiment, the distal end surfaces or edges  808   a ,  808   b  are substantially flat/planar. However, in other embodiments, the distal end surfaces or edges  808   a ,  808   b  may be curved or partially curved in a concave or convex configuration. 
     The tibia rotation gauge  800  further defines a slot or open inner region  810  arranged generally along the longitudinal axis L and extending from an open end adjacent the distal end surfaces or edges  808   a ,  808   b  toward the base plate  802 . The open ended slot  810  has a generally rectangular configuration and is bound/defined by the distal end surfaces or edges  808   a ,  808   b , substantially flat/planar inner side surfaces or edges  805   a ,  805   b  defined by the medial and lateral alignment legs  804   a ,  804  and arranged generally parallel with the longitudinal axis L, and a substantially flat/planar inner end surface  803  defined by the base plate  802  and arranged generally perpendicular to the longitudinal axis L. As will be discussed below, the open ended slot  810  is sized to receive the base plate  310  defined by the main body  302  of the eminence stylus  300  ( FIGS.  17 - 20   ) therein such that the planar inner side surfaces or edges  805   a ,  805   b  of the medial and lateral alignment legs  804   a ,  804   b  are engaged in relatively close tolerance with the substantially flat/planar outer side surface of the base plate  310 . 
     Additionally, in the illustrated embodiment, the tibia rotation gauge  800  is provided as a single-piece, substantially flat/planar plate having a generally uniform and relatively thin plate thickness that is preferably sized in relatively close tolerance with the width of the medial cutting guide  348  defined between the datum block  100  and the eminence stylus  300 . However, other embodiments are also contemplated wherein the tibia rotation gauge  800  may take on other configurations and/or may be provided as multiple pieces or elements that are interconnected with one another to form the tibia rotation gauge  800 . 
     Referring now to  FIGS.  47 - 49   , shown there is a technique according to one form of the invention for using the tibia rotation gauge  800  to align/orient the eminence stylus  300  to the appropriate angular orientation relative to the proximal tibia  12 , which in turn aligns/orients the resection cuts on the proximal tibia  12  to ensure proper alignment of the baseplate implant I on the resected proximal tibia  12  to minimize underhang/overhang of the baseplate implant I on the resected proximal tibia  12 . 
     Referring to  FIGS.  47 A and  47 B , the datum block  100  is initially pinned to the proximal tibia  12 , and the eminence stylus  300  is engaged to the datum block  100  and generally centered/aligned in relation to the proximal tibia  12  or other anatomic structures using the indicator members  306   a ,  306   b , the alignment rod  18  and/or other alignment structures or alignment techniques. Once the eminence stylus  300  is centered/aligned in relation to the proximal tibia  12 , the eminence stylus  300  may be locked in position on the datum block  100  via actuation of the pinch lock mechanism  106 . However, as shown in  FIGS.  47 A and  47 B , in some instances, the eminence stylus  300  may remain in a misaligned angular orientation relative to the proximal tibia  12 . In other words, the central plane P of the eminence stylus  300  (defined between the flat/planar indicator members  306   a ,  306   b ) may not be properly aligned with the central anatomic plane P T  of the tibia (i.e., the central plane P of the eminence stylus  300  is inwardly/outwardly rotational offset from the central anatomic plane P T  of the tibia). 
     Referring to  FIGS.  48  and  49   , the misaligned condition of the eminence stylus  300  ( FIGS.  47 A and  47 B ) may be corrected via use of the tibia rotation gauge  800 . First, the eminence stylus  300  is unlocked from the datum block  100  via de-actuation of the pinch lock mechanism  106  such that the eminence stylus  300  is free to internally/externally rotate relative to the datum block  100 . The tibia rotation gauge  800  is then engaged to the eminence stylus  300  by aligning the open ended slot  810  of the tibia rotation gauge  800  with the base plate  310  of the eminence stylus  300  and inserting the medial alignment leg  804   a  into the medial cutting guide  348  (defined between the cutting guide flange  316  on the eminence stylus  300  and the reference bench  104  on the datum block  100 ). As discussed above in association with  FIGS.  20 A- 20 C , the medial cutting guide  348  is used to form the medial horizontal resection cut C HM  in the proximal tibia  12 , and the cutting plane defined along the medial cutting guide  348  is therefore positioned at the level of resection. The thickness of at least the medial alignment leg  804   a  is preferably sized in relatively close tolerance with the width of the medial cutting guide  348  to maintain the tibia rotation gauge  800  in a substantially co-planar relationship with the cutting plane defined by the medial cutting guide  348 . 
     As should be appreciated, the planar inner side surfaces or edges  805   a ,  805   b  defined by the medial and lateral alignment legs  804   a ,  804   b  of the tibia rotation gauge  800  are engaged in relatively close tolerance with the substantially flat/planar outer side surface of the base plate  310  of the eminence stylus  300 . Accordingly, angular rotation of the tibia rotation gauge  800  will result in corresponding angular rotation of the eminence stylus  300 . As the tibia rotation gauge  800  is displaced along the base plate  310  of the eminence stylus  300  in an anterior-posterior direction (in the direction of arrow A), the distal feet  806   a ,  806   b  of the medial and lateral alignment legs  804   a ,  804   b  will engage the anterior surface of the proximal tibia  12  at the level of resection (i.e., at the level where the horizontal resection cuts will be formed). More specifically, the distal bone-contacting surfaces or edges  808   a ,  808   b  defined by the distal feet  806   a ,  806   b  will engage the anterior tibial cortex  12   AC  to define at least two points or locations of contact between the tibia rotation gauge  800  and the anterior surface of the proximal tibia  12  at the level of resection. As indicated above, the distal bone-contacting surfaces or edges  808   a ,  808   b  are configured to generally match or conform to the profile of the anterior outer surface of the proximal tibia  12  at the level of resection. Accordingly, as the tibia rotation gauge  800  is displaced in the direction of arrow A and into compressed engagement with the proximal tibia  12 , engagement of the distal bone-contacting surfaces or edges  808   a ,  808   b  against the anterior tibial cortex  12   AC  along two established points or locations of contact will draw the tibia rotation gauge  800  into proper alignment with the proximal tibia  12 , which will in turn rotate the eminence stylus  300  into a properly aligned orientation relative to the proximal tibia  12  with the central plane P of the eminence stylus  300  generally aligned with the central anatomic plane P T  of the tibia. At this point, the eminence stylus  300  may once again be locked in position on the datum block  100  via actuation of the pinch lock mechanism  106 , and the tibia rotation gauge  800  can be removed from the eminence stylus  300 . 
     As should be appreciated, use of the tibia rotation gauge  800  to properly align the eminence stylus  300  to the correct angular orientation relative to the proximal tibia  12  will result in formation of the resection cuts at the proper alignment and orientation relative to the proximal tibia  12 , which will in turn ensure proper alignment of the baseplate implant I on the resected proximal tibia  12  to minimize underhang/overhang of the baseplate implant I relative to the outer periphery of the resected proximal tibia  12 . As should also be appreciated, minimizing underhang/overhang of the baseplate implant I on the resected proximal tibia  12  tends to provide a stronger and more secure and stable engagement of the tibial implant on the proximal tibia  12 . Additionally, it should be further appreciated that the tibia rotation guide  800  is ambidextrous, meaning that the tibia rotation guide  800  can be used to perform knee arthroplasty procedures on both the right knee and the left knee. 
     Referring to  FIG.  50   , the points of contact between the tibia rotation guide  800  and the baseplate implant I are substantially similar to the points of contact between the tibia rotation guide  800  and the anterior surface of the proximal tibia  12  at the level of resection. Accordingly, use of the tibia rotation gauge  800  to properly align the eminence stylus  300  relative to the proximal tibia  12  prior to forming the resection cuts will ensure a properly aligned fit of the baseplate implant Ion the resected proximal tibia  12 . As shown in  FIG.  51   , since the shape and configuration of the distal feet  806   a ,  806   b  of the tibia rotation gauge  800  are compatible with multiple sizes of the baseplate implant I (shown in phantom), the same tibia rotation gauge  800  may be used universally across the multiple sizes of the baseplate implants I (i.e., a different tibia rotation gauge  800  is not required to accommodate various sizes of the baseplate implant I). 
     J. Tibia Insert Trial 
     Referring to  FIG.  52   , shown therein is a tibia insert trial  900  according to one form of the present invention. As will be discussed in greater detail below, the tibia insert trial  900  is used in the evaluation of the medial tibial resection R M  ( FIGS.  55 A and  56 A ) to check/verify the size, shape, depth, position and/or orientation of the cuts associated with the medial tibial resection R M  and their relation to the femoral trial  18  attached to the distal femur  10 , and/or in the simultaneous evaluation of the medial and lateral tibial resections R M , R L  ( FIGS.  55 B and  56 B ) to check/verify the size, shape, depth, position and/or orientation of the cuts associated with the medial and lateral tibial resection R M , R L  and their relation to the femoral trial  18  attached to the distal femur  10 . 
     Evaluations using the tibia insert trial  900  can take the form of a variety of different checks on the suitability of the size, shape, depth, position and/or orientation of the medial resection R M  or the medial and lateral resections R M , R L , or the potential need to re-cut or redo the resection cuts at a different depth or orientation (e.g., at a different posterior slope angle, at a different varus-valgus angle, and/or at an inward-outward rotation angle). In some embodiments, evaluations using the tibia insert trial  900  can take the form of articulating a femoral trial ( FIG.  56 A ) on a medial lobe of the tibia insert trial  900 , which may allow the surgeon to check the balance, tightness, and/or laxity of the knee joint in flexion and extension. In other embodiments, evaluations using the tibia insert trial  900  can take the form of simultaneously articulating a femoral trial ( FIG.  56 B ) on medial and lateral lobes of the tibia insert trial  900 , which may also allow the surgeon to check the balance, tightness, and/or laxity of the knee joint in flexion and extension. In still other embodiments, evaluations using the tibia insert trial  900  can involve the selection of one or more shim components (selected from a kit or set of shim components) that are removably attachable to a main trial component to provide various configurations of trial lobes (i.e., varying thicknesses, posterior slope angles, varus-valgus angles, etc.) to evaluate the relationship between the medial/lateral resections of the proximal tibia and a femoral trial attached to the distal femur  10 . In still further embodiments, the tibia insert trial  900  may also be used to simulate the effect of a re-cut of the medial/lateral resections or the use of a different tibial implant articulation on the balance of the knee joint which may, in some embodiments, reduce the risk associated with having to re-cut the resection. 
