Abstract:
Disclosed herein are systems and methods for filling bone voids which may be present at the time of surgery. The systems disclosed herein generally include a baseplate component, a spacer component, and void filler component. The spacer component is generally assembled to the baseplate component with a taper or press-fit, for example, in one of a plurality of selected axial positions. The void filler component is then generally assembled to the spacer component in one of a plurality of selected axial positions. The void filler component preferably has an outer surface with portions having varying diameters such that the outer surface thereof can be received within a canal of a bone and contact the bone forming the canal at different locations in order to aid in stabilizing the assembled components in the canal.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of the filing date of U.S. Provisional Patent Application No. 61/364,070 filed Jul. 14, 2010, the disclosure of which is hereby incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to joint prosthesis systems for filling voids in bones of a patient, and in particular it relates to assembling together the components of a joint prosthesis system in order fill a void in bone as needed and to properly position a support surface of the joint prosthesis system for receiving a corresponding prosthesis. 
     BACKGROUND OF THE INVENTION 
     Joint replacement surgery is a common orthopedic procedure for joint such as the shoulder, hip, knee, ankle and wrist. Prior to implanting prosthetic components in a joint of a patient, a surgeon generally has to resect at least a portion of the patient&#39;s native bone in order to create a recess or cavity for receiving at least a portion of the prosthetic components being implanted. During the process of resecting bone, a surgeon generally only resects the amount of bone that is needed in order to implant the prosthetic components in the joint replacement surgery properly. Once bone is resected from a joint, it generally can no longer be replaced with native bone. Thus, the surgeon attempts to maintain as much native structural integrity of the joint as he or she can during the resection process. 
     An issue generally encountered by surgeons replacing joints is the loss of native bone near the joint being replaced. Defects in a bone adjacent a joint, such as the hip or knee, can occur due to wear and arthritis of the joint, congenital deformity, and following the removal of a failed prosthetic component. When prosthetic components fail for any one of a variety of reasons, a revision procedure is often necessary. When the failed prosthetic component or components are removed from the joint during a revision procedure, it is common for there to have been further native bone loss in the area adjacent the originally implant position of the prosthetic component or components due to movement of the component or components after implantation or even degeneration or further degeneration of the bone. 
     The use of bone graft or cement is known to position prosthetic components with respect to bone or to fill voids in bone. Bone graft and cement is also known to stabilize the position and location of prosthetic components in bone. While bone graft or cement is widely used in orthopedic surgery, in cases where there is a large void in bone it is preferable to implant a solid structure in bone for proper support of a prosthetic component in the bone. It is also known to attach augments and stems to prosthetic components in order to aid in the stabilization of prosthetic components in bone. While such augments and stems are used, the available augments and stems that can be attached to prosthetic components generally do not fill the void sufficiently to stabilize the prosthetic components effectively in bone. 
     There is a need for a joint prosthesis system that optimizes contact with native bone and with minimal removal of native bone and that encourages bone ingrowth and attachment over as large a surface area as possible. There is also a need for giving surgeons the opportunity to attach void fillers to prosthetic components in a plurality of different positions and orientations in order to fill voids sufficiently to stabilize the prosthetic components effectively in bone. 
     BRIEF SUMMARY OF THE INVENTION 
     A first aspect of the present invention is a joint prosthesis system comprising a baseplate component, a spacer component, and a void filler component. The baseplate component preferably has a top surface and a bottom surface, the bottom surface having a stem portion protruding outwardly therefrom, the stem portion having at least one rib located along at least a portion of a length thereof. The spacer component preferably has a top surface, a bottom surface, an inner surface, an outer surface, and an aperture extending through the top and bottom surfaces thereof, the inner surface having at least one recess formed therein and the outer surface having at least one protrusion extending outwardly therefrom. The void filler component preferably has a top surface, a bottom surface, an inner surface, an outer surface, and an aperture extending through the top and bottom surfaces thereof, the inner surface having at least one recess formed therein. 
     In one embodiment of this first aspect of the present invention, the spacer component is preferably coupled to the baseplate component when the aperture of the spacer component receives the stem portion of the baseplate component and the at least one rib of the stem portion is located in the at least one recess of the spacer component. The void filler component is preferably coupled to the spacer component when the aperture of the void filler component receives the outer surface of the spacer component and the at least one protrusion of the spacer component is located in the at least one recess of the void filler component. 
