Abstract:
A prosthesis system includes at least one stem including a cavity, a plurality of heads having a head coupling portion, at least one first coupler including a first upper coupling portion and a first lower coupling portion, the first upper coupling portion configured to couple with the head coupling portion of each of the plurality of heads and the first lower coupling portion configured to couple with the stem with a predetermined version angle and a predetermined inclination angle, and at least one second coupler including a second upper coupling portion and a second lower coupling portion, the second upper coupling portion configured to couple with the head coupling portion of each of the plurality of heads and the second lower coupling portion configured to couple with the stem with any of a plurality of version angles and any of a plurality of inclination angles.

Description:
This application is a divisional of U.S. application Ser. No. 11/241,387 filed Sep. 30, 2005, which issued as U.S. Pat. No. 8,679,185 on Mar. 25, 2014, the entire contents of which is herein incorporated by reference. 
    
    
     BACKGROUND AND SUMMARY 
     The present disclosure relates to joint prostheses, and particularly to prostheses having articulating head components. More specifically, the disclosure relates to a system for achieving variable positions for the head component of a joint prosthesis relative to a bone-engaging portion of the prosthesis. 
     Repair and replacement of human joints, such as the knee, shoulder, elbow and hip, has become a more and more frequent medical treatment. Longer life spans mean that the joints endure more wear and tear. More sports activities mean greater likelihood of serious joint injuries. Treatment of injuries, wear and disease in human joints has progressed from the use of orthotics to mask the problem, to fusion of the joint, to the use of prostheses to replace the damaged joint component(s). 
     As the success rate for total or partial joint replacements has increased, so too has the need for modularity and universality in the joint prosthesis. Patient variety means that no single size or configuration of joint prosthesis will suffice. The physical dimensions of a patient&#39;s joint components vary, as well as the bio-mechanic relationship between these components. For instance, in a shoulder prosthesis, the relationship between the articulating humeral and glenoid components can be significantly different between patients. These relationships are especially important where only one component of the joint is being replaced and must integrate with the existing natural opposing joint component. 
     For instance, in many shoulder surgeries, only the humeral component is replaced, leaving the glenoid component intact. In this case, it is imperative that the articulating surface of the humeral component match the articulating surface of the glenoid component as perfectly as possible, both statically and dynamically. With a typical humeral prosthesis, version and inclination are adjusted by the geometry of the head of the prosthesis. In other words, certain pre-determined head geometries are available that can be selected for a mating glenoid component. Absent an infinite variety of pre-determined head geometries, the resulting humeral prosthesis can often only achieve a best-fit relationship to the glenoid component of the shoulder joint. 
     In a typical surgical procedure, a trial component will be used to determine the optimum final component to be fixed to the bone. In most cases, the surgeon is able to make a good selection that fits the joint very well. However, in some cases, the accuracy of the fit cannot be determined until the surgery is completed and the patient has had an opportunity to exercise the repaired joint. Where significant problems arise, a revision surgery may be necessary to replace an improperly sized or configured joint component. One typical revision surgery requires removal of the entire prosthesis from the bone and replacement with a different prosthesis. 
     There is a significant need for a joint prosthesis that is both modular and universal. Such a prosthesis would be easily manipulated during the surgery and capable of achieving nearly infinite version and inclination angles. Moreover, an optimum prosthesis would be readily available for modification in a revision surgery without having to remove the entire prosthesis. 
     With the disclosed joint prosthesis a joint component is mounted to a bone engaging component of the prosthesis by an articulating mounting element. The articulating mounting element allows the joint component to adopt substantially infinitely variable ranges of angles in three dimensions relative to the bone engaging component. 
     In a one embodiment, the prosthesis is a humeral prosthesis for a shoulder replacement procedure. The humeral prosthesis includes a stem configured for engagement within the humerus. The stem defines a tapered bore facing the glenoid component of the shoulder joint. A distal portion of the mounting element is configured to be initially mobile within the bore, while a proximal end is configured to carry the humeral joint component or trial. The mounting element can be articulated to find the optimum position for the humeral joint component. The mounting element can then be temporarily tightened to hold the humeral joint component in position to verify the version and inclination angles of the component. The mounting element can be finally tightened to complete the humeral prosthesis. 
     The mounting element can be fixed in an orientation relative to the stem so as to fix the joint component in an orientation relative to the stem. Further, the mounting element and stem are configured to facilitate tightening the mounting element to the stem through achieving a friction fit with a tapered bore formed in the stem. 
