Abstract:
Orthopaedic assemblies including a tibial component and one of a fixed tibial insert or a rotatable tibial insert. The assemblies may include structure to prevent undesired movement between the tibial component and insert. For example, a retaining tab may be provided on the tibial component that couples to a tab opening on a surface of the tibial insert (either the fixed or rotatable insert). When assembled, the retaining tab may be covered to avoid possible irritation to the patient&#39;s surrounding anatomy. The fixed tibial insert may be provided with a tab opening that provides a minimal amount clearance with the retaining tab to help prevent rotation of the fixed tibial insert. The rotatable tibial insert may be provided with a tab opening with more clearance with the retaining tab to allow at least some rotation with the tibial component.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of U.S. patent application Ser. No. 13/150,500, filed Jun. 1, 2011, which claims the benefit of U.S. Provisional Patent Application Ser. No. 61/350,346 entitled “Orthopaedic Implant System and Fasteners for use Therein” filed Jun. 1, 2010. The entire contents of U.S. application Ser. No. 13/150,500 and U.S. Application Ser. No. 61/350,346 are incorporated by reference herein. 
     
    
     RELATED FIELDS 
       [0002]    Apparatus and methods for coupling components of orthopaedic implants together are described herein. 
       BACKGROUND OF THE INVENTION 
       [0003]    Orthopaedic implants, including for instance knee implants, can be modular in nature and include several components. For instance, many knee implants include a femoral implant and a tibial implant. The tibial implant may include a base tibial component and one or more inserts. After bone resectioning, the tibial component is positioned on the patient&#39;s tibia and the femoral component is positioned on the patient&#39;s femur. The tibial insert is secured to or captured by the tibial component, and includes a superior surface for contact with one or two (depending on the type of femoral implant) condylar surfaces of the femoral component (or the native femoral condyles). In use, the condylar surfaces of the femoral component and/or native femur will articulate on the superior surface of the tibial insert as the knee joint flexes and extends. 
         [0004]    Tibial inserts may be either fixed or rotatable. A rotatable tibial insert rotates with respect to the tibial component (which is fixedly secured to the tibia) as the knee joint flexes and extends. On the other hand, a fixed tibial insert is not intended to rotate with respect to the tibial component when the knee joint flexes and extends. The type of implant chosen for a particular patient, including whether a fixed or rotating tibial insert is used, depends on a number of factors, including the condition of the patient&#39;s bones, ligamenture and other anatomy. 
         [0005]    The components of a knee implant are subject to large loads and other forces in vivo that are applied over many cycles throughout the implant&#39;s useful life. Accordingly, it is important that the components of the tibial implant, including the tibial component and the tibial insert, be appropriately coupled to one another such that they do not separate or otherwise move in unintended manners once implanted in the patient. 
         [0006]    Prior systems of coupling the components have several problems. First, some prior systems use coupling mechanisms that are “exposed” in that when the knee joint is in flexion, edges, protrusions or other surfaces of the coupling mechanism contact or impinge on the patient&#39;s surrounding anatomy. Such contact or impingement may be painful to the patient, may destroy or damage the ligamenture, bone and/or other anatomy, or may damage the locking component. Second, many prior systems do not provide adequate constraints against movement (both rotational and vertical) of tibial inserts with respect to their associated tibial components, especially as the implant is cycled numerous of times. In some instances, prior systems can fail when the tibial insert “spins outs,” “pulls out,” or otherwise becomes dislocated with respect to the tibial component. Spin out refers to excessive rotation of the tibial insert (particularly for rotatable tibial inserts) such that the tibial insert becomes improperly oriented within the knee joint. Pull out refers to vertical separation between the tibial insert and the tibial component. Third, prior systems with fixed tibial inserts, in some instances, may undesirably allow at least some rotation of the fixed insert. Fourth, prior systems with fixed tibial inserts may use fasteners to secure the insert to the tibial component that may loosen and back out, thus un-coupling the insert from the tibial component. 
         [0007]    Thus, there is a need in some instances for an orthopaedic implant that includes structure to couple a tibial insert to a tibial component, but that avoids contact with the patient&#39;s ligamenture, bone and other surrounding anatomy. 
