Abstract:
Disclosed is a method of engaging a bearing liner within a shell member with an integrated projection portion. The integrated projection portion may deform a selected amount during positioning of the bearing liner within the shell. The shell may include a complementary engaging portion.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of U.S. patent application Ser. No. 13/763,145 filed on Feb. 8, 2013. The entire disclosure of the above application is incorporated herein by reference. 
    
    
     FIELD 
     The present disclosure relates to bearing fixation. 
     BACKGROUND 
     This section provides background information related to the present disclosure which is not necessarily prior art. 
     A subject can have a portion replaced with a replacement member. For example, a human patient subject can have a portion of the anatomy replaced with a prosthetic member. The reason for the replacement can be due to injury, disease, or other failing of the natural anatomy. 
     A prosthetic member can be used to replace a portion of the anatomy to substantially recreate or mimic the natural anatomy and physiology. For example, an acetabular prosthesis can be positioned in a prepared acetabulum of a patient to achieve a substantially natural or selected interaction of a femur and an acetabulum. It is understood in a complete or total hip arthroplasty that a proximal femoral portion may also be replaced. 
     An acetabular prosthesis can include a shell component that contacts a pelvis within an acetabulum. The shell can either interact with the natural femur or with a proximal femoral prosthesis directly, or a bearing can be placed in the shell. A bearing can be fixed in the shell using a separate element that is positioned between the bearing and the shell, such as with the RINGLOC® sold by Biomet, Inc. 
     SUMMARY 
     This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features. 
     An acetabular prosthesis can be positioned in a patient to replace an acetabulum that is damaged or defective. The acetabular prosthesis can be placed in the patient after properly preparing the acetabulum to receive the acetabular prosthesis. The acetabular prosthesis can generally be formed of at least two pieces, including an external shell that is positioned in contact or cemented to the acetabulum of the pelvis and a bearing liner (also referred to herein alone as a liner or bearing) that is positioned and selectively fixed within the shell. Both the shell and the liner can include convex exterior surfaces and concave interior surfaces. The convex exterior surface of the shell can engage the bone of the pelvis and the convex exterior of the liner can engage the concave interior of the shell. The concave interior of the liner can then articulate relative to a proximal femur portion. The proximal femur can be a prosthetic member or natural proximal femur. 
     The liner can be engaged to the shell with an engagement portion defined by the liner. The engagement portion defined by the liner may engage and/or interact with the internal surface of the shell to selectively deform the liner during insertion of the liner into the shell. The engagement portion of the liner may then engage or be received by a depression formed within the shell. Once engaged with the depression the liner is substantially fixed to the shell for the purpose of the implantation. 
     Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
    
    
     
       DRAWINGS 
       The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure. 
         FIG. 1  is an exploded view of a shell and bearing liner, according to various embodiments; 
         FIG. 2  is a cross-section view of the shell of  FIG. 1 ; 
         FIG. 3  is a cross-section view of the bearing liner of  FIG. 1 ; 
         FIG. 4  is a detail cross-section view of an engagement portion taken from  FIG. 3 ; 
         FIG. 5  is a detail cross-section view of an engagement portion, according to various embodiments; 
         FIG. 6  is a detail cross-section view of an engagement portion, according to various embodiments; 
         FIG. 7A  is a detail cross-section view of the bearing liner being inserted into the shell; 
         FIG. 7B  is a detail cross-section view of the bearing liner seated in the shell; 
         FIG. 7C  is a detail cross-section view from  FIG. 7B ; and 
         FIG. 8  is an environmental view of the shell and bearing liner relative to a subject. 
     
    
    
     Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings. 
     DETAILED DESCRIPTION 
     Example embodiments will now be described more fully with reference to the accompanying drawings. 
     With reference to  FIG. 1 , an acetabular prosthesis system can include a shell  20  and an acetabular liner  30 . The shell  20  can include an exterior convex surface  40  that is configured to contact an acetabulum of a pelvis. The shell  20  can include throughbores, such as an apical throughbore defined by a sidewall  44  and one or more screw of fixation throughbores  46  defined by through sidewalls  48 . The throughbores  46  extend from an interior concave surface  50  to the exterior convex surface  40 . The apical hole  42  can generally be used for fixation and positioning of the acetabular shell  20  in the acetabulum. The fixation bore  46  can be used for passing a screw or other fixation member into the acetabular portion during implantation and fixation of the acetabular shell  20 . It is understood that a plurality of the fixation throughbores  46  can be provided at various positions of the shell  20  and a user can selectively pass screws for fixing the shell  20  to the acetabulum of the subject. Additional mechanisms or features can be used to fix the shell to the pelvis as well, for example, projections or spikes, a porous coating or porous outer surface portion. 
