Patent Publication Number: US-8986390-B2

Title: Method of trialing a knee prosthesis

Description:
This application claims priority under 35 U.S.C. §119 to U.S. Patent Application No. 61/503,311, which was filed on Jun. 30, 2011 and is incorporated herein by reference. 
     CROSS-REFERENCE 
     Cross-reference is made to co-pending U.S. Provisional Patent Application Ser. No. 61/503,303 entitled “METHOD OF USING A TRIALING SYSTEM FOR A KNEE PROSTHESIS” by Tom Wogoman et al.; and co-pending U.S. Provisional Patent Application Ser. No. 61/503,300 entitled “TRIALING SYSTEM FOR A KNEE PROSTHESIS” by Tom Wogoman et al., each of which is assigned to the same assignee as the present application, each of which is filed concurrently herewith, and each of which is hereby incorporated by reference. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates generally to orthopaedic surgical instruments and, more particularly, to surgical instruments used with a patient&#39;s tibia. 
     BACKGROUND 
     Joint arthroplasty is a well-known surgical procedure by which a diseased and/or damaged natural joint is replaced by a prosthetic joint. A typical knee prosthesis includes a patella prosthetic component, a tibial tray, a femoral component, and a polymer insert or bearing positioned between the tibial tray and the femoral component. Femoral components are designed to be attached to a surgically-prepared distal end of a patient&#39;s femur. Tibial trays are designed to be attached to a surgically-prepared proximal end of a patient&#39;s tibia. 
     To facilitate the replacement of the natural joint with the knee prosthesis, orthopaedic surgeons use a variety of orthopaedic surgical instruments such as, for example, prosthetic trial components, cutting blocks, drill guides, milling guides, and other surgical instruments. Prosthetic trial components, such as, for example, a femoral trial component and a tibial bearing trial component, are used to size and select the components of the knee prosthesis that will replace the patient&#39;s natural joint. A procedure that utilizes the trial components to size and select the components of the knee prosthesis is often referred to as a trial reduction. 
     SUMMARY 
     According to one aspect of the disclosure, an orthopaedic surgical instrument system includes an orthopaedic surgical instrument adapted to be positioned on a surgically-prepared proximal end of a patient&#39;s tibia. The orthopaedic surgical instrument includes a central post that defines a longitudinal axis. The system also includes a tibial bearing trial assembly coupled to the orthopaedic surgical instrument. The tibial bearing trial assembly includes one of a plurality of tibial bearing surface trial components, each tibial bearing surface trial component having an articular surface, and a shim. The shim is configured to be coupled to a first tibial bearing surface trial component of the plurality of tibial bearing surface trial components in a first orientation in which the tibial bearing trial assembly is permitted to pivot about the axis. The shim is configured to be coupled to a second tibial bearing surface trial of the plurality of tibial bearing surface trial components in a second orientation in which the tibial bearing trial assembly is substantially prevented from rotating about the longitudinal axis. 
     In some embodiments, the shim may have an aperture defined therein. The aperture may include a central passageway sized to receive the central post, a first slot extending from the central passageway, and a second slot extending from the central passageway. In some embodiments, a lug may extend from the central post. The lug may be received in the first slot when the shim is positioned over the central post in the first orientation and received in the second slot when the shim is positioned over the central post in the second orientation. 
     In some embodiments, the orthopaedic surgical instrument may include a tibial base trial component adapted to be positioned on the surgically-prepared proximal end of the patient&#39;s tibia. The tibial base trial component may have an upper surface configured to contact the shim when the tibial bearing trial assembly is coupled to the orthopaedic surgical instrument. Additionally, in some embodiments, the orthopaedic surgical instrument may include a base insert adapted to be positioned in an opening defined in the tibial base trial component. The base insert may have the central post extending therefrom. 
     In some embodiments, the orthopaedic surgical instrument may include a keel punch adapted to be positioned in an opening defined in the tibial base trial component. The keel punch may include a main platform having the central post extending upwardly therefrom, and a pair of arms extending outwardly from the main platform. The pair of arms may be configured to be positioned in the surgically-prepared proximal end of the patient&#39;s tibia. 
     In some embodiments, each tibial bearing surface trial component may include a pair of pegs extending downwardly therefrom, and the shim may include a pair of attachment openings. Each attachment opening may be sized to receive one of the pair of pegs to removably couple each tibial bearing surface trial component to the shim. 
     According to another aspect, an orthopaedic surgical instrument system includes an orthopaedic surgical instrument having a central post defining a longitudinal axis, and a shim including an aperture configured to receive the central post. The shim is configured to be positioned on the orthopaedic surgical instrument in a first orientation in which the shim is permitted to pivot about the longitudinal axis, and a second orientation in which the shim is prevented from rotating about the longitudinal axis. In some embodiments, the aperture may include a central passageway sized to receive the central post of the orthopaedic surgical instrument, and a slot extending from the central passageway. The slot may be defined by an arcuate inner wall extending between a pair of planar inner walls. In some embodiments, the arcuate inner wall may define an arc extending approximately fifty degrees. 
     In some embodiments, the orthopaedic surgical instrument may include a lug extending from the central post. The lug may be configured to be received in the slot when the shim is positioned on the orthopaedic surgical instrument in the first orientation such that when the shim is pivoted in a first direction about the longitudinal axis, a first planar inner wall of the pair of planar inner walls is advanced into contact with the lug, and when the shim is pivoted in a second direction about the longitudinal axis, a second planar inner wall of the pair of planar inner walls is advanced into contact with the lug. 
     In some embodiments, the aperture of the shim may include a second slot extending from the central passageway, and the lug may be received in the second slot when the shim is positioned on the orthopaedic surgical instrument in the second orientation. In some embodiments, the second slot may be defined by a pair of inner walls configured to engage the lug when the lug is received in the second slot such that the shim is substantially prevented from rotating about the longitudinal axis. 
     In some embodiments, the system may further include a tibial bearing surface trial component including an articular surface configured to contact a pair of femoral condyles and a bottom surface having a pair of pegs extending downwardly therefrom. The shim may include a pair of attachment openings. Each attachment opening may be sized to receive one of the pair of pegs to removably couple the tibial bearing surface trial component to the shim. 
     Additionally, in some embodiments, the tibial bearing surface trial component may be permitted to be secured to the shim when the shim is positioned in the first orientation and prevented from being secured to the shim when the shim is positioned in the second orientation. In some embodiments, the pair of pegs may include a first peg and a second peg having a peg size different from the first peg, and the pair of attachment openings may include a first attachment opening sized to receive the first peg and a second attachment opening sized to the receive the second peg. The second attachment opening may have an opening size different from the first attachment opening and configured to match the peg size of the second peg. 
     According to another aspect, an orthopaedic surgical instrument includes a tibial trial shim including a plate having a predetermined thickness. The plate has an aperture defined therein that includes a central passageway, a rectangular slot extending from a first side of the central passageway, and an arcuate slot extending from a second side of the central passageway. 
     In some embodiments, the plate may have a pair of attachment openings defined therein. Each attachment opening may be configured to secure the tibial trial shim to a tibial bearing surface trial component. In some embodiments, a first attachment opening of the pair of attachment openings may be defined through the plate on the first side of the central passageway, a second attachment opening of the pair of attachment openings may be defined through the plate on the second side of the central passageway, and the first attachment opening may have a different size from the second attachment opening. 
     Additionally, in some embodiments, the first attachment opening and the second attachment opening may be circular, and the diameter of the first attachment opening may be greater than the diameter of the second attachment opening. 
     In some embodiments, the orthopaedic surgical instrument may further include a plurality of tibial bearing surface trial components configured to be removably coupled to the tibial trial shim. Each tibial bearing surface trial component may have an upper bearing surface configured to contact a pair of femoral condyles and a bottom surface having a pair of pegs extending therefrom. The first attachment opening of the tibial trial shim may be sized to receive a first peg of the pair of pegs and the second attachment opening of the tibial trial shim may be sized to the receive a second peg of the pair of pegs. 
     In some embodiments, the plate may include a first planar surface, a second planar surface, and a sidewall extending between the first planar surface and the second planar surface. A first channel may be defined in the first planar surface. The first channel may extend inwardly from the sidewall toward the aperture. A second channel may be defined in the second planar surface. The second channel may extend inwardly from the sidewall toward the aperture. 
     In some embodiments, the aperture may be positioned between the first channel and the second channel. In some embodiments, the aperture may include a slot extending from the central passageway through a posterior section of the sidewall. In some embodiments, the central passageway may define an axis through the plate, and the arcuate slot may be defined by an arcuate inner wall having an edge that extends approximately fifty degrees about the axis. In some embodiments, the arcuate slot may be further defined by a pair of planar inner walls and the arcuate inner wall may extend between the pair of planar inner walls. 
     According to another aspect, a method of trialing prosthetic components of a knee prosthesis is disclosed. The method includes positioning a tibial base trial component on a surgically-prepared proximal end of a patient&#39;s tibia, and inserting a base insert into an opening defined in the tibial base trial component. The base insert has a central post extending upwardly from an upper surface thereof. The method also includes selecting a tibial bearing surface trial component, securing a shim to the selected tibial bearing surface trial component to form a tibial bearing trial assembly, positioning the tibial bearing trial assembly over the central post of the base insert, and adjusting the patient&#39;s leg with the tibial bearing trial assembly positioned over the central post of the base insert. If a first tibial bearing surface trial component is selected, securing the shim includes securing the shim to the first tibial bearing surface trial component in a first orientation and adjusting the patient&#39;s leg includes rotating the tibial bearing trial assembly relative to the tibial base trial component. If a second tibial bearing surface trial component is selected, securing the shim includes securing the shim to the second tibial bearing surface trial component in a second orientation such that the tibial bearing trial assembly is substantially prevented from rotating relative to the tibial base trial component. 
     In some embodiments, the base insert may include a lug extending from the central post, and positioning the tibial bearing trial assembly over the central post of the base insert may include positioning the lug and the central post in an aperture defined in the shim. Additionally, in some embodiments, selecting the tibial bearing surface trial component may include selecting a mobile bearing surface trial component, and securing the shim may include securing the shim to the mobile bearing surface trial component in the first orientation. 
     In some embodiments, rotating the tibial bearing trial assembly relative to the tibial base trial component may include moving an arcuate inner wall of the shim relative to the lug. In some embodiments, inserting the base insert into the opening defined in the tibial base trial component may include inserting a spike of the base insert into the proximal end of the patient&#39;s tibia. In some embodiments, selecting the tibial bearing surface trial component may include selecting a fixed bearing surface trial component and securing the shim may include securing the shim to the fixed bearing surface trial component in the second orientation. 
     Additionally, in some embodiments, positioning the tibial bearing trial assembly may include positioning the lug between a pair of planar inner walls of the shim to prevent the tibial bearing trial assembly from rotating relative to the tibial base trial component. 
     In some embodiments, the method may further include locating an alignment etching on the tibial base trial component and marking the proximal end of the patient&#39;s tibia at the alignment etching after adjusting the patient&#39;s leg. Additionally, in some embodiments, the method may further include removing the tibial bearing trial assembly from the base insert, and detaching the shim from the tibial bearing surface trial component. The shim may have a first predetermined thickness. The method may also include selecting a second shim having a second predetermined thickness different from the first predetermined thickness, securing the second shim to the tibial bearing surface trial component to form a second tibial bearing trial assembly, positioning the second tibial bearing trial assembly over the central post of the base insert, and adjusting the patient&#39;s leg with the second tibial bearing trial assembly positioned over the central post of the base insert. 
     In some embodiments, detaching the shim from the tibial bearing surface trial component may include inserting a separator tool into a channel defined in an upper surface of the shim and actuating a lever to engage a bottom surface of the tibial bearing surface trial component to separate the shim from the tibial bearing surface trial component. 
     In some embodiments, adjusting the patient&#39;s leg may include placing the patient&#39;s knee in flexion, attaching an alignment handle to the tibial base trial component, inserting a first alignment rod into a first passageway defined in the alignment handle, and inserting a second alignment rod into a second passageway defined in the alignment handle. The second passageway may extend orthogonal to the first passageway. 