         [0008]    There is a need in some instances for an orthopaedic implant that minimizes excessive or undesirable rotation between the tibial insert and the tibial component. 
         [0009]    There is a need in some instances for an orthopaedic implant that avoids vertical separation of the tibial insert from the tibial component. 
         [0010]    There is a need in some instances for improved fasteners that will not loosen or back out of the tibial insert. 
         [0011]    Finally, there is a need in some instances for a tibial component that may be used interchangeably with either a fixed tibial insert or a rotatable tibial insert. 
       SUMMARY 
       [0012]    Certain embodiments described herein provide an orthopaedic assembly including a tibial component and one of a fixed tibial insert or a rotatable tibial insert. The assemblies may be provided with improved structure to couple the tibial insert to the tibial component to prevent spin out, pull out, other undesired rotations and/or translations, and/or irritation to the patient&#39;s surrounding anatomy. 
         [0013]    The tibial components described herein may include a retaining tab with a hooked edge that couples to a tab opening on an inferior surface of the tibial insert (either the fixed insert or the rotatable insert). The retaining tab may be set back from the outermost anterior edge of the tibial component such that when assembled, a portion of the tibial insert covers the retaining tab. Thus, neither the retaining tab or the tab opening are exposed to the patient&#39;s surrounding anatomy, preventing possible pinch points and irritation when the knee is in flexion. The hooked edge of the retaining tab contacts an inner surface of the tibial insert to prevent vertical separation (or pull out) of the tibial insert from the tibial component. 
         [0014]    Certain embodiments may also be provided with structure to prevent excessive or unwanted rotation between the tibial component and the tibial insert. For example, tibial inserts may be provided with tab openings (such as the tab openings described above) that receive the retaining tab of the tibial component and are structured in a manner to limit movement of the retaining tab in the tab opening. The fixed tibial insert may be provided with a tab opening conforming in at least some dimensions to the size and shape of the retaining tab, such that there is little to no clearance with the retaining tab, thus helping to prevent rotation of the fixed tibial insert. In contrast, the rotatable tibial insert may be provided with a relatively elongated tab opening, such that there is clearance with the retaining tab. This clearance may allow the rotatable tibial insert to rotate with respect to the tibial component. 
         [0015]    Certain embodiments may also be provided with fasteners to further minimize any movement of the fixed tibial insert. Such fasteners may include a deformable portion that creates an interference fit with the fixed tibial insert. The interference fit will help retain the fastener within the fixed tibial insert even if the fastener rotates or otherwise becomes loose. 
         [0016]    In accordance with some embodiments, there may be provided an orthopaedic implant comprising a first implant component, the first implant component comprising: a substantially planar mounting surface configured for mounting to a second implant component; a retaining tab extending upwardly away from the substantially planar mounting surface; and an angled opening configured to receive a fastener, wherein the angled opening extends downwardly from the substantially planar mounting surface at an angle that is non-perpendicular relative to the substantially planar mounting surface. 
         [0017]    The angled opening may be angled away from the retaining tab. 
         [0018]    The angled opening may be at least partially threaded. 
         [0019]    The retaining tab may set back from an outer edge of the first implant component. 
         [0020]    The retaining tab may comprise a hooked portion extending above the substantially planar mounting surface. 
         [0021]    The hooked portion may extend away from the angled opening 
         [0022]    The retaining tab may comprise a substantially vertical portion and wherein the hooked portion extends from an upper end of the substantially vertical portion. 
         [0023]    The hooked portion may be substantially horizontal relative to the substantially vertical portion. 
         [0024]    The hooked portion may include an angled surface on an underside of the hooked portion. 
         [0025]    The first implant component may comprise a tibial tray. 
         [0026]    The orthopaedic implant may further comprise the second implant component, wherein the second implant component comprises a tibial insert, the tibial insert comprising an articular surface on a superior side of the tibial insert and a substantially planar mounting surface on an inferior side of the tibial insert. 
         [0027]    The tibial insert may further comprise a tab opening configured to receive the retaining tab, the tab opening extending from the substantially planar mounting surface of the tibial insert. 
         [0028]    The tab opening may further comprise an angled surface configured to confront the angled surface of the retaining tab. 