     The acetabular shell  20  can also include other features, such as the anti-rotation depressions  56  formed near an upper surface or a rim  58  of the acetabular shell  20 . The acetabular shell  20 , including the anti-rotation depressions  56  can engage the liner  30  to hold the liner substantially rotationally fixed relative to the shell  20 . Additionally, the shell  20  can include an interior groove or depression  60  formed as a substantially annular or circumferential depression within the concave surface  50  of the acetabular shell  20 . 
     The groove  60  formed within the shell  20  can be a groove formed within the shell similar to the groove formed in the shell of the acetabular shell used in the RINGLOC® acetabular prosthesis sold by Biomet, Inc. having a place of business in Warsaw, Ind. The groove  60  formed in the interior surface  50  of the acetabular shell  20  can be formed with appropriate dimensions. The dimensions, as discussed further herein, can assist in fixation of the liner  30  relative to the shell  20  during and after an implantation of the liner  30  into the shell  20 . Generally, the depression  60  substantially extends around the interior  50  of the shell  20  for fixing the liner  30  within the shell  20 . It is understood, however, that alternative or additional fixation mechanisms can be provided or formed within the shell  20  to engage the liner  30 . 
     With continuing reference to  FIG. 1 , and additional reference to  FIG. 3 , the acetabular liner  30  can include an outer convex surface  70  and an inner concave surface  72 . A liner rim  74  can be formed near an upper or equator region of the liner  30  positioned away from an apex  76  of the liner  30 . A wall thickness between the interior concave surface  72  and the exterior convex surface  70  can be provided. It is understood that the wall thickness  78  can be substantially uniform or vary between the apex  76  and the rim  74  of the liner  30 . The variation of the thickness of the wall of the liner  30  can be provided for various purposes such as insertion of the liner  30  within the shell  20  and other bearing characteristics, such as wear resistance or weight bearing. 
     Additionally, the liner  30  can be provided with a one or more anti-rotation projections  80  that extend from the outer surface  70  of the liner near the rim  74 . The anti-rotation projections can engage the anti-rotation depressions  56  defined by the shell  20  for substantially rotationally fixing the liner  30  relative to the shell  20 . Additionally, the anti-rotation projections  80  can assist in aligning the liner  30  relative to the shell  20 . The anti-rotation projections can also assist in aligning the bearing  30  within the shell to ensure proper fixation therein. 
     Additionally, an axial fixation projection  90  can be formed to extend from the surface  70  of the liner  30 . The axial fixation projection  90  can be formed as a substantially continuous projection around an exterior of the liner  30 . Alternatively, the projection  90  can be formed as a segmental projection including discreet projection regions around the exterior of the liner  30 . The axial fixation projection  90  may be formed to engage the axial fixation depression  60  within the shell  20  during an implantation and positioning of the liner  30  within the shell  20 . As discussed herein, the geometry of the axial fixation projection  90  can interact with the inner surface  50  of the shell  20  during positioning of the liner  30  within the shell  20  and engage the depression  60  within the shell  20  for fixing the liner  30  within the shell  20 . 
     With continuing reference to  FIG. 3  and additional reference to  FIG. 4 , the axial fixation projection  90  is shown in detail. The projection  90 , illustrated in  FIG. 4 , is a manufactured or first configuration of the projection  90 . As discussed herein, the projection can deform to engage and/or seat in the shell  20 . The liner  30  can define a central axis  100  that extends substantially through the apex  76  of the liner  30 . The central axis  100  is also generally perpendicular to a place defined near and/or by a rim of the liner  30 . An apical or distal surface  102  of the axial fixation projection  90  can be formed to be substantially perpendicular or at a right angle to the axis  100  of the liner  30 . The perpendicular surface  102  of the axial fixation projection  90  can extend a distance  104  from the exterior surface  70  of the liner  30 . The distance  104  of the edge or surface  102  can provide, as discussed further herein, a sufficient or selected amount of material of the projection  90  to deform relative to the shell  20  for fixation within the depression  60  of the shell  20 . The axial fixation projection  90  can further include a first parallel extending wall  106  that extends a parallel distance  108  of about 0.4 mm to about 0.6 mm, including about 0.5 mm. The parallel wall  108  extends substantially parallel to the central axis  100  of the liner  30 . The parallel wall  106 , however, can form an angle towards the central axis  100  from the perpendicular wall  102 , such as about 68° relative to the perpendicular wall  102  of the axial fixation projection  90 . A third angled wall  110  can extend from the parallel wall  106  to the juncture  110   a  along a distance  112 . The distance  112  can be about 0.6 mm to about 0.8 mm, including about 0.7 mm. The angled wall  110  can extend at an angle towards the central axis  100  from the wall  106  at a generally acute angle towards the central axis  100  of the liner  30 . 
