Abstract:
A combination of a first assembly for guiding resection of a femur and tibia of a knee joint and a second assembly including femoral and tibial knee components. The combination of the first assembly and the second assembly provides optimal placement and positioning of the femoral and tibial knee components to achieve near-normal knee kinematics and tension. The preparation for and placement of the prosthetic knee components provides medial-pivoting kinematics mimicking that of the natural knee thereby promoting improved outcome for the patient.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the priority to U.S. patent application Publication Ser. No. 11/349,772, filed Feb. 8, 2006, and entitled GUIDE ASSEMBLY FOR GUIDING CUTS TO A FEMUR AND TIBIA DURING A KNEE ARTHROPLASTY, which claims priority to U.S. Provisional Patent Application Ser. No. 60/651,102, filed Feb. 8, 2005 and entitled GUIDE ASSEMBLY FOR GUIDING CUTS TO A FEMUR AND TIBIA DURING A KNEE ARTHROPLASTY, each of which is incorporated herein in its entirety by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention is related to the use of instruments for guiding preparation of a knee for installation of an implant during an arthroplasty, and in particular, to the use of ligaments around the knee and other anatomical features to position the guide instruments and making reference cuts to the tibia and the femur. 
     2. Description of Related Art 
     During a knee arthroplasty, a surgeon typically must gain access to the knee joint in order to perform resections of existing bone and cartilage so as to shape the tibia and femur to fit mating surfaces of the implant. Some arthroplasty procedures seek to minimize the invasiveness of the approach to the knee joint by minimizing the size of the incision in the surrounding soft tissue structure of the knee and the patella. Preserving the soft tissue structure also preserves some of the support provided by these tissues. However, preserving the soft tissues surrounding the knee can be difficult at times due to the need to firmly support the resection guides relative to the bone of the tibia and the femur. 
     The manner in which the natural knee joint performs is largely affected by the tension in the collateral ligaments of the knee, as well as by the alignment of the articular surfaces of the knee joint relative to the collateral ligaments. In the natural knee joint, the plane of the articular surfaces of the femur and the tibia bisects the collateral ligaments at an optimal, physiological position. This optimal, physiological position enables the knee joint to flex and extend in a balanced and properly aligned manner. Exemplary arthroplasty procedures resection the femur and the tibia, yet preserve the optimal, physiological position of the knee joint when fitted with a prosthesis. 
     Preservation of the ligamentous and other soft tissue structures around the knee can provide a reference point for accurately positioning the tibial and femoral components of the knee implant, in particular when said structure is in tensed or otherwise loaded condition. For example, ligament tensions can be used to guide placement of resection guides. Conversely, preservation of the soft tissue structures requires balancing of the forces exerted by the soft tissues to promote normal kinematics in the knee and normal patellar tracking. Therefore, ligament forces can play a significant role in restoring normal function to a knee. Generally, therefore, reductions in the invasiveness of the knee arthroplasty procedure combined with improvements in the positioning and installation of knee components can result in a better overall surgical outcome for the patient. 
     It would therefore be advantageous to have instrumentation for guiding resection of the femur, tibia and other structures in the knee during a knee arthroplasty that works well with minimally invasive approaches to the tibia and femur. It would be further advantageous if the instrumentation assisted the balancing of forces between the knee implant components and the preserved ligamentous and soft tissue structures for improved function of the knee implant. Also, it would be advantageous to have instrumentation for guiding resection that uses the ligamentous structure of the knee to guide placement of the instrumentation and the resulting optimal alignment and physiological positioning of the knee prosthesis. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention meets the above needs, and achieves other advantages, by providing an assembly for guiding resection of a femur and tibia of a knee joint in preparation for installing femoral and tibial knee components. The components of the present invention may be configured for use in both total knee replacement and unicompartmental, or partial knee arthroplasty. Embodiments of the present assembly can include tibial and femoral IM rods which are connected through a torque bolt that allows controlled adjustment of the distraction of the tibia and femur during cut positioning in a range of flexion angles. Also, the assembly is usable with relatively small, noninvasive approaches to the knee joint by way of relatively narrow, low profile components that attach to tibial and femoral IM rods. Further, the assembly includes several quick-release components to allow fast assembly and disassembly in a surgical setting. Each of these aspects, along with the ability of the assembly to accurately guide initial reference cuts to the tibia and femur, promotes an improved outcome for the patient. 
     An assembly of one embodiment of the present invention includes femoral and tibial IM rods, a flexion cutting guide, an extension cutting guide and a selection of selectively lockable components. Each of the IM rods includes a shaft portion that is configured to extend within the IM canal of the femur or tibia. The femoral IM rod also includes a femoral mount on an end of the shaft that is configured to extend away from the femur when the shaft is in the femoral IM canal. Similarly, the tibial IM rod includes a tibial mount on an end of the shaft that is configured to extend away from the tibia when the shaft is in the tibial IM canal. Each of the mounts is configured to attach to one or more of the selectively lockable components. The flexion and extension cutting guides define one or more slots wherein the slots are configured to guide the use of cutting and other instruments to make preparatory cuts to the femur and/or the tibia with the knee in flexion and extension. Each of the cutting guides is configured to attach to one or more of the selectively lockable components so as to be supported by the femoral and tibial IM rods. The selectively lockable components are configured to attach to the femoral and tibial IM rods, to have at least one portion with a relatively small cross section extending anteriorly or anterior-medial out of the knee joint compartment and to attach to the flexion and extension cutting guides and support and limit the motion thereof. 
     In one aspect, the femoral mount has a cylindrical shape that extends in an anterior-posterior direction between the femoral condyles and includes a central opening and a plurality of gauge marks extending along its outside surface. The central opening may also include an anterior anti-rotation portion (e.g., a hexagonal shaped portion) and a larger diameter cylindrical portion. The tibial mount can include or support a flexion bolt with a threaded shaft at one end configured to extend into an opening in the tibial IM shaft, a bushing at the other end and an exterior hexagonal flange in between the ends. The bushing is configured to extend into the cylindrical portion and also contains an interior hexagonal bore. The hexagonal flange is configured to allow gripping by an external torque wrench or internal torque driver to urge the femoral mount away from the tibial mount (by turning of the threaded shaft) and distract the tibia and femur to a desired torque reading. This allows the surgeon to apply the appropriate amount of tension to the ligamentous structure as defined by said surgeon and recorded for comparison later in the technique. 
     Included in an exemplary embodiment of the selectively lockable components is a first locking mechanism that has an arm, a plunger assembly and an anti-rotation extension, defined in this instance as a hex. The arm has an elongate portion extending away from a head portion. Also extending from the head portion is the hex-shaped anti-rotation extension. Defined through the head portion and hex extension is an opening that is configured to receive a shaft of the plunger assembly. The plunger assembly includes a thumb press at one end of the shaft and an anti-rotation feature similar to anti-rotation extension, defined in this instance as a hexagonal tip at the other end of the shaft that extends out of the hex extension. Also, the shaft includes a peg that extends into a helically shaped slot defined in the head portion. A spring extends between the head portion and the thumb press. Depression of the thumb press advances the shaft, while the peg and helical slot cause the shaft to rotate, and the flats of the hexagonal tip to align with the hex extension. This allows the hexagonal tip and hex extension to become concentric and to be inserted into the anterior hex portion of the central opening of the femoral mount. In addition, the hexagonal tip is configured to extend out of the hex portion of the opening and into the cylindrical portion, and to rotate (due to the helical slot and peg) into an eccentric position upon release of the thumb press, thereby locking the locking mechanism into the femoral mount. When attached, the head portion of the arm extends proximally out of the knee joint compartment and the elongate portion extends anteriorly (with respect to the tibia) through the surgical incision. 
     A flexion guide support member of the assembly of the present invention includes a slider member and a ratchet bar. The slider member is configured to attach to, and slide along, the elongate portion of the arm of the first locking mechanism, such as by having an opening defined therein matching the cross-section of the elongate portion. The ratchet bar is configured to extend toward a plane defined by the tibial plateau. Preferably, when assembled, the femoral mount, first locking mechanism and flexion guide support member roughly form a U-shape that is relatively narrow in the medial-lateral direction to allow its use with narrow incisions. 
