Abstract:
Devices, apparatus, and systems for replacing at least some of the functionality of the natural hip joint and associated methods of implantation are disclosed. In one aspect a prosthetic acetabular cup system is provided. The system includes a metal shell comprising an outer surface for securely engaging a prepared portion of an acetabulum, an opposing inner surface, and at least one snap-fit engagement feature associated with the inner surface. The metal shell has a thickness less than about 1.0 mm between the outer surface and the inner surface. The system also includes a pliable articulating component having an outer surface including at least one snap-fit engagement feature sized and shaped to snap-fittingly engage the at least one snap-fit engagement feature of the metal shell. The pliable articulating component also includes an inner surface for articulatingly receiving a femoral head. The second component has a thickness less than about 3.0 mm.

Description:
PRIORITY 
       [0001]    This application is a United States national phase application of co-pending international patent application number PCT/US2008/064352, filed May 21, 2008, which claims priority to U.S. Provisional patent application No. 60/946,522, filed Jun. 27, 2007 and U.S. Provisional patent application No. 60/939,327, filed May 21, 2007, the disclosures of which are incorporated herein by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    Embodiments of the present disclosure relate generally to medical prosthetic devices, including prosthetic hip joint components, and associated methods of implantation and treatment. 
       BACKGROUND 
       [0003]    The present disclosure relates to devices, apparatus, and systems for replacing at least some of the functionality of the natural hip joint and methods of implanting such devices, apparatus, and systems. The natural hip joint is a ball-and-socket joint formed by the articulating interaction of the rounded head of the femur with the acetabulum of the pelvis. The articulating surfaces of both the head of the femur and the acetabulum are covered with articular cartilage. Various conditions can cause damage to the hip joint resulting in debilitating pain, arthritis, and/or limited mobility. In some instances, hip arthroplasty has been used to treat such conditions. 
         [0004]    Although existing devices and methods associated with prosthetic hip joint components have been adequate in some respects, they have not been satisfactory in all respects. The present disclosure overcomes one or more of the shortcomings of the existing devices and methods. 
       SUMMARY 
       [0005]    In one embodiment, a prosthetic device for positioning within a hip joint is disclosed. 
         [0006]    In some instances, the prosthetic device is comprised of two components: a thin metal shell and a pliable articulating component. In some embodiments, the pliable articulating component is made of a pliable structural material validated for medical devices used in vivo and having mechanical properties characterized by a non-linear stress-strain relationship defined by a polynomial mathematical curve having more than two coefficients, such as the Mooney Rivlin coefficients. In some instances, the material has strength and/or elasticity substantially similar to human cartilage. In some instances, the material is a polyurethane based material, which may be polycarbonate polyurethane in some embodiments, and may be a Bionate Polyurethane in some embodiments. The material of the metal shell and the pliable articulating component operate together to dissipate bone stress and strain associated with the hip joint during the life of the device to help preserve and/or regenerate bone strength. 
         [0007]    In another embodiment, a prosthetic device for implantation into a hip joint is disclosed. The prosthetic device includes a first component comprising an outer surface for securely engaging a bony portion of an acetabulum and an opposing inner surface for receiving a second component. The outer surface has a generally semi-spherical profile. The inner surface also has a generally semi-spherical profile concentric with the outer surface. The first component has a substantially uniform thickness less than about 1.0 mm between the outer surface and the inner surface. The first component also includes at least one annular protrusion extending circumferentially from the inner surface. The at least one annular protrusion has a height less than about 1.0 mm relative to the inner surface. The first component comprises a substantially rigid first material. The prosthetic device also includes a second component. The second component includes an outer surface having a generally semi-spherical profile for engagement with the inner surface of the first component. In that regard, the outer surface includes at least one annular recess extending circumferentially into the outer surface with a depth less than about 1.0 mm. The at least one annular recess is shaped to receive the at least one annular protrusion of the first component. The second component also includes an inner surface for mating with a femoral head. The inner surface has a generally semi-spherical profile concentric with the outer surface. The second component has a substantially uniform thickness less than about 3.0 mm between the outer surface and the inner surface. The second component comprising a pliable second material. In some instances, the first and second components have a total thickness between the outer surface of the first component and the inner surface of the second component that is approximately equal to a thickness of a native articular cartilage of the acetabulum adjacent the bony portion of the acetabulum. In some instances, the prosthetic device also includes a prosthetic femoral head for mating with the inner surface of the second component. 
