Patent Publication Number: US-2010114323-A1

Title: Knee prosthesis kit with winged sleeves and milling guide

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     Priority is claimed to the following application: U.S. Provisional Patent Application Ser. No. 61/110,174 entitled, “KNEE PROSTHESIS KIT WITH WINGED SLEEVES AND MILLING GUIDE,” filed on Oct. 31, 2008 by Stephanie M. DeRuntz, Timothy G. Vendrely, Brian Haas and Jeffery L. Koenemann (Docket No. DEP6004USPSP). 
    
    
     TECHNICAL FIELD 
     The present disclosure relates generally to prosthetic joints, and more particularly to a modular prosthetic knee joint system that includes a metaphyseal component and an instrument preparing the bone to receive the metaphyseal component. 
     BACKGROUND 
     The knee joint basically consists of the bone interface of the distal end of the femur and the proximal end of the tibia. Appearing to cover or at least partially protect this interface is the patella, which is a sesamoid bone within the tendon of the long muscle (quadriceps) on the front of the thigh. This tendon inserts into the tibial tuberosity and the posterior surface of the patella is smooth and glides over the femur. 
     The femur is configured with two knob like processes (the medial condyle and the lateral condyle) which are substantially smooth and which articulate with the medial plateau and the lateral plateau of the tibia, respectively. The plateaus of the tibia are substantially smooth and slightly cupped thereby providing a slight receptacle for receipt of the femoral condyles. 
     When the knee joint is damaged whether as a result of an accident or illness, a prosthetic replacement of the damaged joint may be necessary to relieve pain and to restore normal use to the joint. Typically the entire knee joint is replaced by means of a surgical procedure that involves removal of the surfaces of the corresponding damaged bones and replacement of these surfaces with prosthetic implants. This replacement of a native joint with a prosthetic joint is referred to as a primary total-knee arthroplasty. 
     On occasion, the primary knee prostheses fails. Failure can result from many causes, including wear, aseptic loosening, osteolysis, ligamentous instability, arthrofibrosis and patellofemoral complications. When the failure is debilitating, revision knee surgery may be necessary. In a revision, the primary knee prosthesis is removed and replaced with components of a revision prosthetic knee system. 
     Knee implant systems for both primary and revision applications are available from a variety of manufacturers, including DePuy Orthopaedics, Inc. of Warsaw, Ind. DePuy and others offer several different systems for both primary and revision applications. For example, DePuy Orthopaedics offers the P.F.C. SIGMA® Knee System, the LCS® Total Knee System, and the S-ROM Modular Total Knee System. Each of these orthopaedic knee systems includes several components, some appropriate for use in primary knee arthroplasty and some appropriate for use in revision surgery. 
     DePuy Orthopaedics also offers other orthopaedic implant systems for other applications. One such system is the LPS System. The LPS System is provided for use in cases of severe trauma and disease. In such cases, the trauma or disease can lead to significant amounts of bone loss. The LPS System provides components that can replace all or significant portions of a particular bone, such as the femur. The DePuy LPS System is described more fully in U.S. patent application Ser. No. 10/135,791, entitled “Modular Limb Preservation System”, filed Apr. 30, 2002 by Hazebrouck et al., which is incorporated by reference herein in its entirety. 
     In some patients, the metaphysis of the bone near the joint presents cavitary defects that are not completely filled by standard knee implants. The presence of such metaphyseal defects can result in loosening of the prosthetic implant over time, compromising the stability of the prosthetic implant and frequently requiring revision of the prosthetic implant. 
     To fill metaphyseal cavitary defects, knee systems with modular metaphyseal sleeves have been provided. Such sleeves are illustrated, for example, in: U.S. Pat. Pub. No. 2006/0030945A1, entitled “Modular Orthopaedic Implant System With Multi-Use Stems;” U.S. Pat. Pub. No. 2005/0107883A1, entitled “Modular Implant System With Fully Porous Coated Sleeve;” U.S. Pat. No. 7,291,174, entitled “Prosthetic Tibial Component With Modular Sleeve;” U.S. Pat. No. 6,171,342, entitled “Medical Fastening System;” U.S. Pat. No. 5,824,097, entitled “Medical Fastening System;” U.S. Pat. No. 5,782,921, entitled “Modular Knee Prosthesis;” and U.S. Pat. No. 4,634,444, entitled “Semi-Constrained Artificial Joint.” Such sleeves have been used in commercially available prosthetic knee implant systems, such as the P.F.C. SIGMA.® Knee System, the LCS® Total Knee System, the S-ROM Modular Total Knee System and the LPS System, all available from DePuy Orthopaedics, Inc. of Warsaw, Ind. 
     Modular sleeves have also been used in hip implant systems, as illustrated, for example, in: U.S. Pat. No. 6,264,699, entitled “ Modular Stem and Sleeve Prosthesis;” and U.S. Pat. No. 4,790,852, entitled “Sleeves for Affixing Artificial Joints to Bone.” Such hip sleeves have been used in commercially available prosthetic hip implant systems, such as the S-ROM hip systems, available from DePuy Orthopaedics, Inc. of Warsaw, Ind. 
     The disclosures of all of the above patent applications and patents are incorporated by reference herein in their entireties. 
     In knee systems with modular metaphyseal sleeves, the conventional shape of many of the sleeves is generally an elliptical cone with a large ellipse profile close to the joint line tapering down to a smaller elliptical or circular profile at the termination of the component distal to the joint line. Generally, the sleeves have a terraced or stepped outer surface and an inner channel for frictional fixation to another component. This geometry fills cavitary defects in the metaphysis, allows for a wider surface area for load transfer through the joint and provides rotational stability for the articulating components of the prosthesis. The current sleeve geometry is conducive to preparation of the bone through broaching. 
     Generally, broaches are tapered tools used to shape or enlarge a cavity in the bone by impacting the broach into the metaphysis of the bone. Typical broaches in knee implant instrument sets have an outer shape generally conforming to the shape of the metaphyseal sleeve component. Generally, the cavity prepared by the broach is preferably aligned with the intramedullary canal of the bone so that the implant that is placed in the cavity is properly positioned. 
     In some patients, the bone presents regions of hard sclerotic bone adjacent to the softer bone of the metaphysis. In such patients, the hard sclerotic bone may force the broaches to remove more bone in softer areas and less bone in harder areas, resulting in the implants being positioned in an undesirable location. This scenario is more prevalent at the distal end of the femur where posterior bone is typically harder than the anterior bone. Conventional broaching may tend to cause the prepared cavity, and hence the implant, to be positioned too anterior, creating a flexion gap and making balancing of the joint more difficult. In addition, improper implant placement can adversely affect the long-term performance and survivorship of the prosthesis. 
     Moreover, in some patients, metaphyseal defects may be single sided: there may be a medial or lateral defect that requires use of metaphyseal sleeve but the opposite side may have healthier bone. To use a conventional symmetric sleeve in such cases would require the sacrifice of some healthy bone that could have been left in place to provide support for the prosthesis. Some have attempted to address single-side defects through use of augments; however, such systems address only peripheral defects and do not account for situations where the peripheral bone is intact but there is a central void. 