     Several embodiments additionally utilize a second fixation mechanism. This second fixation mechanism includes a screw that is threaded into a threaded bore portion of the tapered bore in the stem. The screw bears against the mounting element to lock the element in position within the tapered bore. 
     The proximal portion of the mounting element defines a tapered surface that mates with a tapered feature of a head component for the humeral prosthesis. The head component can include an opening to access the passageway in the proximal portion of the mounting element, thereby providing access to the fixation screw in embodiments utilizing a fixation screw. 
     A number of joint components can be provided for interchangeable use to construct the prosthesis. For instance, a fixed mounting element can replace the articulating mounting element. Similarly, the head component for the joint prosthesis can be configured to mate directly with the stem, with the fixed mounting element or the articulating mounting element. The head component can also be modified to close the end of the passageway in the proximal portion of the articulating mounting element. 
     The joint prosthesis is advantageously both modular and adjustable. The joint prosthesis includes features that permit substantially infinitely variable positioning of a mating joint component relative to a bone engaging portion of the prosthesis. 
     The joint prosthesis is readily available for modification, whether during initial implantation or during a subsequent revision procedure. Preferably these features are combined in a joint prosthesis without creating a profile or prominence greater than is achieved by current joint prostheses. 
     The above-noted features and advantages of the present invention, as well as additional features and advantages, will be readily apparent to those skilled in the art upon reference to the following detailed description and the accompanying drawings, which include a disclosure of the best mode of making and using the invention presently contemplated. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The illustrative devices will be described hereinafter with reference to the attached drawings which are given as non-limiting examples only, in which: 
         FIG. 1  is a side plan view of a typical prior art humeral prosthesis; 
         FIG. 2  is an enlarged cross-sectional view of a portion of an exemplary joint prosthesis according to the present invention; 
         FIG. 3  is a front perspective view of an articulating mounting element used with the joint prosthesis of in  FIG. 2 ; 
         FIG. 4  is a front perspective view of a fixation screw used with the joint prosthesis of in  FIG. 2 ; 
         FIG. 5  is a bottom perspective view of a head component of the joint prosthesis of in  FIG. 2 ; 
         FIG. 6  is a bottom perspective view of an alternative head component for use with the joint prosthesis of  FIG. 2 ; 
         FIG. 7  is a front perspective view of an alternative mounting element that can substitute for the articulating mounting element in the joint prosthesis of  FIG. 2 ; 
         FIG. 8  is an enlarged cross-sectional view of a portion of an exemplary alternative joint prosthesis according to the present invention; and 
         FIG. 9  is a front perspective view of an alternative mounting element particularly configured to be used with the joint prosthesis of  FIG. 8  and capable of being utilized with the joint prosthesis of in  FIG. 2 . 
     
    
    
     Corresponding reference characters indicate corresponding parts throughout the several views. 
     DETAILED DESCRIPTION 
     For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiments illustrated in the drawings and described in the following written specification. It is understood that no limitation to the scope of the invention is thereby intended. It is further understood that the present invention includes any alterations and modifications to the illustrated embodiments and includes further applications of the principles of the invention as would normally occur to one skilled in the art to which this invention pertains. 
       FIG. 1  is a side plan view of a typical prior art humeral prosthesis  1 . The prosthesis  1  is the humeral component of a shoulder prosthesis that can be implanted in the humerus bone for articulating engagement with the natural glenoid or with a glenoid prosthesis. The prosthesis  1  includes a stem  2  configured to be implanted within the humerus bone in a conventional manner. The stem  2  forms a platform surface  5  that faces the glenoid component of the joint when the prosthesis is in its operative position. The platform surface  5  defines a tapered bore for use in mounting an articulating head component  4 . The head component  4  includes a substantially uniformly tapered post  8  that can be press-fit or friction-fit within a substantially uniformly tapered bore  6  to firmly mount the head component  4  to the stem  2 . 
     The prosthesis  1  can be a modular prosthesis, meaning that a number of stem and head geometries can be provided from which a selection can be made that most closely approximates the natural joint components of the patient. Thus, the angle of the platform surface  5  can be different among stems  2 . While all head components  4  will include a generally spherical bearing surface  9 , the orientation of this surface relative to the platform surface  5  can be changed. Specifically, the location of the post  8  relative to the bearing surface  9  can be offset from the center of the surface (i.e., an eccentric head). In some cases, the angle of the post can be different between head components  4 . 