         [0008]    In another embodiment, a prosthetic acetabular cup system is disclosed. The system includes a metal shell comprising an outer surface for securely engaging a prepared portion of an acetabulum, an opposing inner surface for receiving a pliable articulating component, and at least one snap-fit engagement feature associated with the inner surface. The metal shell has a thickness less than about 1.0 mm between the outer surface and the inner surface. The system also includes a pliable articulating component. The pliable articulating component includes an outer surface for engaging the inner surface of the metal shell, including at least one snap-fit engagement feature associated sized and shaped to snap-fittingly engage the at least one snap-fit engagement feature of the metal shell. The pliable articulating component also includes an inner surface for receiving a femoral head. The pliable articulating component has a thickness less than about 3.0 mm between the outer surface and the inner surface. In some instances, the at least one snap-fit engagement feature of the metal shell comprises at least one recess and the at least one snap-fit engagement feature of the pliable articulating component comprises at least one projection. In some instances, the at least one snap-fit engagement feature of the metal shell comprises at least one projection and the at least one snap-fit engagement feature of the pliable articulating component comprises at least one recess. In some instances, the metal shell and the pliable articulating component have a total thickness between the outer surface of the metal shell and the inner surface of the pliable articulating component that is approximately equal to a thickness of a native articular cartilage of the acetabulum. 
         [0009]    In another embodiment, a method of implanting an artificial acetabular component is disclosed. The method includes removing at least a portion of an articular cartilage of an acetabulum to access a bony portion of the acetabulum and engaging an outer surface of a metal shell with the bony portion of the acetabulum, where the metal shell has an opposing inner surface and a thickness of less than about 1.0 mm between the outer surface and the inner surface. The method also includes snap-fitting a pliable articulating component into engagement with the inner surface of the metal shell, where the pliable articulating component has a thickness less than about 3.0 mm between an outer engagement surface and an inner articulating surface such that when snap-fittingly engaged the metal shell and the pliable articulating component have a total thickness between the outer surface of the metal shell and the inner articulating surface of the pliable articulating component that is approximately equal to a thickness of the removed articular. In some instances, snap-fitting the pliable articulating component into engagement with the inner surface of the metal shell comprises snap-fitting at least one projection extending from the inner surface of the metal shell with at least one recess extending into the outer engagement surface of the pliable articulating component. In some instances, the method also includes wetting at least the outer engagement surface of the pliable articulating component prior to snap-fitting the pliable articulating component into engagement with the metal shell. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0010]    Other features and advantages of the present disclosure will become apparent in the following detailed description of embodiments of the disclosure with reference to the accompanying of drawings, of which: 
           [0011]      FIG. 1  is a diagrammatic cross-sectional view of an arrangement incorporating a prosthetic device according one embodiment of the present disclosure. 
           [0012]      FIG. 2  is a diagrammatic perspective view of a component of the prosthetic device of  FIG. 1  according to one embodiment of the present disclosure. 
           [0013]      FIG. 3  is a diagrammatic cross-sectional side view of the component of  FIG. 2 . 
           [0014]      FIG. 4  is a diagrammatic bottom view of the component of  FIGS. 2 and 3 . 
           [0015]      FIG. 5  is a diagrammatic cross-sectional view of another component of the prosthetic device of  FIG. 1  according to one embodiment of the present disclosure. 
           [0016]      FIG. 6  is a diagrammatic cross-sectional view of the component of  FIGS. 2-4  assembled with the component of  FIG. 5  to form the prosthetic device of  FIG. 1 . 
           [0017]      FIG. 7  is a diagrammatic cross-sectional view of a prosthetic device similar to  FIG. 6 , but showing an alternative embodiment of the present disclosure. 
           [0018]      FIG. 8  is a diagrammatic cross-sectional view of a prosthetic device similar to  FIGS. 6 and 7 , but showing another alternative embodiment of the present disclosure. 
           [0019]      FIG. 9  is a diagrammatic cross-sectional view of a patient&#39;s unprepared acetabulum according to one aspect of the present disclosure. 
           [0020]      FIG. 10  is a diagrammatic cross-sectional view of a patient&#39;s prepared acetabulum according to one aspect of the present disclosure. 
           [0021]      FIG. 11  is a diagrammatic cross-sectional view of the component of  FIGS. 2-4  implanted into the patient&#39;s prepared acetabulum according to one aspect of the present disclosure. 
           [0022]      FIG. 12  is a diagrammatic cross-sectional view of the component of  FIG. 5  assembled with the component of  FIGS. 2-4  implanted into the patient&#39;s prepared acetabulum to form the prosthetic device of  FIG. 1  according to one aspect of the present disclosure. 
           [0023]      FIG. 13  is a diagrammatic cross-sectional view of the assembled prosthetic device implanted into the patient&#39;s prepared acetabulum as shown in  FIG. 12  mated with a femoral head according to one aspect of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0024]    For the purposes of promoting an understanding of the principles of the present disclosure, reference will now be made to the embodiments illustrated in the drawings, and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the disclosure is intended. Any alterations and further modifications in the described devices, instruments, methods, and any further application of the principles of the disclosure as described herein are contemplated as would normally occur to one skilled in the art to which the disclosure relates. In particular, it is fully contemplated that the features, components, and/or steps described with respect to one embodiment may be combined with the features, components, and/or steps described with respect to other embodiments of the present disclosure. 
         [0025]    Referring now to  FIGS. 1 ,  2 ,  3 ,  4 ,  5 , and  6 , shown therein is an arrangement  100  incorporating aspects of the present disclosure. The arrangement  100  includes an acetabulum  102  and a prosthetic system  104 . The prosthetic system  104  includes at least a shell  106  and an articulating component  108 . A femoral head  110  is also shown. The femoral head  110  is a prosthetic component in some instances such that the femoral head  110  is considered part of the prosthetic system  104 . In other instances, the femoral head  110  is a natural femoral head and is not considered part of the prosthetic system  104 .  FIG. 1  is a diagrammatic cross-sectional view of the arrangement  100 ;  FIG. 2  is a diagrammatic perspective view of the shell  106  of the prosthetic system  104  according to one embodiment of the present disclosure;  FIG. 3  is a diagrammatic cross-sectional side view of the shell  106 ;  FIG. 4  is a diagrammatic bottom view of the shell  106 ;  FIG. 5  is a diagrammatic cross-sectional view of the articulating component  108  of the prosthetic system  104  according to one embodiment of the present disclosure; and  FIG. 6  is a diagrammatic cross-sectional view of the shell  106  assembled with the articulating component  108 . 
         [0026]    Referring more specifically to  FIGS. 2-4 , the shell  106  includes an outer surface  112  for engaging a prepared portion of the acetabulum  102 . In that regard, in some instances, the outer surface  112  of the shell  106  is treated to enhance engagement between the outer surface and the acetabulum  102 . In some instances, the outer surface  112  is roughened to increase the friction between the acetabulum and the device. Further, the engagement surface may be treated with biologics to encourage ingrowth of bone and/or articular cartilage. In some instances, the engagement surface receives one or more surface treatments as described in U.S. patent application Ser. No. 10/497,897 titled “CUSHION BEARING IMPLANTS FOR LOAD BEARING APPLICATIONS,” hereby incorporated by reference in its entirety. Further, in some instances the outer surface  112  includes structural features (not shown) for encouraging engagement between the shell  106  and the acetabulum  102 . For example, the outer surface  112  includes projections, recesses, and/or combinations thereof in some instances. Generally, the outer surface  112  may be rigidly secured to the acetabulum in any medically suitable manner. In that regard, in some instances the outer surface  112  will engage a bony portion of the acetabulum  102 . In some instances, the outer surface  112  will engage at least some articular cartilage of the acetabulum  102 . 
         [0027]    Referring more specifically to  FIGS. 3 and 4 , the shell  106  includes an inner surface  114  opposite the outer surface  112 . In the present embodiment, the outer surface  112  is substantially semi-spherical. Similarly, the inner surface  114  is also substantially semi-spherical and concentric relative to the outer surface  112 . The outer surface  112  and the inner surface  114  are separated by a thickness  116  of the shell  106 . Generally, the thickness  116  is less than about 1.0 mm and, in some embodiments, is less than about 0.5 mm. In some embodiments, the thickness is between about 0.5 mm and about 1.0 mm. In the present embodiment, three continuous annular protrusions  118 ,  120 , and  122  extend circumferentially about the inner surface  114  of the shell. In that regard, the protrusion  122  at least partially defines the rim or boundary of the shell  106  as shown. The protrusions  118  and  120  are spaced from one another and positioned between the protrusion  122  and an apex of the inner surface  114 . In the present embodiment, the protrusions  118 ,  120 ,  122  each have substantially similar rounded profiles such that the shell has a thickness  124  between the outer surface  112  and the apex of each of the protrusions. In that regard, the thickness  124  is generally less than about 2.0 mm and, in some embodiments, is less than about 0.5 mm. As discussed below, however, in other embodiments the protrusions  118 ,  120 ,  122  may have various other profiles instead of the illustrated rounded profiles. The protrusions  118 ,  120 ,  122  increase the rigidity, stiffness, and/or structural integrity of the shell  106 . In that regard, the protrusions  118 ,  120 ,  122  serve to limit the flexing and deformation of the shell  106  in some instances. In some embodiments, the protrusions  118 ,  120 ,  122  provide a hoop strength to the shell  106  that limits deformation. Depending on the particular material utilized for the shell  106 , additional or fewer protrusions and/or other stiffening structures may be utilized to obtain a desired stiffness for the shell. 
         [0028]    From a center point  126 , the substantially semi-spherical outer surface  112  is defined by a radius of curvature  128 . Similarly, the substantially semi-spherical inner surface  116  is defined by a radius of curvature  130 . The radius of curvature  128  is generally between about 24.0 mm and about 30.0 mm, but in some instances may be larger or smaller. Accordingly, the radius of curvature  130  is generally between about 23.0 mm and about 29.5 mm, but also may be larger or smaller in some instances. 
         [0029]    Referring now to  FIG. 5 , the articulating component  108  includes an outer surface  132  shaped to mate with the inner surface  114  and protrusions  118 ,  120 ,  122  of the shell  106 . In that regard, the outer surface  132  includes a pair of recesses  134 ,  136  sized and shaped to receive and engage the protrusions  118 ,  120 , respectively. In that regard, the recesses  134 ,  136  have rounded profiles that are substantially the inverse of the profile of the protrusions  118 ,  120  of the shell  106 . Generally, the engagement between the recesses  134 ,  136  and the protrusions  118 ,  120  anchors the articulating component  108  within the shell  106  and constrains movement of the articulating component relative to the shell. In some instances, the recesses  134 ,  136  and the protrusions  118 ,  120  snap-fit together. Further, the outer surface  132  includes a taper  138  adjacent its outer edge or rim. In that regard, the taper  138  is sized and shaped to mate with the protrusion  122  of the shell  106 . In some instances, the taper  138  and the protrusion  122  snap-fit together similar to the recesses  134 ,  136  and the protrusions  118 ,  120 . In some instances, the articulating component  108  includes deformation control elements or reinforced material adjacent to and/or defining the recesses  134 ,  136 . In that regard, the deformation control elements and/or the reinforced material can strengthen the structural integrity of the articulating element  108  to prevent unwanted interruption to the inner articulating surface  140  that may be caused by abnormally heavy loading of the hip joint distributed through the projections  118 ,  120  into the articulating element  108 . 
         [0030]    In some embodiments, the articulating component  108  does not include recesses  134 ,  136  and the shell  106  does not include protrusions  118 ,  120 , such that the articulating component  108  is anchored to the shell  106  via engagement of the protrusion or rim  122  with the taper or rim  138  of the articulating component. In that regard, the diameter of the opening defined by the protrusion or rim  122  is less than a maximum diameter of the articulating component  108 , such that the articulating component is held within the shell  106  by the protrusion  122 . In such embodiments, the articulating component  108  may have a substantially smooth outer surface for interfacing the with the shell  106 . In one such embodiment, the articulating component  108  may also be anchored to the shell  106  via a liquid adhesion bond. In such instances, the liquid adhesion bond prevents separation of the articulating component  108  from the shell  106  while the protrusion  122  limits rotation of the articulating component  108  relative to the shell  106 . 
         [0031]    The articulating component  108  also includes an inner surface  140  opposite the outer surface  132 . In the present embodiment, the outer surface  132  is substantially semi-spherical. Similarly, the inner surface  140  is also substantially semi-spherical and concentric relative to the outer surface  132 . The outer surface  132  and the inner surface  140  are separated by a thickness  142  of the articulating component  108 . Generally, the thickness  142  is between about 6.0 mm and about 1.5 mm. In some embodiments, the thickness  142  is less than about 3.0 mm and, in some further embodiments, is about 1.5 mm. The articulating component  108  also has a thickness  144  between the inner surface  140  and the trough or lowest point of each of the recesses  134 ,  136 . In that regard, the thickness  144  is generally between about 5.0 mm and about 0.5 mm. In some embodiments, the thickness  144  is less than about 2.0 mm. As discussed below, however, in other embodiments the protrusions  118 ,  120 ,  122  may have various other profiles instead of the illustrated rounded profiles. 
         [0032]    From a center point  146 , the substantially semi-spherical outer surface  132  is defined by a radius of curvature  148 . Similarly, the substantially semi-spherical inner surface  140  is defined by a radius of curvature  150  extending from the center portion  146 . The radius of curvature  148  is generally between about 23.0 mm and about 29.5 mm, but in some instances may be larger or smaller. Accordingly, the radius of curvature  150  is generally between about 17.0 mm and about 28.5 mm, but also may be larger or smaller in some instances. 
         [0033]    Referring now to  FIG. 6 , the shell  106  and the articulating component  108  are securely engaged with one another. In the present embodiment, the articulating component  108  is snap-fit within the shell  106 . In that regard, the protrusions  118 ,  120  of the shell  106  snap-fit into the recesses  134 ,  136  in the articulating component  108 . Further, the protrusion  122  of the shell  106  engages the taper  138  of the articulating component  108 . In some instances, the interface between the protrusion  122  and the taper  138  provides a boundary to prevent unwanted or accidental disengagement of the articulating component  108  from the shell  106 . In that regard, in some embodiments the protrusion  122  extends more prominently over the outer portion or rim of the articulating component  108  than illustrated in  FIG. 6 . In one such embodiment, the protrusion  122  secures the articulating component  108  to the shell  106  and the shell does not include protrusions  118  and  120 . In some instances, engagement of the protrusions  118 ,  120 ,  122  with the articulating component  108  causes the articulating component  108  to deform as it is positioned within the shell  106 . Specifically, portions of the articulating component, including its outer and inner surfaces are deformed inwardly such that the outer and inner surface are not substantially partially spherical. Instead, the outer and inner surfaces become partially elliptical or oblonged in some instances. For example, in some instances the apex of the outer surface of the articulating component  108  is positioned closer to the inner surface of the shell  106 , than remaining portions of the outer surface until the protrusions  118 ,  120 ,  122  engage the recesses  134 ,  136  and taper  138 , respectively. 
         [0034]    When assembled, the shell  106  and the articulating component  108  have a combined thickness  152  adjacent the apex of the components between the outer surface  112  of the shell  106  and the inner surface  140  of the articulating member  108 . When assembled, the shell  106  and the articulating component  108  also have a combined thickness  154  adjacent the rim of the components between the outer surface  112  of the shell  106  and the inner surface  140  of the articulating member  108 . In the present embodiment, the thicknesses  152 ,  154  are substantially equal such that when assembled the shell  106  and articulating component  108  define a substantially constant thickness between the outer surface  112  and the inner surface  140 . In that regard, the mating of the protrusions  118 ,  120  with the recesses  134 ,  136  and the mating of the protrusion  122  with the taper  138  results in the constant thickness. In other embodiments, the combined thickness extending between the outer surface  112  and the inner surface  140  is not substantially constant. In one particular embodiment, the thickness  154  adjacent the rim of the components is larger than the thickness  152  adjacent the apex of the components. In that regard, an increased thickness  154  adjacent the rim of the components is utilized to at least partially retain a femoral head within the articulating component in some instances. 