     Accordingly, there is a need for a knee implant system that provides a more predictable and reliable means of metaphyseal bone preparation so that the implant is properly positioned, regardless of hard sclerotic bone interference. There is also a need for a knee implant system that addresses single-side defects of the metaphysis. 
     SUMMARY 
     The present invention addresses the need for such a knee implant system by providing new metaphyseal sleeve designs, a new knee implant kit, new instrumentation and a new surgical technique for metaphyseal bone preparation. 
     According to one aspect of the present disclosure, a prosthetic sleeve implant for an artificial knee joint is provided. The joint has a joint motion surface. The sleeve comprises a body having a central longitudinal axis which defines first and second ends, a central portion, a first side wing portion, a second side wing portion and an inner wall defining a channel along the central longitudinal axis. The channel tapers between the first and second ends. The body has an outer surface that includes a plurality of adjacent terraces. Each terrace has an outer edge around its perimeter. The outer edge of each terrace lies in a plane substantially perpendicular to the central longitudinal axis of the body. The outer edge of each terrace at the central portion of the body comprises a pair of diametrically-opposed curved portions having the same radius of curvature. The center of curvature of each of the diametrically-opposed curved portions is along the central longitudinal axis of the body. The diametrically-opposed curved portions define vertices of the outer edge at the central portion of the body. The outer edge of each terrace at the first side wing portion of the body comprises a pair of spaced opposed straight lines connected to the diametrically-opposed curved portions and connected by a curved end segment spaced from the diametrically-opposed curved portions of the central portion. The distance between the spaced opposed lines of the outer edge at the first portion is less than the distance between the diametrically-opposed curved portions of the outer edge at the central portion of the body. The curved end segment defines a vertex of the outer edge at the first side wing portion of the body. The outer edge of each terrace at the second side wing portion of the body comprises a pair of spaced opposed straight lines connected to the diametrically-opposed curved portions of the central portion of the body and by a curved end segment spaced from the diametrically-opposed curved portions. The distance between the opposed lines being of the outer edge at the second side wing portion is less than the distance between the diametrically-opposed curved portions of the outer edge at the central portion of the body. The curved end segment defining a vertex of the outer edge at the second side wing portion of the body. Each terrace has a first transverse dimension between the vertices of the outer edge at the first portion and second portion and a second transverse dimension between the vertices of the diametrically opposed curved portions of the outer edge at the central portion. The first transverse dimension of the terrace nearest the first end is greater than the first transverse dimension of the adjacent terrace and the second transverse dimension of the terrace nearest the first end is greater than the second transverse dimension of the adjacent terrace. 
     In an illustrative embodiment, the sleeve is symmetric and the outer edge of each terrace is indented at the junctions of the diametrically-opposed curved portions of the outer edge and the spaced opposed straight lines of the outer edge. 
     According to another aspect of the present disclosure, a modular knee prosthesis kit is provided. The kit comprises a femoral component with curved convex condylar surfaces, a tibial component with curved concave condylar surfaces to receive the curved convex condylar surfaces of the femoral component, a femoral adapter and a sleeve. The curved concave condylar surfaces of the tibial component and curved convex condylar surfaces of the femoral component define a joint motion surface. The femoral adapter is mountable to the femoral component. The sleeve comprises a body having a central longitudinal axis which defines first and second ends, a central portion, a side wing portion and an inner wall defining a channel along the central longitudinal axis. The channel tapers between the first and second ends. The body has an outer surface which includes a plurality of adjacent terraces, each terrace having an outer edge around its perimeter. The outer edge of each terrace lies in a plane substantially perpendicular to the central longitudinal axis of the body. The outer edge of each terrace at the central portion of the body comprises a pair of diametrically-opposed curved portions defining vertices of the outer edge at the central portion of the body. The outer edge of each terrace at the side wing portion of the body is connected to the diametrically-opposed curved portions and has a curved end segment spaced from the diametrically-opposed curved portions of the central portion. The curved end segment defines a vertex of the outer edge at the first side wing portion of the body. The outer edge of each terrace is indented at the junction of central portion and the side wing portion. Each terrace has a first transverse dimension between the vertices of the outer edge at the side wing portion and a second transverse dimension between the vertices of the diametrically opposed curved portions of the outer edge at the central portion. The first transverse dimension of the terrace nearest the first end is greater than the first transverse dimension of the adjacent terrace and the second transverse dimension of the terrace nearest the first end is greater than the second transverse dimension of the adjacent terrace. The outer surface of the body of the sleeve is configured to fill a non-centralized defect in one of the bones of the knee. 
     In an illustrative embodiment, the sleeve is asymmetric, with a single side wing and central portion. 
     In another illustrative embodiment, the kit includes two sleeves, one of the sleeves being asymmetric and the other sleeve being symmetric. The asymmetric sleeve has a single side wing to accommodate patients with non-centralized metaphyseal defects. The symmetric sleeve has two side wings to accommodate patients with centralized metaphyseal defects. 
     According to another aspect of the invention, a knee prosthesis kit is provided. The kit includes a sleeve, a milling template and a reamer. The sleeve comprises a body having a central longitudinal axis which defines first and second ends, a central portion, a side wing portion and an inner wall defining a channel along the central longitudinal axis. The channel tapers between the first and second ends. The body has an outer surface which includes a plurality of adjacent terraces, each terrace having an outer edge around its perimeter. The outer edge of each terrace lies in a plane substantially perpendicular to the central longitudinal axis of the body. The outer edge of each terrace at the central portion of the body comprises a pair of diametrically-opposed curved portions defining vertices of the outer edge at the central portion of the body. The outer edge of each terrace at the first side wing portion of the body is connected to the diametrically-opposed curved portions and has a curved end segment spaced from the diametrically-opposed curved portions of the central portion. The curved end segment defines a vertex of the outer edge at the first side wing portion of the body. Each terrace has a first transverse dimension at the vertex of the outer edge of the side wing portion and a second transverse dimension between the vertices of the diametrically opposed curved portions of the outer edge at the central portion. The first transverse dimension of the terrace nearest the first end is greater than the first transverse dimension of the adjacent terrace and the second transverse dimension of the terrace nearest the first end is greater than the second transverse dimension of the adjacent terrace. The milling guide is used in forming a cavity to receive the sleeve, and comprises a template member, a base member and a side wall connecting the template member and the base member. The template member has an inner surface defining an elongate milling guide opening. The elongate milling guide opening has a first transverse dimension and a second transverse dimension. The first transverse dimension of the elongate milling guide opening is at least as great as the first transverse dimension of the terrace of the sleeve nearest the first end of the sleeve. The second transverse dimension is less than the first transverse dimension. The base is spaced from the template member, and includes a spherical depression aligned with the milling guide opening. The reamer has a first end, a second end and a central longitudinal axis. The first end of the reamer comprises a convex spherical surface sized and shaped to be received in the spherical depression of the base of the milling guide. The reamer is sized and shaped to extend from the base of the milling guide and through the elongate milling guide opening. 
     In an illustrative embodiment, the kit also includes a stem trial. The stem trial and the milling guide have complementary features so that the stem trial can be connected to the base member of the milling guide. Thus, the milling guide can be positioned and stabilized so that the base is aligned with the intramedullary canal of the bone. 