     The exterior surface  70  generally defines an arc having a center defined relative to the liner  30 . The exterior surface  70  is substantially continuous from the rim of the liner to an apex of the liner  30 . The projection  90 , including the various surfaces  102 ,  106 , and  110  generally extends or diverges from the exterior surface  70  of the liner  30 . Additionally, the measurements are exemplary regarding a liner generally having a diameter of about 31 mm. It is understood that the specific dimensions of the projection  90  can, therefore, differ based upon the dimensions of the liner  30 . 
     According to various embodiments, the axial fixation projection  90  is formed of the same material as the remainder of the liner  30 . Further, the projection  90  can be formed as one piece with the liner  30 . For example, the liner  30  can be molded to include the projection  90  as an integral portion of the liner  30 . 
     The projection  90  can be provided such that a majority of the material within the axial projection  90  is positioned below a midline  140  of the projection  90 . The midline  140  is at the mid-point of the total axial distance of the projection  90 . The total axial distance of the projection  90  can generally be defined as a distance between where the first surface  102  extends at  102   a  from the external surface  70  of the liner  30  to a point  110   a  where the surface  110  rejoins and/or extends from the external surface  70  of the liner  30 . Accordingly, with reference to  FIG. 4 , the midline  140  of the projection  90  can be defined generally along line  140 . Generally, the midline  140  is a first axial distance  140   a  from a line through the point  102   a  and a second axial distance  140   b  from a line through point  110   a . The first axial distance  140   a  and the second axial distance  140   b  are equal when the line  140  is a true-mid-line. The lines through the points  102   a  and  110   a  are perpendicular to the central axis  100 . 
     A vertical line or plane  142  is also defined relative to the liner  30 . The vertical line  142  may be substantially parallel with the central axis  100  of the liner  30  and intersect the point  110   a , where the wall  110  rejoins the outer surface  70 . The mid-line  140  may be substantially perpendicular to the vertical line  142 . 
     The mid-line  140  can define a boundary or a plane that divides material of the projection  90  between the rim and the apex of the liner  30 . The vertical line  142  can define a central boundary of the projection  90 . A majority, such as at least 51% of a volume of the material that defines the axial fixation projection  90  is between the mid-line  140  and the apex  76  of the liner  30  and the vertical line  142  and the outer edge of the projection  90 . Thus, less than 51% of the volume of the material that defines the axial fixation projection  90  is between the line  140  and the upper rim  74  of the liner  30  and the vertical line  142  and the outer edge of the projection  90 . According to various embodiments, however without being bound by the theory, providing a majority of the material in the axial fixation projection  90  closer to the apex  76  can allow for the projection  90  to deform as the liner  30  is moved into the shell  20 . When the projection  90  deforms, the projection  90  can engage the depression  60  of the shell  20  after positioning the liner  30  within the shell  20  in a seated or changed configuration that is different from the original or manufactured configuration illustrated, for example, in  FIG. 4 . 
     According to various embodiments, as illustrated in  FIG. 5 , an alternative axial fixation projection  190  is illustrated. The liner  30  can include the exterior surface  70  and an axial fixation projection  190  that is substantially bulbous or curved. The projection  190  can include an exterior surface  192  that is substantially continuous from the first extension point  194  from the exterior surface  70  to the second diversion point  196 , where the axial fixation projection  190  rejoins the exterior surface  70 . A vertical line  198  extend substantially parallel to the central axis  100  of the liner and intersects the diversion point  194  (nearest the rim of the liner. The axial fixation projection  190  can include a majority of a volume of the material defined within the axial fixation projection  190  between a mid-line  200  and the apex  76  of the liner  30  and the vertical line  198  and an outer edge of the projection. Again, the mid-line  200  can be equidistant from lines that are perpendicular to the central axis  100  through the respective points  194  and  196 . 