     In some embodiments, securing the shim to the tibial bearing surface trial component may include positioning a pair of pegs of the tibial bearing surface trial component into a pair of openings defined in the shim. In some embodiments, the method may further include selecting a prosthetic tibial bearing component corresponding to the selected tibial bearing surface trial component and the selected shim. Additionally, in some embodiments, the method may further include removing the tibial bearing trial assembly from the base insert and the tibial base trial component, removing the base insert from the opening defined in the tibial base trial component, and impacting a keel punch into the proximal end of the patient&#39;s tibia through the opening of the tibial base trial component. The keel punch may have a central post extending upwardly from an upper surface thereof. The method may also include positioning the tibial bearing trial assembly over the central post of the keel punch, and adjusting the patient&#39;s leg with the tibial bearing trial assembly positioned over the central post of the keel punch. 
     According to another aspect, the method of trialing prosthetic components of a knee prosthesis includes positioning an orthopaedic surgical instrument on a surgically-prepared proximal end of a patient&#39;s tibia, and selecting a tibial bearing surface trial component. The tibial bearing surface trial component is one of a mobile bearing surface trial component and a fixed bearing surface trial component. The method also includes positioning a shim and the selected tibial bearing surface trial component on the orthopaedic surgical instrument. A first surface of the shim is positioned in contact with the tibial bearing surface trial component if the tibial bearing surface trial component is the mobile bearing surface trial component. A second surface of the shim is positioned in contact with the tibial bearing surface trial component if the tibial bearing surface trial component is the fixed bearing surface trial component. 
     In some embodiments, the method may further include rotating the tibial bearing surface trial component and the shim relative to the orthopaedic surgical instrument if the mobile bearing surface trial component is selected. Additionally, in some embodiments, the shim may be configured to substantially prevent the tibial bearing surface trial component from rotating relative to the orthopaedic surgical instrument if the fixed bearing surface trial component is selected. In some embodiments, the method may further include selecting a prosthetic tibial bearing component corresponding to the selected tibial bearing surface trial component and the shim. 
     In some embodiments, the method may further include securing the shim to the selected tibial bearing surface trial component prior to positioning the shim and the tibial bearing surface trial component on the orthopaedic surgical instrument. 
     According to another aspect, a method of assembling a surgical instrument includes selecting a tibial bearing surface trial component, orienting a shim relative to the tibial bearing surface trial component, and securing the shim to the tibial bearing surface trial component. The shim is secured in a first orientation relative to the tibial bearing surface trial component if the tibial bearing surface trial component is a first tibial bearing surface trial component. The shim is secured in a second orientation that is opposite the first orientation if the tibial bearing surface trial component is a second tibial bearing surface trial component. 
     According to another aspect of the disclosure, the method includes positioning a polymer femoral trial component on a surgically-prepared distal end of a patient&#39;s femur, assembling a tibial bearing trial component, positioning the tibial bearing trial component on a tibial base trial component seated on a surgically-prepared proximal end of a patient&#39;s tibia, adjusting the patient&#39;s leg with the tibial bearing trial component engaging the polymer femoral trial component, removing the tibial bearing trial component from the tibial base trial component, inserting a keel punch into the surgically-prepared proximal end of the patient&#39;s tibia through an opening of the tibial base trial component, placing the tibial bearing trial component on the tibial base trial component and the keel punch, and readjusting the patient&#39;s leg with the tibial bearing trial component engaging the polymer femoral trial component after positioning the tibial bearing trial component on the tibial base trial component and the keel punch. In some embodiments, adjusting the patient&#39;s leg may include moving the patient&#39;s leg between extension and flexion such that a plurality of teeth of the polymer femoral trial component grip the surgically-prepared distal end of the patient&#39;s femur. 
     In some embodiments, the method may further include inserting a base insert into the opening of the tibial base trial component before positioning the tibial bearing trial component on the tibial base trial component. In some embodiments, assembling the tibial bearing trial component may include securing a shim to a first tibial bearing surface trial component in a first orientation, and positioning the tibial bearing trial component includes positioning a lug of the base insert in a first slot of the shim such that the tibial bearing trial component is prevented from substantially rotating relative to the tibial base trial component. 
     Additionally, in some embodiments, positioning the tibial bearing trial component on the tibial base trial component and the keel punch may include positioning a lug of the keel punch in the first slot of the shim such that the tibial bearing trial component is prevented from substantially rotating relative to the tibial base trial component. In some embodiments, assembling the tibial bearing trial component may include securing the shim to a second tibial bearing surface trial component in a second orientation, positioning the tibial bearing trial component may include positioning the lug of the base insert in a second slot of the shim such that the tibial bearing trial component is permitted to substantially rotate relative to the tibial base trial component, and adjusting the patient&#39;s leg may include rotating the tibial bearing trial component relative to the tibial base trial component. In some embodiments, inserting the base insert may include inserting a spike of the base insert into the patient&#39;s tibia. 
     In some embodiments, positioning the tibial bearing trial component on the tibial base trial component and the keel punch may include positioning a lug of the keel punch in the second slot of the shim such that the tibial bearing trial component is permitted to substantially rotate relative to the tibial base trial component, and readjusting the patient&#39;s leg may include rotating the tibial bearing trial component relative to the tibial base trial component. Additionally, in some embodiments, the method further may include placing a guide tower on the tibial base trial component, and securing the keel punch to a lower end of a handle by engaging a lever of the handle with the keel punch. Further, inserting the keel punch into the surgically-prepared proximal end of the patient&#39;s tibia may include inserting the keel punch and the lower end of the handle through an upper end of the guide tower. 
     In some embodiments, positioning the polymer femoral trial component may include securing an impactor head to the handle, attaching the polymer femoral trial component to the impactor head, and tapping a head end of the handle to attach the polymer femoral trial component to the surgically-prepared distal end of the patient&#39;s femur. Additionally, in some embodiments, the method may further include installing a tibial tray of the knee prosthesis in the surgically-prepared proximal end of the patient&#39;s tibia, positioning the tibial bearing trial component on the tibial tray, and readjusting the patient&#39;s leg after positioning the tibial bearing trial component on the tibial tray. 
     According to another aspect, a method of trialing prosthetic components of a knee prosthesis includes positioning a femoral trial component on a surgically-prepared distal end of a patient&#39;s femur, and selecting a first femoral prosthetic component if a sidewall of the femoral trial component is positioned beyond an outer edge of the surgically-prepared distal end of the patient&#39;s femur and the surgically-prepared distal end of the patient&#39;s femur is visible through a notch defined in the sidewall of the femoral trial component, and a second femoral prosthetic component if the sidewall of the femoral trial component is positioned within the outer edge of the surgically-prepared distal end of the patient&#39;s femur. The first femoral prosthetic component is more narrow than the second femoral prosthetic component. The method also includes positioning a tibial bearing trial component on a tibial base trial component seated on a surgically-prepared proximal end of a patient&#39;s tibia, and adjusting the patient&#39;s leg with the tibial bearing trial component engaging the femoral trial component. 
     In some embodiments, the femoral trial component may be formed from a polymeric material. In some embodiments, the method may further include inserting a keel punch into the surgically-prepared proximal end of the patient&#39;s tibia through an opening of the tibial base trial component, positioning the tibial bearing trial component on the tibial base trial component and the keel punch, and readjusting the patient&#39;s leg with the tibial bearing trial component engaging the femoral trial component after positioning the tibial bearing trial component on the tibial base trial component and the keel punch. 
     In some embodiments, the method may further include selecting a tibial bearing surface trial component from a plurality of tibial bearing surface trial components, orienting a shim relative to the tibial bearing surface trial component, and securing the shim to the tibial bearing surface trial component to assemble the tibial bearing trial component. The shim may be secured in a first orientation relative to the tibial bearing surface trial component if the tibial bearing surface trial component is a first tibial bearing surface trial component. The shim may be secured in a second orientation that is opposite the first orientation if the tibial bearing surface trial component is a second tibial bearing surface trial component. 
     In some embodiments, adjusting the patient&#39;s leg may include rotating the tibial bearing trial component relative to the tibial base trial component if the tibial bearing surface trial component is the first tibial bearing surface trial component. 
     According to another aspect, a method of trialing prosthetic components of a knee prosthesis includes positioning a polymer femoral trial component on a surgically-prepared distal end of a patient&#39;s femur, moving the patient&#39;s leg between extension and flexion such that a plurality of teeth of the polymer femoral trial component grip the surgically-prepared distal end of the patient&#39;s femur, and selecting a femoral prosthetic component of the knee prosthesis for implantation. 
     In some embodiments, the plurality of teeth of the polymer femoral trial component may extend from a posterior fixation surface defined by a plurality of ribs. The posterior fixation surface may extend generally in a superior/inferior direction. In some embodiments, selecting the femoral prosthetic component may include identifying a position of a sidewall of the polymer femoral trial component relative to an outer edge of the surgically-prepared distal end of the patient&#39;s femur. Selecting the femoral prosthetic component may also include selecting a first femoral prosthetic component if the sidewall is positioned beyond the outer edge of the surgically-prepared distal end of the patient&#39;s femur and the surgically-prepared distal end of the patient&#39;s femur is visible through a notch defined in the sidewall, and a second femoral prosthetic component if the sidewall of the polymer femoral trial component is positioned within the outer edge of the surgically-prepared distal end of the patient&#39;s femur. The first femoral prosthetic component may be more narrow than the second femoral prosthetic component. 
     In some embodiments, the method may further include drilling a pair of fixation holes in the surgically-prepared distal end of the patient&#39;s femur. In some embodiments, drilling the pair of fixation holes may include inserting a surgical drill into a guide hole defined in the polymer femoral trial component. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The detailed description particularly refers to the following figures, in which: 
         FIG. 1  is an exploded perspective view of an orthopaedic surgical instrument system; 
         FIG. 2  is a perspective view of a tibial base trial component of the orthopaedic surgical instrument system of  FIG. 1 ; 
         FIG. 3  is a perspective view of a base insert component of the orthopaedic surgical instrument system of  FIG. 1 ; 
         FIG. 4  is a top plan view of the base insert component of  FIG. 3 ; 
         FIG. 5  is a perspective view of a femoral trial component of the orthopaedic surgical instrument system of  FIG. 1 ; 
         FIG. 6  is an exploded perspective view of the tibial base trial component, the base insert component, and a number of tibial bearing trial components of the orthopaedic surgical instrument system of  FIG. 1 ; 
         FIG. 7  is a top plan view of the tibial base trial component, the base insert component, and a fixed bearing trial component; 
         FIG. 8  is a top plan view of the tibial base trial component, the base insert component, and a mobile bearing trial component; 
         FIG. 9  is a perspective view of one embodiment of a trial shim of the tibial bearing trial component of  FIG. 6 ; 
         FIG. 10  is a top plan view of the trial shim of  FIG. 9 ; 
         FIG. 11  is a perspective view of one embodiment of a fixed bearing surface trial component of one of the tibial bearing trial components of  FIG. 6 ; 
         FIG. 12  is a bottom plan view of the fixed bearing surface trial component of  FIG. 11 ; 
         FIG. 13  is a perspective view of one embodiment of a mobile bearing surface trial component of one of the tibial bearing trial components of  FIG. 6 ; 
         FIG. 14  is a bottom plan view of the mobile bearing surface trial component of  FIG. 13 ; 
         FIG. 15  is an exploded perspective view of a keel punch used with the tibial base trial component of the orthopaedic surgical instrument system of  FIG. 1 ; 
         FIG. 16  is a perspective view of a guide tower of the orthopaedic surgical instrument system of  FIG. 1 ; 
         FIG. 17  is a perspective view of an alignment handle of the orthopaedic surgical instrument system of  FIG. 1 ; 
         FIG. 18  is a perspective view of an impaction handle of the orthopaedic surgical instrument system of  FIG. 1 ; 
         FIG. 19  is an exploded perspective view of one embodiment of a fixed bearing knee prosthesis; 
         FIG. 20  is an exploded perspective view of one embodiment of a mobile bearing knee prosthesis; 
         FIG. 21  is a simplified flow chart of one embodiment of a procedure utilizing the orthopaedic surgical instrument system of  FIGS. 1-18 ; and 
         FIGS. 22-40  are views of a patient&#39;s femur, tibia, the knee prostheses of  FIGS. 19 and 20 , and the orthopaedic surgical instrument system of  FIGS. 1-17  as the orthopaedic surgical instrument system is used in the procedure of  FIG. 21 . 