     In one embodiment of this first aspect of the present invention, the baseplate component is a tibial component. Preferably, the upper surface of the baseplate component is a flat surface adapted to receive a tibial insert having an upper surface adapted for engaging an articulating implant. 
     In another embodiment, the baseplate component is a femoral component. 
     In yet another embodiment of this first aspect of the present invention, the stem portion of the baseplate has a tapered outer surface. Preferably, a bottom surface of the stem portion is adapted to receive stem adapter therein. The stem adapter may be coupled to the stem portion by a locknut. In one embodiment, a second stem portion may be coupled to the stem adapted in order to lengthen the joint prosthesis system. 
     In still yet another embodiment, first and second ribs preferably extend outwardly from the stem portion of the baseplate component, wherein each rib extends along at least a portion of a length of the outer surface of the stem portion and are located at different locations around a circumference thereof. 
     In still yet another embodiment of this first aspect of the present invention, first and second keels preferably extend outwardly from the stem portion of the baseplate component, wherein each rib extends along at least a portion of a length of the outer surface of the stem portion and are located at different locations around a circumference thereof. 
     In still yet another embodiment, the spacer component includes an aperture extending through the outer and inner surfaces thereof forming a first space and a second space located around a circumference of the spacer component such that a portion of the first keel can be received in the first space and a portion of the second keel can be received in the second space when the spacer component is coupled to the stem portion of the baseplate component. 
     In another embodiment, the inner surface of the spacer component may include two or three recesses therein. In other embodiment, the inner surface of the spacer component may include more than three recesses therein. Preferably, the recesses are located approximately 30° apart from one another in the inner surface of the spacer component. In one embodiment, the recesses may be located approximately 5° apart and in other embodiments may be located approximately 85° degrees apart or may be located any number of degrees between 5° and 85° degrees apart. 
     In one embodiment, the void filler component includes a plurality of sections having differing diameters. The diameters of the plurality of sections preferably decrease from the top surface to the bottom surface of the void filler component. 
     In another embodiment, the inner surface of the void filler component may include two or three recesses therein. In other embodiment, the inner surface of the void filler component may include more than three recesses therein. Preferably, the recesses are located approximately 30° apart from one another in the inner surface of the void filler component. In one embodiment, the recesses may be located approximately 5° apart and in other embodiments may be located approximately 85° degrees apart or may be located any number of degrees between 5° and 85° degrees apart. 
     In one embodiment of this first aspect of the present invention, the stem portion of the baseplate component has a longitudinal axis and the aperture of the spacer component has a longitudinal axis and when the spacer component is coupled to the stem portion of the baseplate component the longitudinal axes thereof are coaxial. 
     In another embodiment, the stem portion of the baseplate component has a longitudinal axis and the aperture of the spacer component has a longitudinal axis and when the spacer component is coupled to the stem portion of the baseplate component the longitudinal axes thereof are parallel and offset from one another. 
     In one embodiment, the aperture of the void filler component has a longitudinal axis and when the void filler component is coupled to the spacer component the longitudinal axes thereof are coaxial. 
     In another embodiment, the aperture of the void filler component has a longitudinal axis and when the void filler component is coupled to the spacer component the longitudinal axes thereof are parallel and offset from one another. 
     In one embodiment, the aperture of the void filler component has a longitudinal axis and when the void filler component is coupled to the spacer component the longitudinal axes thereof are coaxial. 
     In another embodiment, the aperture of the void filler component has a longitudinal axis and when the void filler component is coupled to the spacer component the longitudinal axes thereof are parallel and offset from one another. 
     A second aspect of the present invention is a method of stabilizing a joint prosthesis system including a baseplate component, a spacer component, and a void filler component in a canal of a bone. The method preferably includes assembling at least one of a plurality of recesses of the spacer component to at least one of a plurality of ribs of a stem portion protruding outwardly from a bottom surface of the baseplate component and assembling at least one of a plurality of recesses of the void filler component to at least one of a plurality of protrusions of the spacer component. The method preferably further includes implanting the assembled baseplate, spacer and void filler components into the canal of the bone. 
     In one embodiment of this second aspect of the present invention, the plurality of recesses are located about a circumference of an inner surface of the spacer component. Preferably, the plurality of ribs are located along at least a portion of a length of the stem portion of the baseplate component. Preferably, the plurality of protrusions are located along at least a portion of a length of an outer surface of the spacer component. 
     In another embodiment of this second aspect of the present invention, the assembled baseplate, spacer and void filler components are implanted into the canal of the bone such that at least a portion of an outside surface of the void filler component contacts the bone forming the canal. 