     In another illustrative embodiment, the kit includes a second reamer with a greater diameter than the first reamer. The second reamer is used to prepare the portion of the cavity that receives the center portion of the sleeve. The second reamer may be connected to a stem extension to be received in the intramedullary canal so that the second reamer is aligned with the intramedullary canal in use. 
     According to another aspect of the invention, a milling guide for use in forming a cavity in a bone to receive a component of a knee prosthesis is provided. The milling guide comprises a template member, a base and a side wall connecting the template member and the base member. The template member has an inner surface defining an elongate milling guide opening, the elongate milling guide opening having a first transverse dimension and a second transverse dimension. The second transverse dimension is less than the first transverse dimension. The base is spaced from the template member and includes a spherical depression aligned with the milling guide opening. The elongate milling guide opening has an edge including two parallel straight portions and two curved end portions. The two curved end portions connect the two parallel straight portions. Each curved end portion has a vertex. The maximum first transverse dimension of the elongate milling guide opening is at the vertices of the curved end portions. The second transverse dimension of the elongate milling guide opening is the distance between the two parallel straight portions. A central longitudinal axis extends from the center of the elongate milling guide opening and through the center of the spherical depression of the base. The vertices of the curved end portions of the elongate milling guide opening and the central longitudinal axis of the milling guide lie in a plane. The spherical depression of the base of the milling guide has a perimeter and opposed vertices lying in the same plane as the vertices of the curved end portions of the elongate milling guide opening and the longitudinal axis of the milling guide. A line from each vertex of the of the curved end portions of the elongate milling guide opening to the nearest vertex of the perimeter of the spherical depression of the base defines an acute angle with the longitudinal axis of the milling guide. 
     In an illustrative embodiment, a stem trial extends outwardly from the base along the central longitudinal axis of the milling guide. 
     According to another aspect of the invention, a method of preparing a long bone to receive a prosthetic implant component is provided. The method comprises preparing an elongate pilot hole aligned with and extending into the intramedullary canal of the bone. A reamer is provided, the reamer having a conical-shaped cutting portion and a shaft extending distally from the conical-shaped cutting portion. The shaft of the reamer is inserted into the pilot hole and the reamer is rotated to prepare a conical concavity aligned with the pilot hole. The reamer is then removed. A milling guide is provided. The milling guide has a template member, a base spaced from the template member, and a shaft extending distally from the base. The template member has a milling guide opening. The shaft of the milling guide is inserted into the pilot hole and the base of the milling guide is inserted into the conical concavity in the bone. A second reamer is provided. The second reamer has a cutting portion and a distal end. The second reamer is inserted through the milling guide opening and into the concavity until the distal end of the second reamer contacts the base of the milling guide. The second reamer is pivoted about the distal end on the base and the reamer is rotated to change the shape of the concavity in the bone. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The detailed description particularly refers to the accompanying figures in which: 
         FIG. 1  is a view of the femoral components of a modular knee prosthesis kit; 
         FIG. 2  is a view of the tibial components of a modular knee prosthesis kit; 
         FIG. 3  is a side view of the single-wing metaphyseal sleeve component of the kit of  FIGS. 1-2 ; 
         FIG. 4  is an end view of the single-wing metaphyseal sleeve component of  FIG. 3 ; 
         FIG. 5  is a top plan view of the single-wing metaphyseal sleeve component of  FIGS. 3-4 ; 
         FIG. 6  is a cross-section of the single-wing metaphyseal sleeve component of  FIGS. 3-5 , taken along line  6 - 6  of  FIG. 3 ; 
         FIG. 7  is a cross-section of the single-wing metaphyseal sleeve component of  FIGS. 3-5 , taken along line  7 - 7  of  FIG. 3 ; 
         FIG. 8  is a cross-section of the single-wing metaphyseal sleeve component of  FIGS. 3-5 , taken along line  8 - 8  of  FIG. 5 ; 
         FIG. 9  is a side view of the double-wing metaphyseal sleeve component of the kit of  FIGS. 1-2 ; 
         FIG. 10  is an end view of the double-wing metaphyseal sleeve component of  FIG. 9 ; 
         FIG. 11  is a top plan view of the double-wing metaphyseal sleeve component of  FIGS. 9-10 ; 
         FIG. 12  is a cross-section of the double-wing metaphyseal sleeve component of  FIGS. 9-11 , taken along line  12 - 12  of  FIG. 9 ; 
         FIG. 13  is a cross-section of the double-wing metaphyseal sleeve component of  FIGS. 9-11 , taken along line  13 - 13  of  FIG. 9 ; 
         FIG. 14  is a cross-section of the double-wing metaphyseal sleeve component of  FIGS. 9-11 , taken along line  14 - 14  of  FIG. 11 ; 
         FIG. 15  is a front view showing an assembly of some of the components of the modular knee prosthesis kit  FIGS. 1 and 2 , illustrating use a single-wing metaphyseal sleeves; 
         FIG. 16  is a side view showing an assembly of some of the components of the modular knee prosthesis kit  FIGS. 1 and 2 , illustrating use a double-wing metaphyseal sleeves; 
         FIG. 17  us a front view of the assembly of  FIG. 16 ; 
         FIG. 18  is a top plan view of an alternative embodiment of a double-wing metaphyseal sleeve; 
         FIG. 19  is a top plan view of another alternative embodiment of a double-wing metaphyseal sleeve; 
         FIG. 20  is a front view of a conical reamer that may be included as an instrument in the knee prosthesis kit; 
         FIG. 21  is a front view of another embodiment of a conical reamer that may be included as an instrument in the knee prosthesis kit; 
         FIG. 22  is an exploded perspective view of a milling guide, straight reamer, handle and stem trial that may be included as instruments in the knee prosthesis kit; 
         FIG. 23  is another exploded perspective view of the instruments of  FIG. 22 ; 
         FIG. 24  is an enlarged perspective view of a portion of the milling guide of  FIGS. 22-23 ; 
         FIG. 25  is an enlarged perspective view of a portion of the milling guide and straight reamer of  FIGS. 22-23 ; 
         FIG. 26  is a perspective view of an assembly of the milling guide, handle and stem trial, shown with the straight reamer received within the milling guide and pivoted to one position in the milling guide opening; 
         FIG. 27  is another perspective view of the assembly of  FIG. 26 , shown with the straight reamer pivoted to another position in the milling guide opening; 
         FIG. 28  is another perspective view of the assembly of  FIGS. 26-27 , shown with the straight reamer pivoted to another position in the milling guide opening; and 
         FIG. 29  is a perspective view of an assembly of the milling guide and the handle mounted on a femoral cutting block and with the straight reamer pivoted to one position in the milling guide opening. 
     
    
    
     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 disclosure to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives following within the spirit and scope of the invention as defined by the appended claims. 