     
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
     While the concepts of the present disclosure are susceptible to various modifications and alternative forms, specific exemplary embodiments thereof have been shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that there is no intent to limit the concepts of the present disclosure to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims. 
     Terms representing anatomical references, such as anterior, posterior, medial, lateral, superior, inferior, etcetera, may be used throughout the specification in reference to the orthopaedic implants and surgical instruments described herein as well as in reference to the patient&#39;s natural anatomy. Such terms have well-understood meanings in both the study of anatomy and the field of orthopaedics. Use of such anatomical reference terms in the written description and claims is intended to be consistent with their well-understood meanings unless noted otherwise. 
     Referring to  FIGS. 1-16 , an orthopaedic surgical instrument system  10  (hereinafter system  10 ) is shown. The system  10  is used during joint arthroplasty procedures, such as a total knee replacement procedure. It should be appreciated, however, that although the system  10  is described below in regard to the performance of a total knee replacement procedure, certain concepts associated with the system  10  may be utilized in replacement procedures of numerous other joints throughout the body. 
     As shown in  FIG. 1 , the system  10  has a number of trial components  12 , including a tibial base trial  14 , a number of base inserts  16 , a femoral trial  18 , and a number of tibial bearing trial assemblies  20 . The system  10  also includes a tibial keel punch  22  (see  FIG. 15 ) and a guide tower  24  (see  FIG. 16 ). Additionally, the system  10  includes a number of surgical tools, such as, for example, an alignment handle  26  (see  FIG. 17 ) and an impaction handle  28  (see  FIG. 18 ), which are used to manipulate the trial components  12  and the other surgical instruments during the performance of an orthopaedic surgical procedure, as described in greater detail below. 
     The system  10  may be utilized to size and select the prosthetic components of a knee prosthesis (see  FIGS. 19 and 20 ) that will replace the patient&#39;s natural joint. To do so, the femoral trial  18  is attached to a surgically-prepared distal end  600  of a patient&#39;s femur  602  (see  FIG. 20 ), whereas the tibial base trial  14  is attached to a surgically-prepared proximal end  604  of a patient&#39;s tibia  606  (see  FIG. 20 ). One of the tibial bearing trials  20 , each of which is a multi-piece assembly, as discussed in greater detail below, is positioned on the tibial base trial  14  between the femoral trial  18  and the base trial  14 . As described in greater detail below, the surgeon uses the system  10  in a trial reduction process to determine the type and configuration of each of the various types of prosthetic components that are to be implanted. 
     The system  10  may be also utilized to surgically prepare the proximal end  604  of a patient&#39;s tibia  606  for implantation of a tibial prosthetic component, such as a tibial tray, during the performance of an orthopaedic surgical procedure. The tibial base trial  14  and the guide tower  24  are positioned on the proximal end  604  of the patient&#39;s tibia  606 , and the surgeon uses the trial  14  and the tower  24  to guide, for example, a surgical drill while reaming the proximal end  604  of the patient&#39;s tibia  606 . Thereafter, the keel punch  22  is impacted into the proximal end  604  of the patient&#39;s tibia  606  before the guide tower  24  is removed. An additional trial reduction may be performed with the keel punch  22  before the surgeon installs the components of the knee prosthesis, as described in greater detail below. 
     Referring now to  FIG. 2 , the base trial  14  includes a plate  30  having an upper surface  32 , a lower surface  34 , and an outer sidewall  36  extending between the surfaces  32 ,  34 . The plate  30  has a plate opening  38  defined in the upper surface  32 . The plate opening  38  has a central opening  40  and a pair of elongated openings  42  extending outwardly therefrom. An inner wall  44  extends downwardly from the opening  38  to define a passageway  46  through the plate  30 . The inner wall  44  includes an upper wall  48  and a lower wall  50  offset or otherwise spaced inwardly from the upper wall  48 . The upper wall  48  and lower wall  50  cooperate to define a shelf surface  52  therebetween. As will be discussed in greater detail below, the configuration of the passageway  46  permits the advancement of various surgical drills, punches, and other instruments into the proximal end  604  of the patient&#39;s tibia  606 . It should be appreciated that the tibial base trial  14  may be formed in a number of different sizes to accommodate tibias of various sizes. 
     The plate  30  also includes a lever-receiving notch  54  that is defined in an anterior aspect  56  thereof. The notch  54  includes a channel  58 that is defined in the upper surface  32  and extends posteriorly from the outer sidewall  36 . An oblong-shaped slot  60  is defined in the posterior end  62  of the channel  58 . The slot  60  extends downwardly through the lower surface  34  of the plate  30 . As shown in  FIG. 2 , a pair of oblong-shaped apertures  64  is defined in the sidewall  36 , one on each side of the notch  54 . As will be discussed in greater detail below, the notch  54  and the apertures  64  are configured to receive a lever  66  and a pair of pins  68 , respectively, associated with the alignment handle  26  (see  FIG. 17 ). 
     A plurality of alignment etchings  70  extend along the upper surface  32  and the outer sidewall  36  of the plate  30 . The surgeon may use one or more of the alignment etchings  70  to mark the proper position of the base trial  14  on the proximal end  604  of the patient&#39;s tibia  606  and ensure that the base trial  14  is consistently positioned at the same location thereon. The plate  30  also includes a number of fastener holes  72  that are defined in the anterior aspect  56  thereof. The fastener holes  72  are configured to receive fasteners such as fixation pins, which may be utilized to secure the base trial  14  to the proximal end  604  of the patient&#39;s tibia  606 . 
     Referring now to  FIG. 3 , the system  10  further includes a pair of evaluation bullets or base inserts  16 . The base inserts  16  are configured to be positioned separately in the plate opening  38  of the base trial  14 . Each base insert  16  has a lower body  78  and an upper body  80  that cooperate to define a rim  82  around the periphery thereof. The rim  82  has a bottom surface  84  configured to engage the shelf surface  52  of the base trial  14  when the base insert  16  is seated on the base trial  14 . The body  80  includes a central platform  86  sized to be received in the central opening  40  of the base trial  14 . The body  80  also includes a pair of prongs  88 ,  90  that extend outwardly from the central platform  86 . The prongs  88 ,  90  are sized to be received in the elongated openings  42  of the base trial  14 . 
     The body  80  of the base trial  14  includes a post  94  extending upwardly from an upper surface  96  thereof. The post  94  extends to a top end  98 , and a lip  100  extends outwardly therefrom. The lip  100  has a bottom surface  102  that extends substantially parallel to the upper surface  96 , and the surfaces  96 ,  102  cooperate to define a lever-receiving notch  104 . The lever-receiving notch  104  is configured to receive a locking flange  498  associated with the impaction handle  28 , as described in greater detail below. 
     As shown in  FIG. 4 , the post  94  also has an opening  106  defined in an upper surface  108  thereof. An inner wall  110  extends downwardly from the opening  106  to define a central passageway  112  through the base insert  16 . The opening  106  is configured to receive a guide pin  508  associated with the impaction handle  28  (see  FIG. 18 ). The inner wall  110  has a keyed section  114  that permits the base insert  16  to be attached to the impaction handle  28  in only a single predetermined orientation. 
     The post  94  of each base insert  16  has a generally curved sidewall  116  and a flat sidewall  118  positioned under the lip  100 . Each base insert  16  includes a block or lug  120  extending outwardly from the curved sidewall  116  of the post  94  toward the prong  90 . As will be described in greater detail below, the lug  120  engages the tibial bearing trial  20  to prevent or permit the tibial bearing trial  20  from rotating relative to the tibial base trial  14 . It should be appreciated that in other embodiments the lug  120  might extend from, for example, the other side of the post  94  toward the prong  88 . It should also be appreciated that in other embodiments the base insert  16  may include additional lugs. In the illustrative embodiment, the lug  120  has a rectangular cross section, but it should be appreciated that in other embodiments the lug  120  may have, for example, a square or other geometrical cross section. As will be described in greater detail below, the post  94  and the lug  120  are positioned in the tibial bearing trial  20  when the tibial bearing trial  20  is positioned on the tibial base trial  14 . 
     The central platform  86  of the body  80  also has a keyed section  122 . The keyed section  122  and the orientation of the prongs  88 ,  90  relative to the platform  86  permit each base insert  16  to be inserted into the plate opening  38  of the base trial  14  in a single, predetermined orientation. 
     Returning to  FIG. 3 , the pair of base inserts  16  includes a spiked base insert  126  and a spikeless base insert  128 . The spiked base insert  126  also includes a pair of mounting spikes  130  that extend downwardly from the prongs  88 ,  90 , respectively. Each spike  130  includes an upper cylindrical section  134  and a pointed conical tip  136  configured to engage the proximal end  604  of the patient&#39;s tibia  606 , thereby temporarily securing the base insert  126  to the proximal end  604  of the patient&#39;s tibia  606 . 
     As discussed above, the system  10  also includes a femoral trial  18  that is configured to be secured to the distal end  600  of the patient&#39;s femur  602 . One example of a femoral trial is shown and described in co-pending U.S. Patent App. Ser. No. 61/503,237, entitled “POLYMER FEMORAL TRIAL COMPONENT” by Thomas Wogoman, which is expressly incorporated herein by reference. The femoral trial  18  is configured to assist the surgeon in selecting a femoral prosthetic component, which will emulate the configuration of the patient&#39;s natural femoral condyles. As such, the femoral trial  18  includes a pair of condyle surfaces  140 ,  142 , which may be shaped (i.e., curved) in a manner that approximates the condyles of the natural femur. The condyle surface  140  and the condyle surface  142  are spaced apart from one another, thereby defining an intercondylar notch  144  therebetween. 
     The condyle surfaces  140 ,  142  are formed in an articular side  146  of the femoral trial  18 . A fixation side  148 , which is the side of the femoral trial  18  that contacts the surgically-prepared distal end  600  of the patient&#39;s femur  602 , is opposite the articular side  146 . The fixation side  148  includes a plurality of ribs  138  that extend in a direction away from the articular side  146 . The outer surfaces  150  of the ribs  138  define multiple surfaces that match and mate with planar surfaces surgically cut into the distal end  600  of the patient&#39;s femur  602 , as described in greater detail below. 
     The femoral trial  18  includes a pair of posterior femoral condyles  152  that form the posterior structure of the femoral trial  18 . One of the femoral condyles  152  is medially positioned and the other laterally positioned when the femoral trial  18  is attached to the distal end  600  of the patient&#39;s femur  602  depending on which knee is being replaced. Each of the posterior femoral condyles  152  includes a planar posterior fixation surface  154  defined by the ribs  138  on the fixation side  148 , with one of the posterior fixation surfaces  154  being the lateral fixation surface and the other being the medial fixation surface. Each posterior fixation surface  154  is positioned opposite a posterior condyle surface  156  on the articulation side  146  of the femoral trial  18 . As shown in  FIG. 5 , the posterior fixation surfaces  154  and the posterior condyle surfaces  156  extend generally in the superior/inferior direction. 
     The femoral trial  18  of the system  10  also includes a plurality of teeth  158  that extend outwardly from each of the posterior fixation surfaces  154  in a direction away from the articular side  146 . The teeth  158  are configured to engage the surgically-prepared distal end  600  of the patient&#39;s femur  602  when the femoral trial  18  is coupled thereto. The illustrative teeth  158  extend parallel to each other in the medial-lateral direction and have a triangular cross section. It should be appreciated that in other embodiments the teeth  158  may be angled relative to each other or arranged in various patterns on the posterior fixation surfaces  154 . Additionally, one or more of the teeth  158  may extend inferiorly-superiorly along the posterior fixation surface  154  in addition to, or instead of, extending medially-laterally. It should also be appreciated that in other embodiments one or more teeth may be formed on any of the other surfaces of the fixation side  148  of the femoral trial  18 . 
     As shown in  FIG. 5 , the femoral trial  18  has a distal condylar region  160  that includes a pair of distal fixation surfaces  162  (one being medially positioned, the other laterally positioned) defined by the outer surfaces  150  of the ribs  138 . Each of the distal fixation surfaces  162  is opposite a distal condyle surface  164 . The distal fixation surfaces  162  extend generally in the anterior-posterior direction. The distal condylar region  160  also includes a pair of apertures or through-holes  166 , one of which is positioned laterally while the other is positioned medially. Each through-hole  166  is sized to receive a surgical drill, as described in greater detail below. 
     A pair of sidewalls  168 ,  170  extends between the articular side  146  and the fixation side  148 , with one sidewall being medially positioned and the other laterally positioned depending on which knee is being replaced. Each of the sidewalls  168 ,  170  has a pair of notches  172 ,  174  defined therein. The notch  172  has a base surface  176  extending between the articular side  146  and the fixation side  148 . Similarly, the notch  174  has a pair of base surfaces  178  extending between the articular side  146  and the fixation side  148 . The sidewalls  168 ,  170  define an outer edge  180  of the femoral trial  18  corresponding to a standard femoral prosthetic component size. The base surfaces  176 ,  178  of the notches  172 ,  174  define another edge  182  of the femoral trial  18  corresponding to a standard, but more narrow, femoral prosthetic component size. In the illustrative embodiment, the notches  172 ,  174  extend inwardly approximately 1.75 millimeters from each of the sidewalls  168 ,  170 , respectively, to the base surfaces  176 ,  178 . As such, a single femoral trial  18  may be used to size multiple femoral prosthetic component sizes. 
     Referring now to  FIGS. 6-14 , a number of tibial bearing trials  20  of the system  10  are shown. As discussed above, each tibial bearing trial  20  is a multi-piece assembly configured to assist the surgeon in selecting a size and configuration of a prosthetic tibial bearing component of the knee prosthesis. As shown in  FIG. 6 , a tibial bearing trial  20  may be assembled with one of a number of tibial bearing surface trials  192  and one of a number of a plurality of trial shims  190 . Each bearing surface trial  192  has a different size and/or configuration, and each shim  190  has a different thickness. Because each shim  190  is configured to be secured to each bearing surface trial  192 , the surgeon is able to assemble a tibial bearing trial  20  of one size and configuration, evaluate the performance of that tibial bearing trial  20 , and then modify the tibial bearing trial  20  as necessary to determine intraoperatively the type and configuration of the prosthetic tibial bearing component to be implanted. 
     Referring now to  FIGS. 9 and 10 , one of the trial shims  190  is shown. The shim  190  includes a plate  194  having a planar surface  196  and a planar surface  198  opposite the planar surface  196 . An outer sidewall  200  extends between the surfaces  196 ,  198  and defines a predetermined thickness  202  of the shim  190 . As discussed above, the system  10  may include a plurality of trial shims, each of which may have a different thickness. 
     As shown in  FIG. 9 , a vertical surface  204  of the sidewall  200  is contoured with a number of ribs  206 . The ribs  206  are sized and positioned to receive the fingertips of the surgeon to assist with the assembly of a trial  20 . The plate  194  has a notch  208  defined in one side  210  thereof. The notch  208  includes a channel  212  that is defined in the planar surface  196  and extends inwardly from the sidewall  200 . The plate  194  has another notch  214  defined in an opposite side  216  thereof. The notch  214  includes a channel  218  that is defined in the planar surface  198  and extends inwardly from the sidewall  200 . As will be described in greater detail below, the notches  208 ,  214  are utilized to separate the shim  190  from the tibial bearing surface trial  192 . 
     The shim  190  has an aperture  220  defined through the plate  194 . As will be described in greater detail below, the aperture  220  is configured to receive the post  94  and the lug  120  of the base insert  16  when the shim  190  is positioned on the base trial  14 . The aperture  220  includes a central passageway  222  extending between an opening  224  defined in the surface  196  of the plate  194  and an opening  226  defined in the surface  198 . The central passageway  222  is sized to receive the post  94  of the base insert  16 . The central passageway  222  also defines an axis  228  extending through the plate  194 . 
     As shown in  FIG. 10 , the aperture  220  also includes a number of slots  230 ,  232 ,  234  extending outwardly from the passageway  222 . The slot  230  extends from a posterior side  236  of the passageway  222  through the outer sidewall  200  of the plate  194 . The slot  232  is rectangular and extends from another side  238  of the central passageway  222  toward the side  212  of the plate  194 . The rectangular slot  232  is defined by substantially planar inner walls  240 ,  242 ,  244 , which extend between the surfaces  196 ,  198  of the plate  194 . As will be described in greater detail below, the lug  120  is received in the rectangular slot  232  when the shim  190  is attached in one orientation to one of the tibial bearing surface trials  192 . 
     The slot  234  is arcuate in shape and extends outwardly from a side  246  of the central passageway  222  opposite the side  238 . The arcuate slot  234  is defined by a pair of substantially planar inner walls  248 ,  250  and an arcuate inner wall  252  extending between the inner walls  248 ,  250 . As will be described in greater detail below, the lug  120  is received in the arcuate slot  234  when the shim  190  is attached to another one of the tibial bearing surface trials  192  in another orientation. 
     The arcuate inner wall  252  has an edge  254  defined in the surface  196 . The edge  254  defines an arc  256  about the axis  228  of the plate  194 . In the illustrative embodiment, the arc  256  has a magnitude of approximately fifty degrees. It should be appreciated that in other embodiments the magnitude of the arc  256  may be greater or lesser than fifty degrees depending on nature of the knee prosthesis to be implanted. 
     The shim  190  also includes a pair of attachment openings  258 ,  260  that are defined in the surface  196  of the plate  194 . The opening  258  is positioned between the side  238  of the passageway  222  and the side  216  of the plate  194 . The opening  260  is positioned between the opposite side  246  of the passageway  222  and the side  212  of the plate  194 . A cylindrical inner wall  262  extends downwardly from the opening  258  to define a through-hole  264 . Similarly, a cylindrical inner wall  266  extends downwardly from the opening  260  to define a through-hole  268 . The through-holes  264 ,  268  are configured to receive pegs  270 ,  272  of the tibial bearing surface trial  192 , as will be described in greater detail below. As shown in  FIG. 9 , each inner wall  262 ,  266  has an indent or channel  274  defined therein sized to receive a corresponding spring  276  of the pegs  270 ,  272  to retain the pegs  270 ,  272  in the through-holes  264 ,  268 . 
     The opening  258  (and through-hole  264 ) has a diameter  275 , while the opening  260  (and through-hole  268 ) has a diameter  276  that is less than the diameter  275 . In that way, the openings  258 ,  260  have the same shape but have a unique size. It should be appreciated that in other embodiments the openings  258 ,  260  may have rectangular, square, triangular, or other geometric shape. Additionally, while in the illustrative embodiment the openings  258 ,  260  have the same shape, it should be appreciated that in other embodiments each opening may have a unique shape. As will be described in greater detail below, the configuration of the openings  258 ,  260  ensures that the shim  190  may be attached to each tibial bearing surface trial  192  in a single, predetermined orientation. 
     Returning to  FIG. 6 , one of the bearing surface trials  192  is a fixed bearing surface trial  300 . The term “fixed bearing surface trial” as used herein refers to a bearing surface trial that is fixed in position relative to the tibial base trial  14  when the bearing surface trial and shim are attached thereto (i.e., it is configured to not substantially rotate or move in the anterior-posterior direction or medial-lateral direction relative to the tibial base trial  14 ). The fixed bearing surface trial  300  may be embodied as a cruciate retaining trial, a posterior stabilized trial, a revision trial, or other surface trial configuration, per the surgeon&#39;s preference. For example, in embodiments where the fixed bearing surface trial  300  is embodied as a posterior stabilized trial, the fixed bearing surface trial  300  may include a spine extending upwardly from the upper bearing surface of the trial  300 . 
     Referring now to  FIGS. 11 and 12 , the fixed bearing surface trial  300  has a platform  302  including a lower surface  304  that contacts the surface  196  of the shim  190  when the shim  190  is secured thereto. The platform  302  of the fixed bearing surface trial  300  also includes a pair of articular surfaces  306 ,  308  that are positioned opposite the lower surface  304 . The articular surfaces  306 ,  308  are configured to rotate with the condyle surfaces  140 ,  142 , respectively, of the femoral trial  18 . The platform  302  is defined by an outer sidewall  310  extending between the lower surface  304  and the articular surfaces  306 ,  308 . A surface  312  of the sidewall  310  is contoured with a number of ribs  314 , which are sized to receive the fingertips of the surgeon and assist with the assembly of a tibial bearing surface trial  192 . 
     The platform  302  also has a notch  316  defined in an anterior aspect  318  thereof. As will be described in greater detail below, the notch  316  is used to separate the tibial bearing trial  20  from the tibial base trial  14  when the tibial bearing trial  20  is positioned thereon. The notch  316  includes a channel  320  that is defined in the lower surface  304 . As shown in  FIG. 12 , the channel  320  is dome-shaped and is defined by a curved inner wall  322  extending inwardly from the sidewall  310 . It should be appreciated that in other embodiments the channel  320  may be defined by substantially straight inner walls such that the channel is, for example, rectangular in shape. 
     As shown in  FIG. 12 , the platform  302  of the fixed bearing surface trial  300  has an aperture  324  defined in the lower surface  304  thereof. The aperture  324  includes a central opening  326  and a slot  328  extending outwardly from the central opening  326 . When the shim  190  is secured to the lower surface  304  of the platform  302 , the central opening  326  is substantially aligned with the central passageway  222  of the shim  190  and the slot  328  is substantially aligned with the rectangular slot  232  of the shim  190 . Thus, the central opening  326  is circular in shape and is sized to receive the top end  98  of the post  94  of the base insert  16 . Similarly, the slot  328  of the aperture  324  is rectangular and is sized to receive the lug  120  of the base insert  16 . 
     The fixed bearing surface trial  300  also includes a pair of pegs  270 ,  272  that extend downwardly from the lower surface  304 . The pegs  270 ,  272  are positioned on each side of the aperture  324 . Each of the pegs  270 ,  272  has a cylindrical body  334 , and each body  334  extends the same length from the lower surface  304 . The peg  270  has a diameter  337  that corresponds to the diameter  275  of the opening  258  of the shim  190 , and the peg  272  has a diameter  338  that corresponds to the diameter  276  of the opening  260  of the shim  190 . In that way, the shim  190  may be attached to the lower surface  304  of the fixed bearing surface trial  300  and positioned on the tibial base trial  14  in only a single orientation. It should be appreciated that in other embodiments the pegs  270 ,  272  may have a rectangular, square, triangular, or other geometrically-shaped cross section. Additionally, while in the illustrative embodiment the pegs  270 ,  272  have the same shape, it should be appreciated that in other embodiments each peg may have a unique shape. 
     As discussed above, each of the pegs  270 ,  272  includes a spring  276  sized to be received in a corresponding channel  274  defined in the shim  190 . Each spring  276  is received in a slot  336  defined in the body  334  of each of the pegs  270 ,  272 . In the illustrative embodiment, each spring  276  is a ring-shaped coil configured to snap into each channel  274  of the shim  190  to secure to the shim  190  to the bearing surface trial  192 . One example of a spring  276  is the Bal Seal Engineering Rotary Seal, which is commercially available from Bal Seal Engineering, Inc. of Foothill Ranch, Calif., U.S.A. It should be appreciated that in other embodiments the spring may take the form of another biasing or friction element, such as, for example, an o-ring, a retaining ring, or other element capable of securing the shim  190  to the surface trial  192 . Additionally, in other embodiments, the bearing surface trial  192  may be secured to the shim  190  via friction between the pegs  270 ,  272  and the inner walls  262 ,  266  of the shim  190 . 
     Returning to  FIG. 6 , the other bearing surface trial  192  is embodied as a mobile bearing surface trial  340 . The term “mobile bearing surface trial” as used herein refers to a bearing surface trial that is permitted to rotate relative to the tibial base trial  14  when the bearing surface trial and the shim are attached thereto (i.e., it is configured to substantially rotate or move in the anterior-posterior direction or the medial-lateral direction relative to the tibial base trial  14 ). The mobile bearing surface trial  340  may be embodied as a cruciate retaining trial, a posterior stabilized trial, a revision trial, or other surface trial configuration, per the surgeon&#39;s preference. For example, in embodiments where the mobile bearing surface trial  340  is embodied as a posterior stabilized trial, the mobile bearing surface trial  340  may include a spine extending upwardly from the upper bearing surface thereof. 