         [0035]    In some instances, the combined thicknesses  152 ,  154  are substantially equal to or less than a thickness of the native cartilage of the acetabulum in some instances. In that regard, in some instances the combined thicknesses  152 ,  154  are substantially equal to or less than a desired or normal amount of articular cartilage, but not necessarily less than the articular cartilage of a particular patient. For example, in the case where a patient&#39;s articular cartilage has been damaged or removed, the thicknesses  152 , 154  may be greater than the thickness of the patient&#39;s articular cartilage. In some instances the combined thicknesses  152 ,  154  are substantially equal to or less than the actual articular cartilage of the patient. In that regard, in some instances the shell  106  and articulating component  108  are sized to substantially replace the space created by removal of articular cartilage and/or bone from the acetabulum prior to insertion of the shell  106  and articulating component  108 . In some instances the shell  106  and articulating component  108  are sized to replace less than the space created by removing articular cartilage and/or bone from the acetabulum prior to insertion of the shell  106  and articulating component  108 , such that a femoral head larger than the natural femoral head may be utilized. 
         [0036]    While the shell  106  is shown as having protrusions  118 ,  120 , and  122 , in other embodiments the shell may have other engagement features for mating the with the articulating component  108 . Similarly, while the articulating component  108  is shown as having recesses  134 ,  136  and taper  138 , in other embodiments the articulating component may have other engagement features for mating with the shell. In that regard, each of the shell  106  and articulating component  108  may include projections, recesses, and combinations thereof sized and shaped to engage corresponding projections, recesses, and combinations thereof of the other component. In some instances the engagement features are similar to the engagement features of one or more of the prosthetic devices described in U.S. patent application Ser. No. 10/289,126 titled “ONE PIECE SNAP FIT ACETABULAR CUP,” U.S. patent application Ser. No. 10/497,897 titled “CUSHION BEARING IMPLANTS FOR LOAD BEARING APPLICATIONS,” U.S. patent application Ser. No. 10/515,486 titled “IMPLANTS,” U.S. patent application Ser. No. 11/688,153 titled “CERAMIC-ON-CERAMIC PROSTHETIC DEVICE COUPLED TO A FLEXIBLE BONE INTERFACE,” or PCT Application No. PCT/IL2006/000343 titled “IMPLANT DEVICES” (published as WO 2006/097932), each incorporated by reference in its entirety. It is recognized that the various combinations of projections and recesses described as being formed in the acetabulum by these references can instead by formed in one of the shell  106  and/or articulating component  108  in accordance with the present disclosure. 
         [0037]    Referring now to  FIG. 7 , shown therein is a diagrammatic cross-sectional view of a prosthetic device  160  according to an alternative embodiment of the present disclosure. The prosthetic device  160  includes a outer shell component  162  and an inner articulating component  164 . In some aspects the outer shell component  162  is similar to the shell  106  described above and, similarly, in some aspects the inner articulating component  164  is similar to the articulating component  108  described above. However, in the present embodiment, the outer shell component  162  includes a pair of continuous annular recesses  166  and  168  extending circumferentially about the inner surface. The outer shell component  162  also includes a continuous annular protrusion  170  that at least partially defines the rim or boundary of the shell component as shown. In that regard, the protrusion  170  is substantially similar to the protrusion  122  of the shell  106  described above. The recesses  166  and  168  are spaced from one another and positioned between the protrusion  170  and an apex of the inner surface. In the present embodiment, the outer surface of the articulating component  164  includes a pair of protrusions  172 ,  174  sized and shaped to engage the recesses  166 ,  168  of the shell component  162 , respectively. In that regard, the protrusions  172 ,  174  have rounded profiles that are substantially the inverse of the profile of the recesses  166 ,  168  of the shell component  162 . In some instances, the protrusions  172 ,  174  and the recesses  166 ,  168  snap-fit together. Further, the outer surface of the articulating component  164  includes a taper  176  adjacent its outer edge or rim. In that regard, the taper  176  is sized and shaped to mate with the protrusion  170  of the shell component  162 . In some instances, the taper  176  and the protrusion  170  snap-fit together similar to the protrusions  172 ,  174  and the protrusions  166 ,  168 . In this manner, the taper  176  is substantially similar to the taper  138  described above. 
         [0038]    Referring now to  FIG. 8 , shown therein is a diagrammatic cross-sectional view of a prosthetic device  180  according to another embodiment of the present disclosure. The prosthetic device  180  includes a outer component  182  and an inner component  184 . In some aspects the outer component  182  is similar to the shell  106  and/or the shell component  162  described above and, similarly, in some aspects the inner component  164  is similar to the articulating component  108  and/or the articulating component  164  described above. In the present embodiment, the outer component  182  has a thickness  186  that is generally less than about 1.0 mm. The outer component  182  has a thickness  188  adjacent its rim or outer boundary that is greater than the thickness  186  and, in some instances, is between about 0.75 mm and about 2.0 mm. In the present embodiment, the inner component  184  has a thickness  190  that is generally less than about 6.0 mm. The inner component  184  has a thickness  192  adjacent its rim or outer boundary that is less than the thickness  190  and, in some instances, is between about 1.0 mm and about 5.25 mm. The outer component  182  includes an annular recess  194  extending circumferentially about its inner surface. Generally, the outer component  182  has the thickness  188  between the recess  194  and its rim and the thickness  186  between the recess  194  and the apex of the outer component. In that regard, the difference in thicknesses  186 ,  188  at least partially defines the recess  194  in some instances. The inner component  184  includes an annular protrusion  196  extending circumferentially about its outer surface. The annular protrusion  196  is sized, shaped, and positioned to engage the recess  194  of the outer component  182  to secure the inner component  184  to the outer component  182 . Generally, the inner component  184  has the thickness  192  between the projection  196  and its rim and the thickness  190  between the projection  196  and the apex of the inner component. In that regard, the difference in thicknesses  190 ,  192  at least partially defines the projection  196  in some instances. In some instances, the increased thickness  188  of the outer component  182  mating with the reduced thickness  192  of the inner component  184  helps to secure the components together. 
         [0039]    When assembled together the outer component  182  and the inner component  184  have a thickness  198  between the outer surface of the outer component and the inner surface of the inner component between the interface of the projection  196  and recess  194  and the apex of the components. When assembled together the outer component  182  and the inner component  184  have a thickness  200  between the outer surface of the outer component and the inner surface of the inner component between the interface of the projection  196  and recess  194  and the rim of the components. In that regard, the thickness  198  is substantially equal to the thickness  200  in the present embodiment. Thus, the difference between the thicknesses  186  and  188  of the outer component and the difference between the thicknesses  190  and  192  of the inner component are substantially equal. In other instances, the differences between the thickness  186 ,  188  and  190 ,  192  are not substantially equal such that the thicknesses  198 ,  200  of the assembled components is not equal. 
         [0040]    Generally, the shell or outer components of the present disclosure are formed of a material that is more rigid than the material of the articulating or inner components. For example, in some embodiments the shell is formed of a medical grade metal suitable for implantation, including but not limited to stainless steel alloys, cobalt-chrome alloys, titanium alloys, nickel-titanium alloys, and other suitable metals. In other embodiments, the shell is formed of a composite material, including but not limited to polyetheretherketone (PEEK), carbon-reinforced PEEK, Dyneema, and other suitable composites. 
         [0041]    In some instances, the prosthetic devices of the present disclosure are fiber reinforced, include one or more deformation control elements, or comprise a material or combination of materials particularly suited for positioning within an articulating joint. In some embodiments, the prosthetic devices are formed of materials or combinations of materials as described in U.S. patent application Ser. No. 10/497,897 titled “CUSHION BEARING IMPLANTS FOR LOAD BEARING APPLICATIONS” and U.S. patent application Ser. No. 12/100,090 titled “MANUFACTURING AND MATERIAL PROCESSING FOR PROSTHETIC DEVICES”, each hereby incorporated by reference in its entirety. 
         [0042]    Referring now to  FIGS. 9 ,  10 ,  11 ,  12 , and  13 , shown therein are various stages of the prosthetic device  104  described above being implanted. Specifically,  FIG. 9  is a diagrammatic cross-sectional view of a patient&#39;s unprepared acetabulum  210 ;  FIG. 10  is a diagrammatic cross-sectional view of a patient&#39;s prepared acetabulum  211 ;  FIG. 11  is a diagrammatic cross-sectional view of the shell  106  implanted into the patient&#39;s prepared acetabulum  211 ;  FIG. 12  is a diagrammatic cross-sectional view of the articulating component  108  assembled with the shell  106  and implanted into the patient&#39;s prepared acetabulum  211 ; and  FIG. 13  is a diagrammatic cross-sectional view of the implanted articulating component  108  assembled with the shell  106  and mated with a femoral component. 