     The exemplary joint prosthesis according to the present invention is modular and introduces an articulating mounting element  30 ,  130  between the stem  12  and a head component  20 , as shown in  FIGS. 2-4, 8 and 9 . In one embodiment of the invention, the mounting element  30  includes a proximal portion  33  that mates with the head component  20 . In a specific embodiment, the proximal portion  33  defines a tapered surface that is press-fit or friction-fit within a complementary bore  21  defined in the head component. 
     The first embodiment of the mounting element  30  further includes a frusto-spherical articulating portion  34 . As at least partially discernable in the drawings, the actual surface of the articulating portion  34  includes only a partial sphere because the distal end of the articulating portion is a flat circular surface perpendicular to the axis of symmetry of the mounting element  30  and the proximal end of the articulating portion is integrally formed to the proximal portion  33 . Hence, the articulating portion  34  is only partially spherical and, more specifically, is frusto-spherical. Nevertheless, it should be noted that the surface of the articulating portion  34  is contiguous and a substantial portion of the surface of the articulating portion  34 , especially that portion which would be adjacent the equatorial region of a complete sphere having its poles intersected by the axis of symmetry of the mounting element  30  is substantially equidistant from a focus located on the axis of symmetry. 
     The articulating portion  34  is sized to achieve a press-fit engagement within the tapered bore  16  of the stem  12  when the portion  34  is pushed sufficiently far into the tapered bore  16 . The partial spherical shape of the articulating portion  34  allows the mounting element  30  to rotate about three dimensional axes x, y, z when the articulating portion  34  contiguously engages the wall of the tapered bore  16  along a great circle of the partial spherical surface. Thus, the mounting element  30  can rotate about its own axis (the x axis), pivot about a version axis (they axis) or pivot about an inclination axis (the z axis). The mounting element  30  can rotate a full 360° about its own axis. However, the pivot range in the other two degrees of freedom is limited by contact between the articulating mounting element  30  or the head component and the platform surface  15  of the stem  12 . The range of motion in these two degrees of freedom are maximized by the intermediate portion  35  connecting the articulating portion  34  to the proximal portion  33 . In particular, the intermediate portion  35  can be angled away from the articulating portion  34  to form an inverted frusto-conical surface to provide clearance as the mounting element  30  is pivoted. While the illustrated proximal portion  33 , articulating portion  34  and intermediate portion  35  are shown as being formed concentrically about the axis of symmetry of the mounting element  30 , it is within the scope of the disclosure for the intermediate portion  35  and the proximal portion  33  to be formed about a second axis intersecting the axis of symmetry of the articulating portion  34  at an angle. 
     In one feature of the exemplary joint prosthesis, a second fixation capability is provided to augment the friction or press-fit between the articulating portion  34  and the tapered bore  16 . In particular, a machine screw  40  is provided that includes a threaded portion  46  configured to mate with a threaded bore  18  in the stem  12 . The bore  18  is concentrically disposed at the base of the tapered bore  16 . The screw  40  is introduced into the threaded bore  18  through the articulating mounting element  30 . 
     As at least partially discernable in  FIG. 2 , the mounting element  30  defines a central passageway  36  that extends through the length of element  30  and that is open at its proximal and distal ends. The passageway defines an internal bearing surface  38  at the distal end of the element  30 , or more specifically at the base of the articulating portion  34 . The screw  40  includes a head  42  that includes an underside surface  44  that is complementary with the internal bearing surface  38 . These two surfaces  38 ,  44  form a spherical bearing interface that allows the mounting element  30  to experience its full range of angular motion without interference from the screw  40 , even when the screw  40  is loosely threaded into the threaded bore  18 . The articulating portion  34  defines a relief  39  at the distal end of the passageway  36  to facilitate this full range of movement of the mounting element  30 . 
     The passageway  36  in the mounting element  30  allows introduction of the screw  40  through the mounting element  30  and into the threaded bore  18 . The screw  40  can be loosely threaded into the bore  18  to permit movement of the mounting element  30 . Once the proper position for the mounting element  30  has been achieved, the screw  40  can be tightened using a tool engaged within the tool recess  43  on the head  42  of the screw  40 . As the screw  40  is tightened, it drives the articulating portion  34  deeper into the tapered bore  16 , thereby fixing the mounting element  30  against further articulation. The screw  40  thus combines with the friction or press-fit feature to lock the construct. 