         [0029]    The tibial insert may comprise an angled opening configured to receive the fastener, wherein the angled opening of the tibial insert extends away from the substantially planar mounting surface of the tibial insert at the same angle as the angled opening of the first implant component extends relative to the substantially planar mounting surface of the first implant component. 
         [0030]    The orthopaedic implant may further comprise the fastener, wherein the fastener includes an interference portion configured to cause an interference fit with respect to at least one of the angled openings of the first implant component and the tibial insert. 
         [0031]    In accordance with some embodiments, there may be provided an orthopaedic implant comprising: a tibial tray, wherein the tibial tray comprises a substantially planar tray surface and an angled opening configured to receive a fastener, wherein the angled opening extends downwardly from the substantially planar tray surface at an angle that is non-perpendicular relative to the substantially planar tray surface; and a tibial insert, wherein the tibial insert comprises an articular surface and a substantially planar mounting surface configured to abut the tray surface; wherein a retaining tab including a hooked edge extends from one of the tray surface and the mounting surface; wherein a tab opening including a recess extends into the other of the tray surface and the mounting surface; and wherein the hooked edge of the retaining tab is configured to engage the recess of the tab opening when the tibia insert is mounted to the tibia tray with the substantially planar mounting surface of the tibial insert in abutment with the tray surface of the tibial tray. 
         [0032]    The tibial insert may be a mobile bearing insert and wherein the substantially planar mounting surface is a second articular surface. 
         [0033]    The tibial insert may be a fixed insert; and wherein the orthopaedic implant further comprises the fastener configured to be received in the angled opening 
         [0034]    The retaining tab may extend from the tray surface; and wherein the hooked edge of the retaining tab and the angled opening extend away from one another. 
         [0035]    In accordance with some embodiments, there may be provided an orthopaedic implant, comprising: a first orthopaedic component, the first orthopaedic component including an articular surface and a mating surface, wherein an opening extends from the mating surface of the first orthopaedic component at least partially through the first orthopaedic component; a second orthopaedic component, the second orthopaedic component including a mating surface configured to abut the mating surface of the first orthopaedic component, wherein a second opening extends from the mating surface of the second orthopaedic component at least partially through the second orthopaedic component; and a threaded fastener configured to secure the first orthopaedic component to the second orthopaedic component and to extend at least partially through the first and second openings, wherein the fastener includes a means for creating an interference fit with at least one of the first and second openings; wherein at least one of the first and second openings is partially threaded. 
         [0036]    In accordance with some embodiments, there may be provided an orthopaedic implant, comprising: a first orthopaedic component, comprising a substantially planar mounting surface; and a second orthopaedic component, comprising a substantially planar mounting surface on a first side of the second orthopaedic component and a condylar articular surface on a second side of the orthopaedic component; wherein the first orthopaedic component is a tibial tray and the second orthopaedic component is a tibial insert; wherein the second orthopaedic component is configured to be secured to the first orthopaedic component in a rotating fashion; wherein an arcuate retaining tab including a hooked edge extends from one of the mounting surfaces of the first and second orthopaedic components; wherein an arcuate tab opening including a recess extends into the other of the mounting surfaces of the first and second orthopaedic components; wherein the arcuate tab opening is configured to receive the arcuate retaining tab when the second orthopaedic component is secured to the first orthopaedic component such that the arcuate retaining tab can rotate in the arcuate tab opening along a rotational arc; and wherein the arcuate tab opening extends along a greater portion of the rotational arc than the arcuate retaining tab. 
         [0037]    The arcuate retaining tab may extend from the mounting surface of the first orthopaedic component; and wherein the arcuate retaining tab is set back from an outer edge of the first orthopaedic component. 
         [0038]    The orthopaedic implant may further comprise a post; wherein at least one of the first and second orthopaedic components is configured to receive the post; and wherein the second orthopaedic component is configured to rotate with respect to the first orthopaedic component about the post. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0039]    The specification makes reference to the following appended figures, in which use of like reference numerals in different features is intended to illustrate like or analogous components. 
           [0040]      FIG. 1  is a perspective view of a tibial component. 
           [0041]      FIG. 2  is a cross-sectional view of the tibial component of  FIG. 1  taken along line  FIG. 2-FIG .  2 . 
           [0042]      FIG. 3  is a perspective view of a fixed insert. 
           [0043]      FIG. 4  is a top plan view of the fixed insert of  FIG. 3 . 
           [0044]      FIG. 5  is a cross-sectional view of the fixed insert of  FIG. 4  taken along line  FIG. 5-FIG .  5 . 
           [0045]      FIG. 6  is a front view of an assembly comprising a fixed insert, a tibial component, and a fastener. 
           [0046]      FIG. 7  is a perspective view of the assembly of  FIG. 6 . 
           [0047]      FIGS. 8A-B  are cross-sectional views of the assembly of  FIG. 7  taken along line  FIG. 8-FIG .  8 . 
           [0048]      FIG. 9  is a top plan view of another assembly comprising a fixed insert, a tibial component, and a fastener. 
           [0049]      FIG. 10  is a cross-sectional view of the assembly of  FIG. 9  taken along line  FIG. 10-FIG .  10 . 
           [0050]      FIG. 11  is a cross-sectional view of the assembly of  FIG. 10  taken along line  FIG. 11-FIG .  11 . 
           [0051]      FIG. 12  is a side view of a fastener. 
           [0052]      FIG. 13  is a perspective view of the fastener of  FIG. 12 . 
           [0053]      FIG. 14  is a detail view of the assembly of  FIG. 10 . 
           [0054]      FIGS. 14A and 14B  are detailed views of another assembly including a fastener. 
           [0055]      FIG. 15  is a top plan view of another assembly including a fixed insert, a tibial component, a fastener, and a post. 
           [0056]      FIG. 16  is a cross-sectional view of the assembly of  FIG. 15  taken along line  FIG. 16-FIG .  16 . 
           [0057]      FIG. 17  is a perspective view of a rotatable insert. 
           [0058]      FIG. 18  is a cross-sectional view of the rotatable insert of  FIG. 17  taken along line  FIG. 18-FIG .  18 . 
           [0059]      FIG. 19  is a side view of an assembly comprising a rotatable insert, a tibial component, and a post. 
           [0060]      FIG. 20  is a perspective view of the assembly of  FIG. 19 . 
           [0061]      FIG. 21  is a top plan view of the assembly of  FIG. 20 . 
           [0062]      FIG. 22  is a cross-sectional view of the assembly of  FIG. 21  taken along line  FIG. 22-FIG .  22 . 
           [0063]      FIG. 23  is a cross-sectional view of the assembly of  FIG. 22  taken along line  FIG. 23-FIG .  23 . 
       
    
    
     DETAILED DESCRIPTION 
       [0064]      FIGS. 1-23  illustrate structures and mechanisms for coupling tibial inserts and tibial components together. Although the orthopaedic implants shown and described herein are for knee joints, the same concepts could potentially be applied to implants for other joints or orthopaedic implants.  FIGS. 3-16  illustrate embodiments of implants that include fixed tibial inserts  40  or other types of fixed constructs, whereas  FIGS. 17-23  illustrate embodiments that include rotatable tibial inserts  90 . In the embodiments shown, the same tibial component  10  may be used, thus providing for interchangability between tibial inserts  40 ,  90 . 
         [0065]      FIGS. 1-2  show a tibial component  10  including a stem portion  12  and a tibial tray  14 . The stem portion  12  may be dimensioned to couple with structure (not shown) that is inserted into a patient&#39;s intramedullary canal (and itself may be inserted into the intramedullary canal). Thus, for example, the stem portion  12  may include at least one opening  32  and/or recess  34  that facilitates coupling the tibial component  10  to other structure. The stem portion  12  may include fins  30  or other structure such as bone-engaging fluting, porous materials to promote bony in-growth or other features to facilitate securing the tibial component in the proximal tibia. 
         [0066]    The tibial tray  14  shown in the figures rests on top of the patient&#39;s resected tibia. The tibial tray  14  may include a tray surface  16  that is generally planar and that contacts a tibial insert  40 ,  90  as described below. The tibial tray  14  shown also includes an outermost anterior edge  17 . 