         [0043]    Referring more specifically to  FIG. 9 , the patient&#39;s unprepared acetabulum  210  comprises a bony portion  212  and an articular cartilage portion  214 . The articular cartilage  214  is shown as having a substantially uniform thickness  216 . Generally, the thickness  216  of the articular cartilage  214  of a healthy acetabulum is approximately 4 mm or less. In the present embodiment the outer articulating surface  217  of the articular cartilage  214  is shown as being defined by a radius of curvature  218  extending from a center point  220 . In some instances, the radius of curvature  218  of the articulating surface  217  is between about 16 mm and about 24 mm. However, the radius of curvature  218  is outside of this range for some patients. While the articular cartilage  214  is shown as having a substantially uniform thickness  216 , it is recognized that the thickness of the articular cartilage will vary slightly to substantially across the acetabulum  210 . For example, in some instances the articular cartilage  214  has degenerated, has been damaged, and/or has been at least partially removed. Accordingly, while the articular cartilage  214  is shown and at times discussed as having a substantially uniform thickness  216  it is understood that the present disclosure is equally applicable to articular cartilage  214  with a non-uniform thickness. 
         [0044]    Referring more specifically to  FIG. 10 , preparation of the acetabulum includes reaming at least the articular cartilage  214  to define a surface  222  having a radius of curvature  224  for receiving the shell  106 . In some instances, the surface  222  is partially spherical. That is, the surface  222  is defined as a portion of an outer surface of a sphere. In some particular embodiments, the surface  222  is substantially semi-spherical. In some instances, at least a portion of the bony portion  212  is reamed or cut to create the surface  222 . In that regard, removing at least a portion of the bony portion  212  can help stimulate bone ingrowth between the surface  222  and the shell  106  after implantation of the shell. Generally, the radius of curvature  224  of the surface  222  is sized to match the radius of curvature  128  of the outer surface  112  of the shell  106 . 
         [0045]    Referring more specifically to  FIG. 11 , after the surface  222  has been prepared the shell  106  is implanted into the prepared acetabulum  211 . In that regard, the shell  106  is fixedly secured to the surface  222  in some instances. Generally, the inner surface  114  of the shell  106  defines a radius of curvature  226  relative to center point  220 , as shown. Referring more specifically to  FIG. 12 , once the shell  106  is secured within the prepared acetabulum  211  the articulating component  108  is positioned within the shell  106  such that the engagement of the projections  118 ,  120 ,  122  with the recesses  134 ,  136  and taper  138  anchors the articulating component  108  to the shell  106 . The inner articulating surface  140  of the articulating component  108  has a radius of curvature  228  relative to the center point  220  after implantation. In some instances, the radius of curvature  228  is substantially similar to the radius of curvature  218  of the natural articular cartilage  214  prior to preparation of the acetabulum. In other instances, the radius of curvature  228  is less than the radius of curvature  218  of the natural articular cartilage  214  prior to preparation of the acetabulum. In some instances, the radius of curvature  228  is larger than the radius of curvature  218  of the natural articular cartilage  214  prior to preparation of the acetabulum. 
         [0046]    Referring more specifically to  FIG. 13 , a femoral head  230  has been mated with the inner articulating surface  140  of the articulating component  108  to provide a functioning hip joint. The femoral head  230  includes an outer articulating surface  232  having a radius of curvature  234  relative to center point  220 . The radius of curvature  234  is substantially equal to or slightly less than the radius of curvature  228  of the inner articulating surface  140 . In some instances, the femoral head  230  is a natural femoral head. In some instances, the femoral head is a natural femoral head that has been reshaped or resurfaced for mating with the articulating component  108 . In other instances, the femoral head  230  is an artificial femoral head. In some embodiments, the femoral head  230  is larger than the natural femoral head of the patient. 
         [0047]    The foregoing outlines features of several embodiments so that those skilled in the art may better understand the aspects of the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions and alterations herein without departing from the spirit and scope of the present disclosure. Also, it will be fully appreciated that variations of the above-disclosed and other features and functions, or alternatives thereof, may be combined into other methods, systems, apparatus, or applications. Similarly, various presently unforeseen or unanticipated alternatives, modifications, and/or variations of the present disclosure subsequently made by those skilled in the art are also encompassed by the present disclosure and the following claims.