     Referring now to  FIGS. 13 and 14 , the mobile bearing surface trial  340  has a platform  344  including a lower surface  346  that contacts the surface  198  of the shim  190  when the shim  190  is secured thereto. The platform  344  of the mobile bearing surface trial  340  also includes a pair of articular surfaces  348 ,  350  that are positioned opposite the lower surface  346 . The articular surfaces  348 ,  350  are configured to rotate with the condyle surfaces  140 ,  142 , respectively, of the femoral trial  18 . The platform  344  is defined by an outer sidewall  352  extending between the lower surface  346  and the articular surfaces  348 ,  350 . A surface  354  of the sidewall  352  is contoured with a number of ribs  356 , which are sized to receive the fingertips of the surgeon and assist with the assembly of the tibial bearing surface trial  192 . 
     The platform  344  also has a notch  358  defined in an anterior aspect  360  thereof. As will be described in greater detail below, the notch  358 , like the notch  316 , is used to separate the tibial bearing trial  20  from the tibial base trial  14  when the tibial bearing trial is positioned thereon. The notch  358  includes a channel  362  that is defined in the lower surface  346 . As shown in  FIG. 12 , the channel  362  is dome-shaped and is defined by a curved inner wall  364  extending inwardly from the sidewall  352 . It should be appreciated that in other embodiments the channel  362  may be defined by substantially straight inner walls such that the channel is, for example, rectangular in shape. 
     As shown in  FIG. 14 , the platform  344  of the mobile bearing surface trial  340  has an aperture  366  defined in the lower surface  346  thereof. The aperture  366  includes a central opening  368  and an arcuate slot  370  extending outwardly from the central opening  368 . When the shim  190  is secured to the lower surface  346  of the platform  344 , the central opening  368  is substantially aligned with the central passageway  222  of the shim  190  and the slot  328  is substantially aligned with the arcuate slot  234  of the shim  190 . Thus, the central opening  368  is circular in shape and is sized to receive the top end  98  of the post  94  of the base insert  16 . Similarly, the slot  370  of the aperture  366  is sized to receive the lug  120  of the base insert  16 . 
     The mobile bearing surface trial  340  also includes a pair of pegs  270 ,  272  that extend downwardly from the lower surface  346 . The pegs  270 ,  272  are positioned on each side of the aperture  366 . Each of the pegs  270 ,  272  has a cylindrical body  334 , and each body  334  extends the same length from the lower surface  346 . The peg  270  has a diameter  337  that corresponds to the diameter  275  of the opening  258  of the shim  190 , and the peg  272  has a diameter  338  that corresponds to the diameter  276  of the opening  260  of the shim  190 . As discussed above, each of the pegs  270 ,  272  also includes a spring  276  sized to be received in a corresponding channel  274  defined in the shim  190 . Each spring  276  is received in a slot  336  defined in the body  334  of each of the pegs  270 ,  272 . In that way, the shim  190  may be attached to the lower surface  346  of the mobile bearing surface trial  340  and positioned on the tibial base trial  14  in only a single orientation that is the reverse of the orientation of the shim  190  when the shim  190  is attached to the fixed bearing surface trial  300 . 
     Returning to  FIG. 6 , the surgeon may assemble one of the shims  190  with one of the bearing surface trials  192  to form a tibial bearing trial  20 . For example, the surgeon may select one of the fixed bearing surface trials  300  and secure the shim  190  thereto to form a fixed bearing trial  372 . To do so, the surgeon aligns the pegs  270 ,  272  of the bearing surface trial  192  with the openings  258 ,  260  and then advances the pegs into the correct opening such that the springs  276  are received in the channels  274  defined in the shim  190 . The surgeon may choose to position the fixed bearing trial  372  on the base trial  14  by aligning the apertures  220 ,  324  of the fixed bearing trial  372  with the post  94  and the lug  120  of the base insert  16 . The fixed bearing trial  372  is then placed over the post  94  and the lug  120  and the surface  198  of the shim  190  is advanced into contact with the upper surface  32  of the base trial  14 . 
     When the fixed bearing trial  372  is properly seated as shown in  FIG. 7 , the lug  120  is received in the slot  232  of the shim  190  and the post  94  is received in the central passageway  222 . The inner walls  240 ,  244  of the shim  190  cooperate with the lug  120  to prevent the fixed bearing trial  372  from rotating relative to the base trial  14 . It should be appreciated that in other embodiments the shim  190  may be positioned on the tibial base trial  14  prior to attaching the fixed bearing surface trial  300  thereto. 
     Alternatively, the surgeon may assemble one of the shims  190  with one of the mobile bearing surface trials  340  to form a mobile bearing trial  374 . The surgeon positions the mobile bearing trial  374  on the base trial  14  by aligning the apertures  220 ,  324  of the mobile bearing trial  374  with the post  94  and the lug  120  of the base insert  16 . The surgeon then places the mobile bearing trial  374  over the post  94  and the lug  120  and advances the surface  196  of the shim  190  into contact with the upper surface  32  of the base trial  14 . 
     When the mobile bearing trial  374  is properly seated as shown in  FIG. 8 , the lug  120  is received in the slot  234  of the shim  190  and the post  94  is received in the central passageway  222 . It should be appreciated that in other embodiments the shim  190  may be positioned on the tibial base trial  14  prior to attaching the mobile bearing surface trial  340  thereto. As shown in  FIG. 8 , the post  94  defines a longitudinal axis  376  extending in a superior/inferior direction along the passageway  112  of the base insert  16 . The arcuate slot  234  of the shim  190  permits the mobile bearing trial  374  to rotate relative to the base trial  14  about the axis  376 . When the mobile bearing trial  374  is rotated in one direction, the lug  120  may be advanced along the arcuate inner wall  252  into contact with the inner wall  248  of the shim  190 ; when the mobile bearing trial  374  is rotated in the opposite direction, the lug  120  may be advanced along the arcuate inner wall  252  into contact with the opposite inner wall  250 . In that way, rotation of the mobile bearing trial  374  about the axis  376  is limited by the arc  256  defined by the arcuate inner wall  252  to approximately fifty degrees. 
     Referring now  FIG. 15 , the system  10  further includes a keel punch  22 . The keel punch  22  is configured to be inserted through the plate opening  38  of the base trial  14  into the proximal end  604  of the patient&#39;s tibia  606  to prepare the patient&#39;s tibia  606  for a prosthetic component. The keel punch  22  has an upper frame  380  and a main body  382  extending downwardly therefrom. The upper frame  380  and the main body  382  cooperate to define a rim  384  around the periphery thereof. The rim  384  has a bottom surface  386  configured to engage the shelf surface  52  of the base trial  14  when the keel punch  22  is seated on the base trial  14  and in the proximal end  604  of the patient&#39;s tibia  606 . 
     As shown in  FIG. 15 , the upper frame  380  of the keel punch  22  has a configuration similar to the upper body  80  of the base trial  14 . The upper frame  380  includes a central platform  86  sized to be received in the central opening  40  of the base trial  14 . The upper frame  380  also includes a pair of prongs  88 ,  90  that extend outwardly from the central platform  86 , which are sized to be received in the elongated openings  42  of the base trial  14 . 
     The upper frame  380  of the keel punch  22  includes a post  94  extending upwardly from an upper surface  96  thereof. The post  94  extends to a top end  98 , and a lip  100  extends outwardly therefrom. The lip  100  has a bottom surface  102  that extends parallel to the upper surface  96 , and the surfaces  96 ,  102  cooperate to define a lever-receiving notch  104 . The lever-receiving notch  104  is configured to receive the locking flange  498  associated with the impaction handle  28 , as described in greater detail below. 
     The post  94  also has an opening  106  defined in an upper surface  108  thereof. An inner wall  110  extends downwardly from the opening  106  to define a central passageway  112  through the keel punch  22 . The inner wall  110  has a keyed section  114  (see  FIG. 15 ) that permits the keel punch  22  to be attached to the impaction handle  28  in only a single predetermined orientation. 
     As shown in  FIG. 15 , the post  94  of the keel punch  22  has a generally curved sidewall  116  and a flat sidewall  118  positioned under the lip  100 . The keel punch  22  also includes a block or lug  120  extending outwardly from the curved sidewall  116  of the post  94  toward the prong  90 . Like the base insert  16 , the post  94  and the lug  120  of the keel punch  22  are positioned in the tibial bearing trial  20  when the tibial bearing trial  20  is positioned on the tibial base trial  14  and the keel punch  22  is positioned in the tibial base trial  14 . 
     The central platform  86  of the keel punch  22  also has a keyed section  122  (see  FIG. 15 ). The keyed section  122  and the orientation of the prongs  88 ,  90  relative to the platform  86  permit the keel punch  22  to be inserted into the plate opening  38  of the base trial  14  in a single, predetermined orientation. 
     The main body  382  of the keel punch  22  includes a central bullet  390  and a pair of lower arms  392  that are positioned below the prongs  88 ,  90  and extend outwardly from the central bullet  390 . The central bullet  390  has circular cross section that varies in diameter along its length (i.e., the diameter of the bullet  390  tapers in the superior-inferior direction). In that way, the cross sectional diameter of the bullet  390  at an upper end  394  is greater than the cross sectional diameter of the bullet  390  at a lower end  396 . A number of downwardly extending teeth  398  are defined in each of the lower arms  392 . The teeth  398  are configured to engage the patient&#39;s tibia  606  to define an opening  672  in the proximal end  604  of the patient&#39;s tibia  606  sized to receive the tibial implant (see  FIG. 37 ). 
     As described above, the system  10  also includes the guide tower  24 , which is configured to be positioned on the base trial  14  during use. One example of a guide tower is shown and described in co-pending U.S. Patent App. Ser. No. 61/503,324, entitled “KEEL PUNCH AND IMPACTION HANDLE ASSEMBLY AND ASSOCIATED SURGICAL INSTRUMENTS FOR USE IN SURGICALLY PREPARING A TIBIA FOR IMPLANTATION OF A PROSTHETIC COMPONENT” by David Waite et al., which is incorporated herein by reference. As shown in  FIG. 16 , the guide tower  24  includes a tower base  400  and a pair of fixation pins  402  extending downwardly from the tower base  400 . The tower base  400  includes a main body  404  and a pair of arms  406  extending outwardly from the main body  404 . A bottom surface  408  of the tower base  400  is configured to be positioned on the base trial  14 , and the fixation pins  402  extend downwardly therefrom. The main body  404  also has an upper aperture  410  and a lower aperture  412  defined therein, and the main body  404  has a height  414 , which may correspond to a predetermined drilling depth in the patient&#39;s tibia  606 , as described in greater detail below. 
     As shown in  FIG. 16 , the tower base  400  has an upper guide opening  416  defined therein. The tower base  400  has an inner wall  418  that extends downwardly from the upper guide opening  416  to a lower guide opening (not shown) defined in the bottom surface  408 . The inner wall  418  defines a vertically-extending passageway  420  through the main body  404  and the arms  406 . The cross sectional shape of the passageway  420  of the tower base  400  substantially matches the cross sectional shape of the passageway  46  of the base trial  14 . When the guide tower  24  is properly positioned on the base trial  14 , the passageways  46 ,  420  are substantially aligned. In that way, the configuration of the passageway  420 , like the configuration of the passageway  46 , permits the advancement of various surgical drills, punches, and other instruments into the proximal end  604  of the patient&#39;s tibia  606 , as will be described in greater detail below. The apertures  410 ,  412  extend inwardly and are in communication with the passageway  420 . 
     The fixation pins  402  extending from the bottom surface  408  are sized to be received in a corresponding pair of the fastener holes  72  defined in the base trial  14 . Each fixation pin  402  includes an upper section  432  and a lower section  434  extending downwardly from the upper section  432 . Each fixation pin  402  further includes a pointed conical tip  436  configured to engage the proximal end  604  of the patient&#39;s tibia  606 . It should be appreciated that in other embodiments the guide tower  24  may include additional or fewer fixation pins  402 . 
     In the illustrative embodiment, the base trial  14 , the base insert  16 , the keel punch  22 , and the guide tower  24  are formed from an implant-grade metallic material such as steel, titanium, or cobalt chromium. The femoral trial  18 , the shims  190 , and the tibial bearing surface trials  192  are formed from a polymeric material such as polyethylene or ultra-high molecular weight polypropylene (UHMWPE). 