         [0067]    As shown in  FIGS. 1-2 , the tibial component  10  includes an opening  28  to receive a post  100  (see  FIG. 16 ). Posts  100  may be used with either rotatable inserts  90  (as shown in  FIGS. 19-23 ) or with fixed inserts  40  (as shown in  FIGS. 15 and 16 ). It should be understood that post  100  is not a necessity for the functionality of fixed insert  40 . But if fixed insert  40  is used in an orthopaedic implant incorporating a hinge design, then post  100  may be provided to connect a femoral component (not shown) to the tibia. In some embodiments, post  100  may be used to capture, constrain or secure a femoral implant to the tibial implant, while still allowing for certain desired articulations, rotations, and/or other movements between the femoral and tibial implants. Even when the tibial component  10  is provided with an opening  28  it is not necessary to provide a post  100 . Rather, opening  28  may remain vacant in some uses, as shown in  FIGS. 9-11 . In still other embodiments the tibial component  10  does not include such an opening  28  (such as in  FIGS. 8A and 8B ). It should be understood that the opening  28  is non-limiting and is not required for all embodiments; however, it may be preferred to provide a tibial component  10  with an opening  28  such that a surgeon may decide interoperatively whether to use a post  100 . 
         [0068]    As illustrated in  FIGS. 1-2 , certain embodiments of the tibial component  10  include a retaining tab  18  having a hooked edge  19 . The retaining tab  18  may be set back from the anterior edge  17  of the tibial tray  14  such that the tab  18  is not exposed to the patient&#39;s anatomy when implanted. As described in more detail herein, the retaining tab  18  acts as a “hook” to couple the tibial insert  40 ,  90  to the tibial component  10 . In one embodiment at least a portion of the hooked edge  19  may include an angled surface  20 . The angled surface  20  may be provided on the entire length of the hooked edge  19 , or only a portion of the length. The particular angle β of the angled surface  20  (see  FIG. 2 ) may vary between embodiments and is not limiting. In certain embodiments the hooked edge  19  does not have an angled surface  20 , such that the hooked edge  19  is generally parallel to the tray surface  16  of the tibial tray  14 . 
         [0069]    In some embodiments, the retaining tab  18  could be part of a tibial insert  40 ,  90  rather than the tibial component  10 , and the tibial component  10  could include structure for interacting with the retaining tab  18  (described below). In these or other embodiments, the retaining tab  18  does not necessarily have to be hooked-shaped (or be a tab) to accomplish the functions set forth herein. 
         [0070]    The tibial component  10  may also be provided with an angled opening  22  to receive a fastener  70 . As shown in  FIG. 2 , angled opening  22  is angled by angle θ with respect to a perpendicular line from the tibial tray  14 . Although the angle θ may vary between different embodiments, the magnitude of the angle θ may be constrained by the size of the tibial tray  14 . For example, smaller tibial trays  14  may have a smaller angle θ than larger tibial trays  14 . In certain embodiments the angled opening  22  includes threads  26  (to mate with threads  76  of the fastener  70 ) and a counterbore portion  24 . Counterbore portion  24  is not required, but may be provided in order to more easily machine threads  26  into the angled opening  22 . As described in more detail herein, the angled opening  22  helps to provide a more secure connection between the fixed tibial insert  40  and the tibial component  10 . 
         [0071]    The tibial component  10  may be made of any suitable material, including either metal (such as but not limited to titanium, oxidized zirconium, surgical stainless steel, or others), plastics (such as but not limited to high molecular weight polyethylene (either cross-linked or not cross-linked)), ceramics, other materials, or combinations of these or other materials. If desired, the tibial component  10  may be porous or coated with material (such as hydroxyapatite) to increase fixation of the tibial component  10  within the bone. In general the material and surface treatments of the tibial component  10  are non-limiting. 
         [0072]      FIGS. 3-16  show a fixed insert  40  for connection to a tibial component. The fixed insert  40  may be coupled to the tibial component  10  such that there is little to no rotation between the fixed insert  40  and the tibial component  10 . The fixed insert  40  may include a superior surface  42  that is shaped to provide an articular surface or surfaces for the condyles of a femoral component (not shown) and/or the native femur. An inferior surface  44  may be provided opposite the superior surface  42 , and is generally planar (in the embodiment shown) to contact the tray surface  16  of the tibial tray  14 . Sidewalls  46  extend between the superior surface  42  and the inferior surface  44 . The height of the sidewalls  46  (and consequentially the thickness of the fixed insert  40 ) may vary between embodiments and is in no way limiting. 