       FIGS. 1 and 2  illustrate an example of components of a modular knee prosthesis kit. As illustrated in  FIG. 1 , on the femoral side, the kit includes a distal femoral component  10  with curved convex condylar surfaces  12 ,  14 . The illustrated distal femoral component is a posterior stabilized component. A femoral adapter  16  is also provided, along with a collar  18  for placement between the adapter  16  and the distal femoral component  10 . A bolt  20  is provided for connecting the adapter  16 , collar  18  and distal femoral component  10  together. The adapter  16  has an outer surface that is smooth and tapered. A stem extension  22  is also provided. All of the above components may be standard parts of the P.F.C. SIGMA.® Knee System available from DePuy Orthopaedics, Inc. of Warsaw, Ind. The adapter may have features such as those illustrated in U.S. Pat. Pub. No. 2006/0030945, entitled “Modular Orthopaedic Implant System with Multi-Use Stems,” or those illustrated in U.S. Pat. No. 6,171,342, entitled “Medical Fastening System,” U.S. Pat. No. 5,824,097, entitled “Medical Fastening System,” U.S. Pat. No. 5,782,921, entitled “Modular Knee Prosthesis.” Also as described in U.S. Pat. Pub. No. 2006/0030945, the stem extension may have features other than those illustrated in  FIG. 1 . It should be understood that these components are described for purposes of illustration only; the present invention is not limited to any particular type of distal femoral component or stem or any other particular component unless expressly called out in the claims. 
     As illustrated in  FIG. 1 , the femoral components of the kit also include two types of metaphyseal sleeves  24 ,  26 . As described in more detail below, one of the metaphyseal sleeves  24  is provided for use in a single-side defect in the metaphysis of the bone and the other metaphyseal sleeve  26  is provided for use where both sides of the metaphysis are to be filled. 
     As illustrated in  FIG. 2 , on the tibial side, the kit includes a tibial tray component  30 , a tibial bearing insert  32  and a stem extension  34 . The illustrated tibial tray component  30  is a commercial MBT Revision tibial tray, available from DePuy Orthopaedics, Inc. of Warsaw, Ind. The tray component  30  has an integral stem portion  36  with a bore (not shown) with internal threads to which the stem extension  34  may be attached. The outer surface of the stem portion  36  has a smooth finish, and tapers away from the joint motion surface. The joint motion surface corresponds with the juncture of the curved convex condyles  12 ,  14  of the distal femoral component  10  and the curved concave condylar surfaces of the tibial bearing insert  32  (an illustrative curved concave condylar surface is shown at  37  in  FIG. 16 ). 
     As illustrated in  FIG. 2 , the tibial components of the kit also include two types of metaphyseal sleeves  38 ,  40 . As described in more detail below, one of the metaphyseal sleeves  38  is provided for use in a single-side defect in the metaphysis of the bone and the other metaphyseal sleeve  40  is provided for use where both sides of the metaphysis are to be filled. 
     A first example of a prosthetic metaphyseal sleeve implant is illustrated in  FIGS. 3-8 . The first illustrated sleeve  24  is designed for use in a bone wherein the condition of the bone requires additional support or fixation on either the medial or lateral side of the metaphysis of the bone, but not on both sides; such a defect in the bone may be characterized as a non-centralized defect. The illustrated sleeve  24  comprises a body with a central portion  44  and a side wing portion  46 . The central portion  44  has a central longitudinal axis  48  that defines a first end  50  and a second end  52 . As shown in FIGS.  5 - 8 , an inner wall  54  in the central portion  44  defines a channel  56  along the central longitudinal axis  48  of the central portion  44 . The channel  56  tapers between the first and second ends. The tapered channel  56  may have any suitable taper angle for frictional locking with another element; for example, the tapered channel  56  may define a Morse taper. The channel  56  is designed to receive the tapered surface of the adapter  16  on the femoral side or the tapered surface of the stem portion  36  of the tibial tray  30  and to frictionally lock with one of these elements. Although it may be desirable to provide a set of sleeves  24  that can be used on either the tibial or the femoral side, it should be understood that it is also within the scope of the present invention to provide sleeves  24  that are designed to be used on the femoral side and a separate set of sleeves that are designed to be used on the tibial side; the shape of the channels  56  in such elements may vary to frictionally engage the adapter  16  if the sleeve is a femoral metaphyseal sleeve or to frictionally engage the stem portion  36  of the tibial tray  30 . 
     The body of the sleeve  24  has an outer surface  58  that includes a plurality of adjacent terraces or steps. In the embodiment illustrated in  FIGS. 3-8 , the sleeve has eight terraces or steps, designated  60   a - 60   h  in  FIGS. 3 and 4 . As shown in  FIG. 3 , each terrace  60   a - 60   h  has an outer edge  62   a - 62   h  around its perimeter. The first terrace  60   a  has two outer edges of similar shape, one edge  62   a  being at the end  50  of the sleeve  24  and the edge, also designated  60   a  in  FIG. 3 , at the juncture of the first terrace  60   a  and the second terrace  60   b.  As shown in  FIGS. 3-4 , the outer edges  62   a - 62   h  of the terraces  60   a - 60   h  lie in planes that substantially perpendicular to the central longitudinal axis  48  of the central portion  44  of the body. 
     The shapes of the outer edges of representative terraces  60   a,    60   c  and  60   d  are illustrated in  FIGS. 5-7  at  62   a ,  62   c  and  62   d . The outer edge  62   a,    62   c,    62   d  of each terrace  60   a,    60   c,    60   d  at the central portion  44  of the body comprises a pair of diametrically-opposed curved portions  64   a,    64   c,    64   d,    65   a,    65   c,    65   d  having the same radius of curvature. The center of curvature of each of the diametrically-opposed curved portions  64   a,    64   c,    64   d,    65   a,    65   c,    65   d  is along the central longitudinal axis  48  of the body. The diametrically-opposed curved portions  64   a,    64   c,    64   d,    65   a,    65   c,    65   d  define vertices  66   a,    66   c,    66   d,    67   a,    67   c,    67   d  of the outer edges  62   a,    62   c,    62   d  at the central portion  44  of the body. Lines tangent to the vertices  66   a,    66   c,    66   d,    67   a,    67   c,    67   d  of the outer edges  62   a,    62   c,    62   d  of the central portion  44  of the body are illustrated in  FIGS. 4  at  68  and  70 . These tangent lines  68 ,  70  each define an angle of about 2-4 degrees in the illustrated embodiment. The angle may vary depending on whether the sleeve is intended for use on the femoral or tibial side: for a femoral metaphyseal sleeve, for example, the angle may be about 2 degrees; for a tibial metaphyseal sleeve, for example, the angle may be about 4 degrees. Alternatively, a universal sleeve could be provided usable on either the tibial or femoral side. Thus, the diameter of each terrace, that is, the transverse dimension between opposite vertices, decreases between the first end  50  and the second end  52 ; illustratively, diameter d a  shown in  FIG. 5  for the center portion first terrace  60   a  is greater than diameter d c  shown in  FIG. 6  for the center portion of terrace  60   c  that is closer to the second end  52  and diameter d c  of the center portion of terrace  60   c  is greater than diameter d d  shown in  FIG. 7  for the center portion of terrace  60   d  that is still closer to the second end  52  of the sleeve. 