     As described above, the system  10  further includes the detachable alignment handle  26 , which the surgeon may use to adjust the position of the base trial  14 . Referring now to  FIG. 17 , the alignment handle  26  includes an elongated body  440  and the lever  66 , which is pivotally coupled to elongated body  440 . The elongated body  440  has a back end  442  and a front end  444 , and a grip  446  is positioned therebetween. A plurality of alignment rod holes  448 ,  450  extend through the elongated body  440 , with the alignment rod hole  448  extending orthogonal to the alignment rod hole  450 . As will be described in greater detail below, the holes  448 ,  450  are sized to receive a pair of alignment rods  662 ,  664  (see  FIG. 30 ) that are used to confirm the overall alignment of the trial components  12  in the patient&#39;s knee. 
     The lever  66  of the alignment handle  26  includes a rocker arm  454  having a latching end  456  and an actuation end  458 . A flange or catch  460  extends downwardly from the rocker arm  454  at the latching end  456 . The catch  460  is sized to be received in the slot  60  of the base trial  14 . The lever  66  is pivotally coupled to the body  440  via a joint  462 . A biasing element (not shown) is positioned between actuation end  458  of the rocker arm  454  and the body  440 . The lever  66  also includes a user-operated button  464  that is secured to the rocker arm  454  at the actuation end  458 . In the illustrative embodiment, the button  464  includes a contoured outer surface  466  that is configured to receive a fingertip of a surgeon or other user. 
     As shown in  FIG. 17 , the pins  68  of the alignment handle  26  are positioned on each side of the lever  66 . Each pin  68  has a body  468  that extends outwardly from the front end  444  of the elongated body  440  to a tip  470 . The body  468  has an oblong-shaped cross section that corresponds to the oblong-shape of the apertures  64  defined in the base trial  14 . As described above, each pin  68  is configured to be received in a corresponding aperture  64  defined in the base trial  14 . 
     In use, the alignment handle  26  may be secured to the base trial  14  by positioning the tips  470  of the pins  68  in the apertures  64  defined in the base trial  14 . The pins  68  may be then advanced into the apertures  64  to bring the catch  460  into contact with the sidewall  36  of the base trial  14 . The bias exerted by the biasing element may be overcome by pressing down on the button  464 , thereby causing the lever  66  to pivot about joint  462  and aligning the catch  460  with the channel  58  of the notch  54  defined in the base trial  14 . The latching end  456  of the lever  66  may then be advanced into the notch  54 . When the latching end  456  is positioned at the posterior end  62  of the notch  54 , the catch  460  is positioned over the oblong-shaped slot  60 . After the button  464  is released, the biasing element urges the lever  66  to pivot such that the catch  460  is advanced into the slot  60 , thereby securing the base trial  14  to the alignment handle  26 . 
     As described above, the system  10  also includes the impaction handle  28 , which may be attached to the base insert  16 , the keel punch  22 , or the guide tower  24 . Referring now to  FIG. 18 , the impaction handle  28  includes an elongated body  472 , a mounting shaft  474  connected to an end  476  of the elongated body  472 , and a attachment mechanism  478  configured to attach the base insert  16 , the keel punch  22 , or the guide tower  24  to the handle  28 . The elongated body  472  includes a neck  480  extending from the end  476  and a head  482  connected to the neck  480  at the opposite end of the elongated body  472 . 
     A grip  486  is secured to the neck  480  and is configured to receive the hand of a surgeon or other user. The head  482  of the impaction handle  28  includes a metal plate  488  positioned at the end  484 . In use, the surgeon holds the impaction handle  28  via the grip  486  and strikes the metal plate  488  with a mallet, sledge, or other impaction tool to drive the keel punch  22  into the proximal end  604  of the patient&#39;s tibia  606 . 
     The attachment mechanism  478  of the impaction handle  28  includes a lever  490  pivotally coupled to the mounting shaft  474 . The lever  490  includes a latching arm  492  and an actuation arm  494  extending at an angle from an end  496  of the latching arm  492 . The locking flange  498  is positioned at an opposite end  500  of the latching arm  492  and extends downwardly therefrom. As described above, the locking flange  498  is configured to engage the lip  100  of the base insert  16  or the keel punch  22  to secure the base insert  16  or the keel punch  22  to the impaction handle  28 . Another locking flange or catch  502  is positioned adjacent to the end  496  of the latching arm  492 . As will be described in greater detail below, the aperture  410  of the guide tower  24  is sized to receive the catch  502  such that the guide tower  24  may be secured to the impaction handle  28 . 
     As shown in  FIG. 18 , the mounting shaft  474  of the impaction handle  28  includes a housing  504  extending from the end  476  of the elongated body  472  and a rod  506 , which extends from the housing  504 . A guide pin  508  of the impaction handle  28  extends from an end face  510  of the rod  506 . The guide pin  508  has a cross section that substantially matches the shape of the opening  106  defined in the post  94  of the base insert  16  and the keel punch  22 . As shown in  FIG. 18 , the guide pin  508  includes a flat face  512  that is sized to be received in the keyed section  114  of the inner wall  110  of the post  94 . 
     The latching arm  492  of the lever  490  extends beyond the housing  504  such that the locking flange  498  is positioned over the guide pin  508  and extends toward the flat face  512 . This arrangement permits the locking flange  498  to be positioned in the notch  104  of the post  94  and the guide pin  508  to be positioned in the opening  106  of the post  94  to secure the base insert  16  or the keel punch  22  to the impaction handle  28 . 
     To secure, for example, the base insert  16  to the impaction handle  28 , the guide pin  508  is positioned in the opening  106  of the post  94 . By pressing down on the actuation arm  494  with a predetermined amount of force, the bias exerted by a biasing element may be overcome, thereby causing the lever  490  to pivot. As the lever  490  is pivoted, the locking flange  498  is moved away from the flat face  512  of the guide pin  508 . 
     The guide pin  508  may be advanced along the passageway  112  of the base insert  16  until the top end  98  of the post  94  is placed in contact with the end face  510  of the rod  506 . In that position, the locking flange  498  is positioned over the lever-receiving notch  104 . When the actuation arm  494  is released, the lever  490  is urged to pivot by the biasing element and the locking flange  498  is advanced into the notch  104  of the base insert  16 . 
     Referring now to  FIG. 19 , one embodiment of a knee prosthesis (hereinafter fixed bearing knee prosthesis  520 ) that may replace the patient&#39;s natural joint is shown. The fixed bearing knee prosthesis  520  includes a femoral component  522 , a tibial tray  524 , and a tibial bearing  526 . One example of a fixed bearing knee prosthesis is shown and described in U.S. Patent App. Pub. No. 2010/0063594, entitled “FIXED-BEARING KNEE PROSTHESIS HAVING INTERCHANGEABLE COMPONENTS” by Stephen A. Hazebrouck et al., which is expressly incorporated herein by reference. 
     The tibial tray  524  includes a platform  528  having a fixation member, such as an elongated stem  530 , extending away from its lower surface  532 . The elongated tibial stem  530  is configured to be implanted into the surgically-prepared end  604  of a patient&#39;s tibia  606 . A generally Y-shaped posterior buttress  534  extends upwardly from an upper surface  536  of the platform  528 . The posterior buttress  534  includes a pair of arms  538 ,  540  extending along a posterior section of the perimeter of the platform  528 . A third arm  542  extends anteriorly away from the intersection of the lateral arm  538  and the medial arm  540  (i.e., in a direction toward the center of the platform). 
     The bearing  526  is securable to the tibial tray  524 . In particular, the bearing  526  may be snap-fit to the tibial tray  524 . In such a way, the bearing  526  is fixed relative to the tibial tray  524  (i.e., it is not rotatable or moveable in the anterior-posterior or medial-lateral directions). The bearing  526  also includes a lateral bearing surface  544  and a medial bearing surface  546 . 
     The femoral component  522  is configured to be implanted into a surgically-prepared end  600  of the patient&#39;s femur  602 . Specifically, the femoral component  522  includes a body  550  having a pair of mounting lugs  552  extending therefrom. The mounting lugs  552  are configured to be received in the surgically-prepared end  600  of the patient&#39;s femur  602  to secure the femoral component  522  to the patient&#39;s femur  602 . 
     The femoral component  522  is configured to emulate the configuration of the patient&#39;s natural femoral condyles. As such, the body  550  has a lateral condyle surface  554  and a medial condyle surface  556  that are configured (e.g., curved) in a manner that approximates the condyles of the natural femur. The surfaces  554 ,  556  are configured to articulate with the bearing surfaces  544 ,  546 , respectively, of the bearing  526 . The lateral condyle surface  554  and the medial condyle surface  556  are spaced apart from one another thereby defining an intercondylar notch  558  therebetween. 
     Referring now to  FIG. 20 , another embodiment of a knee prosthesis (hereinafter mobile bearing knee prosthesis  560 ) that may replace the patient&#39;s natural joint is shown. The mobile bearing knee prosthesis  560  includes a femoral component  562 , a tibial tray  564 , and a tibial bearing  566 . One example of a mobile bearing knee prosthesis is shown and described in U.S. Pat. No. 7,731,755 entitled “POSTERIOR STABILIZED MOBILE BEARING KNEE” by Joseph G. Wyss et al., which is expressly incorporated herein by reference. 
     The tibial tray  564  includes a platform  568  having a fixation member, such as an elongated stem  570 , extending away from its lower surface  572 . The elongated tibial stem  570  is configured to be implanted into the surgically-prepared end  604  of a patient&#39;s tibia  606 . A cavity or bore  574  is defined in an upper surface  576  of the platform  568  and extends downwardly into the stem  570 . 
     The bearing  566  is configured to be coupled to the tibial tray  564 . The bearing includes a platform  578  having a lateral bearing surface  580 , a medial bearing surface  582 , and a bottom surface  584 . The bearing  566  also includes a stem  586  extending downwardly from the bottom surface  584 . When the bearing  566  is coupled to the tibial tray  564 , the stem  586  of the bearing  566  is received in the bore  574  of the tibial tray  564 . In that way, the tibial bearing  566  is configured to rotate about an axis defined by the stem  586  relative to the tibial tray  564 . 
     The femoral component  562 , like the femoral component  522  of the fixed bearing knee prosthesis  520 , is configured to be implanted into a surgically-prepared end  600  of the patient&#39;s femur  602 . Specifically, the femoral component  562  includes a body  588  having a pair of mounting lugs  552  extending therefrom. The mounting lugs  552  are configured to be received in the surgically-prepared end  600  of the patient&#39;s femur  602  to secure the femoral component  562  to the patient&#39;s femur  602 . 
     The femoral component  562  is configured to emulate the configuration of the patient&#39;s natural femoral condyles. As such, the body  588  has a lateral condyle surface  554  and a medial condyle surface  556  that are configured (e.g., curved) in a manner that approximates the condyles of the natural femur. The surfaces  554 ,  556  are configured to articulate with the bearing surfaces  580 ,  582 , respectively, of the bearing  566 . The lateral condyle surface  554  and the medial condyle surface  556  are spaced apart from one another thereby defining an intercondylar notch  558  therebetween. 
     The system  10  may be utilized during the performance of an orthopaedic surgical procedure similar to that shown in  FIG. 21 . As shown in  FIGS. 22-32 , the femoral trial  18  is attached to a distal end  600  of a patient&#39;s femur  602 , and the tibial base trial  14  is attached to a proximal end  604  of a patient&#39;s tibia  606 . A tibial bearing trial  20  is positioned on the tibial base trial  14  between the femoral trial  18  and the base trial  14  and a trial reduction is performed to determine the size and configuration of the knee prosthesis to be implanted. 
     In another part of the surgical procedure, the guide tower  24  of the system  10  is positioned on tibial base trial  14 , and the surgeon uses the trial  14  and the tower  24  to guide, for example, a surgical drill while reaming the proximal end  604  of the patient&#39;s tibia  606 . Thereafter, the keel punch  22  is impacted into the proximal end  604  of the patient&#39;s tibia  22  before the guide tower  24  is removed. 