     In another embodiment, the void filler may be implanted into a bone canal and be positioned within the canal and a spacer component assembled to a baseplate component may then be received within the aperture of the void filler component at a desired location. 
     In yet another embodiment, the engagement of the spacer component to the baseplate component prohibits axial rotation of the spacer and baseplate components with respect to one another. Preferably, the axial rotation is prohibited along a longitudinal axis of the joint prosthesis system. 
     In yet another embodiment, engagement of the void filler component to the spacer component prohibits axial rotation of the void filler and spacer components with respect to one another. Preferably, the axial rotation is prohibited along a longitudinal axis of the joint prosthesis system. 
     In another aspect of the present invention a void filler may be oriented at one of multiple possible angles with respect to a tibial prosthesis during implantation of the components into a bone canal. This capability for multiple implant angles is preferable because tibial voids can occur at a range of orientations and this capability allows the void filler to be implanted with minimal removal of native bone. 
     In one embodiment, the void filler may be oriented with respect to the tibial prosthesis at one of multiple possible angles using a spline-and-slot arrangement. The advantage of this design is that, in comparison to fixing the rotation by impacting a Morse taper feature, this method is less sensitive to user technique and strength of force application. 
     In another embodiment, fine angular adjustments, such as 3 degrees, may be made between the rotational orientation of the void filler and tibial prosthesis. The combination of fine adjustments and robust components is achieved by having multiple attachment orientations for each of the baseplate, spacer, and void filler components. 
     In another embodiment, revisions to the angular orientation of the spacer component and the baseplate component with respect to the void filler component can be made without the need to remove the void filler component from its implanted position within a bone canal in bone. 
     One embodiment of the present invention is the splined attachment method, which permits rotational fixation of the void filler at multiple orientations without requiring the impaction of a tapered joint. 
     Another embodiment of the present invention is the use of two splined attachment joints, with a relatively small difference in angular spacing of the two attachment joints, so that splined features can be large (and thus mechanically strong) yet still provide for fine rotational adjustment. 
     Another embodiment of the present invention is the use of a splined spacer component between a baseplate component and a void filler component, in which the splined spacer component is available in multiple versions with different relative rotation between internal and external fixation features, so that changing spacer components can provide a different range of relative angles between the void filler component and baseplate component. 
     Another embodiment of the present invention is the use of a spacer component between a baseplate component and a void filler component, in which the spacer component has internal and external fixation features which are relatively either concentric or eccentric, so that changing spacer components can provide a desired positional offset between the void filler component and the baseplate component. 
     Another embodiment of the present invention uses the combination of baseplate component, spacer component, void filler component, and an offset stem adapter. A stem portion of the offset stem adapter preferably has an axis that does not need to coincide with an axis of the assembled baseplate, spacer and void filler components. This feature allows better anatomic fits for both the void filler component and the stem portion, and minimizes the need to remove sound bone. 
     Another embodiment of the present invention is the combination of a baseplate component, a spacer component, a void filler component, and an offset stem adapter. In this embodiment, the baseplate component, the spacer component, and the offset stem adapter may be removed while leaving the void filler component implanted. The ability to remove (revise) components separately preferably makes the revision process easier for the surgeon. 
    
    
     
       DESCRIPTION OF THE FIGURES 
       A more complete appreciation of the subject matter of the present invention and the various advantages thereof can be realized by reference to the following detailed description in which reference is made to the accompanying drawings in which: 
         FIG. 1  is an isometric view of an exemplary bone having a canal therein. 
         FIG. 2  is an exploded isometric view of one embodiment of a joint prosthesis system of the present invention. 
         FIG. 3  is an assembled isometric view of the joint prosthesis system shown in  FIG. 2 . 
         FIG. 4  is a top isometric view of one embodiment of a baseplate component and a spacer component of the present invention showing a rib of the baseplate component aligned for engagement with a recess of the spacer component. 
         FIG. 5  is a bottom isometric view of the spacer component shown in  FIG. 4 . 
         FIG. 6  is a bottom isometric view showing the spacer component of  FIG. 5  in a position just prior to being assembled to a void filler component. 
         FIG. 7  is a bottom view of one embodiment of a spacer component assembled to a baseplate component. 
         FIG. 8  is a bottom view of the assembled spacer and baseplate components shown in  FIG. 7  including a void filler component assembled to the assembled spacer and baseplate components with a horizontal axis of the void filler component being parallel to a horizontal axis of the baseplate component. 