     According to various embodiments, with reference to  FIG. 6 , a liner  230  can be formed similar to the liner  30 . The liner  230 , however, can include a generally cylindrical outer surface region  232 , such as near a rim of the liner  230 . An axial fixation projection  234  can be formed to have a generally bulbous of continuous outer surface  236  or to have any appropriate geometry, such as that discussed above. The outer surface of the projection  234  can diverge/converge from the outer surface  232  of the liner  230  at a first divergence point  238  and converge or diverge at a second divergence point  240 . A mid-line  242  can be defined as a line that is half way between the first point  238  and the second point  240 . The outer surface region  232  can be substantially parallel to a central axis  244  of the liner  230 . Thus, the outer surface  232  can define a substantially vertical line. Near an apex of the liner  230  a curved outer surface region  246  can be defined by the liner  230 . The axial projection  234 , however, can be defined substantially entirely within the cylindrical outer surface region  232 . 
     Accordingly, it is understood that a specific geometry of the axial fixation projection or the liner is not required. For example, the axial fixation projection need not include the specific dimensions illustrated in  FIG. 4  and the liner need not be entirely curved. Nevertheless, the axial fixation projection may include dimensions where a majority of the volume of the material of the axial fixation projection is between the mid-line of the axial fixation projection and the apex of the liner  30 . 
     Generally, according to various embodiments, the axial fixation projection  90 ,  190 ,  236  initially or is manufactured and provided to include a majority, such as more than 51%, of a material of the axial fixation projection, between the respective midlines and the apex of the liner  30 . For example, regarding the axial fixation projection  90  at least 51% of the material that is included in the axial fixation projection  90  is below the midline  140 . Thus, the projection  90 ,  190 ,  236  according to various embodiments, is asymmetrical about the mid-line  140 ,  200 . 
     With reference to  FIGS. 7A-7C , the liner  30  is initially placed relative to the shell  20  in the manufactured configuration where a majority of the material of the axial fixation projection is between the midline and the apex of the liner  30 . The liner  30  is then moved into and may be positioned within the shell  20  by applying a substantially axial force in the direction of Arrow A that can generally be along the axis  100  of the liner  30 . As the liner  30  is pressed into the shell  20 , the axial fixation projection  90  engages the inner wall surface  50 , such as in region  300 , of the shell  20 . 
     As the axial fixation projection  90  engages the inner wall surface  50  of the shell  20 , the projection  90  is urged generally in the direction of Arrow B that is substantially in a direction opposite of Arrow A. The projection  90  is generally forced in the direction of Arrow B due to a reaction of pressing the liner  30  into the shell  20 . Friction caused between the projection  90  and the inner surface  50  of the shell  20  causes the projection  90  to be urged in the direction of Arrow B. The material of the projection  90  generally does not compress or collapse, but may be mobile under the force of the insertion of the liner  30  into the shell  20 . A movement zone can be formed near or at the interface of the projection  90  with the outer surface  70  of the liner  30 . The movement zone can include movement of the material from the projection  90  towards the rim  74  of the liner  30 . In other words, there is movement of material in the projection  90  from below the mid-line  140  (i.e. an area or volume between the apex  76  and the mid-line  140 ) to an area above the mid-line  140  (i.e. an area or volume between the rim  74  and the mid-line  140 ). As the liner  30  is pressed into the shell  20  the friction or engagement between the projection  90  and the inner surface  50  of the shell  20  continues. 
     As the liner  30  moves into a substantially seated position, as illustrated in  FIGS. 7B and 7C , the projection  90  achieves a substantially locking configuration, which can also be viewed as a reverse pullout ramp configuration. In the locking configuration, which can be a second and/or deformed configuration, a portion of the material of the projection  90  that was between the mid-line  140  and the apex  76  of the liner  30  has moved between the line  140  and the rim  74  of the liner  30 . In the locked configuration, the projection  90 ,  190 , according to various embodiments, may be asymmetrical about the mid-line  140 ,  200  and biased towards the rim  74  of the liner  30 . 
     In the locked configuration, the material of the projection  90  has been altered or moved to engage the depression or groove  60  of the shell  20  in a locked configuration. The surface of the deformed projection that was initially provided as surface  110  is substantially perpendicular to the central axis of the liner  30  and would engage a surface  60   a  of the depression prior to other surfaces of the deformed projection. Moreover, the initially provided surface  102  and part or all of surface  106  are angled towards the rim  74  and the central axis  100  of the liner  30 . 