     The outer edge  62  of each terrace  60  at the side wing portion  46  of the body comprises a curved portion  72  joined to the diametrically-opposed curved portions  64  of the outer edge  62  at the center portion  44 . Examples are illustrated in  FIGS. 5-7  for terraces  60   a,    60   c  and  60   d.  As shown in  FIGS. 5 and 6 , the outer edges of the terraces of the side wing portion  46  may include a pair of spaced opposed straight lines  74   a,    74   c,    76   a,    76   c  connected to the diametrically-opposed curved portions  64   a,    64   c,    65   a,    65   c  and to the curved end segments  72   a,    72   c.  Thus, the curved end segments  72   a,    72   c  may be spaced from the diametrically-opposed curved portions  64   a,    64   c,    65   a,    65   c,  of the outer edges of the central portion  44 . As shown in  FIG. 7 , the curved segments  72   d  of the outer edge  62   d  may be directly connected to the segments  64   d,    65   d  of the outer edge  62   d  at the center portion  44 , with no intervening straight segments. Each curved segment  72  of the outer edge  62  of each terrace  60  has a vertex, illustrated in  FIGS. 5-7  at  78   a ,  78   c ,  78   d.    
     Lines tangent to the juncture of side wing portion  46  and the central portion  44  of the body of the sleeve  24  are illustrated in  FIGS. 4  at  80  and  82 . These tangent lines  80 ,  82  each define an angle of about 2-4 degrees with the plane of the central longitudinal axis  48  in the illustrated embodiment. The angle may vary depending on whether the sleeve is intended for use on the femoral or tibial side: for a femoral metaphyseal sleeve, for example, the angle may be about 2 degrees; for a tibial metaphyseal sleeve, for example, the angle may be about 4 degrees. Alternatively, a universal sleeve could be provided usable on either the tibial or femoral side. Thus, the width of the side portion of each terrace, that is, the maximum transverse dimension of the side portion of each terrace, decreases between the first end  50  and the second end  52 ; illustratively, width w a  shown in  FIG. 5  for the center portion first terrace  60   a  is greater than width w c  shown in  FIG. 6  for the center portion of terrace  60   c  that is closer to the second end  52  and width w c  of the center portion of terrace  60   c  is greater than width w d  shown in  FIG. 7  for the center portion of terrace  60   d  that is still closer to the second end  52  of the sleeve. As can also be seen in  FIG. 4 , the width of the side portion  46  of each terrace is less than the width of the center portion  44  of each terrace  60 . Each terrace  60 , including its outer edge  62 , is thus indented at the junctions of the diametrically-opposed curved portions  64   a,    64   c,    64   d,    65   a,    65   c,    65   d  of the outer edge  62  at the center portion  44  and the segments of the outer edge at the side wing portion  46 . 
     The overall lengths of each terrace  60  also decrease between the first end  50  and the second end  52 . As shown in  FIG. 3 , a line tangent with the vertices  78  of the side portions  46 , shown at  84  in  FIG. 3 , may define a variety of angles with the plane of the central longitudinal axis  48 ; the angle would depend, for example, on the size of the implant. A line tangent with a point on each outer edge of each terrace opposite to the line  84 , shown at  86  in  FIG. 3 , defines an angle of about 2-4 degrees with the plane of the central longitudinal axis  48  in the illustrated embodiment. The angle may vary depending on whether the sleeve is intended for use on the femoral or tibial side: for a femoral metaphyseal sleeve, for example, the angle may be about 2 degrees; for a tibial metaphyseal sleeve, for example, the angle may be about 4 degrees. Alternatively, a universal sleeve could be provided usable on either the tibial or femoral side. Thus, the length, that is the maximum transverse dimension of each terrace, decreases between the first end  50  and the second end  52 ; illustratively, width l a  shown in  FIG. 5  for the center portion first terrace  60   a  is greater than length l c  shown in  FIG. 6  for the center portion of terrace  60   c  that is closer to the second end  52  and width w c  of the center portion of terrace  60   c  is greater than width w d  shown in  FIG. 7  for the center portion of terrace  60   d  that is still closer to the second end  52  of the sleeve. 
     The sleeve  24  illustrated in  FIGS. 3-8  is asymmetric about one transverse plane through the central longitudinal axis  48  and symmetric about a perpendicular plane through the central longitudinal axis  48 . It should be understood that the above description of the features of sleeve  24  also applies to the single-winged sleeve  38  of  FIG. 2 . 
     In contrast, the second illustrated sleeve  26  of  FIGS. 9-13  is symmetric about two perpendicular planes through the central longitudinal axis  148  of the sleeve. The second illustrated sleeve  26  is designed for use in a bone wherein the condition of the bone requires additional support or fixation on both the medial and lateral sides of the metaphysis of the bone. 
     The second illustrated sleeve  24  comprises a body with a central portion  144 , a first side wing portion  145  and a second side wing portion  146 . The central portion  144  has a central longitudinal axis  148  that defines a first end  150  and a second end  152 . As shown in  FIGS. 5-8 , an inner wall  154  in the central portion  144  defines a channel  156  along the central longitudinal axis  148  of the central portion  144 . The channel  156  tapers between the first and second ends. The tapered channel  156  may have any suitable taper angle for frictional locking with another element; for example, the tapered channel  156  may define a Morse taper. The channel  156  is designed to receive the tapered surface of the adapter  16  on the femoral side or the tapered surface of the stem portion  36  of the tibial tray  30  and to frictionally lock with one of these elements. Although it may be desirable to provide a set of sleeves  26  that can be used on either the tibial or the femoral side of the joint motion surface, it should be understood that it is also within the scope of the present invention to provide sleeves  26  that are designed to be used on the femoral side and a separate set of sleeves that are designed to be used on the tibial side; the shape of the channels  156  in such elements may vary to frictionally engage the adapter  16  if the sleeve is a femoral metaphyseal sleeve or to frictionally engage the stem portion  36  of the tibial tray  30 . 
     The body of the sleeve  26  has an outer surface  158  that includes a plurality of adjacent terraces or steps. In the embodiment illustrated in  FIGS. 9-14 , the sleeve  26  has eight terraces or steps, designated  160   a - 160   h  in  FIGS. 9 and 10 . As shown in  FIG. 9 , each terrace  160   a - 160   h  has an outer edge  162   a - 162   h  around its perimeter. The first terrace  160   a  has two outer edges of similar shape, one edge  162   a  being at the end  150  of the sleeve  26  and the edge, also designated  60   a  in  FIG. 3 , at the juncture of the first terrace  160   a  and the second terrace  160   b.  As shown in  FIGS. 9-10 , the outer edges  162   a - 162   h  of the terraces  160   a - 160   h  lie in planes that are substantially perpendicular to the central longitudinal axis  148  of the central portion  144  of the body. 