     Referring now to  FIG. 21 , an illustrative orthopaedic surgical procedure  700  utilizing the system  10  is shown. In block  702 , the surgeon performs a resection of the distal end  600  of the patient&#39;s femur  602  and a resection of the proximal end  604  of the patient&#39;s tibia  606  to surgically prepare those ends for trial reduction. For example, as shown in  FIG. 22 , the patient&#39;s femur  602  and the patient&#39;s tibia  606  may be resected such that the surgically-prepared distal end  600  of the patient&#39;s femur  602  includes a resected medial condyle  608  and a resected lateral condyle  610 . The resected medial condyle  608  and the resected lateral condyle  610  include a number of resected surfaces  612  configured to receive the femoral trial  18 . Similarly, the surgically-prepared proximal end  604  of the patient&#39;s tibia  606  also includes a resected surface  614  configured to receive the tibial base trial  14 . 
     Returning to  FIG. 21 , the procedure  700  continues to block  704  in which the surgeon performs an initial trial reduction. In doing so, the surgeon uses the system  10  to evaluate and check the stability and kinematics of the patient&#39;s femur  602  and tibia  606  for implantation of a fixed bearing knee prosthesis  520  or a mobile bearing knee prosthesis  560 . In the trial reduction process, the surgeon positions the femoral trial  18  over the distal end  600  of the patient&#39;s femur  602 , as shown in  FIG. 23 . The impaction handle  28  may be used to tap the femoral trial  18  onto the distal end  600 . 
     To do so, the surgeon may attach an impactor head  620  to the mounting shaft  474  of the impaction handle  28 . The surgeon may position an engagement end  622  of the impactor head  620  in contact with the articular side  146  of the femoral trial  18  and apply force to the impaction handle  28  using the grip  486  or by tapping on the head  482  of the handle  28 . The surgeon applies force until the fixation side  148  of the femoral trial  18  contacts the resected medial condyle  608  and the resected lateral condyle  610 . Once the femoral trial  18  is properly positioned on the distal end  600  of the patient&#39;s femur  602 , the surgeon may remove the impactor head  620  and the impaction handle  28 . It should be appreciated that in other embodiments the surgeon may position the femoral trial  18  on the patient&#39;s femur  602  by hand without using the impaction handle  28 . 
     When the femoral trial  18  is positioned on the distal end  600  of the patient&#39;s femur  602 , the posterior fixation surfaces  154  of the femoral trial  18  engage posterior planar surfaces  624  of the patient&#39;s femur  602 . One or more of the teeth  158  of the posterior fixation surfaces  154  of the femoral trial  18  engages with, or grips, the posterior planar surfaces  624  of the condyles  608 ,  610 . The engagement of the teeth  158  with the posterior planar surfaces  624  secures the femoral trial  18  to the distal end  600  of the patient&#39;s femur  602 . 
     As shown in  FIG. 23 , the sidewalls  168 ,  170  of the femoral trial  18  indicate where the outer edge of a standard femoral prosthetic component would be located on the resected condyles  608 ,  610 . Conversely, the base surfaces  176 ,  178  of the notches  172 ,  174  in the femoral trial  18  indicate where the outer edge of a narrow femoral prosthetic component would be located. If the sidewalls  168 ,  170  extend beyond the condyles  608 ,  610 , the surgeon may select the narrow femoral prosthetic component for implantation. 
     As shown in  FIG. 24 , the surgeon also positions the tibial base trial  14  on the resected surface  614  of the patient&#39;s tibia  606  during the trial reduction process. To do so, the surgeon may attach the alignment handle  26  to an appropriately-sized base trial  14  and, as shown in  FIG. 24 , use the alignment handle  26  to position the base trial  14  on the resected surface  614 . Alternatively, the surgeon may choose to position the base trial  14  by hand. It should be appreciated that a number of base trials  14  may be provided, which are configured in a number of different sizes. As a result, the base trial  14  providing maximum coverage of the resected surface  614  of the patient&#39;s tibia  606  without overhang may be selected. 
     The surgeon may select one of the base inserts  16  to be placed in the plate opening  38  of the base trial  14 . If the surgeon desires a fixed bearing trial  372 , the surgeon may select a spikeless base insert  128  and position the base insert  128  in the plate opening  38  by hand so that the bottom surface  84  of the base insert  128  engages the shelf surface  52  of the base trial  14 . If the surgeon desires a mobile bearing trial  374 , the surgeon may select a spiked base insert  126 , as shown in  FIG. 25 . 
     To position the spiked base insert  126  in the plate opening  38  of the base trial  14 , the surgeon may attach the base insert  126  to the impaction handle  28 . To do so, the surgeon positions the guide pin  508  of the impaction handle  28  in the opening  106  of the base insert  126  and presses on the actuation arm  494  of the lever  490  with a predetermined amount of force to overcome the bias exerted by the biasing element, thereby causing the lever  490  to pivot. As the lever  490  is pivoted, the locking flange  498  is moved away from the flat face  512  of the guide pin  508 , and the guide pin  508  may be advanced along the passageway  112  defined in the base insert  126  until the top end  98  of the post  94  is placed in contact with the end face  510  of the impaction handle  28 . In that position, the locking flange  498  is positioned over the lever-receiving notch  104 . When the surgeon releases the actuation arm  494 , the biasing element urges the lever  490  to pivot and the locking flange  498  is advanced into the notch  104 , thereby securing the base insert  126  to the impaction handle  28 . 
     As shown in  FIG. 25 , the base insert  126  and impaction handle  28  are positioned over the plate opening  38 , and the surgeon may then apply force to the handle  28  to tap the base insert  126  into the proximal end  604  of the patient&#39;s tibia  606 . In doing so, the spikes  130  extending from the prongs  88 ,  90  of the base insert  126  are driven into the proximal end  604  of the patient&#39;s tibia  606 . The surgeon continues driving the base insert  126  into the patient&#39;s tibia  606  until the bottom surface  84  of the base insert  126  engages the shelf surface  52  of the tibial base trial  14 . 
     Once the selected base insert  16  (i.e., spiked or spikeless) is properly seated, the surgeon may select a trial shim  190  and a tibial bearing surface trial  192 . If the surgeon desires a fixed bearing trial  372 , a fixed bearing surface trial  300  may be selected and attached to one of the trial shims  190 . To do so, the surgeon positions the trial shim  190  in the fixed bearing orientation shown in  FIG. 26 . Once the trial shim  190  is in the correct orientation, the surgeon attaches the trial shim  190  to the fixed bearing surface trial  300  by aligning the openings  258 ,  260  of the shim  190  with the pegs  270 ,  272 , respectively, of the fixed bearing surface trial  300 . The surgeon then advances the pegs  270 ,  272  into the respective openings  258 ,  260  such that the lower surface  304  of the fixed bearing surface trial  300  is placed in contact with the surface  196  of the shim  190  to assemble the fixed bearing trial  372 . 
     As shown in  FIG. 26 , the surgeon positions the fixed bearing trial  372  on the base trial  14  by aligning the apertures  220 ,  324  of the fixed bearing trial  372  with the post  94  and the lug  120  of the base insert  16 . The surgeon then places the fixed bearing trial  372  over the post  94  and the lug  120  and advances the surface  198  of the shim  190  into contact with the upper surface  32  of the base trial  14 . When properly seated, the lug  120  is received in the slot  232  of the shim  190  and the post  94  is received in the central passageway  222 . The inner walls  240 ,  244  of the shim  190  cooperate with the lug  120  to prevent the fixed bearing trial  372  from rotating relative to the base trial  14 . 
     As shown in  FIG. 27 , when the fixed bearing trial  372  is in place, the surgeon carefully extends the knee of the patient, noting the anteroposterior stability, medial-lateral stability, and overall alignment in the anterior-posterior (“A/P”) plane and medial-lateral (“M/L”) plane. Rotational alignment of the tibial base trial  14  may be adjusted with the knee in full extension, using the handle  26  to rotate the trial  14  and the bearing trial  372  relative to the femoral trial  18 . The rotation of the base trial  14  is usually centered on the junction between the medial and central one-third of the tibial tubercle. 
     As the range of motion is evaluated, the load on the femoral trial  18  translates posteriorly as the knee is moved between extension (see  FIG. 27 ) and flexion (see  FIG. 30 ). As the load moves posteriorly, the force normal to the posterior condyle surfaces  156  of the femoral trial  18  increases, thereby causing the teeth  158  of the posterior fixation surfaces  154  of the femoral trial  18  to further engage, or grips, the posterior planar surfaces  624  of the surgically-prepared distal end  600  of the patient&#39;s femur  602 . The engagement of one or more of the teeth  158  of the femoral trial  18  with the distal end  600  of the patient&#39;s femur  602  retains the femoral trial  18  on the patient&#39;s femur  602 . 
     To improve performance, the surgeon may remove the fixed bearing trial  372  from the tibial base trial  14  to exchange the shim  190  or the bearing surface trial  192 . As shown in  FIG. 28 , a removal tool  626  may be used to detach the fixed bearing trial  372  from the base trial  14 . The removal tool  626  has an elongated body  628  and a tip  630  configured to be received in the notch  316  of the fixed bearing surface trial  300 . When the tip  630  is positioned in the notch  316  of the shim  190 , an upper surface  632  of the tip  630  contacts the bottom of the channel  320  of the shim  190  while a lower surface  634  of the tip  630  contacts the upper surface  32  of the base trial  14 . The surgeon may then pivot the elongated body  628  of the removal tool  626  downward, thereby disengaging the fixed bearing trial  372  from the base trial  14 . 
     As shown in  FIG. 29 , the surgeon may use a separator tool  640  to detach the shim  190  from the fixed bearing surface trial  300 . The separator tool  640  has a housing  642  and a lever  644  pivotally coupled to the housing  642  at a joint  646 . The housing  642  includes a main body  648  and a plate  650  extending from the main body  648 . 
     The lever  644  includes a lift arm  652  and an actuation arm  654 . The lift arm  652  is wedge-shaped and includes a lower surface  656  configured to contact the plate  650 . The actuation arm  654  includes a contoured upper surface  658  configured to receive the fingertip of the surgeon. A biasing element, illustratively embodied as a leaf spring  660 , is positioned between the actuation arm  654  of the lever  644  and the main body  648  of the housing  642 , thereby biasing the lift arm  652  in contact with the plate  650 . 
     To detach the shim  190  from the fixed bearing surface trial  300 , the surgeon positions the lift arm  652  and the plate  650  of the separator tool  640  in the notch  208  of the shim  190 . By pressing down on the contoured upper surface  658  of the actuation arm  654 , the surgeon may overcome the bias of leaf spring  660  and pivot the lever  644  about the joint  646 . The lift arm  652  is advanced into contact with the lower surface  304  of the fixed bearing surface trial  300 . As the surgeon continues to press down on the actuation arm  654 , the pegs  270 ,  272  may be withdrawn from the openings  258 ,  260  and shim  190  may be separated from the fixed bearing surface trial  300 . 
     The surgeon may then select another shim  190  having a different thickness or choose a fixed bearing surface trial  300  with an alternative configuration, such as, for example, a fixed bearing surface trial  300  that is cruciate retaining or posterior stabilized. In some cases, the surgeon may switch to a mobile bearing surface trial  340 . The surgeon may continue to try various combinations of shims  190  and bearing surface trials  192  to ascertain which final implant will have the best stability in flexion and extension while permitting full extension. 
     As shown in  FIG. 30 , the surgeon may confirm overall alignment with two alignment rods  662 ,  664 . The alignment rod  662  is positioned in the hole  448  while the alignment rod  664  is positioned in one of the holes  450  extending through the handle  26 . Once a combination is selected and the appropriate position on the patient&#39;s tibia is located, the surgeon may etch marks  668  on the anterior tibial cortex using, for example, an electrocautery tool (not shown). The marks  668  are aligned with the alignment etchings  70  defined in the anterior aspect  56  of the tibial base trial  14 . 
     If the surgeon desires instead a mobile bearing trial  374 , a mobile bearing surface trial  340  may be selected and attached to one of the trial shims  190 . To do so, the surgeon positions the trial shim  190  in the mobile bearing orientation shown in  FIG. 31 . Once the trial shim  190  is in the correct orientation, the surgeon attaches the trial shim  190  to the mobile bearing surface trial  340  by aligning the openings  258 ,  260  of the shim  190  with the pegs  270 ,  272 , respectively, of the mobile bearing surface trial  340 . The surgeon then advances the pegs  270 ,  272  into the respective openings  258 ,  260  such that the lower surface  346  of the mobile bearing surface trial  340  is placed in contact with the surface  198  of the shim  190 , thereby assembling the mobile bearing trial  374 . 