     The movement of the material from the projection  90  from the manufactured configuration (also referred to as the initial configuration) to the locked configuration, as illustrated in  FIGS. 7B and 7C , can provide a substantially strong push-out and lever-out force of the liner  30  relative to the shell  20 . 
     The amount of material that moves from the initial position (e.g. as illustrated according to various embodiments in  FIGS. 4-6 ) to the locked position (e.g. as illustrated in  FIGS. 7B and 7C ) may be selected based upon various considerations and selections. For example, the amount of material that moves can be selected based on materials for the liner  30 , the various dimensions of the axial fixation projection  90  (e.g. the first wall  102 ), the distance from the rim  58  to the recessed depression  60  of the shell  20 , and other factors. Generally, according to the various embodiments, projection  90  may include at least 51% of the material of the projection between the mid-line and the apex of the liner and in the locked configuration the projection  90  has at least 51% of the material moved between the mid-line  140  and the rim  74 . 
     The liner  30  can be pre-assembled to the shell  20  prior to insertion into a patient. Alternatively, and according to various embodiments, however, the shell  20  can initially be positioned within a patient  320 , as illustrated in  FIG. 8 , and then the liner  30  can be positioned within the shell  20 . Assembly of the liner  30  into the shell  20  and positioning the shell  20  into the patient  320  can be performed according to various and commonly known methods, such as that used with the RINGLOC® prosthesis system sold by Biomet, Inc. having a place of business in Warsaw, Ind. Generally, the liner  30  can be pressed into the shell  20  using an insertion tool that can apply enough force to overcome the friction between the projection  90  and the inner surface  50  of the shell  20  and allow the projection  90  to deform for engagement into the groove of the shell  20 . 
     As discussed above, the projection  90  can be formed with the other portions of the liner  30  according to generally known manufacturing techniques. Generally, the liner  30  can be molded using generally known molding and forming techniques. Accordingly, the projection  90  need not be an additional piece that is added to the liner or to the assembly of the shell  20  with the liner  30 . The projection  90  being integral with the liner  30  allows for an efficient assembly of the liner  30  with the shell  20 . Additionally, additional machining and manufacturing steps for a separate locking mechanism may not be required. Further, the material forming the projection  90  can generally be substantially anatomically and physiologically compatible and additional materials need not be offered to the assembly. 
     The interaction of the liner  30 , including the projection  90 , with the inner surface  50  of the shell  20  can provide for a substantially strong lever-out and push-out force. Various standards have been developed in the art to measure forces that act on acetabular prostheses to attempt to disassemble or disconnect the liner  30  from the shell  20 . For example, a lever out test, according to the standard ASTM F1820-97 (2009) can measure the amount of force required to lever out the liner  30  from the shell  20 . Generally, the liner  30  can be assembled into the shell  20 . The shell  20  is then held fixed within an assembly and a leaver arm engages the liner  30  by being pressed into the liner  30  across the diameter of the liner  30 . The lever arm is then pressed over a fulcrum to apply a force to attempt to lever out the liner  30  from the shell  20 . Generally, the lever out force of the liner  30  including the projection is about 140 foot/pounds (ft/lb) to about 190 ft/lb, including about 160 ft/lb to about 190 ft/lb, and further including about 170 ft/lb to lever out the liner  30  from the shell  20 . 
     Additionally, a push-out force test can also be performed according to the standard ASTM F1820-97 (2009) standard. In a push-out test, the liner  30  is assembled into the shell  20  and the shell  20  is supported by an assembly while the liner  30  is free to move when a force is applied. The force is supplied through the apical hole  42  with a push bar. The push-out force for the liner  30  with the projection  90  assembled within the shell  20  can generally be about 320 ft/lb to about 400 ft/lb, including about 350 ft/lb to about 380 ft/lb, and further including about 370 ft/lb. Accordingly, the assembly of the liner  30  into the shell  20  including only the axial fixation projection  90  can provide a substantial lever-out and push-out forced resistance. Additionally, it is understood, that the other configurations, including that illustrated in  FIG. 5 , can include similar lever-out and push-out force resistance given the configuration of the axial fixation projection  190  to interact with the shell  20 . Generally, the achieved lever-out and push-out forces can be achieved when the projection, according to various embodiments, can achieve the seated or deformed configuration that moves the selected amount of material past a mid-line of the projection. Further, it is understood, that the material of the projection  90  remains in the second or implanted configuration after implantation until acted upon by a member that produces the forces discussed above. That is, the projection  90  does not substantially elastically deform, but maintains the implanted configuration. 
     The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.