     Also included in the selectively lockable components is a quick release mechanism that is configured to slide along and lock to the ratchet bar of the flexion guide support member. For example, the quick release mechanism may define an opening configured to extend and slide along the ratchet bar, and a locking pin that is spring loaded to extend into a portion of the ratchet to stop the sliding motion. The locking pin is spring biased, but can be overcome with a manual draw pull (for example) to allow further sliding or repositioning of the quick release mechanism. The quick release mechanism may also include a spring-biased locking lever that, along with an engagement member of the quick release mechanism, can extend into an opening and lock to the flexion cutting guide. Depressing the locking lever again easily releases the flexion cutting guide after k-wire or other fasteners have been used to secure the flexion cutting guide in place to the tibia or femur. This allows the resection guide to translate toward the proximal tibia and away from the tensioning assembly with the knee in flexion. 
     Once the flexion resection guide is fixed to the proximal tibia, the resection guide has a plurality of slots for which to resect multiple components of the femur and tibia, most notably a measured proximal tibial resection and a posterior condylar resection. Making these resections with the knee in tension at 90 degrees will allow the user to theoretically make a tensed flexion gap resection. 
     The selectively lockable components may also include components configured to attach to the femoral and tibial IM rods when the knee is in extension. For example, the components may include a cannulated extension bolt, a tibial angulation guide, an extension guide support member and a second locking mechanism. The tibial angulation guide is configured to attach to the tibial IM rod through the cannulated extension bolt which is, in turn, coupled to the tibial IM rod and extend around the femoral mount, such as by having a block defining an arc-shaped channel that is configured to receive the cylindrical outer surface of the femoral mount. Included on the tibial angulation guide are a plurality of gauge marks that, when correlated to gauge marks on the outer surface of the femoral mount, register an amount of valgus angulation of the tibia with respect to the femur. The tibial angulation guide may be configured to extend into the bushing of the bolt described above, or to have its own threaded shaft and hexagonal flange allowing it to be used to distract the tibia and femur in extension to a torque value corresponding to the torque value previously measured with the knee in flexion. 
     The extension guide support member is configured to have a relatively narrow profile and extend anteriorly out of the joint compartment through the incision providing access thereto. For example, the extension guide support member may include a mounting portion that is cylindrical and defines a cylindrical opening and a support arm that is configured to extend proximally from the mounting portion. The second locking mechanism is generally configured similar to the first, except it lacks the fixed elongate portion of the arm. Rather, it includes a cylindrical head portion that is configured to extend through the cylindrical opening of the mounting portion of the extension guide support member so as to connect the extension guide support member to the femoral mount while allowing said support member to rotate in a desired position independent of the previously selected valgus angle. 
     The extension guide support member also includes a support arm that is configured to extend proximally from the mounting portion when the mounting portion is attached to the femoral mount using the second locking member. The extension cutting guide is configured to slidably attach over the support arm, such as via a channel defined in its body. Also, the extension cutting guide preferably includes a swivel arm that can be swung into an abutting relationship with the tibial plateau and the plateau flange of the tibial mount to provide an additional reference point for making a femoral resection with the knee in extension. The extension cutting guide, similar to the flexion cutting guide, may also define a plurality of fixation openings allowing fasteners to extend therethrough and attach the extension cutting guide to the tibia or femur. This allows removal of the selectively lockable components to provide room for the cuts to the tibia and/or the femur. 
     The swivel arm, once referenced off the proximal tibial resection, will allow the extension cutting guide to make a pre-determined resection of the distal femur. Resecting with the knee tensed in the extended position will allow the user to make a balanced extension gap resection when compared with the tensed resections made with the knee previously positioned in flexion. 
     The assembly of the present invention has many advantages. For example, it provides a relatively narrow and low profile collection of locking components that securely attach cutting guides to tibial and/or femoral IM rods. This provides a robust guide to reference cuts being made to the tibia and the femur with an approach to the joint that minimizes invasiveness. Further, many of the components, such as the first and second locking mechanisms and the quick release mechanism, facilitate quick assembly, easy adjustment and quick disassembly for improved efficiency. Additionally, the use of the flexion bolt in flexion and the extension bolt in extension, combined with the other components of the tensioning assembly, allow the tibia and femur to be distracted under a matching amount of tension in flexion and extension to ensure a better fit for the tibial and femoral knee replacement components throughout a range of flexion. Spacers, as well as limited radial movement of the tensioning assembly components further allow the knee to adjust to accommodate the natural physiology of the patient&#39;s knee throughout the tensioning and resection processes. Thus, the described procedures and assemblies allow the surgeon to adjust the amount of valgus angulation of the tibia as desired to match the anatomy of the patient. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S) 
       Having thus described the invention in general terms, reference will now be made to the accompanying drawings, which are not necessarily drawn to scale, and wherein: 
         FIG. 1  is a plan view of a tibial intramedullary (IM) rod and femoral IM rod of an assembly of one embodiment of the present invention; 
         FIG. 2  is a perspective view of the femoral IM rod of  FIG. 1  inserted into a femur; 
         FIG. 3  is a cross-section of a femoral mount of the femoral IM rod shown in  FIG. 2 ; 
         FIG. 4  is a perspective view of a femoral and tibial IM rods of  FIG. 1  inserted in the femur and tibia of a knee, respectively; 
         FIG. 5  is a perspective view of a bushing extending from an extension bolt of the assembly of the present invention wherein the extension bolt is coupled to the tibial IM rod of  FIG. 1 ; 
         FIG. 6  is a plan view of the extension bolt of  FIG. 5  and of a tibial angulation guide and flexed knee cutting guide of the assembly of the present invention; 
         FIG. 7  is a perspective view of the bushing and IM rods of  FIG. 5 , wherein the bushing of the extension bolt is advanced to connect the IM rods; 
         FIG. 8  is a side elevation view of a first locking mechanism of the assembly of the present invention; 
         FIG. 9  is a perspective view of the first locking mechanism being connected to the assembled IM rods and bolt of  FIG. 7 , torqued to a desired load; 
         FIG. 10  is another perspective view of the first locking mechanism in the unlocked position, assembled IM rods and bolt of  FIG. 9 , torqued to a desired load; 
         FIG. 11  is yet another perspective view of the first locking mechanism assembled and locked to the IM rods and extension bolt of  FIG. 9 , torqued to a desired load; 
         FIG. 12  is a perspective view of a flexion guide support member of the assembly of the present invention connected to the first locking mechanism of  FIG. 11 ; 
         FIG. 13  is a perspective view of a flexed knee cutting guide assembly of the assembly of the present invention connected to the flexion guide support member of  FIG. 12 ; 
         FIG. 14  is a side elevation view of the assembly of  FIG. 13 ; 
         FIG. 15  is a rear elevation view of the assembly of  FIG. 13 ; 
         FIG. 16  is a bottom elevation view of a quick release mechanism of the flexed knee cutting guide assembly of  FIG. 13 ; 
         FIG. 17  is a perspective view of the quick release mechanism of  FIG. 16  and the flexion guide support member of  FIG. 12 ; 
         FIG. 18  is a perspective view of a flexed knee cutting guide of the flexed knee cutting guide assembly of  FIG. 13 ; 
         FIG. 19  is a front elevation view of a tibial angulation guide of the assembly of the present invention extending between the femoral and tibial IM rods of  FIG. 1 , coupled with an extension bolt; 
         FIG. 20  is an enlarged view of the IM rods and tibial angulation guide of  FIG. 19 ; 
         FIG. 21  is another enlarged view of the IM rods and tibial angulation guide of  FIG. 19 ; 
         FIG. 22  is a perspective view of a second locking mechanism and extension guide support member of the assembly of the present invention being assembled to the femoral IM rod of  FIG. 1 ; 
         FIG. 23  is an enlarged perspective view of the assembly of the extension guide support member of the present invention to the second locking mechanism of  FIG. 22 ; 
         FIGS. 24-26  are various a perspective views of an extended knee cutting guide of the assembly of the present invention attached to the extension guide support member and second locking mechanism of  FIG. 22 , and the femoral IM rod of  FIG. 1 ; 
         FIG. 27  is a perspective view illustrating disassembly of the second locking mechanism of  FIG. 22 , from the femoral IM rod of  FIG. 1 , once the extended knee cutting guide is fixed in position to the distal femur; 
         FIG. 28  is a front elevation view of the extended knee cutting guide of  FIG. 24 ; 
         FIG. 29  is a side elevation view of the extended knee cutting guide of  FIG. 24 ; 
         FIG. 30  is a plan view of an L-shaped cutting block of the assembly the present invention; 
         FIG. 31  is a side elevation view of the L-shaped cutting block of  FIG. 30  being used to cut an anterior condyle of a femur; 
         FIGS. 32-40  show various modular options of the present invention that promote quick assembly and facilitate minimally invasive intra-operative use; 
         FIG. 41  shows a hinged retractor as used in one embodiment of the present invention; and 
         FIG. 42  shows an embodiment of the present invention that implements mini-trials. 