     The shapes of the outer edges of representative terraces  160   a,    160   c  and  160   d  are illustrated in  FIGS. 11-13  at  162   a ,  162   c  and  162   d . The outer edge  162   a,    162   c,    162   d  of each terrace  160   a,    160   c,    160   d  at the central portion  144  of the body comprises a pair of diametrically-opposed curved portions  164   a,    164   c,    164   d,    165   a,    165   c,    165   d  having the same radius of curvature. The center of curvature of each of the diametrically-opposed curved portions  164   a,    164   c,    164   d,    165   a,    165   c,    165   d  is along the central longitudinal axis  148  of the body. The diametrically-opposed curved portions  164   a,    164   c,    164   d,    165   a,    165   c,    165   d  define vertices  166   a,    166   c,    166   d,    167   a,    167   c,    167   d  of the outer edges  162   a,    162   c,    162   d  at the central portion  144  of the body. Lines tangent to the vertices  166   a,    166   c,    166   d,    167   a,    167   c,    167   d  of the outer edges  162   a,    162   c,    162   d  of the central portion  144  of the body are illustrated in  FIGS. 10  at  168  and  170 . These tangent lines  168 ,  170  each define an angle of about 2-4 degrees in the illustrated embodiment. The angle may vary depending on whether the sleeve is intended for use on the femoral or tibial side: for a femoral metaphyseal sleeve, for example, the angle may be about 2 degrees; for a tibial metaphyseal sleeve, for example, the angle may be about 4 degrees. Alternatively, a universal sleeve could be provided usable on either the tibial or femoral side. Thus, the diameter of each terrace, that is, the transverse dimension between opposite vertices, decreases between the first end  150  and the second end  152 ; illustratively, diameter d a  shown in  FIG. 11  for the center portion first terrace  160   a  is greater than diameter d c  shown in  FIG. 12  for the center portion of terrace  160   c  that is closer to the second end  152  and diameter d c  of the center portion of terrace  160   c  is greater than diameter d d  shown in  FIG. 13  for the center portion of terrace  160   d  that is still closer to the second end  152  of the sleeve  26 . 
     As can also be seen in  FIGS. 5-7 , the overall length “l” of each terrace  60  is the largest dimension of each terrace  60 . The length of each terrace “l” is greater than its diameter “d”: l a &gt;d a ; l c &gt;d c ; and l d &gt;d d . 
     The outer edge  162  of each terrace  160  at each side wing portion  145 ,  146  of the body comprises a curved portion  172  joined to the diametrically-opposed curved portions  164 ,  165  of the outer edge  162  at the center portion  144 . Examples are illustrated in  FIGS. 11-13  for terraces  160   a,    160   c  and  160   d.  As shown in  FIGS. 11 and 12 , the outer edges of the terraces of the side wing portions  145 ,  146  may each include a pair of spaced opposed straight lines  174   a,    174   c,    176   a,    176   c  connected to the diametrically-opposed curved portions  164   a,    164   c,    165   a,    165   c  and to the curved end segments  172   a,    172   c.  Thus, the curved end segments  172   a,    172   c  may be spaced from the diametrically-opposed curved portions  164   a,    164   c,    165   a,    165   c,  of the outer edges of the central portion  144 . As shown in  FIG. 7 , the curved segments  172   d  of the outer edge  162   d  may be directly connected to the segments  164   d,    165   d  of the outer edge  162   d  at the center portion  144 , with no intervening straight segments. Each curved segment  172  of the outer edge  162  of each terrace  160  has a vertex, illustrated in  FIGS. 11-12  at  178   a ,  178   c ,  178   d.    
     Lines tangent to the junctures of the first side wing portion  145  and the central portion  144  of the body of the sleeve are illustrated in  FIGS. 10  at  180  and  182 . These tangent lines  180 ,  182  each define an angle of about 2-4 degrees with the plane of the central longitudinal axis  148  in the illustrated embodiment. The second side wing portion  146  is similarly shaped. The angle may vary depending on whether the sleeve is intended for use on the femoral or tibial side: for a femoral metaphyseal sleeve, for example, the angle may be about 2 degrees; for a tibial metaphyseal sleeve, for example, the angle may be about 4 degrees. Alternatively, a universal sleeve could be provided usable on either the tibial or femoral side. Thus, the widths of the side portions  145 ,  146  of each terrace, that is, the maximum transverse dimensions of the side wing portions of each terrace, decreases between the first end  150  and the second end  152 ; illustratively, width w a  shown in  FIG. 11  for the center portion first terrace  160   a  is greater than width w c  shown in  FIG. 12  for the center portion of terrace  160   c  that is closer to the second end  152  and width w c  of the center portion of terrace  160   c  is greater than width w d  shown in  FIG. 13  for the center portion of terrace  160   d  that is still closer to the second end  152  of the sleeve. As can also be seen in  FIGS. 11-13 , the width of the side portions  145 ,  146  of each terrace is less than the width of the center portion  144  of each terrace  160 . Each terrace  160 , including its outer edge  162 , is thus indented at the junctions of the diametrically-opposed curved portions  164   a,    164   c,    164   d,    165   a,    165   c,    165   d  of the outer edge  162  at the center portion  144  and the segments of the outer edge at the side wing portion  146 . 
     The overall lengths of each terrace  160  also decrease between the first end  150  and the second end  152 . As shown in  FIG. 9 , lines tangent with the vertices  178 ,  179  (shown in  FIGS. 11-13 ) of the side portions  145 ,  146 , shown at  184  and  185  in  FIG. 9 , may define a variety of angles with the plane of the central longitudinal axis  148 ; the angle would depend, for example, on the size of the implant. Thus, the length, that is the maximum transverse dimension of each terrace  160 , decreases between the first end  150  and the second end  152 ; illustratively, length l a  shown in  FIG. 11  for the center portion of the first terrace  160   a  is greater than length l c  shown in  FIG. 12  for the center portion of terrace  160   c  that is closer to the second end  152  and length l c  of the center portion of terrace  160   c  is greater than length l d  shown in  FIG. 13  for the center portion of terrace  160   d  that is still closer to the second end  152  of the sleeve. As can also be seen in  FIGS. 11-13 , the overall length of each terrace  160  is the largest dimension of each terrace  160 . 
     It should be understood that the above description of sleeve  26  also applies to the double-winged metaphyseal sleeve  40  of  FIG. 2 . 
     It should be understood that a typical modular knee prosthesis kit would include several sizes of metaphyseal sleeves, and may include several sizes of each of the illustrated sleeves  24 ,  26 ,  38 ,  40 . All of such sleeves may have features like those described above. In addition, the sleeves of the kit may have additional features, such as porous coating, for example, to enhance fixation. For example, as disclosed in U.S. Pat. Pub. No. 2005/0107883A1, entitled “Modular Implant System With Fully Porous Coated Sleeve.” It should be understood that the sleeves could also use less porous coating than described in that publication. 
     In the illustrated embodiments, the terraces  60 ,  160  of the sleeves  24 ,  26  provide parallel planar surfaces perpendicular to the axis  48 ,  148 . The distances between these parallel planar surfaces define the height of each terrace  60 ,  160  or step. In the illustrated embodiments, the heights of the terraces are all substantially the same, although it should be understood that any given sleeve could have terraces of different heights, and different sizes of sleeves could have terraces of the same or different heights. 
     As discussed above, the channels  56 ,  156  of the illustrated sleeves  24 ,  26  are tapered to allow for frictional connection to components of the femoral side and tibial side. Examples of assemblies of the modular knee prostheses components of  FIGS. 1-2  are shown in  FIGS. 15-17 . Although not shown, the combined assemblies could also include a single-winged metaphyseal sleeve  24  on one side of the joint motion surface and a double-winged metaphyseal sleeve  26  on the other side of the joint motion surface, or a metaphyseal sleeve of either type  24 ,  26  could be used on only one side of the joint motion surface. Use of these variations will depend on the condition of the patient&#39;s bone. Advantageously, with the modular system of the present invention, the implants can be substantially customized intraoperatively to fit the needs of the individual patient. 