         [0073]    In certain embodiments the fixed insert  40  is provided with a central opening  48  and an angled opening  50 . The angled opening  50  may include a counterbore portion  52  and a threaded portion  54 . As shown in  FIGS. 8A-B , a fastener  70  may be inserted into the angled openings  50 ,  22  of the fixed insert  40  and the tibial component  10 . Thus, as shown in  FIG. 8A , the angles θ of both angled openings  50 ,  22  are approximately equal. The central opening  48  provides access to the angled opening  50  such that the surgeon has room to insert and secure the fastener  70 . Also, if it is desired to use a post  100  (such as in  FIGS. 15 and 16 ), the central opening  48  provides room for the post  100 . 
         [0074]    As shown in  FIG. 5 , in certain embodiments the fixed insert  40  includes a tab opening  56 . As shown in  FIGS. 8A-B , the tab opening  56  receives the retaining tab  18  of the tibial component  10 . If the hooked edge  19  of the retaining tab  18  includes an angled surface  20 , then the tab opening  56  may also include an angled surface  58 . Otherwise, both the hooked edge  19  and the tab opening  56  can be substantially parallel to the tray surface  16  (and will not have angled surfaces  20 ,  58 ). As mentioned above, in other embodiments, tabs  18  and tab openings  56  can have other shapes and configurations. 
         [0075]      FIGS. 8A and 8B  both show an assembly comprising a tibial component  10 , a fixed insert  40 , and a fastener  70 . In  FIG. 8A  the fastener  70  is inserted through the angled opening  50  of the fixed insert  40 . As shown in  FIG. 8B , when the fastener  70  is seated in the opening  50  with its head  72  bearing against the shoulder of counterbore  52  and the threads  76  engaged with the threaded portion  26  of opening  22 , fastener  70  can exert a compressive force F 1  between the tibial component  10  and the fixed insert  40  along the angle θ. Because force F 1  is non-perpendicular to the tibial component  10  and fixed insert  40 , a component of this force will act on the fixed insert  40  in an anterior to posterior direction, as indicated by force F 2  in  FIG. 8B . Thus, the fixed insert  40  may be drawn (or at least disposed) in the direction of the force F 2 , which causes the angled surface  58  of the tab opening  56  to contact and press against the angled surface  20  of the retaining tab  18 . Thus, a wedge-like effect may be effected between the angled surfaces  20 ,  58  of the tab opening  56  and the retaining tab  18 . This wedge effect securely fastens the fixed insert  40  to the tibial component  10  such that vertical separation (or pull out) between the fixed insert  40  to the tibial component  10  is minimized or eliminated, and, in some embodiments, may also help to minimize or eliminate the tendency of the fixed insert  40  to rotate with respect to tibial component  10 . Additionally, and as discussed in more detail below, the engagement between the fastener  70  and the angled openings  22 ,  50  also prevents vertical separation. Rotation between the fixed insert  40  and the tibial component  10  may be further minimized in some embodiments due to the close fit between the tab opening  56  and the retaining tab  18 . Specifically, as shown in  FIG. 11 , the projected angles of the tab opening  56  (A 2 ) and the retaining tab  18  (A 1 ) are approximately equal such that there is a close fit between the two components, leaving the fixed insert  40  with little (if any) room to rotate. 
         [0076]    As shown in  FIGS. 8A and 8B , the retaining tab  18  is set back from the anterior edge  17  of the tibial component  10 . When assembled, a portion of the fixed insert  40  covers the retaining tab  18  such that neither the retaining tab  18  or the tab opening  56  are exposed to the patient&#39;s surrounding anatomy. 
         [0077]      FIGS. 12-14  illustrate a fastener  70  with structure to more securely fasten the fixed insert  40  to the tibial component  10 . Fastener  70  may include a shaft  74  with a threaded portion  76  and an interference portion  78  along at least a portion of its length. Optionally, the fastener  70  may include a head  72 . As shown in  FIG. 14 , the fastener  70  may also be provided with a counterbore  84  to receive a driver. 