     The articulating mounting element  30  can be utilized with the stem  12  engaged within the bone, such as the humerus. In order to determine the proper configuration for the joint prosthesis, a head component, such as component  20  is carried by the proximal portion  32  of the mounting element. As can be seen in  FIG. 2 , the head component  20  is closed over the passageway  36 , thereby preventing access to the screw  40  unless the head portion is removed. 
     In one embodiment, a head component  70  can be provided as at least partially discernable in  FIG. 5  (which is a bottom perspective view of the head component  70 ). This head component  70  includes a tapered bore  72  that is configured for mating engagement with the proximal portion  32 . However, unlike the head component  20 , the bore  72  includes an opening  74  at the proximal face of the component. Thus, the opening  74  provides complete access to the screw  40 , even when the head component  70  is mounted on the mounting element  30 . 
     In use the mounting element  30  can be initially mated with a head component  70 . The component can be a final component or a trial. In the preferred embodiment, the two components mate by way of a socket taper as is known in the art. The mounting element  30 , with the head component  70  mounted thereon, can be maneuvered to position the articulating portion  34  within the tapered bore  16 . The screw  40  can be introduced through the opening  74  and along the passageway  36  so that the screw can be threaded into the threaded bore  18  in the stem  12 . 
     The screw  40  can be loosely tightened so that the articulating portion  34  can rotate, but the screw head  42  offers some resistance to help hold the head component  70  in position. The head component  70  can be manipulated as necessary to achieve an angular orientation that will mate efficiently with the opposite component of the joint (the glenoid component in the case of a shoulder prosthesis). The screw  40  can be tightened and loosened as necessary to hold the head component  70  in position to verify proper mating fit between the joint components. 
     If it is determined that a different head component is needed, the component can be removed from the mounting element  34  without disturbing the position of the mounting element relative to the stem  12 . Once the proper head component  70  has been selected and situated at its optimum orientation, the screw  40  can be fully tightened into the bore  18 . 
     Here, it is noted that the present invention provides, among other things, a modular system that can accommodate a wide range of joint constructs. For instance, a head component  80  can be provided as shown in  FIG. 6 . This head component includes a mounting post  82  with a tapered engagement surface  84  that is configured to be mounted directly within the tapered bore  16 . The head component  80  can be used where no angular variations are required. 
     The head component  80  can also be press-fit into the passageway  36  of the mounting element  30 . In this case, the passageway is formed as a tapered bore, similar to the tapered bore  16  in the stem  12 . With this specific embodiment, the post  82  can define a bore therethrough that communicates with the passageway  36  in the mounting element to permit introduction of the screw  40  therethrough. 
     A further component of the modular system is the fixed mounting element  50  shown in  FIG. 7 . This fixed element includes a mounting portion  56  having a tapered surface  58  configured for press or friction-fit engagement with the tapered bore  16 . The proximal portion  50  can have a tapered surface  52  for engagement within the bore  21  of the head component  20  ( FIG. 2 ), or within the bore  72  of the head component  70  ( FIG. 5 ). As is apparent from  FIG. 7 , the mounting element  50  does not accommodate changes in version or inclination angle, the degrees of freedom of movement of the element being limited to the longitudinal axis of the element. 
     The mounting element  50  can include a bore  54  that can be tapered to receive the post  82  of the head portion  80  ( FIG. 6 ). In addition, the bore can provide a passageway for introduction of a mounting screw, like the screw  40  depicted in  FIG. 4 . The bore can form a bearing surface  60  against which the surface  44  of the screw  40  bears to clamp the mounting element  50  to the stem  12 . 
     The exemplary embodiment includes a machine screw  40  for final securing of the mounting element  30  to the stem by way of the mating threaded bore  18 . Other forms of mechanical fastener are contemplated that can effect final fixation of the mounting element to the stem. For instance, a press-fit pin can be provided that is pressed into a complementary bore (in lieu of the threaded bore  18 ). The pin would retain the configuration of the head  42  of the screw  40 , most particularly the spherical underside surface  44  and would operate to press the articulating portion  34  into the tapered bore  16 . 
     As shown, for example, in  FIGS. 8 and 9 , an exemplary alternative joint prosthesis according to the present invention includes a head component  20 , an alternative embodiment of the stem  112 , and an alternative embodiment of the mounting element  130 . The alternative embodiment of the stem  112  is substantially identical to the prior art stem  12  except that the alternative embodiment of the stem  112  is not formed to include the threaded bore  18 . Illustratively, the head component  20  is identical to head component  20  of the exemplary joint prosthesis of  FIG. 2 . 
     The mounting element  130  is also substantially similar to mounting element  30  so similar reference numerals will be used to describe similar components and identical reference numerals will be utilized to describe identical components. The mounting element  130  is formed to include a bore  136  extending through an opening in the proximal end of the proximal portion  33  and only partially through the mounting element  130  instead of the passageway  36  formed in mounting element  30 . Thus, mounting element  130  is configured for utilization without the screw  40  for locking the orientation of the mounting element  130  relative to the stem  112 . 
     The mounting element  130  includes a proximal portion  33  that mates with the head component  20 . In a specific embodiment, the proximal portion  33  defines a tapered external surface that is press-fit or friction-fit within a complementary bore  21  defined in the head component. 
     As at least partially discernable in  FIGS. 8 and 9 , the mounting element  130  further includes a solid frusto-spherical articulating portion  134 . As at least partially discernable in the drawings, the actual surface of the articulating portion  134  includes only a partial sphere because the distal end of the articulating portion is a flat circular surface perpendicular to the axis of symmetry of the mounting element  130  and the proximal end of the articulating portion is integrally formed to the proximal portion  33 . Hence, the articulating portion  134  is only partially spherical and, more specifically, is solid and frusto-spherical. Nevertheless, it should be noted that the surface of the articulating portion  134  is contiguous and a substantial portion of the surface of the articulating portion  134 , especially that portion which would be adjacent the equatorial region of a complete sphere having its poles intersected by the axis of symmetry of the mounting element  130  is substantially equidistant from a focus located on the axis of symmetry. 
     The articulating portion  134  is sized to achieve a press-fit engagement within the tapered bore  16  of the stem  12  when the portion  134  is pushed sufficiently far into the bore. When pushed into the tapered bore  16  by hand or otherwise, the frictional forces created by the press-fit engagement are sufficient to maintain the orientation of the mounting element  130  relative to the stem  112  even when the head component is coupled to the mounting element  130  so long as the component is not subjected to a load. Once it is established that the component has the desired orientation, the articulating portion  134  is pressed or driven further into the tapered bore  16  by impaction, by hand, or otherwise to mechanically lock the mounting element  130  in the desired orientation relative to the stem  112 . Alternatively, the mounting element  130  is chilled to reduce the diameter of the articulating portion  134  or the stem is warmed to increase the diameter of the tapered bore  16  to facilitate seating and locking the mounting element relative to the stem  112 . Thus, the mounting element  130  avoids use of the locking screw  40 . Once the mounting element  130  is locked in the desired location, the component can be subjected to the loads and stresses normally associated with the joint that it is partially replacing without the mounting element changing its orientation. 
     The frusto-spherical shape of the articulating portion  134  allows the mounting element  130  to rotate about three dimensional axes x, y, z. Thus, the mounting element  130  can rotate about its own axis (the x axis), pivot about a version axis (the y axis) or pivot about an inclination axis (the z axis). The mounting element  130  can rotate a full 360° about its own axis. However, the pivot range in the other two degrees of freedom is limited by contact between the articulating mounting element or the head component and the platform surface  15  of the stem  112 . The range of motion in these two degrees of freedom are maximized by the intermediate portion  135  connecting the articulating portion  134  to the proximal portion. In particular, the intermediate portion  135  can be angled away from the articulating portion  134  to provide clearance as the mounting element  130  is pivoted. 
     While the invention has been illustrated and described in detail in the drawings and foregoing description, the same should be considered as illustrative and not restrictive in character. It is understood that only the preferred embodiments have been presented and that all changes, modifications and further applications that come within the spirit of the invention are desired to be protected. 
     For instance, while the illustrated embodiments relate to a humeral component of a shoulder prosthesis, the connection element of the present invention can be utilized in other joints such as hip, knee, or elbow joints to engage a joint component to a bone engaging component of the prosthesis. 
     Furthermore, while the preferred embodiment contemplates angular adjustment capabilities in all degrees of freedom, the mounting element can be configured to limit angular movement to specific directions. For instance, instead of a spherical interface, the articulating portion  34 ,  134  can include a flat side opposing a corresponding flat side to the tapered bore  16  such that rotation of the portion  34 ,  134  between the two flat sides is prohibited.