     Referring collectively to  FIGS.  52  and  53   , in the illustrated embodiment, the tibia insert trial  900  is configured as a two-piece assembly including a main trial component  902  and a shim component  904  that are removably attachable to one another to form the tibia insert trial  900 . In one embodiment, the main trial component  902  and the shim component  904  each have substantially identical outer cross-sectional shapes/profiles that substantially match up with another when assembled together. In another embodiment, the shim component  904  is removably attachable to the main trial component  902  by way of one or more magnetic attraction forces. As shown in  FIG.  54   , the inferior side of the main trial component  902  is provided with a series of magnets  906  projecting therefrom that are received in corresponding openings  908  formed in the shim component  904  ( FIG.  53   ). As should be appreciated, at least the portion of the shim component  904  surrounding the openings  908  may be formed of a ferrous material to generate a magnetic attraction force with the magnets  906  to maintain a connection between the main trial component  902  and the shim component  904 . Positioning of the magnets  906  within the openings  908  not only serves to draw the main trial component  902  and the shim component  904  into connection with one another via magnetic attraction forces, but also serves as a positive interconnection or catch that prevents the components from sliding off of one another. Although the shim component  904  has been illustrated and described as being removably attachable to the main body component  902  by way of one or more magnetic attraction forces, other structures and techniques may alternatively be used to removably attach the shim component  904  to the main body component  902  including, for example, a friction fit, a clamp fit, a tongue-and-groove arrangement, one or more fasteners, or by other suitable structures or techniques for removable attachment of the shim component  904  to the main body component  902 . 
     In the illustrated embodiment, the magnets  906  and the openings  908  have been illustrated as having a circular configuration. However, other suitable shapes and configurations of the magnets  906  and the openings  908  are also contemplated. Additionally, although the magnets  906  have been illustrated as being associated with the main trial component  902  and the openings  908  have been illustrated as being associated with the shim component  904 , it should be understood that a reverse configuration is also contemplated. Further, in the illustrated embodiment, the magnets  906  project from a surface of the main trial component  902  for receipt within corresponding openings  908  in the shim component  904 . However, in other embodiments, the magnets  906  may be embedded within portions of either the main trial component  902  or the shim component  904 . Moreover, although the magnets  906  have been illustrated as extending from each of the three lobed regions of the main trial component  902  and the openings  908  have been illustrated as being defined in each of the three lobed regions of the shim component  904 , it should be understood that the magnets  906  and the openings  908  can alternatively be associated with other portions/regions of the main trial component  902  and the shim component  904  such as, for example, the interconnecting handle  910 . Additionally, although the main trial component  902  has been illustrated as including three magnets, it should also be understood that any number of the magnets  906  positionable within a corresponding number of openings  908  may be used to removably attach the shim component  904  to the main trial component  902 . 
     As discussed above, in the illustrated embodiment, the main trial component  902  and the shim component  904  each have substantially identical outer cross-sectional shapes/profiles that substantially match up with another when assembled together. However, the main trial component  902  and the shim component  904  may be provided with one or more outer profile regions that do not correspond to one another to facilitate separation of the components. For example, in one embodiment, the shim component  904  is provided with a cut-out or recessed region  904   a  ( FIGS.  53  and  56 B ) that is not found in the corresponding area of the main trial component  902 , thereby allowing the user to more easily grasp and manipulate the main trial component  902  relative to the shim component  904  to facilitate separation of the components. Additionally, the shim component  904  may be provided with a projecting region or flange  904   b  ( FIGS.  53  and  56 A ) that is not found in the corresponding area of the main trial component  902 , thereby allowing the user to more easily grasp and manipulate the shim component  904  relative to the main trial component  902  to facilitate separation of the components. It should be understood that other features associated with the main trial component  902  and/or the shim component  904  may be provided that facilitate separation of the components from one another. Additionally, in still other embodiments, multiple shim components may be provided that are removably attached to just the lobed regions of the main body component  902 , or multiple trial components may be provided that are removably attached to just the lobed regions of the shim component. Moreover, although the tibia insert trial  900  has been illustrated and described as a two-piece assembly including a main trial component  902  removably attached to a shim component  904 , other embodiments are also contemplated wherein the tibia insert trial  900  comprises a unitary, single-piece structure. 
     Referring collectively to  FIGS.  52 - 54   , in the illustrated embodiment, the tibia insert trial  900  includes an elongate connector portion or handle  910 , a single-lobe trial portion  912  located at a first end of the handle  910  and including a medial tibia trial lobe  912   a , and a dual-lobe trial portion  914  located at an opposite second end of the handle  910  and including both a medial tibia trial lobe  914   a  and a lateral tibia trial lobe  914   b . The medial tibia trial lobes  912   a ,  914   a  each have a hemi-elliptical or hemi-ovular configuration sized and shaped to generally match the size and shape of the corresponding medial portion of the tibia implant to be installed on the proximal tibia  12 . Similarly, the lateral tibia trial lobe  914   b  has a hemi-elliptical or hemi-ovular configuration sized and shaped to generally match the size and shape of the corresponding lateral portion of the tibia implant to be installed on the proximal tibia  12 . Accordingly, the tibia insert trial  900  can be used to evaluate/check the suitability of the size and shape of the medial resection R M  or the medial and lateral resections R M , R L  and whether the resections will accommodate the tibial implant to be installed on the proximal tibia  12 . Additionally, each of the tibia trial lobes  912   a ,  914   a  and  914   b  includes a substantially flat/planar inferior surface  916  (defined by the shim component  904 ) that is configured to rest against/abut the superior horizontal surfaces of the medial and lateral resections R M , R L  of the proximal tibia  12 . Each of the tibia trial lobes  912   a ,  914   a  and  914   b  also includes a superior articulation surface  918  (defined by the main trial component  902 ) that is curved/contoured to match a particular implant and to mate with the corresponding curved/contoured inferior surface defined by the femoral trial  18  attached to the distal femur  10 . 
     In the illustrated embodiment, the dual-lobe trial portion  914  includes an open ended slot or spacing  920  which separates the medial and lateral tibia trial lobes  914   a ,  914   b  and which has a width w S  slightly larger greater than the width w T  of the tibial eminence  14  ( FIG.  55 B ) so as to allow the medial and lateral tibia trial lobes  914   a ,  914   b  to be simultaneous positioned on the medial and lateral resections R M , R L , and with the tibial eminence  14  positioned within the open ended slot  920  ( FIG.  56 B ). Additionally, in some embodiments, the dual-lobe trial portion  914  is used to evaluate the medial and lateral resection R M , R L  prior to resection of the anterior tibial eminence  14   A  (discussed below). Thus, the overall length is of the slot  920  must be sized to accommodate the full anterior-posterior length of the tibial eminence  14  prior to anterior resection of the tibial eminence  14 . Accordingly, the slot  920  is provided with an extended portion  920   a  that extends beyond the anterior ends of the medial and lateral tibia trial lobes  914   a ,  914   b  adjacent the handle portion  910  for receipt of the unresected anterior tibial eminence  14   A . Stated another way, the handle portion  910  includes a notched bridge region  910   a  that interconnects the medial and lateral tibia trial lobes  914   a ,  914   b  and which is sized to receive the unresected anterior tibial eminence  14   A  therein. 
     As should be appreciated, the medial tibia trial lobe  912   a  of the single-lobe trial portion  912  is configured for positioning on the medial resection R M  ( FIGS.  55 A and  56 A ) for evaluation of the size, shape, depth, position and/or orientation of the medial resection R M  and their relation to the femoral trial  18  attached to the distal femur  10 . As should also be appreciated, the medial and lateral tibia trial lobe  914   a ,  914   b  of the dual-lobe trial portion  914  are configured for simultaneous positioning on the medial and lateral resections R M , R L  ( FIGS.  55 B and  56 B ) for simultaneous evaluation of the size, shape, depth, position and/or orientation of the medial and lateral tibial resections R M , R L  and their relation to the femoral trial  18  attached to the distal femur  10 . As should be further appreciated, due to the unique configuration of the tibia insert trial  900 , each of these evaluations can be performed using a single instrument as opposed to two separate instruments. Additionally, although not specifically illustrated in  FIGS.  52 - 54   , it should be understood that in an alternative embodiment, another single-lobe trial portion may extend from a central portion of the handle  910  which includes a single lateral tibia trial lobe configured for positioning on the lateral resection R L  for evaluation of the size, shape, depth, position and/or orientation of the lateral resection R L  and their relation to the femoral trial  18 . 
     In another form of the present invention, the tibia insert trial  900  may be provided in a kit or set including multiple main trial components  902  and multiple shim components  904 . The main trial components  902  may be provided in various sizes/articulation configurations that correspond to the various sizes/articulation configurations associated with the tibial implants that may be installed on the proximal tibia  12 . The shim components  904  may be provided in various sizes that correspond to the sizes of the main trial components  902 , and in various incremental thicknesses (i.e., +1, +2, +3, etc.) that serve to vary the overall thickness of the tibia trial lobes  912   a ,  914   a  and  914   b  to simulate the thickness of the tibial implant to be installed on the proximal tibia  12 , and to check/verify whether the depth of the medial resection R M  or the medial and lateral resections R M , R L  are correct/appropriate or if a re-cut is necessary. Additionally, a shim component  904  having a particular thicknesses may be selected and attached to the main trial component  902  to simulate the effect of a re-cut (i.e., a “re-cut simulation” to simulate a different resection cut depth) to check/verify whether the proposed re-cut is desired prior to actually making the re-cut. In this way, the surgeon may investigate options for compensating for laxity or tightness in flexion/extension without actually performing the proposed re-cut. As should be appreciated, the number of potential re-cuts is therefore minimized. 
     In addition to providing the shim components  904  in various incremental thicknesses, the insert trial kit/set may also be provided with shim components  904  having various incremental posterior slope angles (i.e., −2, −1, 0, +1, +2, etc.) that serve to vary the posterior slope angle associated with the tibia trial lobes  912   a ,  914   a  and  914   b  to simulate the posterior slope angle of the tibial implant to be installed onto the proximal tibia  12 , and to check/verify whether the medial resection R M  or the medial and lateral resections R M , R L  are correct/appropriate or whether a re-cut is necessary. Additionally, the insert trial kit/set may also be provided with shim components  904  having various incremental varus/valgus angles (i.e., −2, −1, 0, +1, +2, etc.) that serve to vary the varus/valgus angles associated with the tibia trial lobes  912   a ,  914   a  and  914   b  to simulate the varus/valgus angle of the tibial implant to be installed onto the proximal tibia  12 , and to check/verify whether the medial resection R M  or the medial and lateral resections R M , R L  are correct/appropriate or whether a re-cut is necessary. Accordingly, a shim component  904  having a particular posterior slope angle and/or a particular varus/valgus angle may be selected and attached to the main trial component  902  to simulate the effect of a re-cut (i.e., a “re-cut simulation” to simulate a different posterior slope angle and/or a different varus/valgus angle) to check/verify whether the proposed re-cut is desired prior to actually making the re-cut. 
     In other embodiments, multiple shim components  904  may be attached to the main trial component  902  to vary both the overall thickness of the tibia trial lobes  912   a ,  914   a  and  914   b , and to vary the posterior slope angle and/or the varus/valgus angle. For example, a first shim component  904   a  having a particular thicknesses may be selected and attached to the main trial component  902 , and a second shim component  904   b  having a particular posterior slope angle and/or varus/valgus angle may be selected and attached to the first shim component  904   b . As should be appreciated, this additional degree of modularity may reduce the number of shim components  904  included in the kit/set associated with the tibia insert trial  900  (i.e., eliminating the need for shim components  904  having varying posterior slope angles and/or varus/valgus angles in multiple thickness levels). As should also be appreciated, each of the shim components  904  is ambidextrous, meaning that the shim component  904  can be flipped over and used in association with the other knee. Accordingly, individual shim components  940  can be used to perform knee arthroplasty procedures on both the right knee and the left knee. 
     K. Tibia Size Templates 
     Referring to  FIGS.  57 - 60   , shown therein is a tibia size template  1000  according to one form of the present invention. Unlike the tibia insert trial  900  illustrated and described above which is used to evaluate the medial resection R M  or the medial and lateral tibial resections R M , R L  in relation to a femoral trial  18  attached to the distal femur  10  (i.e., to evaluate articulation, balance, tightness, and/or laxity of the knee joint in flexion and extension), use of the tibia size template  1000  is limited to evaluation of the peripheral size and shape of the medial resection R M  individually, or the medial and lateral tibial resections R M , R L  simultaneously. Accordingly, the primary evaluation feature associated with the tibia size template  1000  is the peripheral outer cross-sectional profile of the lobed regions. Due to the simple design associated with the tibia size template  1000 , manufacturing costs may be significantly reduced compared to the tibia insert trial  900 . 
     The tibia size template  1000  is configured as a single-piece structure including an elongate connector portion or handle  1010 , a single-lobe template portion  1012  located at a first end of the handle  1010  and including a medial tibia template lobe  1012   a , and a dual-lobe template portion  1014  located at an opposite second end of the handle  1010  and including both a medial tibia template lobe  1014   a  and a lateral tibia template lobe  1014   b . The medial tibia template lobes  1012   a ,  1014   a  each have a hemi-elliptical or hemi-ovular configuration sized and shaped to generally match the size and shape of the corresponding medial portion of the tibia implant to be installed on the medial resection R M  of the proximal tibia  12 . Similarly, the lateral tibia template lobe  1014   b  has a hemi-elliptical or hemi-ovular configuration sized and shaped to generally match the size and shape of the corresponding lateral portion of the tibia implant to be installed on the lateral resection R L  of the proximal tibia  12 . Additionally, each of the tibia template lobes  1012   a ,  1014   a  and  1014   b  includes a substantially flat/planar inferior surface  1016  and a substantially flat/planar superior surface  1018  ( FIGS.  58 A / 58 B and  59 A/ 59 B) so that the template lobes rest steadily on the planar horizontal resected surfaces of the medial and lateral tibial resections R M , R L . 
     In a further embodiment, the inferior and superior surfaces  1016 ,  1018  of the tibia size template  1000  each define reference marks or lines  1016   a ,  1018   a , respectively, along the mesial linear portion of each of the template lobes  1012   a ,  1014   a  and  1014   b . These reference marks  1016   a ,  1018   a  are each located at the same offset position relative to the end of the handle  1010  (i.e., relative to the inward end of each of the lobes  1012   a ,  1014   a  and  1014   b ). As shown in  FIGS.  59 B and  60 B , the reference marks  1016   a ,  1018   a  are used as a template to form a reference mark/line M vertically along the vertical medial and lateral resection cuts C VM , C VL  and across the superior surface of the anterior tibial eminence  14   A . These reference marks M serve as cut reference lines during removal of the anterior tibial eminence  14   A  using the anterior chisel  1100  illustrated and described below, and represent the ideal location of the vertical cut along the anterior tibial eminence  14   A . Although the reference marks M are illustrated as being formed using the dual-lobe template portion  1014  of the tibia size template  1000 , it should be understood that the reference marks M can also be made using the single-lobe template portion  1012 . Additionally, the reference marks M can be formed on the surface of the bone by scribing, burning, or by any other suitable method for marking bone tissue. Further, each of the tibia template lobes  1012   a ,  1014   a  and  1014   b  includes a hollow interior region  1019  (i.e., the template lobes  1012   a ,  1014   a  and  1014   b  are formed by relatively thin frame-like sections of material) to permit visualization through the template lobes  1012   a ,  1014   a  and  1014   b  when placed on the horizontal resected surfaces of the medial and lateral tibial resections R M , R L , to aid in identifying any misfit or misaligned regions. 
     The dual-lobe template portion  1014  includes a slot or spacing  1020  separating the medial and lateral tibia template lobes  1014   a ,  1014   b  having a width w S  ( FIG.  59 A ) that is slightly larger than the width w T  ( FIG.  59 B ) of the anterior tibial eminence  14   A  so as to allow the medial and lateral tibia template lobes  1014   a ,  1014   b  to be simultaneous positioned on the medial and lateral tibial resections R M , R L , ( FIGS.  59 B and  60 B ). Additionally, in some embodiments, the dual-lobe template portion  1014  is used to evaluate the medial and lateral tibial resections R M , R L , prior to resection of the anterior tibial eminence  14   A  (discussed below). Thus, the overall length l S  of the slot  1020  ( FIG.  59 A ) must be sized to accommodate the full anterior-posterior length of the tibial eminence  14  prior to prior to resection of the anterior tibial eminence  14   A . Accordingly, the slot  1020  includes an extended portion  1020   a  that extends beyond the anterior ends of the medial and lateral tibia template lobes  1014   a ,  1014   b  adjacent the handle  1010  for receipt of the unresected anterior tibial eminence  14   A . Stated another way, the handle portion  1010  includes a notched bridge region  1010   a  that interconnects the medial and lateral tibia template lobes  1014   a ,  1014   b  and which is sized to receive the unresected anterior tibial eminence  14   A  therein. 
     As should be appreciated, the medial tibia template lobe  1012   a  of the single-lobe template portion  1012  is configured for positioning on the medial tibial resection R M  ( FIGS.  59 A and  60 A ) for evaluation of the peripheral size and shape of the medial tibial resection R M . As should also be appreciated, the medial and lateral tibia template lobes  1014   a ,  1014   b  of the dual-lobe template portion  1014  are configured for simultaneous positioning on the medial and lateral tibial resection R M , R L  ( FIGS.  59 B and  60 B ) for simultaneous evaluation of the peripheral size and shape of the medial and lateral tibial resection R M , R L . As should be further appreciated, due to the unique configuration of the tibia size template  1000 , each of these evaluations can be performed using a single instrument as opposed to two separate instruments. It should also be appreciated that the tibia size template  1000  is ambidextrous, meaning the tibia size template  1000  can be flipped over and used in association with the other knee. Accordingly, a single tibia size template  1000  can be used to perform knee arthroplasty procedures on both the right knee and the left knee. Additionally, although not specifically illustrated in  FIGS.  57 - 60   , it should be understood that in an alternative embodiment, another single-lobe template portion may extend from a central portion of the handle  1010  which includes a lateral tibia template lobe configured for positioning on the lateral tibial resection R L  for evaluation of the peripheral size and shape of the lateral tibial resection R L . 
     L. Anterior Chisel 
     Referring to  FIGS.  61 A and  61 B , shown therein is an anterior chisel  1100  according to one form of the present invention. As will be discussed in greater detail below, the anterior chisel  1100  is designed and configured to form both vertical and horizontal cuts along the anterior portion  14   A  of the tibial eminence  14  ( FIGS.  64 A and  64 B ) for resection/removal of the anterior tibial eminence portion  14   A  ( FIG.  64 C ) to provide sufficient clearance for receipt of a tibial implant. 
     In one embodiment, the anterior portion of the tibial eminence  14   A  is removed prior to forming keel slots/openings in the resected region of the proximal tibia  12  using the keel formation instrument  1200  illustrated and described below. It should be appreciated that prior removal of the anterior tibial eminence  14   A  may make formation of the anterior keel slot somewhat easier (i.e., requiring less axial cutting force) because of not having to penetrate through the thickness of the anterior tibial eminence  14   A . Additionally, removal of the anterior tibial eminence  14   A  prior to forming the keel slots/openings allows for the use of a tibial baseplate trial having a shape/profile that generally matches that of the tibial implant to be installed on the fully resected proximal tibia  12  to aid in gauging/trialing and/or formation of the keel slots/openings ( FIGS.  68  and  69   ). However, in other embodiments, the anterior tibial eminence  14   A  may be removed subsequent to forming the keel slots/openings in the resected region of the proximal tibia  12 . 
     In the illustrated embodiment, the anterior chisel  1100  generally includes a cutting block  1102  and an elongate shaft  1104  connected to the cutting block  1102  and extending along a longitudinal axis L. A proximal handle or gripping portion (not shown) may be attached to the proximal end of the elongate shaft  1104  to facilitate manipulation and handling of the anterior chisel  1100  by the user, and to aid in the application of an axial cutting force F onto the elongate shaft  1104  generally along the longitudinal axis L. The axial cutting force F is transmitted along the elongate shaft  1104  and is transferred to the cutting block  1102  to form the vertical and horizontal cuts along the anterior tibial eminence portion  14   A . The cutting block  1102  includes a substantially flat/planar axially-facing end surface  1106  that is arranged generally perpendicular to the longitudinal axis L. 
     In one embodiment, the cutting block  1102  is a single-piece monolithic block defining a hollow interior surrounded by outer walls that define a first slot  1110  sized and configured for receipt of a first cutting blade  1112  extending along a first cutting plane arranged generally parallel with the longitudinal axis L. The first cutting blade  1112  is attached to the cutting block  1102  via a fastener  1114  and includes a distal cutting edge  1116  positioned in general alignment with the planar end surface  1106  of the cutting block  1102  ( FIGS.  63 A / 63 B). The outer walls of the cutting block  1102  further define a second slot  1120  sized and configured for receipt of a second cutting blade  1122  extending along a second cutting plane arranged generally parallel with the longitudinal axis L. The second cutting blade  1122  is attached to the cutting block  1102  via a fastener  1124  and includes a distal cutting edge  1126  that is also positioned in general alignment with the planar end surface  1106  of the cutting block  1102 . In the illustrated embodiment, the first cutting plane defined by the first cutting blade  1112  extends substantially parallel with the second cutting plane defined by the second cutting blade  1122 . However, other embodiments are also contemplated wherein the first and second cutting planes are not arranged parallel with one another. As will be discussed in greater detail below, the first cutting blade  1112  is arranged to form the vertical cut C VA  along the anterior tibial eminence  14   A  ( FIGS.  62 A,  63 A and  64 A ), and the second cutting blade  1122  is arranged to form the horizontal cut C HA  along the anterior tibial eminence  14   A  ( FIGS.  62 B,  63 B and  64 B ). 
     In the illustrated embodiment, the anterior chisel  1100  also includes alignment and guide features that serve to properly align and guide the cutting blades  1112 ,  1122  relative to the proximal tibia  12  to form the vertical and horizontal cuts C VA , C HA  along the anterior tibial eminence  14   A . The anterior chisel  1100  further includes stop features that limit the bone penetration depth of the vertical and horizontal cuts C VA , C HA  to prevent the cutting blades  1112 ,  1122  from cutting too deep into the anterior tibial eminence  14   A . 
     In one embodiment, the anterior chisel  1100  includes a pair of elongate legs or axial projections  1130   a ,  1130   b  that extend from the cutting block  1102  in a direction substantially parallel with the longitudinal axis L and which are positioned on opposite sides of the longitudinal axis L. The axial projections  1130   a ,  1130   b  define substantially flat/planar surfaces  1132  along a first side that are arranged generally co-planar with one another, and substantially flat/planar surfaces  1134  along an opposite second side that are arranged co-planar with one another. The planar surfaces  1132  extend along a guide/alignment plane arranged substantially parallel with and offset from the cutting plane of the first cutting blade  1112 , and the planar surfaces  1134  extend along a guide/alignment plane arranged substantially parallel and co-planar with the cutting plane of the second cutting blade  1122 . As will be discussed below, the flat/planar surfaces  1132 ,  1134  serve to properly align and guide the cutting blades  1112 ,  1122  relative to the proximal tibia  12  to form the vertical and horizontal cuts C VA , C HA  along the anterior tibial eminence  14   A . Although the axial projections  1130   a ,  1130   b  have been illustrated and described as having a particular configuration, it should be understood that other structures and means for aligning and guiding the anterior chisel  1100  and the cutting blades  1112 ,  1122  relative to the proximal tibia  12  are also contemplated including, for example, shoulder portions, flange portions, plate portions, lip portions, step portions, or any other structure suitable to align and guide the anterior chisel  1100  and the cutting blades  1112 ,  1122  relative to the proximal tibia  12 . 
     In another embodiment, the anterior chisel  1100  includes a pair of stop members or feet  1140   a ,  1140   b  that extend from the cutting block  1102  in a direction substantially perpendicular to the longitudinal axis L and which are positioned on opposite sides of the longitudinal axis L. The stop members  1140   a ,  1140   b  define substantially flat/planar axially-facing surfaces  1142  that are arranged substantially co-planar with one another and with the planar end surface  1106  of the cutting block  1102 , and which are also arranged substantially perpendicular to the cutting plane of the first cutting blade  1112 . As will be discussed below, the flat/planar surfaces  1142  of the stop members  1140   a ,  1140   b  and the planar end surface  1106  of the cutting block  1102  serve to limit the penetration depth of the vertical cut C VA  to prevent the cutting blade  1112  from cutting too deep into the anterior tibial eminence  14   A . Although the stop members  1140   a ,  1140   b  have been illustrated and described as having a particular configuration, it should be understood that other structures and means for limiting travel of the anterior chisel  1100  and the bone penetration depth of the cutting blade  1112  are also contemplated including, for example, shoulder portions, flange portions, lip portions, step portions, interference portions, or any other structure suitable to limit the travel of the anterior chisel  1100  and the bone penetration depth of the cutting blade  1112  into proximal tibia  12 . 
     In a further embodiment, the anterior chisel  1100  includes a stop member or shoulder  1150  defining an axially-facing edge or end surface  1152  (i.e., facing a direction generally along longitudinal axis L). The axially-facing edge or end surface  1152  may be curved or contoured for abutment against a corresponding curved/contoured/irregular anterior surface of the proximal tibia  12 , or may alternatively define a substantially flat/planar axially-facing edge or end surface. Additionally, although the shoulder  1150  has been illustrated as extending continuously across the entire width of the cutting block  1102 , it should be understood that the shoulder  1150  may alternatively extend across less than the entire width of the cutting block  1102  and/or my extending discontinuously across the width of the cutting block  1102 . As will be discussed below, the axially-facing edge or end surface  1152  of the shoulder  1150  serves to limit the bone penetration depth of the horizontal cut C HA  to prevent the cutting blade  1122  from cutting too deep into the anterior tibial eminence  14   A . Although the or shoulder  1150  has been illustrated and described as having a particular configuration, it should be understood that other structures and means for limiting travel of the anterior chisel  1100  and the bone penetration depth of the cutting blade  1122  are also contemplated including, for example, flange portions, lip portions, step portions, interference portions, or any other stop structure suitable to limit the travel of the anterior chisel  1100  and the bone penetration depth of the cutting blade  1122  into proximal tibia  12 . 
     Referring to  FIGS.  62 - 64   , reference will now be made to techniques for using the anterior chisel  1100  to form both vertical and horizontal cuts C VA , C HA  along the anterior portion  14   A  of the tibial eminence  14  for ultimate removal of the anterior portion  14   A  to provide sufficient clearance for receipt of a tibial implant. However, it should be understood that other techniques for using the anterior chisel  1100  other than those specifically described herein are also contemplated. 
     Referring specifically to  FIGS.  62 A,  63 A and  64 A , shown therein is the step of forming a vertical anterior cut C VA  along the anterior tibial eminence  14   A  using the anterior chisel  1100 . The anterior chisel  1100  is initially positioned above and generally aligned with the anterior tibial eminence  14   A , with the longitudinal axis L of the elongate shaft  1104  arranged generally parallel with the anatomic mechanical axis  13  of the proximal tibia  12 . The planar guide/alignment surfaces  1132  defined by the axial projections  1130   a ,  1130   b  are then positioned in contact with the anterior surface S A  of the proximal tibia  12 , and the cutting edge  1116  of the first cutting blade  1112  is positioned adjacent the superior surface of the anterior tibial eminence  14   A . Additionally, the cut reference marks/lines M ( FIGS.  59 B / 60 B) previously formed along the vertical medial and lateral resection cuts C VM , C VL  and across the superior surface of the anterior tibial eminence  14   A  (using the tibia size template  1000 ) are used as an alignment/verification aid prior to and during formation of the vertical anterior cut C VA . As indicated above, the reference marks M represent the ideal location for the vertical anterior cut C VA , and are used as a check/verification via alignment of the cutting edge  1116  of the first cutting blade  1112  with the reference marks M. 
     An axial cutting force F is then applied to the elongate shaft  1104  which is transmitted to the cutting block  1102  and the first cutting blade  1112  to form the vertical anterior cut C VA  along the anterior tibial eminence  14   A  ( FIG.  64 A ). During formation of the vertical anterior cut C VA , the planar guide/alignment surfaces  1132  defined by the axial projections  1130   a ,  1130   b  slide along the anterior surface S A  of the proximal tibia  12  to guide the anterior chisel  1100  along the proper cutting plane and to maintain the anterior chisel  1100  in a generally parallel relationship with the anatomic mechanical axis  13  of the proximal tibia  12 . Furthermore, displacement of the anterior chisel  1100  is limited by abutment of the flat/planar stop surfaces  1142  defined by the feet  1140   a ,  1140   b  and the planar end surface  1106  of the cutting block  1102  against the horizontal planar surfaces of the medial and lateral resections R M , R L  on either side of the tibial eminence  14 . Notably, the penetration depth of the first cutting blade  1112  is limited by such abutment so as to prevent the first cutting blade  1112  from cutting too deep into the anterior tibial eminence  14   A  and potentially weakening the remaining portion of the tibial eminence  14 . The penetration depth of the first cutting blade  1112  is preferably limited to the plane defined by the flat/planar stop surfaces  1142  of the feet  1140   a ,  1140   b  and the planar end surface  1106  of the cutting block  1102  (which corresponds to the resection plane defined by the planar horizontal surfaces of the medial and lateral resections R M , R L  on either side of the tibial eminence  14 ). 
     As should be appreciated, the location of the vertical anterior cut C VA  along the anterior tibial eminence  14   A  in the anterior-posterior direction is determined by the cut reference marks/lines M ( FIGS.  59 B / 60 B) previously formed along the vertical medial and lateral resection cuts C VM , C VL  and across the superior surface of the anterior tibial eminence  14   A  using the tibia size template  1000 , and are used as an alignment/verification aid prior to and during formation of the vertical anterior cut C VA . In an alternative embodiment, the location of the vertical anterior cut C VA  along the anterior tibial eminence  14   a  is determined by the offset distance d 1  between the planar guide/alignment surfaces  1132  defined by the axial projections  1130   a ,  1130   b  and the cutting plane defined by the first cutting blade  1112 . As should also be appreciated, the anterior chisel  1100  may be designed with the appropriate offset distance d 1  to accommodate for a desired anterior-posterior location of the vertical anterior cut C VA . Additionally, a set of anterior chisels  1100  may be provide having different offset distances d 1  to accommodate for varying anterior-posterior locations of the vertical anterior cut C VA . In the illustrated embodiment, the anterior chisel  1100  is configured to provide a vertical anterior cut C VA  along the anterior tibial eminence  14   A  that is substantially vertical and parallel with the anatomic mechanical axis  13  of the tibia, and substantially perpendicular to the vertical surfaces of the medial and lateral resections R M , R L . However, other embodiments are also contemplated where the vertical anterior cut C VA  may be tapered relative to a true vertical orientation, angled either in a superior-inferior direction or a medial-lateral direction (i.e., internal/external rotation). 
     Referring to  FIGS.  62 B,  63 B and  64 B , shown therein is the step of forming a horizontal anterior cut C HA  along the anterior tibial eminence  14   A  using the anterior chisel  1100 . The anterior chisel  1100  is initially positioned anterior to and generally aligned with the anterior tibial eminence  14   A , with the longitudinal axis L of the elongate shaft  1104  oriented generally perpendicular to the anatomic mechanical axis  13  of the proximal tibia  12 . The planar guide/alignment surfaces  1134  defined by the axial projections  1130   a ,  1130   b  are then positioned in contact with the horizontal planar surfaces of the medial and lateral resections R M , R L  on either side of the tibial eminence  14 , and the cutting edge  1126  of the second cutting blade  1122  is positioned in contact with the anterior surface of the anterior tibial eminence  14   A . 
     An axial cutting force F is then applied to the elongate shaft  1104  which is transmitted to the cutting block  1102  and the second cutting blade  1122  to form the horizontal anterior cut C HA  along the anterior tibial eminence  14   A  ( FIG.  64 A ). During formation of the horizontal anterior cut C HA , the planar guide/alignment surfaces  1134  defined by the axial projections  1130   a ,  1130   b  slide along the horizontal planar surfaces of the medial and lateral resections R M , R L  on either side of the tibial eminence  14  to guide the anterior chisel  1100  along the proper cutting plane and to maintain the anterior chisel  1100  in a generally perpendicular orientation relative to the anatomic mechanical axis  13  of the proximal tibia  12 . Furthermore, displacement of the anterior chisel  1100  is limited by abutment of the axially-facing edge or end surface  1152  defined by the shoulder  1150  against the anterior surface S A  of the proximal tibia  12 . Notably, the penetration depth of the second cutting blade  1122  is limited by such abutment so as to prevent the second cutting blade  1122  from cutting too deep into the anterior tibial eminence  14   A  and potentially weakening the remaining portion of the tibial eminence  14 . The penetration depth of the second cutting blade  1122  is preferably limited to the plane defined by the planar end surface  1106  of the cutting block  1102 . 
     As should be appreciated, the penetration depth of the horizontal anterior cut C HA  in the anterior-posterior direction is determined by the offset distance d 2  between the axially-facing edge or end surface  1152  defined by the shoulder  1150  and the distal cutting edge  1126  defined by the second cutting blade  1122  (with the cutting edge  1126  preferably aligned with the planar end surface  1106  of the cutting block  1102 ). As should also be appreciated, the anterior chisel  1100  may be designed with the appropriate offset distance d 2  to accommodate for a desired penetration depth of the second cutting blade  1122  in an anterior-posterior direction to form the horizontal anterior cut C HA . The penetration depth of the second cutting blade  1122  is preferably determined such that the horizontal anterior cut C HA  just intersects the vertical anterior Cut C VA  but does not extend significantly beyond the vertical anterior cut C VA . Additionally, a set of anterior chisels  1100  may be provide having different offset distances d 2  to accommodate for varying penetration depths of the second cutting blade  1122  in an anterior-posterior direction to form the appropriate horizontal anterior cut C HA . In the illustrated embodiment, the anterior chisel  1100  is configured to provide a horizontal anterior cut C HA  along the anterior tibial eminence  14   A  that is substantially parallel and co-planar with the horizontal planar surfaces of the medial and lateral resections R M , R L  on either side of the tibial eminence  14 . However, other embodiments are also contemplated where the horizontal anterior cut C HA  may be tapered relative to the horizontal planar surfaces of the medial and lateral resections R M , R L . 
     Referring to  FIG.  64 C , upon formation of the vertical anterior cut C VA  and the horizontal anterior cut C HA , the bone fragment defining the anterior tibial eminence  14   A  may be removed to thereby complete the anterior resection R A , which in combination with the medial and lateral resections R M , R L  provides sufficient clearance for installation of a tibial implant onto the resected proximal tibia  12 . Additionally, the antero-medial and antero-lateral corners of the tibial eminence  14  shown in  FIG.  64 C  can be rounded to form eminence radii along the corners ( FIG.  68   ). The eminence radii generally serve to provide additional clearance for receipt of the installed tibial implant, and are made by trimming the sharp antero-medial and antero-lateral eminence corners with a rongeur tool or other bone cutting/contouring instruments. Alternatively, the eminence radii may be formed by cutting die features incorporated into the first cutting blade  1112 , the cutting block  1100  or, in other embodiments, the keel cavity formation instrument  1200  illustrated and described below. 
     As should now be appreciated, the anterior chisel  1100  can be used to form both the vertical anterior cut C VA  and the horizontal anterior cut C HA  to resect the anterior tibial eminence  14   A , as opposed to using two separate cutting instruments to form these cuts. Additionally, the anterior chisel  1100  includes built-in alignment and guide features that serve to properly align and guide the cutting blades  1112 ,  1122  to form the vertical and horizontal cuts C VA , C HA , and also included built-in stop features that limit the bone penetration depth of the vertical and horizontal cuts C VA , C HA  to prevent the cutting blades  1112 ,  1122  from cutting too deep into the anterior tibial eminence  14   A  which might otherwise weaken the remaining portion of the tibial eminence  14  and risk a tibial eminence fracture. These built-in features significantly reduce the risks normally associated with resection of the anterior tibial eminence  14   A . 
     M. Keel Cavity Formation Instrument 
     Referring to  FIGS.  65 - 67   , shown therein is a keel cavity formation instrument  1200  according to one form of the present invention. As will be discussed in greater detail below, the keel cavity formation instrument  1200  is used to form a keel cavity including one or more slots/openings in the medial and lateral resected regions R M , R L  and the anterior resected region R A  of the proximal tibia  12  ( FIGS.  71 A- 71 C ), with the slots/openings sized and shaped to receive keels or other projections extending from the tibial implant to be installed onto the proximal tibia  12 . 
     In the illustrated embodiment, the keel cavity formation instrument  1200  is configured to form various portions of the keel cavity in multiple steps to lower the maximum input or impaction force that would otherwise be necessary if the entire keel cavity were formed simultaneously in a single step. Forming the keel cavity in multiple steps also allows portions of the keel cavity to be formed via an input/impaction force exerted along the anatomic mechanical axis of the tibia (which is the preferred direction of the input/impaction force to minimize potential harmful effects on the tibia such as a tibial fracture), and also allows the portions of the keel cavity that must be formed via an oblique input/impaction force (a force exerted at an angle relative to the anatomic mechanical axis of the tibia) to be formed separately, thereby reducing the extent of the oblique input/impaction force necessary to form the overall keel cavity. Additionally, portions of the keel cavity are formed via drilling or boring, thereby further reducing the input/impaction force necessary to form the overall keel cavity. 
     The keel cavity formation instrument  1200  generally includes a main body  1210 , a vertical punch handle  1230  rigidly connected to the main body  1210  and extending along a vertical punch axis A 1  ( FIG.  67   ), a keel punch plate  1240  removably attached to the main body  1210 , an angled punch handle  1250  movably connected to the main body  1210  and extending along an angled punch axis A 2  ( FIG.  67   ), an angled keel punch blade  1260  ( FIG.  70 B ) extending from the angled punch handle  1250  and also arranged along the angled punch axis A 2 , and a drill bit  1270  displaceable along drill guide passages formed in the angled punch handle  1250  and the main body  1210 . Additionally, the keel cavity formation instrument  1200  is used in association with a tibial baseplate trial  1280  attached to the resected proximal tibia  12  which serves as both a gauge and a foundation/guide for the keel cavity formation instrument  1200 . Details regarding each of these elements will be set forth below. 
     In the illustrated embodiment, the main body  1210  generally includes an angled passage  1212  ( FIG.  66   ) extending therethrough along the angled punch axis A 2 , and a pair of drill guide passages or barrels  1214   a ,  1214   b  ( FIG.  66   ) extending along guide axes arranged generally parallel with the angled punch axis A 2  and arranged symmetrically on opposites sides of the angled punch axis A 2  and the angled passage  1212 . The drill guide passages or barrels  1214   a ,  1214   b  are sized and configured to guidingly receive a proximal guide shaft portion  1272   a  of the drill bit  1270  therethrough for guiding displacement of the drill bit  1270  in a direction generally parallel with the angled punch axis A 2 . In the illustrated embodiment of keel cavity formation instrument  1200 , the angled punch axis A 2  is oriented at an offset angle α ( FIG.  67   ) of approximately 20° relative to the vertical punch axis A 1 . However, it should be understood that other offset angles α between the angled punch axis A 2  and the vertical punch axis A 1  are also contemplated, including offset angles α greater than 20° or offset angles α less than 20°. 
     The main body  1210  further includes a pair of transverse flanges or tongues  1216   a ,  1216   b  ( FIG.  66   ) extending from opposite sides of an inferior portion of the main body  1210  in a medial-lateral direction, and a fastener or lock member  1218  extending through an opening (not shown) in an anterior portion of the main body  1210  and arranged along an axis generally parallel with the angled punch axis A and configured to releasably attach the keel punch plate  1240  to the main body  1210 . The main body  1210  also defines a visualization window  1220  extending transversely therethrough and positioned in communication with the angled passage  1212  to provide visualization of the angled punch handle  1250  positioned in the angled passage  1212 , and a visualization window  1222  extending transversely therethrough and positioned in communication with the drill guide passages  1214   a ,  1214   b  and the angled passage  1212  to provide visualization of the angled keel punch blade  1260  positioned in the angled passage  1212  and the drill bit  1270  positioned in either of the drill guide passages  1214   a ,  1214   b . The fastener or lock member  1218  includes a shaft  1224  having a distal end portion  1224   a  configured for engagement/disengagement within an opening  1248  in the keel punch plate  1240 , and also having a proximal head portion  1224   b  extending from a superior surface of the main body  1210 . The fastener or lock member  1218  further includes a lever or handle  1228  extending transversely from the proximal head portion  1224   b  and configured to facilitate rotation of the lock member  1218  and engagement/disengagement of the distal end portion  1224   a  within the opening  1248 . 
     In the illustrated embodiment, the vertical punch handle  1230  generally includes an axial shaft portion  1232  extending generally along the vertical punch axis A 1  and having a distal end connected to the main body  1210  and a proximal end connected to a proximal handle portion or impaction plate  1234  which defines a substantially flat/planar superior impaction surface  1234   a . As indicated above, the vertical punch handle  1230  is rigidly connected to the main body  1210 . However, in alternative embodiments, the vertical punch handle  1230  may be removably and/or movably attached to the main body  1210 . As should be appreciated, the flat/planar superior impaction surface  1234   a  of the impaction plate  1234  is configured for receipt of an axial force F 1 , such as an impaction force, applied to the impaction plate  1234  in a direction generally along the vertical punch axis A 1 . The impaction force F 1  is transmitted along the axial shaft portion  1232 , through the main body  1210 , and transmitted to the keel punch plate  1240  to drive a pair of keel formation wings or fins  1244   a ,  1244   b  of the keel punch plate  1240  into the medial and lateral resected regions R M , R L , of the proximal tibia  12 . Although the axial force F 1  is illustrated and described as being applied to the impaction plate  1234  (e.g., via a mallet), other structures and techniques for applying the axial force F 1  to the keel formation instrument  1200  are also contemplated including, for example, via a slap hammer coupled to the main body portion  1210  or connected directly to the keel punch plate  1240 . 
     In the illustrated embodiment, the keel punch plate  1240  generally includes a generally flat plate portion  1242  including a pair of keel formation wings or fins  1244   a ,  1244   b  extending from an inferior surface  1242   a  of the plate portion  1242 . When the keel punch plate  1240  is attached to the main body  1210  and the keel formation instrument  1200  is properly positioned relative to the proximal tibia  12 , the keel formation fins  1244   a ,  1244   b  are arranged on opposite sides of the vertical punch axis A 1  and include fin lengths that are outwardly tapered relative to one another in an anterior-posterior direction ( FIG.  71 A ). Additionally, as illustrated in  FIG.  67   , the keel formation fins  1244   a ,  1244   b  each include a posterior surface  1245   a  extending generally along the vertical punch axis A 1 , an anterior surface  1245   b  extending generally along the angled punch axis A 2 , and an inferior surface  1245   c  extending from the posterior surface  1245   a  to the anterior surface  1245   b  and arranged generally perpendicular to the anterior surface  1245   b . In this arrangement, the keel formation fins  1244   a ,  1244   b  each defines a generally pointed distal-most corner or edge  1245   d  that facilitates penetration of the keel formation fins  1244   a ,  1244   b  into tibial bone. As shown in  FIG.  71 A , the keel formation fins  1244   a ,  1244   b  are sized and shaped to form medial and lateral keel receiving slots S M , S L  in the medial and lateral resected regions R M , R L  of the proximal tibia  12 . 
     The generally flat plate portion  1242  also includes a pair of L-shaped connection flanges  1246   a ,  1246   b  extending from a superior surface  1242   b  of the plate portion  1242  and each defining a transversely extending groove  1247  sized and configured for receipt of the transverse flanges or tongues  1216   a ,  1216   b  of the main body  1210  therein to removably engage the keel punch plate  1240  to the main body  1210 . The generally flat plate portion  1242  also defines an opening  1248  configured to receive the distal end portion  1224   a  of the lock member  1218  associated with the main body  1210  to removably lock the keel punch plate  1240  to the main body  1210 . Additionally, the generally flat plate portion  1242  of the keel punch plate  1240  also defines an open region  1249  sized and configured to receive the tibial eminence  14  therein when the keel punch plate  1240  is positioned on the resected proximal tibia  12 , and which is also sized and configured to receive the angled keel punch blade  1260  and the distal cutting portion of the drill bit  1270  therethrough during formation of the anterior keel slot and openings in the anterior region of the resected proximal tibia  12 , further details of which will be set forth below. As should be appreciated, the keel punch plate  1240  is a modular feature of the keel cavity formation instrument  1200  that can be easily removed from the main body  1210  of the instrument and replaced with a different keel punch plate  1240  having a different size and/or different keel formation fins  1244   a ,  1244   b . It should be further appreciated that multiple keel punch plates  1240  having different sizes and/or fin features can be provided in a kit or set, thereby allowing for the selection of a keel punch plate  1240  having the appropriate size/fin features to accommodate the specific requirements of a particular knee arthroplasty procedure. 
     In the illustrated embodiment, the angled punch handle  1250  generally includes an axial shaft portion  1252  extending generally along the angled punch axis A 2  and movably positioned in the angled passage  1212  in the main body  1210  for guided axial movement or displacement generally along the angled punch axis A 2  relative to the main body  1210 . The axial shaft portion  1252  includes a distal end connected to the angled keel punch blade  1260  and a proximal end connected to a proximal drill guide plate  1254 , which in turn defines a pair of drill guide passages  1254   a ,  1254   b  extending along axes positioned on opposite sides of the angled punch axis A 2  and arranged generally parallel with the angled punch axis A 2 . The drill guide passages  1254   a ,  1254   b  are sized and configured to guidingly receive a proximal guide shaft portion  1272   a  of the drill bit  1270  therethrough for guiding displacement of the drill bit  1270  in a direction generally parallel with the angled punch axis A 2 . An impaction plate  1256  extends from a superior surface of the drill guide plate  1254  and defines a substantially flat/planar superior impaction surface  1256   a . As should be appreciated, the flat/planar superior impaction surface  1256   a  of the impaction plate  1256  is configured for receipt of an axial force F 2 , such as an impaction force, applied to the impaction plate  1256  in a direction generally along the angled punch axis A 2 . The impaction force F 2  is transmitted along the axial shaft portion  1252  and is transmitted to the angled keel punch blade  1260  to drive the angled keel punch blade  1260  into the anterior resected region R A  of the proximal tibia  12 . Although the axial force F 2  is illustrated and described as being applied to the impaction plate  1256  (e.g., via a mallet), other structures and techniques for applying the axial force F 2  to the angled punch handle  1250  are also contemplated including, for example, via a slap hammer coupled to the axial shaft portion  1252  or connected directly to the angled keel punch blade  1260 . The angled punch handle  1250  further includes a biasing member or spring  1258  extending about the axial shaft portion  1252  and positioned within the angled passage  1212  in the main body  1210  to bias the angled punch handle  1250  (and the angled keel punch blade  1260 ) in an axial direction generally along the angled punch axis A 2  toward a superior or retracted position for protection of the cutting edges of the angled keel punch blade  1260  during periods of non-use. 
     In the illustrated embodiment, the angled keel punch blade  1260  generally includes a distal keel formation blade  1262  arranged generally along the angled punch axis A 2 . When the keel formation instrument  1200  is properly positioned relative to the proximal tibia  12 , the distal keel formation blade  1262  includes a blade length that generally extends in a medial-lateral direction and transverse to the lengths of the keel formation fins  1244   a ,  1244   b  on the keel punch plate  1240 . The distal keel formation blade  1262  also defines a generally pointed distal-most corner or edge  1262   a  that facilitates penetration of the keel formation blade  1262  into tibial bone. As shown in  FIG.  71 B , the distal keel formation blade  1262  is sized and shaped to form an anterior keel receiving slot S A  in the anterior resected region R A  of the proximal tibia  12  positioned anterior to the tibial eminence  14  and extending generally along the angled punch axis A 2 . As indicated above, the angled keel punch blade  1260  is connected to the distal end of the angled punch handle  1250 . Alternatively, the angled keel punch blade  1260  and the angled punch handle  1250  may be formed as unitary, single-piece element. Additionally, when the angled punch handle  1250  is positioned in a retracted or non-actuated position ( FIG.  70 A ), the distal keel formation blade  1262  is retracted into the angled passage  1212  in the main body  1210  and is fully retracted inwardly beyond the inferior surface of the tibial baseplate trial  1280 . However, when the angled punch handle  1250  is positioned in an extended or actuated position ( FIG.  70 B ), the distal keel formation blade  1262  extends out of the angled passage  1212  in the main body  1210  and projects outwardly beyond the inferior surface of the tibial baseplate trial  1280  to form the anterior keel receiving slot S A  in the anterior resected region R A  of the proximal tibia  12 . 
     In the illustrated embodiment, the drill bit  1270  extends along a longitudinal axis L and generally includes a drill shaft  1272  having a proximal guide shaft portion  1272   a  and distal shaft portion  1272   b . The proximal guide shaft portion  1272   a  is sized and configured for guided displacement in a direction generally parallel with the angled punch axis A 2  along the drill guide passages  1254   a ,  1254   b  in the proximal drill guide plate  1254  of the angled punch handle  1250 , and along the drill guide barrels  1214   a ,  1214   b  defined through the main body  1210  of the keel cavity formation instrument  1200 . The drill bit  1270  also includes a proximal head  1274  including connection portion  1274   a  configured for rotational coupling with a rotary driver (e.g., a rotary motor or a torque application handle) to facilitate the application of a rotational force or torque onto the drill bit  1270 , and an enlarged stop portion or ring  1274   b  defining a shoulder  1274   c  configured to abut the superior surface defined by the drill guide plate  1254  of the angled punch handle  1250  to limit penetration of the distal cutting portion  1276  of the drill bit  1270  into tibial bone. The distal cutting portion  1276  extends axially from the distal shaft portion  1272   b  and defines one or more cutting flutes  1278  configured for drilling into tibial bone, and may also defined a pointed distal tip to facilitate initial penetration into tibial bone. When the keel cavity formation instrument  1200  is properly positioned relative to the proximal tibia  12 , the drill bit  1270  may be inserted through one of the drill guide passages  1254   a ,  1254   b  in the proximal drill guide plate  1254  and a corresponding one of the drill guide barrels  1214   a ,  1214   b  in the main body  1210 , with the distal cutting portion  1276  extending outwardly beyond the inferior surface of the tibial baseplate trial  1280  for drilling into the proximal tibia  12 . As indicated above, abutment of the shoulder  1274   c  defined by the enlarged stop portion or ring  1274   b  of the drill bit  1270  limits penetration/drill depth of the distal cutting portion  1276  into the proximal tibia  12 . In one embodiment, the penetration depth of the drill bit  1270  into the proximal tibia  12  is approximately equal to the penetration depth of the keel formation blade  1262  into the proximal tibia  12 . 
     As shown in  FIG.  71 C , the drill bit  1270  is used to form medial and lateral keel receiving openings O M , O L  in the medial and lateral resected regions R M , R L  of the proximal tibia  12 , with each of the openings arranged on opposite sides of the tibial eminence  14  and extending generally along the angled punch axis A 2 . In the illustrated embodiment, the drill bit  1270  is used to form the medial and lateral keel receiving openings O M , O L  when the angled punch handle  1250  and the distal keel formation blade  1262  are positioned in an extended or actuated position ( FIG.  70 C ) to provide additional stability and support to the keel cavity formation instrument  1200  during the drilling operations. In one embodiment, the angled punch handle  1250  and the distal keel formation blade  1262  are maintained in the extended or actuated position via friction forces exerted onto the distal keel formation blade  1262  by the surrounding bone. However, other embodiments are also contemplated wherein the angled punch handle  1250  and the distal keel formation blade  1262  may be maintained in the extended or actuated position via a positive catch or lock mechanism. Additionally, in other embodiments, the drilling operations may be performed when the angled punch handle  1250  and the distal keel formation blade  1262  are positioned in the retracted or non-actuated position. 
     Referring to  FIG.  68   , in the illustrated embodiment, the tibial baseplate trial  1280  acts as both a datum reference for the formation of portions of a keel cavity in the proximal tibia  12  and as a tibial gauge, the details of which will become apparent below. The tibial baseplate trial  1280  generally comprises a plate  1282  defining substantially flat/planar superior and inferior surfaces  1284   a ,  1284   b  and an outer peripheral surface or edge  1286  defining an outer perimeter or profile that generally matches/corresponds to the outer profile of the resected proximal tibia  12  (i.e., the outer peripheral surface or edge  1286  is generally alignable with the outer peripheral edge of the resected proximal tibia  12 ). The plate  1282  may also be provided with an anterior plate extension portion  1282   a  defining a visualization window  1288  extending therethrough to allow visual inspection/alignment of the anterior region  1286   a  of the outer peripheral surface  1286  with the anterior peripheral edge of the resected proximal tibia  12 . The anterior plate extension portion  1282   a  provides additional stability and support to the keel cavity formation instrument  1200  during formation of the keel slots/openings in the proximal tibia  12  to aid in counteracting the impaction forces F 1  and F 2  applied to the keel cavity formation instrument  1200 , and may also provide other benefits and advantages. 
     Additionally, in the illustrated embodiment, the plate  1282  defines a centrally positioned U-shaped slot  1290  extending therethrough between the superior and inferior surfaces  1284   a ,  1284   b  and having an open end at the posterior peripheral surface  1286  and extending in a posterior-anterior direction. The slot  1290  defines an open inner region of the plate  1282  that is sized and shaped to receive the tibial eminence  14  therein when the tibial baseplate trial  1280  is positioned on the resected proximal tibia  12 . The plate  1282  also defines a pair of passages  1292   a ,  1292   b  extending therethrough between the superior and inferior surfaces  1284   a ,  1284   b  and positioned along medial and lateral portions of the plate  1282 , respectively. The passages  1292   a ,  1292   b  are sized to receive fasteners or pins (not shown) to attach the tibial baseplate trial  1280  to the resected proximal tibia  12 . The plate  1282  further defines a pair of slots or slits  1294   a ,  1294   b  extending therethrough between the superior and inferior surfaces  1284   a ,  1284   b  and positioned along medial and lateral portions of the plate  1282 , respectively. The slots  1294   a ,  1294   b  inwardly taper toward one another in a posterior-anterior direction and are sized and positioned to receive the keel formation fins  1244   a ,  1244   b  of the keel punch plate  1240  during formation of the medial and lateral keel receiving slots S M , S L  in the resected proximal tibia  12 . The slots  1294   a ,  1294   b  are preferably sized and shaped for relatively close tolerance with the keel formation fins  1244   a ,  1244   b  so as to guide the keel punch plate  1240  generally along the vertical punch axis A 1  during the medial/lateral keel slot formation process. Additionally, the plate  1282  defines an elongate opening  1296  extending therethrough between the superior and inferior surfaces  1284   a ,  1284   b  and positioned along an anterior portion of the plate  1282 , and including a length extending in a medial-lateral direction and communicating with each of the slots  1294   a ,  1294   b . The elongate opening  1296  is sized and positioned to receive the distal keel formation blade  1262  of the angled keel punch blade  1260  and the distal cutting portion  1276  of the drill bit  1270  during formation of the anterior keel receiving slot S A  and the medial and lateral keel receiving openings O M , O L  in the resected proximal tibia  12 . The elongate opening  1296  need not be configured to guide the angled keel punch blade  1260  and the drill bit  1270  during the during the anterior keel slot and medial and lateral opening formation process since these elements are guided by other features associated with the keel cavity formation instrument  1200 . Further, interior medial and lateral surfaces of the plate  1282  extending between the central slot  1290  and the medial/lateral slots  1294   a ,  1294   b  define recesses or grooves  1298   a ,  1298   b , the purpose of which will be set forth below with regard to the anterior gauge  1300 . As should be appreciated, the tibial baseplate trial  1280  is ambidextrous, which means that the tibial baseplate trial  1280  can be flipped over and used in association with the other knee. Accordingly, a single tibial baseplate trial  1280  can be used to perform knee arthroplasty procedures on both the right knee and the left knee. 
     Referring collectively to  FIGS.  68 - 71   , having described the components, elements and features associated with the keel cavity formation instrument  1200 , reference will now be made to methods and techniques for forming a keel cavity (including slots and openings) in the resected proximal tibia  12 . However, it should be understood that other methods and techniques regarding the use of the keel cavity formation instrument  1200  are also contemplated. 
     Referring first to  FIG.  68   , the tibial baseplate trial  1280  is initially positioned atop the resected proximal tibia  12  with the tibial eminence  14  positioned within the central U-shaped slot  1290 , and with the planar inferior surface  1284   b  resting on the substantially flat/planar resected surfaces of the proximal tibia  12 . The position and orientation of the tibial baseplate trial  1280  on the resected proximal tibia  12  can then be adjusted to generally align the outer peripheral surface or edge  1286  of the plate  1282  with the outer peripheral edge of the resected proximal tibia  12 . As indicated above, the anterior peripheral edge of the resected proximal tibia  12  can be viewed through the visualization window  1288  defined by the anterior plate extension portion  1282   a  to aid in the alignment of the anterior surface or edge of the plate  1282  with the anterior edge of the resected proximal tibia  12 . If the outer peripheral surface or edge  1286  of the tibial baseplate trial  1280  does not properly align with the outer peripheral edge of the resected proximal tibia  12 , a tibial baseplate trial  1280  having a different size can be chosen for positioning and alignment on the resected proximal tibia  12 . It should be understood that a kit or set of multiple tibial baseplate trials  1280  having different sizes can be provided to aid in the selection of an appropriately sized tibial baseplate trial  1280 . Once a tibial baseplate trial  1280  having the correct size is found and is properly aligned on the resected proximal tibia  12  (e.g., properly positioned and oriented), the plate  1282  can be connected/anchored to the resected proximal tibia  12  by passing a pair of fasteners or pins (not shown) through the medial and lateral passages  1292   a ,  1292   b  and into engagement with tibial bone. 
     Referring to  FIGS.  69 ,  70 A and  71 A , the keel cavity formation instrument  1200  is then positioned in a superior position above the tibial baseplate trial  1280  and the keel formation fins  1244   a ,  1244   b  of the keel punch plate  1240  are positioned in the corresponding slots  1294   a ,  1294   b  in the plate  1282 . With the vertical punch axis A 1  generally aligned with the anatomic axis  13  of the tibia, an axial impaction force F 1  is applied to the superior impaction surface  1234   a  of the impaction plate  1234  to drive the keel formation fins  1244   a ,  1244   b  of the keel punch plate  1240  into the medial and lateral resected regions R M , R L  of the proximal tibia  12 , which in turn forms the medial and lateral keel receiving slots S M , S L  in the resected proximal tibia  12  ( FIG.  71 A ). 
     Referring to  FIGS.  70 B and  71 B , an axial impaction force F 2  is then applied to the superior impaction surface  1256   a  of the impaction plate  1256  on the angled punch handle  1250  in a direction generally along the angled punch axis A 2  to drive the distal keel formation blade  1262  of the keel punch blade  1260  into the anterior resected region R A  of the proximal tibia  12 , which in turn forms the anterior keel receiving slot S A  in the anterior resected region R A  of the proximal tibia  12  ( FIG.  71 B ). 
     Referring to  FIGS.  70 C and  71 C , with the angled punch handle  1250  and the distal keel formation blade  1262  remaining in the extended or actuated position (i.e., to provide additional stability and support to the keel cavity formation instrument  1200 ), the drill bit  1270  is inserted through one of the drill guide passages  1254   a ,  1254   b  and a corresponding one of the drill guide barrels  1214   a ,  1214   b  and is drilled into the proximal tibia  12  in a direction generally parallel with the angled punch axis A 2  to form one of the medial and lateral keel receiving openings O M , O L  in the medial and lateral resected regions R M , R L  of the proximal tibia  12 . The drill bit  1270  is then inserted through the other of the drill guide passages  1254   a ,  1254   b  and the corresponding drill guide barrel  1214   a ,  1214   b  and drilled into the proximal tibia  12  in a direction generally parallel with the angled punch axis A 2  to form the other of the medial and lateral keel receiving openings O M , O L  in the medial and lateral resected regions R M , R L  of the proximal tibia  12  ( FIG.  71 C ). 
     Following the formation of the medial and lateral keel receiving slots S M , S L , the anterior keel receiving slot S A  and the medial and lateral keel receiving openings O M , O L , the keel cavity formation instrument  1200  may be disengaged and removed from the tibial baseplate trial  1280 . However, the tibial baseplate trial  1280  is preferably left anchored to the resected proximal tibia  12  to perform an anterior gauging technique using the anterior gauge  1300  illustrated and described below. 
     As should be appreciated, the medial and lateral keel receiving slots S M , S L , the anterior keel receiving slot S A  and the medial and lateral keel receiving openings O M , O L  form an overall keel cavity in the resected proximal tibia  12  having a U-shaped configuration, and with the keel receiving slots/openings sized, positioned and oriented to receive or provide clearance for corresponding keels or other projections extending from a tibial implant (not shown) upon installation of the tibial implant onto the resected proximal tibia  12 . As should also be appreciated, the keel cavity formation instrument  1200  can be used in association with multiple sizes of proximal tibias and tibial implants, as well as both left and right hand proximal tibias and tibial implants, thereby reducing the need to provide multiple keel cavity formation instruments  1200  to accommodate various knee arthroplasty procedures. Additionally, the precision and accuracy offered by the tibial baseplate trial  1280  when used as a controlled datum reference and/or guide is desirable as it can help ensure that there is no mismatch conflict between the tibial eminence  14  and the portions of the U-shaped keel cavity when the tibial implant is installed onto the resected proximal tibia  12 . Since the tibial implant will mate or at least correspond/relate to both the tibial eminence  14  and the portions of the U-shaped keel cavity, it can be important that these two features are positioned/oriented correctly relative to one another so that the tibial implant does not bind, become tilted, sit too proud after installation onto the resected proximal tibia  12 , or compromise the remaining portion of the preserved tibial eminence  14 . 
     As should be further appreciated, the keel cavity formation instrument  1200  is configured to form various portions/sections of the overall keel cavity in multiple steps to thereby lower the maximum input or impaction forces that would otherwise be necessary if the entire keel cavity were formed simultaneously in a single step, thereby lowering the risks associated with tibial fractures via application of reduced input or impaction forces. Additionally, forming the keel cavity in multiple steps also allows various portions of the keel cavity (i.e., the medial and lateral keel receiving slots S M , S L ) to be formed via an input/impaction force exerted generally along the anatomic mechanical axis of the tibia (i.e., generally along the vertical punch axis A 1 ), which is a preferred direction for application of the input/impaction force, and also allows portions of the keel cavity (i.e., the anterior keel receiving slot S A ) that must be formed via an oblique input/impaction force (i.e., generally along the angled punch axis A 2 ) to be formed separately, thereby reducing the extent of the oblique input/impaction force necessary to form the overall keel cavity. Further, still other portions of the keel cavity are formed via drilling (i.e., the medial and lateral keel receiving openings O M , O L ), thereby further reducing the input/impaction force necessary to form the overall keel cavity. Therefore, it should be apparent that the design of the keel cavity formation instrument  1200  provides several benefits and advantages over conventional instruments and techniques. 