         FIG. 43  shows an exploded view of an embodiment of the present invention for resection in knee flexion. 
         FIG. 44  shows a perspective view of the assembled embodiment of  FIG. 43 . 
         FIG. 44A  shows a perspective view of an implementation of the current invention having a ratcheting device in place of the flexion bolt. 
         FIG. 45  shows a perspective view of an embodiment of the present invention having the cutting block attached and secured. 
         FIG. 46  shows an exploded view of an embodiment of the present invention for resection in knee extension. 
         FIG. 47  shows a perspective side view of the assembled embodiment of  FIG. 46 . 
         FIG. 48  shows a perspective view of an embodiment of the present invention having the cutting block attached and secured. 
         FIG. 49  shows a perspective front view of an embodiment of the resectioned knee having been fitted with a knee prosthesis. 
         FIG. 50  shows a perspective side view of the embodiment of  FIG. 49 . 
         FIG. 51  shows a partially cross-sectioned view of an implementation of the knee prosthesis. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all embodiments of the invention are shown. Indeed, this invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Like numbers refer to like elements throughout. 
     An assembly  10  of the present invention for facilitating preparation of a knee joint, including guiding positioning of cuts to a femur  11  and tibia  12  of the knee joint, for later mating with femoral and tibial knee replacement components, is shown in the accompanying figures. Generally, the assembly  10  includes various components selected and arranged to attach to a reference point inside the knee joint compartment (such as one or more intramedullary (IM) rods), extend through a relatively narrow, small or noninvasive approach defined in the soft-tissues of the knee and attach outside the knee to a selection of resection guides. 
     Anatomical directions as used herein are in reference to the knee during the preparatory surgery and correspond to the illustrated embodiment of the assembly  10 . However, depending upon the handedness of the knee, or variations in individual morphology and ligamentous structure, these directions could vary and should not typically be considered limiting. 
     The assembly  10  can be configured to be applied at different knee flexion angles to facilitate positioning of the components throughout the range of flexion or extension. Illustrated herein are components of the assembly  10  for guiding cuts and preparation of the knee at two different flexion angles, namely 90° and full extension. However, the components can be adjusted or configured, or other components employed within the spirit and scope of the present invention, to extend through relatively non-invasive approaches to the knee joint at any range of flexion be it hyper-extension, 30°, 45°, 60°, etc., through to hyper-flexion. 
     In the illustrated embodiment, the assembly  10  includes two IM rods, a femoral IM rod  13  and a tibial IM rod  14  that provide a reference point for supporting the remainder of the assembly  10  with the knee in flexion, in this case 90° of flexion. The femoral IM rod  13  includes a femoral mount  15  and a main shaft  16 , as shown in  FIG. 1 . The main shaft  16  of the femoral IM rod  13  is preferably an elongate, relatively rigid shaft that, when installed, extends within the IM canal of the femur  11  in a proximal-distal direction, as shown in  FIG. 2 . The main shaft  16  can include structure that facilitates its insertion into the femur  11 , such as a tapered end  17 . Preferably, the main shaft  16  is constructed of a relatively rigid material, such as a hard plastic, stainless steel, titanium or other metal or material that is capable of insertion into bone without damage and of stably supporting the femoral mount  15 . 
     Attached to the distal end of the main shaft  16 , opposite the tapered end  17 , is the femoral mount  15 . Generally, the femoral mount has a cylindrical shape with an axis extending perpendicular to a long axis of the main shaft  16 . Defined along the axis of the femoral mount  15  is a central opening  18 , as shown by the cross-sectional view of the femoral mount in  FIG. 3 . The central opening includes two portions, an anti-rotation portion, in this instance a hex portion,  19  and a cylindrical portion  20  which allow locking of other components of the assembly  10  to the femoral mount  15 , as will be described in greater detail below. Regardless, once the femoral IM rod  13  is installed, the femoral mount  15  and its central opening  18  preferably extend in an anterior-posterior direction along the femoral notch between the femoral condyles. Defined on the outer cylindrical surface of the femoral mount  15  is a plurality of longitudinally extending gauge marks  21  that aid in positioning of the tibial and femoral components, as will be described in more detail below. 
     As shown in  FIGS. 1 and 4 , the tibial IM rod  14  includes a main shaft  22  supporting a tibial mount  23 . Similar to the main shaft  16  of the femoral IM rod  13 , the main shaft  22  has an elongate structure with a tapered distal end  24  to facilitate its insertion into the IM canal of the tibia. However, the main shaft  22  preferably includes one or more flutes  25  extending along its length in order to further facilitate insertion and to resist rotation within the IM canal of the tibia. These flutes may also, optionally, be included on the main shaft  16 . Defined in the main shaft  22  at its proximal end is an opening  27  that extends into the flutes  25 . These openings further facilitate insertion into the IM canal of the tibia. As with the main shaft  16  of the femoral IM rod  13 , the main shaft  22  may be constructed of a range of relatively rigid materials to provide firm support for the tibial mount  23 . In some embodiments of the current invention, the main shaft  22  of the tibial IM rod is truncated to form a short extension for engaging an opening in the upper surface of the tibia. As such, the tibial IM canal is not accessed but rather the tibial mount  23  and the truncated tibial IM rod primarily engage and interface with the external surface of the tibia. In other embodiments, the tibial mount  23  is provided without a tibial IM rod, such that a flat surface of the tibial mount  23  seats directly on the resectioned surface of the tibia. As such, the interface between the tibial mount  23  the tibia is completely extramedullary. In these embodiments, the position of the tibial mount  23  with respect to the tibia is maintained by the perpendicular compression force between the tibial mount  23  and the tibia. In other embodiments, the flat surface of the tibial mount  23  is modified to include a plurality of spikes which further interface with the resectioned tibial surface to prevent undesirable movement of the tibial mount component  23  during tensioning. 
     Included in the tibial mount  23  are a thickened cylindrical portion  26  and a plateau flange  28 , as shown in  FIG. 4 . The cylindrical portion  26  is preferably sized to fit the IM canal of the tibia  12 . The cylindrical portion is connected at its distal end to the main shaft  22  and at its proximal end supports the plateau flange  28 . The plateau flange extends outward at right angles from the cylindrical portion  26  and has three flat sides and one crescent-shaped side. The crescent shaped side is a cutout to provide room for the anterior cruciate ligament prior to resection of the proximal tibia. The flat sides can further aid in guide positioning and cutting, such as during a tibial compartmental resection in a unicondylar arthroplasty procedure wherein only a single condyle and a portion of the tibial plateau are reconstructed. 
     A threaded opening  29  extends into the tibial mount  23  and provides a coupling attachment for the flexion bolt  30 , which includes a threaded shaft  31 , a hex flange  32  and a bushing  33 , as shown in  FIGS. 5 and 6 . The threaded shaft  31  has a plurality of threads and extends away from the hex flange  32 , while the bushing  33  is a smooth, cylindrical shaft that extends opposite the threaded shaft from the other side of the hex flange  32 . The hex flange  32  is shaped to allow gripping by a torque or other wrench to provide motivation for advancement of the threaded shaft  32 . 
     The threaded shaft  31  is configured to be advanced into the threaded opening  29  of the tibial mount  23  until it is flush with the plateau flange  28  thereby positioning the bushing  33  at its lowest profile position, as shown in  FIG. 5 . This position allows the femur  11  and femoral mount  15  extending therefrom to be slipped into position above the bushing  33 . Then, the torque wrench is used to reverse the advancement of the threaded shaft  31  until the bushing  33  engages the cylindrical portion  20  of the central opening  18  in the femoral mount  15 , as shown in  FIG. 7 . Advancement is reversed until a pre-selected torque measurement is reached on the torque wrench, or adequate tension of the ligamentous structure is obtained. Once the appropriate ligament tension is obtained, this torque value is recorded for comparison later in the technique. The resulting assembly emulates a static linkage of the femur and tibia with the knee in flexion (e.g., at 30°, 60°, or 90° of flexion or increments therebetween) from which the surgeon can reference subsequent resection instruments as described below. 
     Also included in the assembly  10  is a quick connect locking mechanism  34  that connects into the hex portion  19  of the central opening  18 , as shown in  FIGS. 8 and 9 . Included in this embodiment of the locking mechanism are a static outrigger arm  35 , a spring-biased plunger  36  and a static clocking extension  37  which emulates the anti-rotation feature  19 , and in this instance has a hexagonal shape. The arm  35  has an elongate portion  38  and a rounded head portion  39 . The elongate portion  38  of the arm  35  has a square cross-section and extends from the rounded head portion  39  which has a partially cylindrical shape with a pair of opposing flats at its ends. Extending from one of the flats of the rounded head portion is the hex extension  37 . The hex extension  37  has a hexagonal cross-section configured to snugly fit within the hex portion  19  of the central opening  18  defined in the femoral mount  15 . As shown in  FIG. 8 , defined in one rounded surface of the head portion  39  is a helically extending slot  43  which, as will be described below, guides motion of the plunger  36 . 
     Defined through the rounded head portion  39  and the hex extension  37  is a cylindrical opening  40  through which the plunger  36  extends. In particular, the plunger  36  includes a thumb press  41 , a shaft  42 , a spring  45  and rotating extension  44  which emulates the anti-rotation feature  37 , in this instance is a hex, but could be any non-cylindrical shape, such as square, triangle or ellipse, capable of limiting rotation. The thumb press  41  is positioned at one end of the plunger  36  and has the shape of a circular disk with ridges to promote pressing with a thumb. Subjacent the thumb press  41  is the spring  45  which is preferably in the shape of a coil and extends around the shaft  42  and between the thumb press and head portion  39  so as to bias them apart. 
     The shaft  42  includes a peg  46  that extends perpendicular to the shaft and into the helical slot  43  defined in the head portion  39 , as shown in  FIG. 8 . Thus, depression of the thumb press  41  advances the shaft  42  within the opening  40  in the head portion  39 , and also results in rotation of the shaft as the peg  46  fixed thereto helically travels in the helical slot  43 . The hexagonal end  44  of the plunger  36  is fixed to the end of the shaft  42  opposite the thumb press  41 , extends along a free end of the hex extension  37  and has a hexagonal shape and size matching that of the hex extension  37 . 
     Due to its connection to the shaft  42 , depression of the thumb press  41  also causes rotation of the hexagonal end  44  of the plunger  36  until the flats of the hexagonal end match the orientation of the flats of the hex extension  37 , as shown in  FIG. 10 . Matching of this orientation allows insertion of the hex extension  37  and the hexagonal end  44  into the hex portion  19  of the central opening  18  of the femoral mount  15 , as shown in  FIG. 11 . Once the thumb press  41  is released, the spring  45  biases the thumb press, shaft  42  and hexagonal end  44  upwards, causing the flats of the hexagonal end to return to their non-matching, out-of-phase position (shown in  FIG. 9 ) with respect to the flats of the hexagonal extension  37 . 
     At this point, the hexagonal end  44  of the plunger  36  resides in the cylindrical portion  20  of the central opening  18  and, due to its non-matching position, cannot be withdrawn through the hex portion  19  of the central opening. As a result, the locking mechanism  34  becomes rotationally and translationally locked with respect to the femoral mount  15  and the femoral IM rod  13 . Once locked in place, the arm  35  of the locking mechanism  34  extends anteriorly outward from the femoral mount  15  and the condyles of the femur  11 . Notably, the combination of the relatively narrow femoral mount  15  and narrow, elongate structure of the arm  35  allows passage through relatively small surgical approach openings, facilitating use of the assembly  10  with less invasive procedures. For example, a modified mid-vastus, medial mid-vastus or subvastus approach could be used with a small 8-10 cm cut which allows avoidance of a release of the quadriceps from the anterior tibia. 
     Also included in the assembly  10  of the illustrated embodiment of the invention is a flexion guide support member  47  which is supported by the locking mechanism  34 . Included in the flexion guide support member is a slider member  48  and a ratchet bar  49 . The slider member defines a rectangular opening  50  which is sized and shaped to allow the slider member to be supported by, and slide along, the rectangular cross-section of the arm  35  of the locking mechanism  34 . This motion allows the ratchet bar  49 , which is attached to the slider member  48 , to move toward and away from the knee joint. The slider member  48  is preferably shaped to have finger grips (e.g., the tapered portion of the illustrated slider member) and may also include some type of a pin or locking assembly to resist, but not prohibit its sliding relative to the arm  35 . The ratchet bar  49  itself is also rectangular shaped in cross-section and, when assembled, extends distally from the arm  35  of the locking mechanism  34 , as shown in  FIG. 12 . The ratchet bar  49  also includes a pair of chamfered corners supporting a plurality of adjacent ratchet grooves  51  extending along the length of the ratchet bar. 
     The assembly  10  also includes a flexed knee cutting guide assembly  52  that attaches to the flexion guide support member  47 , as shown in  FIGS. 13 ,  14  and  15 . The flexed knee cutting guide assembly  52  includes a quick release mechanism  53  and a cutting guide  54 . The quick release mechanism  53  includes a body  55 , a draw pin  56 , first and second springs  57 ,  58 , a locking lever  59  and a locking pin  60 . As shown in  FIG. 16 , the body  55  defines a rectangular opening  61  which allows the body to be slid over the rectangular cross-section of the ratchet bar  49 . In addition, the body  55  includes a side opening into which the draw pin  56  extends so that its end engages the ratchet grooves  51 . In particular, the first spring  57  biases the draw pin into a position normally engaging the ratchet grooves so as to lock the draw pin, and hence the body  55 , into a particular position on the slider member  48 . The locking pin  60  extends through the body and through the draw pin  56  to secure the draw pin  56  and prevent it from disassembly. 
     The body  55  additionally includes a clevis  62  that extends outwards from the opposite side of the body from the draw pin  56  and which supports rotation of the locking lever  59  about its middle portion. As well shown in  FIG. 17 , the locking lever has a curved finger grip biased outward from the body  55  by the second spring  58  and the opposite end of the locking lever includes a tapered tongue  63  which, as will be described below, engages the cutting guide  54  so as to lock the quick release mechanism  53  thereto. Extending away from the clevis  62 , opposite the locking lever, is an engagement member  64  of the body  55 . The engagement member  64  has a rectangular cross-section and, in the assembled condition shown in  FIG. 13 , extends into a connection with the cutting guide  54 . 
     As shown in  FIG. 13 , the cutting guide  54  extends posteriorly (when assembled) from the quick release mechanism  53  and includes a mounting portion  65 , a k-wire guide or fixation pin portion  66 , a crosspin portion  71 , a proximal tibial cut guide portion  67  and a posterior condylar femoral cut guide portion  68 . The mounting portion  65  defines a rectangular opening  69  that is sized and shaped to slidably receive the engagement member  64  of the body  55  of the quick release mechanism  53 . The mounting portion  65  also defines a notch  70  in one of the sidewalls of the rectangular opening  69 , as shown in  FIG. 18 . The notch  70  is sized, shaped and positioned to receive the tapered tongue  63  of the locking lever  59  when the locking lever is under the bias of the second spring  58 , as shown in  FIG. 15 . Release of the cutting guide  54  is easily accomplished by depressing the free end of the locking lever  59 , overcoming the bias of the second spring  58  and disengaging the tapered tongue from the notch  70  of the mounting portion  65 . 
     The fixation pin (or k-wire) guide portion  66 , the tibial cut guide portion  67  and the femoral cut guide portion  68  each have a crescent shape that extends in a medial-lateral direction around the anatomical curvature of the anterior-medial or anterior-lateral tibia (depending upon which cut is being made), as shown in  FIG. 13 . The fixation pin guide portion  66  is adjacent the mounting portion  65  and defines a plurality of fixation pin holes  72  that extend in a posterior direction at an angle so as to guide fixation pins (used to fix the cutting guide  54  before release of the other components of the assembly  10 ) into the thickest anterior portions of cortical bone on the tibia  12 . Although less preferred, the number and orientation of the fixation pin holes could be varied depending upon the firmness of the connection desired, size and morphology of the tibia  12 , etc. 