         [0078]    If desired, the threaded portion  76  (and/or the female threads of the aperture in which the fastener  70  is used) may incorporate threads such as the SPIRALOCK® thread made by Emhart Teknologies (based in Shelton Conn.), or threads as described in (inter alia) U.S. Pat. Nos. 4,171,012, 4,150,702, or 4,076,064. Such threads incorporate a wedge ramp design that distributes the loads of the threaded joint more evenly throughout all of the engaged threads, and also minimizes loosening under vibration. But it should be understood that such threads are not required, and the threaded portion  76  may incorporate any type of standard thread. 
         [0079]    Together with the threaded portion  76 , or by itself, a means for creating an interference fit (e.g. the interference portion  78 ) may act to minimize loosening and pull-out of the fastener  70 . The interference portion  78  may be provided anywhere along the length of the fastener  70 , and may be provided in many different shapes, lengths, or diameters. For example, in  FIGS. 12 and 13  the interference portion  78  has approximately the same diameter as the major diameter of the threaded portion  76 . In other embodiments the interference portion  78  may have a smaller or larger diameter. If desired, the interference portion  78  may include a chamfer  80 . In certain embodiments the interference portion  78  is separated by the threaded portion  76  and the head  72  (respectively) by necks  82 . But the necks  82  are not required; for example, in another embodiment the interference portion  78  could contact the threaded portion  76 . 
         [0080]      FIG. 14  is a detail view of a fastener  70  secured within angled openings  22 ,  50 . The threaded portion  76  of the fastener  70  threadedly engages with the threaded portions  26 ,  54  of the tibial component  10  and the fixed insert  40 , respectively. As the fastener  70  is drawn further within angled opening  50 , an interference fit is created between the interference portion  78  and the threads  54  or other portions of the angled opening  50 . It may be desirable to create an interference fit through more than one turn of the fastener  70 . In certain embodiments the threads  54  cut into and/or otherwise deform the interference portion  78 . In other embodiments the interference portion  78  may cut into and/or otherwise deform the threads  54  (or other portions of a threaded or non-threaded opening) In still other embodiments both the threads and the interference portion  78  are deformed. The selection of materials for the threads  54  and the interference portion  78  may determine which of the components becomes deformed. Upon deformation, the fastener  70  becomes securely fixed within the angled opening  50  of the fixed insert  40 . Embodiments of fasteners  70  have been found to remain securely fastened within one or both of the angled openings  22 ,  50  and/or resistant to back-out even if a portion of the threads  26 ,  54 ,  76  become loosened or if fastener  70  rotates in the openings  22 ,  50 . 
         [0081]    In other embodiments, the fastener  70  or the openings  22 ,  50  may be provided with still additional or alternative structure by which to create an interference fit within the angled openings  22 ,  50 . For example, the threaded portion  76  of the fastener  70  could be provided with threads having a different pitch than the threaded portion  54  of the fixed insert  40  (or of the threaded portion  26  of the tibial component  10 ). The different pitched threads create an interference fit. As other examples, the fastener  40  and/or the openings  22 ,  50  may be provided with structure other than threads (such as barbs, ribbing, dove-tails, or any other shape) that would create an interference fit. 
         [0082]    In other embodiments, fastener  70  may be used in contexts other than coupling the fixed insert  40  to the tibial component  10 . For example, fastener  70  may be used to couple any two components together relating to any other implant, joint, or anatomy. Non-limiting examples include coupling the following components together: an acetabular cup and a shell, a bone plate and bone, a glenoid and a base, a unicondylar insert and a unicondylar base, or a non-hinge insert and a tibial base. Thus,  FIGS. 14A and 14B  are detailed views of fastener  70  in use with such other applications, where the reference number “X” generally refers to a first component and reference number “Y” generally refers to a second component. In  FIG. 14A  the contact between components X, Y is generally planar, such as might be seen when coupling a bone plate to bone. In  FIG. 14B  the contact between components X,Y is curved, such as might be seen when coupling a cup and a shell. 