     It should be understood that although the curved segments  64 ,  65 ,  72 ,  164 ,  165 ,  172  of the metaphyseal sleeves illustrated in  FIGS. 5-7  and  11 - 13  comprise circular arcs, the curved segments could have other shapes. For example, the diametrically-opposed curved segments could be elliptical in shape, such as shown in  FIG. 18 . In the embodiment of  FIG. 18 , the same reference numerals are used for elements similar to those of the embodiment of  FIGS. 11-13 , followed by the prime symbol. Thus, the metaphyseal sleeve is designated  26 ′. It should also be understood that not all segments of the outer edges of all the terraces would need to have the same shape. For example, the outer edges of the terraces near end  150 ′ may have elliptical-shaped diametrically-opposed curved segments  164 ′,  165 ′ but the outer edges of the terraces near end  152 ′ may have diametrically-opposed curved segments  164 ,  165  that define circular arcs. Similar variations are possible for the curved edges  172  of the side wing portions  145 ,  146 . 
     If the sleeves on the tibial side are to be used with a tibial tray of the type having keels, then it may be desirable to include reliefs in the terraces at the end nearest the joint motion surface to accommodate the keels. Suitable reliefs allowing for rotational adjustment of the sleeve with respect to the tibial tray are disclosed in U.S. Pat. No. 7,291,174, entitled “Prosthetic Tibial Component with Modular Sleeve,” and may similarly be employed with the sleeves of the present invention. An example of a double-winged metaphyseal sleeve with such reliefs is illustrated in  FIG. 19 . In the embodiment of  FIG. 19 , the same reference numerals are used for elements similar to those of the embodiment of  FIGS. 11-13 , followed by the double prime symbol. Thus, the metaphyseal sleeve is designated  26 ″. The reliefs are designated  190  and  192  in  FIG. 19 . These reliefs  190 ,  192  would extend down through the first few terraces nearest end  150 ″ to accommodate the keels on the tray. Keels are illustrated in  FIG. 2  at  194 ,  196 . 
     The complete kit for the knee prosthesis system will also include instrumentation to be used in preparing the bone to receive the implants. The complete kit of the present invention will preferably include reamers and milling guides for use in preparing the bone to receive a metaphyseal sleeve of the types described above. 
     One of the reamers (not shown) may comprise a standard straight reamer for preparing a straight pilot hole into the intramedullary canal. Such a reamer may be like that disclosed in U.S. Pat. No. 4,790,852. A typical instrument set would include several sizes of such straight reamers. 
     Examples of a second type of reamer are illustrated in  FIGS. 20-21 . The reamer  300  of  FIG. 20  is used to prepare a conical cavity in the bone, aligned with the intramedullary canal, to receive the central portion  44 ,  144  of one of the metaphyseal sleeves  24 ,  26 ,  26 ′,  26 ″. The conical reamer  300  includes a pilot shaft  302  at its distal end  304  for aligning the conical reamer  300  with the intramedullary canal or the pilot hole formed by the straight reamer. The reamer also includes a fluted cutting portion  306  between the pilot shaft  302  and the proximal end  308  of the conical reamer  300 . The fluted cutting portion  306  defines a tapered cutting envelope having a length L. The fluted cutting portion  306  tapers from a maximum diameter toward the proximal end  308  to a minimum diameter at the juncture with the pilot shaft  302 . The length of the fluted cutting portion  306 , shown at  310  in  FIG. 20 , corresponds with the length of a selected metaphyseal sleeve, such as shown at  312  and  314  in  FIGS. 8 and 14 . The maximum diameter of the fluted cutting portion is shown at  316  in  FIG. 20  and the minimum diameter is shown at  318  in  FIG. 20 . The maximum diameter  316  of the fluted cutting portion corresponds with the maximum diameter of the central portion  44 ,  144 ,  144 ′,  144 ″ of the selected metaphyseal sleeve  24 ,  26 ,  26 ′,  26 ″, such as diameter d a  shown in  FIGS. 5 and 11 . The minimum diameter  318  of the fluted cutting portion corresponds with the minimum diameter of the central portion  44 ,  144 ,  144 ′,  144 ″ of the selected metaphyseal sleeve  24 ,  26 ,  26 ′,  26 ″. The taper angle for the fluted cutting portion  306  corresponds with the taper angles defined by the tangent lines  68 ,  70 ,  168 ,  170  shown in  FIGS. 4 and 10 . The proximal end  308  of the conical reamer  300  provides a fitting for connecting the conical reamer to a handle or power source for rotating the conical reamer to prepare the conical cavity. 
       FIG. 21  illustrates a second example of a conical reamer with a longer pilot shaft than in the embodiment of  FIG. 20 . In the embodiment of  FIG. 21 , the same reference numerals are used for elements similar to those of the embodiment of  FIG. 20 , followed by the prime symbol. Thus, the conical reamer is designated  300 ′. 
     Examples of other instruments that would be included in the kit are illustrated in  FIGS. 22-28 . These other instruments include a straight reamer  350 . The straight reamer  350  may be similar to standard reamers with a proximal end  352 , a distal end  354  and a fluted cutting portion  356  between the two ends. The reamer has a central longitudinal axis  358 . 
     The proximal end  352  of the straight reamer  350  provides a fitting for connecting the reamer  350  to a handle or power source for rotating the reamer to prepare the bone cavity. The fluted cutting portion  356  defines a substantially cylindrical cutting envelope. The distal end  354  of the straight reamer  350  comprises a convex spherical surface  360 , best seen in  FIG. 23 . 
     The other instruments that would be included in the kit also include a milling guide. An example of a milling guide that may be used in preparing bone to receive metaphyseal sleeves such as double winged metaphyseal sleeve  26  is illustrated in  FIGS. 22-28 . The illustrated milling guide  400  comprises a template member  402 , a base  404  and a pair of side walls  406 ,  408  connecting the template member  402  and the base  404 . The template member  402  has an inner surface  410  defining an elongate milling guide opening  412 . The elongate milling guide opening  412  is shaped to correspond with the shape defined by the two side wing portions  145 ,  145 ′,  145 ″,  146 ,  146 ′,  146 ″ of the double winged metaphyseal sleeve  26 ,  26 ′,  26 ″. 
     As illustrated in  FIG. 24 , the elongate milling guide opening  412  has an edge  418  including two parallel straight portions  420 ,  422  and two curved end portions  424 ,  426 . The two curved end portions  424 ,  426  connect the two parallel straight portions  420 ,  422 . Each curved end portion  424 ,  426  has a vertex  428 ,  430 . The maximum first transverse dimension  432  of the elongate milling guide opening  412  is at the vertices  428 ,  430  of the curved end portions  424 ,  426 . The second transverse dimension  434  of the elongate milling guide opening  412  is the distance between the two parallel straight portions  420 ,  422 , and is less than the first transverse dimension  432 . A central longitudinal axis  436  extends from the center  437  of the elongate milling guide opening  412  and through the center of the spherical depression of the base. The vertices  428 ,  430  of the curved end portions  424 ,  426  of the elongate milling guide opening  412  and the central longitudinal axis  436  of the milling guide lie in a plane. 