     The tibial cut guide portion  67  is positioned adjacent the fixation pin guide portion  66  and defines a slot for guiding the tibial cut. The slot extends along the length of the crescent shape of the guide portion  67  and generally has a parallel orientation with respect to the tibial plateau. However, the resection plane defined by guide portion  67  may vary in posterior slope (sagittal plane angularity) and varus/valgus (coronal plane angularity), depending on the desired position and preference of the surgeon for the cutting guide  54 . An example of such a cut is illustrated in  FIG. 19 , wherein the tibia has a flat planar cut extending in the anterior-posterior and medial-lateral planes on the proximal end of the tibia  12 . The femoral cut guide portion  68  is proximally spaced from the tibial cut guide portion  67  by a pair of connection flanges  73  so as to bridge the knee joint compartment. Similar to the tibial cut guide portion  67 , the femoral cut guide portion  68  defines a slot that extends along the length of the crescent shape. However, because the knee is in flexion, the cut is guided through the posterior of the condyles of the femur  11 . 
     An advantage of the components of the assembly  10  for positioning cuts with the knee in flexion, including the femoral mount  15 , the tibial mount  23 , the flexion bolt  30 , the locking mechanism  34 , the flexion guide support member  47  and the flexed knee cutting guide assembly  52 , is their usability with relatively non-invasive, narrow cuts in the anterior soft tissues of the knee (and with a retracted patella). Generally, as can be seen in  FIGS. 14 and 15 , the assembled components for making the cuts in knee flexion are relatively narrow as they extend out of the joint space in a U-shape, while at the same time providing a firm connection for supporting the cutting guide  54 , a quick assembly and release of the components and accurate positioning of the flexed knee cutting guide. Considering the cutting guide  54  by itself (which can be positioned inside of the capsular incision), the width of this component is small compared to conventional cutting guides, for example, within a range of up to 4 to 5 cm thereby allowing their use with minimally invasive approaches to the knee joint. 
     The assembly  10  also includes instrumentation configured to guide cuts with the knee in extension (i.e., with the tibia and femur generally aligned, or at 0° of flexion), as shown in  FIGS. 19-29 . For knee extension, both the femoral IM rod  13  and the tibial IM rod  14  remain in place, as shown in  FIG. 19 . However, instead of attachment of the tibial mount  23  to the tibial IM rod  14 , a tibial angulation guide  74  is attached to the tibial IM rod. The tibial angulation guide  74  includes a gauge block  76  and a post  97  which fits into an extension bolt  96  (similar to the flexion bolt  30 , but without the bushing  33 ). The extension bolt  96  also has a hex flange  75 . Alternatively, a separate gauge block  76  may be employed with a shaft (as shown in  FIG. 6 ) that extends into an opening in the bushing  33 , allowing removal of the bolt  30  to be avoided. 
     Regardless, gauge block  76  extends upward from the plateau flange  28  of the tibial mount  23  when the threaded shaft of the extension bolt  96  extends into the threaded opening  29  and defines an arc surface  77  and a plurality of gauge marks  78  defined on its anterior surface, as shown in  FIGS. 19-21 . The arc surface  77  is shaped and sized to receive the outer surface of the cylindrically shaped femoral mount  15  and allow the femoral mount  15  to rotate in the varus-valgus direction and slide in the anterior-posterior direction therein. These motions are left free so as to not over-constrain the femur  11  and tibia  12 , but still promote anterior-posterior alignment of the instruments and rotational position selection, for better positioning of the tibial and femoral cuts. Other variations and combinations of shapes of the femoral mount  15  and tibial angulation guide  74  could be employed to allow these ranges of motion, such as by reversing the shapes of the gauge block  76  (it having a cylindrical shape) and the femoral mount  15  (it having the arc shape), by having a rounded shape between two plates, extending the angulation readings away from the instrument assembly, etc., and still be within the purview of the present invention. 
     Adjustment of the relative proximal-distal positioning of the femur  11  and the tibia  12  is accomplished, similar to the technique in the flexion position, by adjusting the rotation of the hex flange  75  of the extension bolt  96  with a torque wrench. This motion advances or retracts the threaded shaft of the tibial extension bolt  96  into and out of the threaded opening  29  in the tibial mount  23  and advances the tibial angulation guide  74  toward the femoral mount  15 . Preferably, the femur  11  and tibia  12  are distracted until the torque wrench has a reading similar to that for the knee in flexion to ensure that the joint is not overly tight in knee extension. With respect to the torque wrench and the amount of joint space, the torque wrench may be equipped with an extender that extends the length of the wrench, has hex-shaped jaws at its end and is relatively thin or low profile. If this is the case, the torque measurements may be adjusted to compensate for the additional length of the extender. In either case, the objective is to match the torque value obtained when the instrument construct constrained the knee in some degree of flexion, in this instance 90° of flexion or increments therebetween, and torque the bolt to a similar torque measurement that was reached on the torque wrench in the previous step, or until adequate tension of the ligamentous structure is obtained. 
     Referring again to  FIGS. 20 and 21 , the gauge marks  78  of the gauge block  76  radiate outward from the center of rotation of the femoral mount  15 , starting at the outer surface of the femoral mount, and are positioned on the anterior surface of the gauge block. The gauge marks  78  of the gauge block  76  are configured to match up with gauge marks  21  of the femoral mount  15  (as shown by the arrow) to indicate a valgus angle of the tibia  12  with respect to the femur  11 . Generally, the valgus angle should be within a range of 3 to 7 degrees, or even 2 to 9 degrees, depending upon the knee&#39;s morphology, surgeon preference, etc. 
     Once the angulation and proximal-distal positioning of the tibia  12  with respect to the femur  11  has been adjusted, an extension guide support member  79  is attached to the femoral mount  15  using a second locking mechanism  84 , as shown in  FIGS. 22 and 23 . Generally, the second locking mechanism  84  includes the plunger  36  (and its components including hexagonal end  44 ), hex extension  37  and helical slot  43  which are similarly numbered as they share a similar function with the same components of the first locking mechanism  34 . The second locking mechanism  84  differs in that the head portion  39  is somewhat longer, is cylindrical and lacks the elongate portion  38  of the arm  35 . Also, the second locking mechanism  84  includes a grip flange  86  positioned adjacent the plunger  36  to facilitate a finger grip when depressing the plunger. Regardless, the hexagonal end  44  has the same rotating motion that facilitates quick attachment of the end of the second locking mechanism  84  to the femoral mount  15 . 
     The extension guide support member  79  includes a mounting portion  80 , a support arm  81  and a fixation flange  82 . The mounting portion  80  has a cylindrical shape with a cylindrical opening  83  extending therethrough that is configured to slidably receive the second locking mechanism  84 , but is not rotationally constrained by said second locking mechanism  84 . Extending away from one side of the mounting portion  80  is the support arm  81  which is an elongate structure with a T-shaped cross section. Extending away from the other side of the mounting portion  80  is an additional flange  82  that acts as a housing for a mechanism, in this case a ball and spring  85 , to provide some resistance to rotation of the extension guide support member  79  with respect to the second locking mechanism  84 . 
     Also included in the illustrated embodiment of the assembly  10 , is an extended knee cutting guide  87  that is supported by the extension guide support member  79  during positioning, as shown in  FIGS. 24-29 . The extended knee cutting guide  87  includes a mounting portion  88 , a fixation pin (or k-wire) guide portion  89 , a femoral cut guide portion  90  and a reference lever  91 . The mounting portion  88  is generally centered in a body portion of the extended knee cutting guide  87  and defines a channel  92  that has a cross-sectional shape matched to the T-shaped cross-section of the support arm  81 . The matching shapes allow the extended knee cutting guide  87  to slide in the proximal-distal direction along the support arm  81 . 
     The fixation pin guide portion  89  defines a plurality of k-wire (or other type of fastener, e.g., screws, nails, etc.) holes  93  that allow fixation using fixation pins after positioning of the extended knee cutting guide  87 . The holes  93  are positioned on medial and lateral sides of the anterior femur when positioned so as to allow fixation to relatively thick cortical bone, as shown in  FIG. 25 . As with the k-wire holes  72 , the k-wire holes  93  can be oriented at various angles or selectively positioned to guide fasteners into and through larger lengths of denser bone on the femur  11 . 
     The femoral cut guide portion  90  extends either laterally or medially for a uni-compartmental reconstruction (as with the illustrated embodiment), or in both directions for a full resection of the femoral condyles. Notably, the guide portion  90  extends distally in the shape of a U that fits around the second locking mechanism  84  when the extended knee cutting guide  87  is in place, as well shown in  FIG. 29 . Regardless, the guide portion  90  extends distally from the k-wire guide portion  89  and then laterally or medially to define a guide slot  94 . The guide slot  94  is of sufficient width to allow passage of cutting instruments or blades but still promote a relatively straight or planar resection. Notably, extension medially allows the laterally shifted patella to be avoided in a medially oriented approach to the knee joint compartment. 