         [0083]      FIGS. 17-23  show a rotatable insert  90 . Rotatable insert  90  rotates with respect to the tibial component  10  during at least some portions of flexion and extension of the knee joint. As shown in  FIG. 18 , rotatable insert  90  may include a superior surface  42  that is shaped to contact condyles of a femoral component and/or a native femur (not shown). An inferior surface  44  may be provided opposite the superior surface  42  to contact the tray surface  16  of the tibial tray  14 . The inferior surface  44  may be provided with a recess  92  that is generally aligned with the angled opening  22  of the tibial component  10 . The recess  92  may be provided in order to avoid any contact between the inferior surface  44  of the rotatable insert  90  and any sharp edges or burrs that might be present adjacent to opening  22 . Such contact may produce undesirable debris. It should be understood that the recess  92  is optional, and is not required for any embodiments. Sidewalls  46  extend between the superior surface  42  and the inferior surface  44 . The height of the sidewalls  46  (and consequentially the thickness of the rotatable insert  90 ) may vary between embodiments and is in no way limiting. In certain embodiments the rotatable insert  90  is provided with a central opening  48 . 
         [0084]      FIGS. 19-23  show an assembly comprising a tibial component  10 , a rotatable insert  90 , and a post  100 . As shown in  FIG. 22 , the tab opening  56  of the rotatable insert  90  receives the retaining tab  18  of the tibial component  10 . If the hooked edge  19  of the retaining tab  18  includes an angled surface  20 , then the tab opening  56  may also include an angled surface  58 . Otherwise, both the hooked edge  19  and the tab opening  56  can be substantially parallel to the tray surface  16  or positioned in other configurations. The rotatable insert  90  shown is constrained from vertical separation (thus preventing pull-out) by the contact between the hooked edge  19  and the tab opening  56 . At the same time, irritation to the patient&#39;s surrounding anatomy is lessened because the retaining tab  18  is set back from the anterior edge  17  of the tibial component  10  such that a portion of the rotatable insert  90  covers the retaining tab  18 . Thus, neither the retaining tab  18  or the tab opening  56  are exposed to the patient&#39;s surrounding anatomy. 
         [0085]    A post  100  may be received within the openings  48 ,  28  of the rotatable insert  90  and the tibial component  10 , respectively. A lower portion of the opening  48  in insert  90  may at least roughly correspond to the outer diameter of post  100 , thus fixing the translational positioning of the insert  90  on the tibial component  10 , while still allowing the insert  90  to rotate with respect to the tibial component  90 . 
         [0086]    As shown in  FIG. 23 , the interaction between the retaining tab  18  and tab opening  56  allows some rotation of the rotatable insert  90  (unlike the fixed insert  40  embodiment described above) because the tab opening  56  extends along a greater portion of a rotational arc (defined by a radius extending from the center of rotation of the insert  90 ) than the retaining tab  18 . Specifically, the projected angle of tab opening  56  (A 2 ) is greater than the projected angle of the retaining tab  18  (A 1 ). Thus, the rotatable insert  90  may rotate by an angle equal to the difference between the projected angles A 2  and A 1 . But the rotatable insert  90  is constrained from excessive rotation when the retaining tab  18  contacts the tab opening  56 . Additionally, the interaction between retaining tab  18  and tab opening  56  helps to resist pull out of the insert  90  from the tibial component  10  in a similar manner to that described above for the fixed insert  40  (although that resistance may be somewhat lessened in this particular embodiment since an angled fastener  70  is not necessarily used). 
         [0087]    The fixed insert  40  and/or the rotatable insert  90  may be made of any suitable material, including either metal (such as but not limited to titanium, oxidized zirconium, surgical stainless steel, or others), plastics (such as but not limited to high molecular weight polyethylene (either cross-linked or not cross-linked)), ceramics, other materials, or combinations of these or other materials. If desired, the inserts  40 ,  90  may be polished, coated, or have other surface treatments. In general the material and surface treatments of the inserts  40 ,  90  are non-limiting. 
         [0088]    The foregoing is provided for purposes of illustration and disclosure of embodiments of the invention. It will be appreciated that those skilled in the art, upon attaining an understanding of the foregoing may readily produce alterations to, variations of, and equivalents to such embodiments. For example, although the orthopaedic implants have generally been described as a knee joint replacement, the same concepts could be applied to orthopaedics for other joints or other implants. Accordingly, it should be understood that the present disclosure has been presented for purposes of example rather than limitation, and does not preclude inclusion of such modifications, variations and/or additions to the present subject matter as would be readily apparent to one of ordinary skill in the art.