         FIG. 9  is a bottom assembled view of the baseplate, spacer, and void filler components shown in  FIG. 8  with a horizontal axis of the void filler component being angled with respect to the horizontal axis of the baseplate component. 
         FIG. 10  is a bottom assembled view of the baseplate, spacer, and void filler components shown in  FIG. 9  with a horizontal axis of the void filler component being angled with respect to the horizontal axis of the baseplate component in an alternate configuration as shown in  FIG. 9 . 
         FIG. 11  is an isometric view of one embodiment of assembled baseplate, spacer, adapter and stem components showing a void filler component prior to being assembled to the assembled components. 
         FIG. 12  is a side view of the assembled baseplate, spacer, adapter and stem components shown in  FIG. 11 . 
         FIG. 13  shows on the left-hand side a bottom view of one embodiment of a spacer component assembled to a baseplate component and on the right-hand side a bottom view of the spacer component being angled with respect to the baseplate component. 
         FIG. 14  shows on the left-hand side a bottom view of the assembled spacer and baseplate components shown on the left-hand side of  FIG. 13  including a void filler component assembled to the assembled spacer and baseplate components and on the right-hand side is a bottom assembled view of the baseplate, spacer, and void filler components with the void filler component being angled with respect to the baseplate component. 
         FIG. 15  shows an isometric view of one embodiment of assembled baseplate, spacer and void filler components with the spacer component having a plurality of protrusions engaged to a plurality of recesses of the void filler component. 
         FIG. 16  shows an isometric view of one embodiment of a spacer component prior to being assembled to a baseplate component, the spacer component having an outer surface configured as a twelve-sided polygon. 
     
    
    
     DETAILED DESCRIPTION 
     As used herein, when referring to the drill guides of the present invention, the term “proximal” means closer to the surgeon or in a direction toward the surgeon and the term “distal” means more distant from the surgeon or in a direction away from the surgeon. The term “anterior” means towards the front part of the body or the face and the term “posterior” means towards the back of the body. The term “medial” means toward the midline of the body and the term “lateral” means away from the midline of the body. 
       FIG. 1  shows a bone  180  having a canal  190 . Bone  180  may be any type of bone, but as shown it represents a tibia of a patient. Canal  190  can be formed through a reaming procedure or may be present due to a previous joint replacement procedure in which a tibial prosthesis was implanted in canal  190  and has now been removed leaving a void in bone  180 . Canal  190  can also be present because of bone degeneration such as osteoporosis. The present invention includes systems and methods for implanting a joint prosthesis in order fill a void in bone as needed, such as canal  190 , and to properly position a support surface of the joint prosthesis for receiving a corresponding prosthesis such as a tibial or femoral insert. 
     Referring to  FIGS. 2-14 , there is shown an embodiment of a joint prosthesis system of the present invention designated generally by reference numeral  100 . As shown in those figures, system  100  includes a baseplate component  110 , a spacer component  120 , a void filler component  130 , an adapter component  140 , a locknut, a stem component  160  and an insert component  170 . 
     Baseplate component  110  preferably has a top surface  112  and a bottom surface  114 , the bottom surface having a stem portion  116  protruding outwardly therefrom, the stem portion having at least one rib  210  located along at least a portion of a length thereof. First and second keels  117 ,  119  preferably extend outwardly from the stem portion  116  of the baseplate component  110 , wherein each rib  210  extends along at least a portion of a length of the outer surface of the stem portion and are located at different locations around a circumference thereof. 
     Spacer component  120  preferably has a top surface  122 , a bottom surface  124 , an inner surface  126 , an outer surface  128 , and an aperture  129  extending through the top and bottom surfaces  124 ,  122  thereof. Inner surface  126  preferably has at least one recess  200  formed therein and the outer surface  128  preferably has at least one spline or protrusion  220  extending outwardly therefrom. Spacer component  120  preferably includes an aperture  125  extending through the inner and outer surfaces  126 ,  128  thereof forming a first space  127   a  and a second space  127   b  located around a circumference of the spacer component such that a portion of the first keel  117  can be received in the first space  127   a  and a portion of the second keel  119  can be received in the second space  127   b  when the spacer component  120  is coupled to the stem portion  116  of the baseplate component  110 . 