     Extending further distally from the femoral cut guide portion  90  is a portion of the extended knee cutting guide  87  that defines a clevis  95  that rotationally supports the reference lever  91 . The reference lever extends laterally or medially and rotates in an anterior-posterior direction to allow positioning in the joint compartment, as shown in  FIGS. 24 and 25 . The reference lever  91  has a broad, flat distal surface that is configured to rest against the flat tibial cut and a flat lateral surface is configured to abut the side surface of the plateau flange  28 . These surfaces provide a stop for the distal movement of the extended knee cutting guide  87  along the support arm  81  of the extension guide support member  79 . With the reference lever  91  and the second locking mechanism  84  in place, fixation pins can be inserted through the pin holes  93  in the guide portion  89  to fix the femoral cut guide portion  90  to the femur  11 . This allows removal of the extension guide support member  79 , as shown in  FIGS. 27 ,  28  and  29 . 
     Advantageously, the components for positioning the cuts with the knee in extension, including the extension bolt  96 , tibial angulation guide  74 , the extension guide support member  79  and the extended knee cutting guide  87  are configured for passage through an anterior and medial approach to the knee compartment due to the narrow width and profile of the components. For example, as shown in  FIG. 25 , the posterior portion of the second locking mechanism  84  and the reference lever  91  would pass through the incision and exhibit the aforementioned narrowness and low-profile. Preferably, the width of this component is small compared to conventional cutting guides, for example, within a range of up to 4 to 5 cm thereby allowing their use with minimally invasive approaches to the knee joint. 
     After these initial cuts, further cuts can then be made using the initial cuts as a reference. As shown in  FIGS. 30 and 31 , an L-plate  99  is employed to abut the posterior and distal flat surface of the femur  11  to guide an anterior cut. Chamfer cuts (anterior and posterior) can be made using a chamfer cut block and other finishing cuts can be references from the initial cuts made using the assembly  10  of the present invention. Additional description of these finishing cuts can be found in U.S. patent application Ser. No. 10/794,188 filed on Mar. 5, 2004, entitled “Reference Mark Adjustment Mechanism for a Femoral Caliper and Method of Using the Same,” which is hereby incorporated herein by reference. 
     In another embodiment of the present invention, as shown by  FIGS. 32 through 40 , the assembly  10  includes additional modular options to promote quick assembly. As shown in  FIG. 32 , the femoral IM rod  13  includes a secondary femoral mount  100 . The secondary femoral mount  100  has a saddle or crescent shape that extends laterally and distally from a central attachment to the distal end of the main shaft  16  of the femoral IM rod  13 . Defined in the inner, convexly curved surface of the saddle is an opening  101  that is configured to receive a femoral mount rod  102  that supports the femoral mount  15 , as shown in  FIG. 33 . 
     Referring again to  FIG. 32 , the tibial IM rod  14  includes a modified version of tibial mount  23  supported by the shaft  22 . In particular, the plateau flange  28  of the tibial mount  23  has a widened rectangular shape that extends laterally outward from the threaded opening  29 . Defined at the anterior side of the plateau flange  28  are a pair of guide mount openings  103  that extend posteriorly into the plateau flange. As shown in  FIG. 34 , the flexion bolt  30  may also be further modularized by providing a post  104  for mounting the bushing  33  and hex flange  32  within a central opening defined in a hex-head bolt  105  that includes the threaded shaft  31  extending from its head  105 .  FIGS. 35 and 36  show the assembly of the femoral mount  15  and tibial mount  32 , along with tightening adjustment by elevation of the hex head bolt  105 . 
     As shown in  FIG. 37 , the assembly  10  also includes a flexed knee cutting guide assembly  52  that includes a flexed knee cutting guide  54  and a direct mount  106 . The direct mount includes a pair of posts  107  that are spaced apart and extend from a mounting block  108 . The spacing and size of the posts  107  are configured to extend into the guide mount openings  103  defined in the plateau flange  28 . Mounting block  108  can be coupled to tibial mount  32 , such as by hermetically sealed magnets  111 . The flexed knee cutting guide  54  is attached to and extends distally from the mounting block  108 . The flexed knee cutting guide defines a selection of slots  109  for guiding tibial and femoral cuts. 
     The posterior femoral cut can be accomplished by turning the flexed knee cutting guide assembly  52  upside down or by using another block which would be a modification of the upside down cutting guide assembly  52  where the cutting guide  54  and selection of slots  109  is moved toward the posts  107  and therefore, closer to the posterior femoral condyles of the knee. The selection of slots  109  of cutting guide assembly  52  can be as shown with the slots attached centrally or could be open centrally and attached along both sides of the cutting guide  54 . 
     As shown in  FIGS. 38 and 39 , the tibial IM rod  14  may also include a valgus adapter member  110  or a modified version of femoral mount  15  that has its own post that is configured to insert into the central opening of the hex head bolt  105 . As shown in  FIG. 40 , the valgus adapter member  110  has a convex shape that is configured to extend into the concave shape of the secondary femoral mount  100 . This mating allows varus-valgus angulation to position the cuts when the knee is in extension, similar to the first embodiment disclosed above. Extended knee cutting guides can be mounted similar to the flexed knee cutting guide via posts  107 . 
     The assembly  10  of the present invention has many advantages. It provides a relatively narrow and low profile collection of locking components that securely attach cutting guides to tibial and/or femoral IM rods. This provides a robust guide to reference cuts being made to the tibia and the femur with an approach to the joint that minimizes invasiveness. Further, many of the components, such as the first and second locking mechanisms  34 ,  84  and the quick release mechanism  53 , facilitate quick assembly, easy adjustment and quick disassembly for improved efficiency. The use of the bolts  30  and  96  or  105  and the tibial angulation guide  74  or valgus adapter member  110  allow the tibia and femur to be distracted under a matching amount of torque in flexion and extension to ensure a better fit for the tibial and femoral knee replacement components throughout a range of flexion. Also, the tibial angulation guide allows the surgeon to adjust the amount of valgus angulation of the tibia as desired to match the anatomy of the patient. 
     As shown in  FIG. 41 , in another embodiment of the present invention a modified femoral mount rod  102  and femoral mount  15  with a hinge mechanism attaching mount  15  to the femoral mount rod  102  could be used with a retractor rod placed thru the hole  18  in the femoral mount  15  and guided posterior to the tibia thus providing a fulcrum and lever arm for the retractor to displace the tibia forward or anterior to allow exposure for placement of the tibial component of the total knee arthroplasty after the bone cuts have been made. Since the IM rods fix rigidly to the bone, other retractors could also be attached to the Guide Assembly to facilitate knee exposure during the knee surgery. 
     As shown in  FIG. 42 , in another embodiment of the present invention mini-trial components or trial components which are smaller but shaped with identical thickness and radii to the actual knee arthroplasty implants, designed to fit in holes  101  of femoral IM rod  13  and  29  of tibial IM rod  14  and articulate in the center portion of the knee could be used to check alignment and ligament stability prior to placement of the actual final knee arthroplasty implants. This design of a centrally placed mini-knee arthroplasty implant system could become a stand alone total knee arthroplasty. One advantage of this embodiment of the present invention is that the smaller instruments take up less space. The mini-trial femoral component could be designed with cutting surfaces or slots for making the chamfer cuts and other finishing cuts, thus eliminating the need for a chamfer cut block and L-plate  99  shown in  FIGS. 30 and 31 . 
     Referring now to  FIGS. 43-48 , another embodiment of the present invention is shown. Specifically,  FIGS. 43-45  illustrate an implementation of the current invention for resecting a patient&#39;s knee in flexion, and  FIGS. 46-48  illustrate an implementation of the current invention for resecting a patient&#39;s knee in extension. The femoral mount  150  of the femoral IM rod  113  of each embodiment comprises a planar flange that is substantially inset, and flush with the insertion site of the femur  11 . In one embodiment, a rongeur is used to prepare the distal femur for a ⅜ inch drill entry. Following insertion of the drill, a planar is then used to clear the remaining bone from the insertion site and to provide a recessed surface into which the femoral mount  150  is seated. A threaded opening  129  extends into the femoral mount  150  and provides a coupling attachment for an extension bolt  130 , which includes a threaded shaft  131 , a circular flange  132  with mounting holes  133 , and a centralizing ball  134 , as shown in  FIGS. 46 and 47 . Additionally, the threaded opening  129  provides a mounting channel into which a non-threaded post  114  of a threaded barrel  115  is inserted. The interaction between the non-threaded post  114  and the threaded opening  129  sufficiently retains the threaded barrel  115  within the femoral IM rod  113  and permits axial rotation of the threaded barrel  115  relative to the IM rod  113 . Axial rotation is desirable to permit limited movement of the surgical tool relative to the natural physiology of the patient&#39;s knee. As such, the threaded barrel  115  is permitted to rotate and facilitate the natural alignment of the patient&#39;s knee throughout the tensioning process, as described below. 