     The base  404  is spaced from the template member  402  and includes a concave spherical depression  438  aligned with the milling guide opening  412  along the central longitudinal axis  436 . As illustrated in  FIG. 25 , the concave spherical depression  438  of the base  404  of the milling guide  400  has a perimeter  440  and opposed vertices  442 ,  444  lying in the same plane as the vertices  428 ,  430  of the curved end portions  424 ,  426  of the elongate milling guide opening  412  and the longitudinal axis  436  of the milling guide. A line from each vertex  428 ,  430  of the of the curved end portions  424 ,  426  of the elongate milling guide opening  412  to the nearest vertex  442 ,  444  of the perimeter  440  of the concave spherical depression  438  of the base  404  defines an acute angle with the longitudinal axis  436  of the milling guide  400 . 
     The concave spherical depression  438  is sized and shaped to receive the convex spherical surface  360  of the straight reamer  350  and allow the straight reamer  350  to be pivoted about the convex spherical surface  360  as illustrated in  FIGS. 26-28 . As the straight reamer  350  is so pivoted in depression  438  about convex spherical surface  360 , the fluted cutting portion  356  of the reamer  350  cuts a concavity in the bone corresponding with a shape defined by the envelope of the side wing portions  145 ,  145 ′,  145 ″,  146 ,  146 ′,  146 ″ of the metaphyseal sleeve  26 ,  26 ′,  26 ″. 
     As shown in  FIGS. 22-23 , the base  404  of the milling guide  400  includes a threaded male member  446  extending distally away from the base  404  along the central longitudinal axis  436 . The threaded male member  446  is received in a female threaded bore  448  in a stem trial  450 . When assembled, as shown in  FIGS. 26-28 , the stem trial  450  extends distally from the base  404  along the central longitudinal axis  436  of the milling guide  400 . The stem trial  450  is sized and shaped to be received in the bore created in the area of the intramedullary canal by the first straight reamer. Thus, the concavity created by the reamer  350  will be centered on and aligned with the intramedullary canal. 
     The side walls  406 ,  408  of the milling guide  400  taper from a maximum width at the juncture with the template member  402  to a minimum width at the juncture with the base  404 . The maximum width is shown at  461  and the minimum width is shown at  463  in  FIG. 27 . The overall length of the milling guide between the distal side of the template member  402  and the concave spherical depression  438  is shown at  465  in  FIG. 27 . These dimensions  461 ,  463  and  465  correspond generally with the dimensions  310 ,  310 ′,  316 ,  316 ′,  318 ,  318 ′ (see  FIGS. 20-21 ) of the fluted cutting portion  306 ,  306 ′ of the conical reamer  300 ,  300 ′. Thus, the side walls  406 ,  408  and base  404  of the milling guide  400  should fit within the conical concavity created by the conical reamer. 
     The instrument set may also include a handle  470 , shown in  FIGS. 22-23  and  26 - 28 . The handle  470  and the template member  402  may include complementary mounting members and apertures, shown generally at  472  and  474  in  FIGS. 22-23 . In the illustrated embodiment, two sets of apertures  474  are provided on the template member  402  to allow the handle to be attached to either the medial or lateral side of the template member. The complementary mounting members and apertures may include features described in U.S. Pat. No. 5,733,290, entitled “Quick-Release Tibial Alignment Handle”, the disclosure of which is incorporated by reference herein in its entirety. 
     It will be appreciated that, like the implant components of the knee prosthesis kit, the above-described instruments, including the reamers and the milling guide, will typically be provided in a variety of sizes corresponding with the sizes of the metaphyseal sleeve implant components. 
     In use, the surgeon will typically make initial bone cuts to the tibia and femur and determine whether the condition of the patient&#39;s bone would make it desirable to use a metaphyseal sleeve component. If so, the surgeon will determine whether the bone condition makes a single-wing metaphyseal sleeve or a double-wing metaphyseal sleeve is desirable and determine the appropriate size of sleeve. 
     On the tibial side, the surgeon would first use a straight reamer to prepare a pilot hole aligned with and extending into the intramedullary canal of the bone. Next, based on the diameter of the central portion  44 ,  144  of the selected metaphyseal sleeve  24 ,  26 ,  26 ′,  26 ″, the surgeon selects an appropriate sized conical reamer  300 . The pilot shaft  302  of the conical reamer  300  is inserted into the pilot hole prepared with the straight reamer, and the conical reamer  300  is rotated and moved distally so that the fluted cutting portion  306  creates a conical concavity in the bone. This conical concavity will correspond in size and shape with the size and shape of the central portion  44 ,  144  of the metaphyseal sleeve  24 ,  26 ,  26 ′,  26 ″, and will be aligned with the intramedullary canal. The conical reamer is removed. 
     The surgeon would then, assemble the appropriately-sized milling guide  400  with the appropriately sized stem trial  450 . The stem trial portion  450  is inserted into the concavity created by the reaming steps and the milling guide  400  is moved distally so that the base  404  and side walls  406 ,  408  are received in the concavity. A straight reamer  350  is inserted into the milling guide opening  412  and moved distally until the convex spherical surface  360  is received in the concave spherical depression  438  of the base  404  of the milling guide  400 . The straight reamer  350  is then rotated about its central longitudinal axis  358  while it is pivoted about the convex spherical surface  360  in the depression  438 .  FIGS. 27 and 28  illustrate the straight reamer  350  pivoted as described above. If the defect is non-centralized and the surgeon has selected a single-wing metaphyseal sleeve, the surgeon would pivot the straight reamer  350  either medially or laterally. If the defect is centralized and the surgeon has selected a double-wing metaphyseal sleeve, the straight reamer  350  would be pivoted both medially and laterally. After the straight reamer  350  has been so rotated and pivoted and moved along the edge  418  of the milling guide opening  412 , a concavity should be created that is sized and shaped to receive one of the metaphyseal implant components  24 ,  26 ,  26 ′,  26 ″,  38 ,  40 . 
     A similar procedure would be followed on the femoral side. As illustrated in  FIG. 29 , the milling guide  400  can be used while a separate femoral cutting block  500  is in place on the distal femur. 
     It should be understood that the same instruments and a similar procedure can be used when the metaphyseal implant is a single-winged sleeve such as sleeve  24 . In such a case, instead of pivoting the straight reamer  350  along the entire length of the milling guide opening  412 , the straight reamer  350  would only be pivoted along a portion of the length of the milling guide opening. Alternatively, a separate set of milling guides with milling guide openings sized and shaped to correspond with the size and shape of the proximal ends of the single winged sleeves  24  could be used. 
     There are a plurality of advantages of the concepts of the present disclosure arising from the various features of the systems described herein. For example, since the conical reamer and milling guide are positioned to be aligned with the intramedullary canal, the concavity created should be properly positioned regardless of whether the metaphyseal bone is harder in places or not. Accordingly, the metaphyseal implant should be properly positioned, rather than positioned too anterior or too posterior, avoiding flexion gaps and problematic joint balancing. 
     It will be noted that alternative embodiments of each of the systems 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 a system that incorporate one or more of the features of the present disclosure and fall within the spirit and scope of the invention as defined by the appended claims.