     As shown in  FIG. 31 , the surgeon positions the mobile bearing trial  374  on the base trial  14  by aligning the apertures  220 ,  366  of the mobile bearing trial  374  with the post  94  and the lug  120  of the base insert  16 . The surgeon then places the mobile bearing trial  374  over the post  94  and the lug  120  and advances the surface  196  of the shim  190  into contact with the upper surface  32  of the base trial  14 . When properly seated, the lug  120  is received in the slot  234  of the shim  190  and the post  94  is received in the central passageway  222 . 
     With the femoral trial  18 , tibial base trial  14 , and mobile bearing trial  374  in place, the surgeon may extend the knee and note the anteroposterior stability, medial-lateral stability, and overall alignment in the A/P and M/L planes, as shown in  FIG. 32 . The surgeon is also able to assess the bearing rotation and patellofemoral tracking because the mobile bearing trial  374  is rotatable about the base trial  14 . As discussed above, when the mobile bearing trial  374  is attached to the base trial  14 , the post  94  defines a longitudinal axis  376  extending along the passageway  112  of the base insert  16 . The arcuate slot  234  of the shim  190  permits the mobile bearing trial  374  to rotate relative to the base trial  14  about the axis  376 . When the mobile bearing trial  374  is rotated in one direction, the lug  120  may be advanced along the arcuate inner wall  252  into contact with the inner wall  248  of the shim  190 ; when the mobile bearing trial  374  is rotated in the opposite direction, the lug  120  may be advanced along the arcuate inner wall  252  into contact with the inner wall  250 . 
     Overall alignment can be confirmed by attaching alignment rods  662 ,  664  to the handle  26 , which is reattached to the base trial  14 . If there is any indication of instability, the surgeon may remove the mobile bearing trial  374  from the tibial base trial  14  using the removal tool  626  and disassemble the trial  374  using the separator tool  640  to exchange the shim  190  or the bearing surface trial  192 . For example, the surgeon may select the next greater thickness shim  190  before repeating the trial reduction. The surgeon may continue to try various combinations of shims  190  and bearing surface trials  192  to ascertain which implant size and configuration (e.g., the thickness of the implant, the mobility of the implant, etc.) will have the best stability in flexion and extension while permitting the desired kinematics. 
     Returning back to  FIG. 21 , after the surgeon has performed the trial reduction of block  704 , the procedure  700  proceeds to block  706  in which further surgical preparation of the proximal end  604  of the patient&#39;s tibia  606  is performed. Specifically, as shown in  FIG. 33 , the guide tower  24  is positioned on tibial base trial  14  so that fixation pins  402  extend through the fastener holes  72  of the tibial base trial  14  and into the proximal end  604  of the patient&#39;s tibia  606 . As shown in  FIG. 34 , the surgeon uses the base trial  14  and the tower  24  to guide, for example, a surgical drill  670  while reaming the proximal end  604  of the patient&#39;s tibia  606 . Thereafter, as shown in  FIG. 35 , the keel punch  22  is impacted into the proximal end  604  of the patient&#39;s tibia  606  using the impaction handle  28  before the guide tower  24  is removed. An exemplary procedure for reaming the patient&#39;s tibia  606  and installing the keel punch  22  is set forth in U.S. Patent App. Ser. No. 61/503,331, entitled “METHOD OF SURGICALLY PREPARING A TIBIA FOR IMPLANTATION OF A PROSTHETIC COMPONENT” filed by David Waite et al., which is incorporated herein by reference. 
     Subsequently, in block  707 , the surgeon determines whether any additional trial reduction is necessary. If so, the procedure  700  continues to block  708  in which the surgeon may utilize the keel punch  22  seated on the tibial base trial  14  in the proximal end  604  of the patient&#39;s tibia  606  to perform an additional trial reduction. As shown in  FIG. 36 , the surgeon may assemble a fixed bearing trial  372  or a mobile bearing trial  374  and position the trial  372  or trial  374  over the post  94  and the lug  120  of the keel punch  22 . If a fixed bearing trial  372  is selected, the surgeon advances the surface  198  of the shim  190  into contact with the upper surface  32  of the base trial  14 . When properly seated, the lug  120  of the keel punch  22  is received in the slot  232  of the shim  190  and the post  94  is received in the central passageway  222  of the shim  190 . 
     With the fixed bearing trial  372  in place, the knee is again extended and the surgeon may note the anteroposterior stability, medial-lateral stability, and overall alignment in the A/P and M/L planes. Overall alignment can be confirmed by attaching alignment rods  662 ,  664  to the handle  26 . If there is any indication of instability, the surgeon may remove the fixed bearing trial  372  from the tibial base trial  14  using the removal tool  626  and disassemble the trial  372  using the separator tool  640  to exchange the shim  190  or the bearing surface trial  192 . The surgeon may then repeat the trial reduction until satisfied with the alignment and the stability of the knee. 
     If a mobile bearing trial  374  is selected, the surgeon advances the surface  196  of the shim  190  into contact with the upper surface  32  of the base trial  14 . When properly seated, the lug  120  of the keel punch  22  is received in the slot  234  of the shim  190  and the post  94  is received in the central passageway  222 . With the mobile bearing trial  374  in place, the knee is again extended and the surgeon may note the anteroposterior stability, medial-lateral stability, and overall alignment in the A/P and M/L planes. Overall alignment can be confirmed by attaching alignment rods  662 ,  664  to the handle  26 . If there is any indication of instability, the surgeon may remove the mobile bearing trial  374  from the tibial base trial  14  using the removal tool  626  and disassemble the trial  374  using the separator tool  640  to exchange the shim  190  or the bearing surface trial  192 . The surgeon may then repeat the trial reduction until satisfied with the alignment and the stability of the knee. 
     When the additional trial reduction of block  708  is complete or if the surgeon determines in block  707  that an additional trial reduction is not needed, the surgeon may use the impaction handle  28  to remove the keel punch  22  from the patient&#39;s tibia  606 . As shown in  FIG. 37 , the resultant features, including an opening  672 , of the proximal end  604  of the patient&#39;s tibia  606  are configured to receive a tibial tray, such as the tray  524  of the fixed bearing knee prosthesis  520  or the tray  564  of the mobile bearing knee prosthesis  560 . 
     In block  710  of the procedure  700 , further surgical preparation of the distal end  600  of the patient&#39;s femur  602  is performed. As shown in  FIG. 38 , the surgeon positions the femoral trial  18  on the distal end  600  of the patient&#39;s femur  602 . The distal fixation surfaces  162  are advanced into contact with the condyles  608 ,  610  of the patient&#39;s femur  602 . A surgical drill  674  is advanced sequentially through the through-holes  166  defined in the femoral trial  18  to drill a hole  676  in each of the condyles  608 ,  610 . Each hole  676  is sized to receive a corresponding lug  552  of the femoral component  522  of the fixed bearing knee prosthesis  520  or the femoral component  562  of the mobile bearing knee prosthesis  560 . In block  712  of the surgical procedure  700 , the surgeon may attach the selected femoral component of the knee prosthesis to the distal end  600  of the patient&#39;s femur  602 . 
     In block  714  of the surgical procedure  700 , the surgeon attaches the selected tibial tray (e.g., tibial tray  524  or tibial tray  564 ) to the proximal end  604  of the patient&#39;s tibia  606 . To do so, the surgeon inserts the stem (e.g., stem  530  of the tibial tray  524  or stem  570  of the tibial tray  564 ) into the opening  672  defined in the resected surface  614  of the proximal end  604  of the patient&#39;s tibia  606 . The surgeon may attach a tibial impactor (not shown) to the impaction handle  28 , and, with the selected tibial tray fully seated, the surgeon may tap on the head  482  of the impaction handle  28  with a mallet or other instrument. It should be appreciated that the selected tibial tray may be press fit into the tibia  606  or, alternatively, may be secured to the tibia  606  by use of bone cement. 
     Subsequently, in block  715 , the surgeon determines whether an additional trial reduction is necessary. If the surgeon determines that a trial reduction is needed, the procedure  700  continues to block  716  in which the surgeon may perform an additional trial reduction with the selected tibial tray installed in the patient&#39;s tibia  606  and the selected femoral component installed on the patient&#39;s femur  602 . If the surgeon has selected the fixed bearing knee prosthesis  520 , the surgeon again selects a fixed bearing trial  372  for the trial reduction. As shown in  FIG. 39 , the tibial tray  524  of the fixed bearing knee prosthesis  520  is installed in the proximal end  604  of the patient&#39;s tibia  606 . The surgeon attaches the fixed bearing surface trial  300  to the shim  190  to assemble to the fixed bearing trial  372  and positions the fixed bearing trial  372  over the tibial tray  524 . The surface  198  of the shim  190  is then advanced into contact with the upper surface  536  of the tibial tray  524 . When properly seated, the third arm  542  of the posterior buttress  534  of the tibial tray  524  is positioned in the slot  230  and the central passageway  222  of the shim  190 . 
     With the fixed bearing trial  372  in place on the tibial tray  524 , the knee is again extended and the surgeon may note the anteroposterior stability, medial-lateral stability, and overall alignment in the A/P and M/L planes. Overall alignment can be confirmed by attaching alignment rods  662 ,  664  to the handle  26 . If there is any indication of instability, the surgeon may remove the fixed bearing trial  372  from the tibial tray  524  using the removal tool  626  and disassemble the trial  372  using the separator tool  640  to exchange the shim  190  or the bearing surface trial  192 . The surgeon may then repeat the trial reduction until satisfied with the alignment and the stability of the knee. 
     Alternatively, if the surgeon has selected the mobile bearing knee prosthesis  560 , the surgeon again selects a mobile bearing trial  374  for the trial reduction. As shown in  FIG. 40 , the tibial tray  564  of the mobile bearing knee prosthesis  560  is installed in the proximal end  604  of the patient&#39;s tibia  606 . A trial stem  680  is positioned in the bore  574  of the tibial tray  564  to approximate the function of the stem  586  of the mobile bearing  566 . The upper end  682  is configured to be received in the central passageway  222  of the shim  190  while the lower end  684  is seated in the bore  574 . 
     The surgeon attaches the mobile bearing surface trial  340  to the shim  190  to assemble to the mobile bearing trial  374  and positions the mobile bearing trial  374  over the tibial tray  564 . The surface  196  of the shim  190  is then advanced into contact with the upper surface  576  of the tibial tray  564 . When properly seated, the upper end  682  of the trial stem  680  is received in the central passageway  222  of the shim  190 . 
     With the mobile bearing trial  374  in place on the tibial tray  564 , the knee is again extended and the surgeon may note the anteroposterior stability, medial-lateral stability, and overall alignment in the A/P and M/L planes. Overall alignment can be confirmed by attaching alignment rods  662 ,  664  to the handle  26 . If there is any indication of instability, the surgeon may remove the mobile bearing trial  374  from the tibial tray  564  using the removal tool  626  and disassemble the trial  372  using the separator tool  640  to exchange the shim  190  or the bearing surface trial  192 . The surgeon may then repeat the trial reduction until satisfied with the alignment and the stability of the knee. 
     When the additional trial reduction of block  716  is complete, or if the surgeon determines in block  715  that an additional trial reduction is not needed, the procedure  700  continues to block  718  in which the surgeon installs the selected tibial bearing. The surgeon may then continue with other parts of the surgical procedure. 
     While the disclosure has been illustrated and described in detail in the drawings and foregoing description, such an illustration and description is to be considered as exemplary and not restrictive in character, it being understood that only illustrative embodiments have been shown and described and that all changes and modifications that come within the spirit of the disclosure are desired to be protected. 
     There are a plurality of advantages of the present disclosure arising from the various features of the method, apparatus, and system described herein. It will be noted that alternative embodiments of the method, apparatus, and system of the present disclosure may not include all of the features described yet still benefit from at least some of the advantages of such features. Those of ordinary skill in the art may readily devise their own implementations of the method, apparatus, and system that incorporate one or more of the features of the present invention and fall within the spirit and scope of the present disclosure as defined by the appended claims.