     The threaded barrel  115  comprises a non-threaded post  114  perpendicularly coupled to an outer surface of a threaded opening  116 . The threaded opening  116  extends through the threaded barrel  15  and provides a coupling attachment for a flexion bolt  120 . The flexion bolt  120  includes a threaded shaft  121 , a circular flange  122  with mounting holes  123 , and a non-threaded tip  124 . The threaded shaft  121  compatibly threads through the threaded opening  116  such that the non-threaded tip  124  exits and extends beyond the threaded barrel  115 . The circular flange  122  is perpendicularly attached to the threaded shaft  121  opposite the non-threaded tip  124 . The flange  122  is circular and generally disk-shaped having a plurality of mounting holes  123  evenly spaced around the circumferential edge of the flange  122 . The mounting holes  123  are sized and configured to compatibly receive a torque wrench  140  or other device for turning the flexion bolt  120 . 
     The current embodiment further comprises a tibial tensioning adapter  160 . The tibial tensioning adapter  160  is stably supported by the tibial IM rod  170  and positioned generally perpendicular to the main shaft of the tibial IM rod  170 . The tibial tensioning adapter  160  comprises a base member  161  and a resection block guide  165 . The base member  161  is generally planar and disc-like, having a centrally located opening  162  that extends into the main shaft of the tibial IM rod  170 . A bushing  125  is further provided to compatibly seat within the opening  162 . The bushing  125  comprises a post portion  126  having a first diameter, and a sleeve portion  127  having a second diameter and an opening  128 . The diameter of the post portion  126  is selected to compatibly insert within the opening  162  of the base member  161 , while the diameter of the sleeve portion  127  is selected to be greater than the diameter of the opening  162 . As such, the sleeve portion  127  rests on the upper surface of the base member  161  and is prevented from inserting into the opening  162 . The opening  128  of the sleeve portion  127  is non-threaded and sized to compatibly receive the non-threaded tip portion  124  of the flexion bolt  120 . Additionally, the interaction between the post  126  and the opening  162  does not utilize threads thereby allowing the bushing  125  to freely rotate within the opening  162  of the tibial tensioning adapter  160 , and allowing the non-threaded tip  124  of the flexion bolt  120  to freely rotate within the opening  128  of the bushing  125 . These freely rotating interactions prevent rigid structuring or position of the surgical tools thereby further permitting the natural physiology of the patient&#39;s knee to be maintained during the tensioning and resection processes. Thus, the flexion bolt  120 , the threaded barrel  115 , and the bushing  125  are combined with the femoral mount  150  and the tibial tensioning adapter  160  to apply tension to the patient&#39;s knee preparatory to performing the desired resections. 
     The base  161  further comprises a pair of spacers  163  forming a portion of the base member upper surface. The spacers  163  are generally pyramid shape and linerally configured on opposing sides of the opening  162 . The spacers  163  are provided to create a gap between the circular flange  132  of the extension bolt  130  and the upper surface of the base member  161 , as shown in  FIG. 47 . The pyramidal shape of the spacers  163  permits limited radial movement of the extension bolt  130  relative to the base member  161 . This limited movement is desirable to accommodate the natural physiology of the patient&#39;s knee throughout the tensioning process, described below in connection with  FIGS. 46 and 48 . 
     The resection block guide  165  is fixedly coupled to an edge surface of the base member  161  and extends outwardly therefrom. The block guide  165  is generally aligned with the spacers  163  and positioned to extend outwardly from the anterior surface of the knee. The block guide  165  further comprises a plurality of notches  166  occupying an upper surface of the guide  165 . The notches  166  span a portion of the upper surface and provide a coupling attachment for a resection block  180 , as shown in  FIGS. 45 and 48 . The notches  166  further provide a plurality of reference points or positions by which to gauge the position of the resection block  180 . 
     Referring now to  FIG. 44 , an embodiment of the assembled invention is shown. Once the surgical device is assembled, a torque wrench  140  is inserted into a hole  123  of the circular flange  122  and the flexion bolt  120  is rotated. Alternatively, in one embodiment the flexion bolt  120  is initially rotated by hand until the femur  11  begins to lift away from the tibia  12 . The torque wrench  140  is then utilized to further rotate the flexion bolt  120  to a desired tension. This will typically result in a final tension of about 10-20 in/lbs. The amount of tension will differ for each patient based on individual physiology, injury, and ligament viscoelasticity of the knee. Once the final tension in flexion has been attained, the final amount of tension placed on the ligaments in is recorded for future reference. 
     Referring now to  FIG. 44A , an embodiment of the assembled invention is shown. In this embodiment, the flexion bolt  120  is substituted with a ratcheting device  142 . The ratcheting device  142  generally comprises a handle portion  143 , a biasing portion  144 , and a gear box  145 . The biasing portion  144  of the ratcheting device  142  is interposed between the threaded barrel  115  and the bushing  125 . The handle portion  143  is then actuated to cause the biasing portion  144  to lift the femur  11  away from the tibia  12 . The gear box  145  converts the motion, or actuation of the handle portion  143  to change the position of the biasing portion  144  and separate the knee joint. 
     The handle portion  143  may include any configuration whereby a physician may manipulate the handle portion  143  to actuate the biasing portion  144  of the device  142 . For example, in one embodiment the handle portion  143  comprises a pair of opposing levers  146  and  147 , each having a grip  148  at a distal end and extending into the gear box  145  at a proximal end. The biasing portion  144  of the device  142  is actuated by gripping the handle portion  143  and squeezing, such that the pair of opposing levers  146  and  147  is brought to a proximal position. The action of the opposing levers  146  and  147  manipulates the gear box  145  causing the biasing portion  144  to move away from a proximal position. Additionally, in one embodiment the gear box  145  includes a release for returning the biasing portion  144  to a proximal position. 
     In another embodiment, the handle portion  143  comprises a single shaft having a handle at the distal end, and extending into the gear box  145  at the proximal end. In this embodiment, the biasing portion  144  of the device  142  is actuated by rotating the handle portion  143  in a clockwise or counter-clockwise direction. The rotating action of the handle portion  143  manipulates the gear box  145  causing the biasing portion  144  to move away from, or towards a proximal position. In one embodiment, the gear box  145  further includes a pawl or other device for maintaining the biased position of the biasing portion  144  during use. As such, a physician may actuate the device  142  to separate the knee to a desired position or tension, and then maintain the tension hands-free. 
     The biasing portion  143  may include any configuration capable of mounting into the threaded barrel  115  and the bushing  125 . For example, in one embodiment the biasing portion  143  includes a pair of jaws  148  having a first end for engaging the threaded barrel  115  and the bushing  125 , and having a second end extending into the gear box  145 . In another embodiment, the first end further includes a jointed connector  149  for engaging the threaded barrel  115  and the bushing  125 . The jointed connector  149  permits the pair of jaws  148  to separate the knee joint, yet provide limited movement of the knee joint to accommodate the natural physiology of the patient&#39;s knee throughout the tensioning process. 
     The gear box  145  may include any configuration of gears compatible with the handle portion  143  and the biasing portion  144  to achieve controlled separation of the knee joint. The gear box  145  may also include any means for limiting or measuring the tension placed on the knee joint. For example, in one embodiment the gear box  145  further comprises a tension meter  151  whereby the tension placed on the knee joint, by the ratcheting device,  142  is displayed. In another embodiment, the gear box  145  further comprises an adjusting screw  152  whereby the maximum allowed tension of the ratcheting device  142  is set. In this embodiment, a physician adjusts the adjusting screw  152  to a desired tension. Once set, the physician actuates the ratcheting device  142  to separate the knee joint. When the desired tension is achieved, further tensioning by actuation of the ratcheting device  142  is prevented, thus maintaining the desired tension for the knee. 