     Void filler component  130  preferably has a top surface  132 , a bottom surface  134 , an inner surface  136 , an outer surface  138 , and an aperture  139  extending through the top and bottom surfaces  132 ,  134  thereof, the inner surface  136  having a plurality of recesses  230 ,  240 ,  250  formed therein. Outer surface  138  of void filler component preferably includes a plurality of sections having different diameters. Preferably, the diameters of the sections decrease form the top surface  132  to the bottom surface  134 . Examples of properties of void filler component  130  is aiding in carrying patient weight by distributing the weight over the remaining bone, such as bone  180 ; and providing stability by helping to position the baseplate component  110  and preventing undesired rotation thereof. 
     Spacer component  120  is coupled to baseplate component  110  when aperture  129  of the spacer component  120  receives the stem portion  116  of the baseplate component  110  and the at least one rib  210  of the stem portion  116  is located in the at least one recess  200  of the spacer component  120 . 
     Void filler component  130  is coupled to the spacer component  120  when the aperture  139  of the void filler component  130  receives the outer surface  128  of the spacer component  120  and the at least one protrusion  220  of the spacer component  120  is located in the at least one recess  230 ,  240 ,  250  of the void filler component  130 . Void filler component  130  preferably slides over spacer component  120  and provides support for the baseplate component  110  in joint prosthesis system  100 . 
     Adapter component  140  preferably fastens to stem portion  116  of baseplate component  110  with locknut  150 . Stem component  160  preferably fastens into adapter component  140 . Insert component  170  preferably rests on top surface  112  of baseplate component  110 . In an alternative embodiment, stem component  160  could connect directly to stem portion  116 . 
     Spacer component  120  preferably includes a longitudinal axis  320  passing through the center of spacer component  120  in a superior to inferior direction or vice versa. Alternatively, spacer component may be offset such that longitudinal axis  320  does not pass through the center of spacer component  120 . Void filler component  130  preferably includes a longitudinal axis  360  passing through the center of void filler component  130  in a superior to inferior direction or vice versa. Alternatively, void filler component  130  may be offset such that longitudinal axis  360  does not pass through the center of void filler component  130 . 
     As shown in  FIG. 4 , the spacer component  120  includes three orientation slots or recesses  200  to define its angular orientation as it is installed on the baseplate component  110 . These three slots  200  are angularly spaced approximately 30 degrees apart from the longitudinal axis  320  of the spacer component  120 . During assembly, one of these orientation slots or recesses  200  is mated with a indexing boss or rib  121  on the baseplate component  110 . While this embodiment shows three orientation slots, which are spaced approximately 30 degrees apart, other embodiments may contain a different number of slots and may be spaced different degrees apart. 
     As shown in  FIG. 5 , the spacer component  120  includes external spline features or protrusions  220 . As shown in  FIG. 6 , these features mate with corresponding slots or recess pairs  230 ,  240 ,  250  in the void filler component  130 . The recess pairs  230 ,  240 ,  250  provide different installation angles between the spacer component  120  and the void filler component  130 . Slot pairs  240  and  250  are preferably oriented 27 degrees clockwise and counterclockwise, respectively, from the central pair of slots  230 . Slot pairs  240  and  250  may be oriented between 5 and 85 degrees clockwise and counterclockwise, respectively, from central pair of slots  230 . While this embodiment shows three recess pairs spaced apart approximately 27 degrees, other embodiments may contain a different number of recess pairs and may be spaced different degrees apart. 
       FIG. 7  shows a bottom view of the baseplate component  110  with the spacer component  120  installed with the central slot of the three orientation slots  200  (not shown) mated with the indexing boss or rib  210  (not shown) of the baseplate component  110 .  FIG. 8  shows the void filler component  130  installed with its central slots  230  mating with the external spline features  220  of the spacer component  120 . As can be seen in  FIG. 8 , a horizontal axis  260  of the void filler component  130  is aligned parallel with a horizontal axis  270  of the baseplate component  110 . 
       FIG. 9  shows the baseplate component  110  installed or assembled with the spacer component  120  with the left-most slot of its three orientation slots  200  (not shown) mated with the indexing boss or rib  210  (not shown) of the baseplate component  110 . This view also shows the void filler component  130  installed with alternate slots  240  mating with the external spline features  220  of the spacer component  120 . In this assembly orientation, the horizontal axis  260  of the void filler component  130  preferably makes a 3 degree clockwise angle to the horizontal axis  270  of the baseplate component  110  (3 degrees being the difference between the 30 degree angular spacing on the spacer component  120  and the 27 degree spacing on the void filler component  130 . 