     N. Anterior Gauge 
     Referring to  FIGS.  72 A / 72 B, shown therein is an anterior gauge  1300  according to one form of the present invention. As will be discussed below, in one embodiment, the anterior gauge  1300  is used in combination with the tibial baseplate trial  1280  to gauge/inspect various features and aspects associated with the resected anterior portion of the tibial eminence  14  (i.e., position, orientation, size and shape) relative to the tibial baseplate trial  1280  after formation of the keel receiving slots/openings associated with the keel cavity in the resected proximal tibia  12 . The anterior gauge  1300  is designed to check and verify the accuracy of these features and aspects to ensure compatibility of the resected proximal tibia  12  with the selected tibial implant prior to installation of the tibial implant. However, it should be appreciated that in other embodiments, the anterior gauge  1300  may be used in combination with the tibial baseplate trial  1280  to gauge/inspect various features and aspects associated with the resected anterior portion of the tibial eminence  14  (i.e., position, orientation, size and shape) to check and verify the accuracy of these features and aspects prior to formation of the keel receiving slots/openings associated with the keel cavity in the resected proximal tibia  12 . Other embodiments directed to further uses of the anterior gauge  1300  with or without the tibial baseplate trial  1280  are also contemplated as falling within the scope of the present invention. 
     In the illustrated embodiment, the anterior gauge  1300  generally includes a connection portion  1302  and a handle portion  1304  extending axially from the connection portion  1302  along a longitudinal axis L. The connection portion  1302  is generally configured for removable connection with the tibial baseplate trial  1280  and for abutment/engagement with the resected anterior portion of the tibial eminence  14 . The handle portion  1304  is generally configured to aid in the manipulation and handling of the anterior gauge  1300  and the tibial baseplate trial  1280 , and/or for attachment to an alignment rod or “up rod” (not shown), or potentially to other alignment devices or support structures. 
     In one embodiment, the connection portion  1302  is ambidextrous in that it is configured for removable attachment to both a left hand configuration of the tibial baseplate trial  1280  ( FIGS.  73  and  74   ) and a right hand configuration of the tibial baseplate trial  1280  (formed by flipping the tibial baseplate trial  1280  over). To provide this ambidextrous capability, the connection portion  1302  includes a left hand region  1310  configured for removable attachment to the left hand configuration of the tibial baseplate trial  1280 , and a right hand region  1312  configured for removable attachment to the right hand configuration of the tibial baseplate trial  1280 . In the illustrated embodiment, the left hand and right hand regions  1310 ,  1312  are positioned on opposite superior/inferior portions of the connection portion  1302 , arranged general symmetric to one another relative to the longitudinal axis L. As should be appreciated, the left hand and right hand regions  1310 ,  1312  of the connection portion  1302  that are removably connectable with a corresponding left/right hand configuration of the baseplate trial  1280  are appropriately marked with “L” and “R” designations ( FIGS.  74 A and  74 B ) along a superior surface of the connection portion  1302 , and are also marked with a numeric range which indicates the size of the tibial baseplate trial  1280  (i.e., “1-4” which corresponds to the size of the tibia implant) for which the connection portion  1302  may be attached to. As should also be appreciated, the tibial baseplate trials  1280  are also appropriately marked with “L” and “R” designations along a superior surface of the plate  1282 , as well as being marked with a numeric size number which indicates the size of the tibial baseplate trial  1280  and the corresponding size of the tibia implant. 
     The left hand and right hand regions  1310 ,  1312  of the connection portion  1302  each include a pair of medial and lateral sections  1310   a ,  1310   b  and  1312   a ,  1312   b , respectively, which each include an axially-facing posterior surface defining a detent mechanism or ball  1314  extending therefrom. The detent mechanisms or balls  1314  are sized and shaped for receipt within corresponding ones of the recesses/grooves  1298   a ,  1298   b  formed along the interior medial and lateral surfaces of the tibial baseplate trial  1280  for removable attachment of the connection portion  1302  with the tibial baseplate trial  1280 . Additionally, the connection portion  1302  includes a pair of central alignment members  1311   a ,  1311   b  positioned on opposite sides of the longitudinal axis L and between the left hand and right hand regions  1310 ,  1312  of the connection portion  1302 . The central alignment members  1311   a ,  1311   b  define opposite substantially flat/planar abutment surfaces configured for abutment against a corresponding superior surface of the tibial baseplate trial  1280 . The connection portion  1302  also defines a curved or contoured posterior-facing gauge surface  1316  extending between the medial and lateral sections  1310   a ,  1310   b ,  1312   a ,  1312   b . The curved or contoured posterior-facing gauge surface  1316  of the connection portion  1302  is sized and shaped for close-fitting abutment against the resected anterior portion of the tibial eminence  14  ( FIG.  74 B ). 
     In one embodiment, the handle portion  1304  includes a shaft portion  1320  extending axially from an anterior surface of the connection portion  1302 , and a proximal gripping portion  1322  extending axially from the shaft portion  1320  and configured to be grasped and manipulated by a user. The proximal gripping portion  1322  further defines a series of openings  1324  sized and configured for optional receipt of an alignment rod or “up rod” (not shown) or to other alignment devices or support structures. 
     Referring to  FIGS.  73 A and  73 B , shown therein is the tibial baseplate trial  1280  attached to the resected proximal tibia  12 , with the tibial eminence  14  positioned within the central U-shaped slot  1290  of the baseplate trial  1280 , and with the planar inferior surface  1284   b  resting on the substantially flat/planar resected surfaces of the proximal tibia  12 . As should be appreciated, the anterior gauge  1300  may be removably attached to the tibial baseplate trial  1280  to aid in the manipulation and handling of the baseplate trial  1280  relative to the resected proximal tibia  12  by positioning the appropriate left or right hand region  1310 ,  1312  of the connection portion  1302  into the anterior elongate opening  1296  in the baseplate trial  1280  until the detent mechanisms or balls  1314  snap or click into the recesses/grooves  1298   a ,  1298   b  formed along the interior medial and lateral surfaces of the baseplate trial  1280 . The position and orientation of the tibial baseplate trial  1280  relative to the resected proximal tibia  12  can be adjusted to generally align the outer peripheral surface or edge  1286  of the plate  1282  with the outer peripheral edge of the resected proximal tibia  12  prior to anchoring of the baseplate trial  1280  to the proximal tibia. Additionally, the anterior gauge  1300  is used to check/verify the accuracy and precision of various aspects and features associated with the tibial eminence  14  (i.e., position, orientation, size and shape) via a close-fitting arrangement between the curved or contoured posterior-facing gauge surface  1316  of the anterior gauge  1300  and the resected anterior portion of the tibial eminence  14 . Notably, this check/verification can be conducted either before and/or after formation of the keel cavity in the resected horizontal surfaces of the proximal tibia  12 . Additionally, the anterior gauge  1300  can be easily removed from the tibial baseplate trial  1280  to avoid interference with formation of the slots/opening associated with the keel cavity by simply pulling up on the handle portion  1304  in a generally vertical direction until the detent mechanisms or balls  1314  become disengaged from the recesses/grooves  1298   a ,  1298   b  in the tibial baseplate trial  1280 . 
     Referring to  FIGS.  74 A and  74 B , shown there is the anterior gauge  1300  removably attached to the tibial baseplate trial  1280 . As indicated above, the anterior gauge  1300  is removably attached to the tibial baseplate trial  1280  by positioning the appropriate left or right hand region  1310 ,  1312  of the connection portion  1302  into the anterior elongate opening  1296  in the tibial baseplate trial  1280  until the detent mechanisms or balls  1314  snap or click into the recesses/grooves  1298   a ,  1298   b  formed along the interior medial and lateral surfaces of the tibial baseplate trial  1280 . At this point, the substantially flat planar abutment surfaces defined by the central alignment members  1311   a ,  1311   b  should abut against the superior surface of the tibial baseplate trial  1280 , and the curved or contoured posterior-facing gauge surface  1316  of the connection portion  1302  should abut the resected anterior portion of the tibial eminence  14  in a close-fitting arrangement ( FIG.  74 B ). If these abutting surfaces appropriately mate with one another in a close fitting arrangement, the accuracy and precision of the aspects and features of the tibial eminence  14  (i.e., position, orientation, size and shape) in relation to tibia implant fit have been confirmed, and the baseplate trial  1280  can be removed from the proximal tibia  12  followed by final installation of the tibial implant onto the prepared proximal tibia  12  in a conventional manner. However, if these abutting surfaces do not appropriately mate with one another, additional modifications to the tibial eminence  14  and/or other portions of the resected proximal tibia  12  may be necessary prior to accommodate for the installation of the tibial implant. 
     It should be understood that method steps disclosed herein may be performed in any order regardless of the order in which they are presented, discussed or illustrated, and that while a medial cut first method may be preferable in some embodiments, the surgical techniques provided herein may be adapted for a lateral cut first method. It should also be understood that any experiments, experimental examples, or experimental results provided herein are intended to be illustrative of the present invention, and should not be construed to limit or restrict the invention scope. Further, any theory, mechanism of operation, proof, or finding stated herein is meant to further enhance understanding of the present invention and is not intended to limit the present invention in any way to such theory, mechanism of operation, proof, or finding. 
     In reading the claims, words such as “a”, “an”, “at least one”, and “at least a portion” are not intended to limit the claims to only one item unless specifically stated to the contrary. Additionally, when the language “at least a portion” and/or “a portion” is used, the claims may include a portion and/or the entire item unless specifically stated to the contrary. Furthermore, when the term “distal” is used with respect to a structure, the term refers to the far end of the structure, and when the term “proximal” is used with respect to a structure, the term refers to the near end of the structure. Moreover, the terms “superior”, “inferior”, “medial”, “lateral”, “anterior”, “posterior”, “up”, down”, “left”, “right”, “front”, “rear”, “horizontal” and “vertical” refer to general directions defined from a normal/upright view point looking toward the anterior region of the proximal tibia. 
     Various changes and modifications to the described embodiments described herein will be apparent to those skilled in the art, and such changes and modifications can be made without departing from the spirit and scope of the invention and without diminishing its intended advantages. Additionally, while the invention has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered illustrative and not restrictive in character, it being understood that only selected embodiments have been shown and described and that all changes, equivalents, and modifications that come within the scope of the inventions described herein or defined by the following claims are desired to be protected.