     Referring now to  FIG. 45 , the resection block  180  is attached to the resection block guide  165  and slid into position against the anterior surface of the femur  11 . The resection block  180  is secured to the resection block guide  165  by tightening a set screw  183  against the notches  166  of the guide  165 . The resection block  180  is then secured to the femur  11  via a plurality of screws  181 . Once the resection block  180  is secured in position, the flexion bolt  120  is removed from the surgical tool assembly and the cutting guides  182  of the resection block  180  are used to resect the exposed distal surfaces of the lateral and medial condyles. 
     Referring now to  FIGS. 46-48 , an implementation of the current invention is provided for operation in knee extension. Referring to  FIG. 46 , the extension bolt  130  is shown prior to being interposed between the femoral mount  150  and the tibial tensioning adapter  160 . The extension bolt  130  generally comprises a threaded shaft  131 , a circular flange  132  and a centralizing ball  134 . The threaded shaft  131  is configured to compatibly thread within the threaded opening  129  of the femoral mount  150 . The circular flange  132  is perpendicularly attached to the threaded shaft  131  and interposed between the threaded shaft  131  and the centralizing ball  134 . The flange  132  is disk shaped having a plurality of mounting holes  133  evenly space around the circumferential edge of the flange  132 . The mounting holes  133  are sized and configured to compatibly receive a torque wrench  140  or other device for turning the extension bolt  130 . 
     The centralizing ball  134  comprises a hemispherically shaped surface that is sized and configured to partially insert within opening  162  of the tibial tensioning adapter  160 . As such, the centralizing ball  134  partially engages the opening  162  yet remains sufficiently free to provide axial rotation between the femur  11  and the tibia  12 . The interface between the centralizing ball  134  and the opening  162  further ensures accurate alignment of the femoral mount  150  with the tibial tensioning adapter  160 . Radial rotation is further provided to the femur  11  and the tibia  12  due to the interface  158  between the circular flange  132  and the spacers  163 , as previously discussed and as shown in  FIG. 47 . Thus, the extension bolt  130  provides both alignment and limited free adjustment to the femur  11  and tibia  12  during the tensioning and resection procedures. 
     In one embodiment, the extension bolt  130  is first coupled to the femoral mount  150  by threading the threaded shaft  131  into the threaded opening  129  of the femoral mount  150 , with the knee in flexion, as shown in  FIG. 46 . The extension bolt  130  is maximally inserted into the threaded opening  129  to minimize the distance between the femur  11  and the tibia  12 . The knee is then brought into extension and the centralizing ball  134  is inserted into opening  162 , as shown in  FIG. 47 . A torque wrench  140  is then utilized to rotate the extension bolt  130  and apply tension the knee. The torque wrench  140  is inserted into a hole  133  of the circular flange  132  and turned to gradually remove the extension bolt  130  from the threaded opening  129 . In one embodiment, the physician immobilizes the resection block guide  165  to prevent rotation of the tibia  12  during rotation of the extension bolt  130 . The physician continues to turn the extension bolt  130  until the desired tension is placed on the ligaments of the knee. Alternatively, a ratcheting device (see  FIG. 44A ) may be used with the knee in extension to place the desired tension on the ligaments of the knee. In one embodiment, the final tension in extension is equal to the final tension in flexion. In another embodiment, the final tension in extension is different than the final tension in flexion. 
     Referring now to  FIG. 48 , the resection block  180  is attached to the resection block guide  165  and slid into position against the anterior surface of the femur  11 , as discussed above in connection with  FIG. 45 . Once positioned, the resection block  180  is secured to the femur  11  with screws  181  and the anterior surfaces of the lateral and medial condyles are resectioned. 
     In another embodiment, since the guide assembly is fixed rigidly to the bone and left in place during the essential steps of the knee preparation, computer assisted guides are attached to the guide assembly instruments thus facilitating computer assisted total knee replacement. In other embodiments of the present invention, the guide assembly instruments are modified for use in a partial or unicompartmental knee arthroplasty procedure. 
     In some embodiments, the Guide Assembly Instruments can be modified for use with short IM rods or a tibial platform instead of an IM rod for extramedullary knee preparation. 
     In some embodiments, the Guide Assembly holds a patient&#39;s leg in place. This decreases the need for medical assistants to hold the patient&#39;s leg. 
     Following a completed resection of the patient&#39;s knee joint, the resectioned portions of the femur  11  and the tibia  12  are replaced by a knee prosthesis or implant  200 , such as shown in  FIGS. 49 and 50 . The knee implant  200  generally comprises a femoral component  202  and a tibial component  204 . Although the instruments of the invention can be used with any type of knee prosthesis  200 , the instruments are particularly well-suited for use in accurately resecting the knee for receipt of a knee prosthesis that employs a constant radius through out the primary range of flexion, such as Wright Medical Technology, Inc.&#39;s ADVANCE® medial pivot knee implant. The features and characteristics of constant radius knee prostheses are well known to those of skill in the art, but have not previously been used with knee tensioning resection instruments. As will be described below, a synergistic and previously unappreciated effect is obtained by using the tensioning instruments in combination with prior art constant radius knee implants. It is anticipated that the end result of this synergistic combination will be greater overall accuracy in the implantation of constant radius knee implants, with resulting improvements in clinical outcomes. 
     One of the benefits of a properly designed and implanted constant radius knee prosthesis is that it provides the patient with constant ligament tension throughout the primary range of flexion. As discussed herein, the use of the instruments of the invention to resect the knee while under optimum tension helps insure accurate placement of the knee implant components. The combined use of tensioning instruments and constant radius knee implants improves the likelihood of achieving constant ligament tension throughout the primary range of flexion. Various embodiments of knee implants that incorporate a constant radius are discussed in the following prior art documents, which are incorporated herein by reference: U.S. Pat. Nos. 7,261,740; 6,013,103; 6,013,103; 5,824,100; 5,330,533; 5,326,361; 5,314,482; 5,219,362; 5,133,758; 4,085,466; German Patent Application 3314038A1. 
     In the prior art ADVANCE® Medial Pivot knee implant, the femoral component  202  has a spherical condyle  206  on the medial side. As indicated in  FIG. 51 , in the sagittal or A-P plane, the medial femoral condyle  206  has a constant radius  226  over at least the primary range of flexion, which extends from about 0 degrees in extension to about 90 degrees in flexion, depending on the patient. The lateral femoral condyle  222  also has an A-P constant radius  226  throughout the primary range of flexion. The medial side of the tibial base  204  of the ADVANCE® Medial Pivot knee has a shallow spherically concave bearing surface  232 , which is sized to closely receive the medial femoral condyle  206  in a ball-and-socket manner. The lateral side of the tibial base  204  is generally in the form of an elongated arcuate trough  230 . These features allow the medial femoral condyle  206  to pivot in the medial tibial bearing  232  during flexion, while simultaneously permitting the lateral femoral condyle  222  to translate posteriorly in the lateral tibial bearing  218 . This action is designed to mimic the function of the natural knee, in which the medial femoral condyle exhibits less rollback than the lateral condyle during motion. Features and characteristics of the ADVANCE® Medial Pivot knee are discussed in greater detail in U.S. Pat. Nos. 5,964,808 and 6,013,103, which are incorporated herein by reference. Although the ADVANCE® Medial Pivot knee implant is an exemplary implant design for optimizing and complementing the use of the tensioning instruments of the invention, other constant radius knee implant designs can be used to similar or equal effect. 
     One of the drawbacks of prior art knee instruments is that overstuffing or under filling the joint sometimes occurs, with resulting tightness or laxity, respectively, in the ligaments. As discussed above, use of the tensioning instruments to resect with the knee tensed in the extended position allows the user to make a balanced extension gap resection when compared with the tensed resections made with the knee previously positioned in flexion. The resection cuts are made off of a single reference point, the single reference point being the desired amount of tension. The use of equal flexion and extension gaps automatically balances the mid-flexion gap at all points in between. By then implanting a constant radius knee implant onto the resectioned knee, the surgeon effectively transfers the optimum tension obtained by the tensioning instruments to the constant radius knee implant, resulting in a stable, smoothly functioning knee throughout at least the primary range of flexion. In mechanical terms, the tensioning technique preloads the bearing, the bearing being the constant radius knee implant. 
     In contrast, if a conventional J-curve or varying radius knee implant is used with the tensioning technique, rather than a constant radius implant, it becomes necessary to vary the cuts instead of using an equal flexion and extension gap. The use of a varying radius knee implant thus necessarily complicates the process and the use of the instruments. 
     Many modifications and other embodiments of the inventions set forth herein will come to mind to one skilled in the art to which these inventions pertain having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the inventions are not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.