       FIG. 10  shows the baseplate component  110  installed with the spacer component  120  with the right-most slot of its three orientation slots  200  (not shown) mated with the indexing boss  210  (not shown) of the baseplate component  110 . This view also shows the void filler component  130  installed with alternate slots  250  mating with the external spline features  220  of the spacer component  120 . In this assembly orientation, the horizontal axis  260  of the void filler component  130  makes a 3 degree counter-clockwise angle to the horizontal axis  270  of the baseplate component  110 . 
       FIG. 11  shows one embodiment of a final assembly of the joint prosthesis system  100 , with void filler component  130  shown exploded. Once the spacer component  120  is in place on the baseplate component  110  it is held in place by preferably screwing down the adapter component  140  and tightening the locknut  150 . Typically, the stem component  160  will also be installed at this time. 
     Void filler component  130  can be removed and/or installed while the baseplate component  110 , the adapter component  140 , the locknut  150  and the stem component  160  are attached to each other. This is a particular advantage if the joint prosthesis system  100  needs to be later removed from the patient, since the baseplate component  110  along with the adapter component  140 , the locknut  150  and the stem component  160  can be removed from the patient as one assembly without needing to remove the void filler component  130  at the same time. 
     One design detail shown in  FIG. 12  is that the adapter component  140  is optionally offset such that a longitudinal axis  290  thereof is offset from a longitudinal axis  280  of baseplate component  110 . This offset feature allows optimum coverage of the baseplate component  110  on the resected bone  180 , and also ensures that the stem component  160  can be implanted down canal  190  of bone  180 . 
       FIGS. 8 ,  9 , and  10  show that this particular combination of components will provide relative rotation between the baseplate component  110  and void filler component  130  of 0°, +3°, and −3°. In instances where more rotation is necessary, the preferred method is to use a spacer component  120  for which the external spline features  220  are at a different angular orientation with respect to the orientation slots  200 . 
       FIGS. 13 and 14  show side-by-side views of (left) the previously shown −3°/0°/+3° spacer component  120 , and (right) a spacer component  120  which will orient the void filler component  130  at −12°/−9°/−6°. Similarly, a spacer component  120  can have external spline features which will orient the void filler component  130  at +6°/+9°/+12°. While the external spline features may orient the void filler component at the above mentioned degrees, other embodiments may include a different number of splines and may orient the void filler component at different degrees. 
     In another embodiment, splines or protrusions (or other rotation prevention features) are located on one interface only.  FIG. 15  shows an example of such a design in which finer splines  220  are used on only the interface between the spacer component  120  and the void filler component  130 . As shown in  FIG. 15 , multiple splined features  220  are in contact with recesses on void filler component  130 . This version of the design has the same angular adjustment capability as described with respect to the embodiment shown in  FIGS. 2-14 , with the multiple splined features  220  adding to the torsional strength of the assembled joint prosthesis. 
     In other embodiments, rotation control is provided by features other than splines. For example, semicircular protrusions on spacer component  120  may mate with semicircular clearances in the void filler component  130 . As another example, the spacer component  120  can have an outer surface polygonal in shape, with a matching shape to an aperture in the void filler component.  FIG. 16  shows a 12-sided polygon for this interface, which gives the same 30 degree angular rotation between locking positions that can be seen in the embodiment shown in  FIG. 6 . Many other shapes could be used to control rotation between the components of the prosthetic knee. 
     Other embodiments preferably include the use of different materials and/or coatings for each of the components of the system. In addition to the titanium alloy used in the preferred embodiment, cobalt chrome alloys, Nitinol, Stainless Steel, PEEK, and other metals, polymers or composites could be used in embodiments of this invention. Also, surface treatments to improve wear and/or galling resistance can be added. One example of this type of coating is titanium nitride. Other coatings preferably have the same beneficial effect. Surface treatments to encourage bony attachment such as porous coatings, hydroxyapatite, and TCP, for example, may be included in the design. Also, surface treatments or additives in one or more of the materials used for the components in the systems described herein could be used to provide beneficial effects such as anti-microbial, analgesic or anti-inflammatory properties. 
     Spacer component  120  and void filler component  130  are both preferably made of a titanium alloy. Other metals (such as a cobalt-chromium alloy), polymer, or composite materials could also be used. 
     The embodiments of the joint prosthesis system described herein are shown with respect to the tibial portion of a prosthetic knee. The present invention is equally applicable for use in both the femoral and tibial portions of a prosthetic knee, as well as in other joints such as the shoulder, hip, elbow, and wrist, for example. 
     Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims.