Abstract:
Apparatus for repairing a shoulder joint, said apparatus comprising: a baseplate for mounting to a glenoid, said baseplate comprising: a base portion comprising a medially-facing surface and a laterally-facing surface, and at least one opening passing through said medially-facing surface and said laterally-facing surface for receiving at least one base portion screw; and an anterior flange carried by said base portion, said anterior flange comprising an anteriorly-facing surface and a posteriorly-facing surface, said anterior flange extending away from, and perpendicular to, said medially-facing surface of said base portion, said anterior flange further comprising at least one opening passing through said anteriorly-facing surface and said posteriorly-facing surface for accepting at least one flange screw; an articulating surface component for mounting to said laterally-facing surface of said base portion so as to substantially cover said laterally-facing surface of said base portion; and an anterior cover for mounting to said anteriorly-facing surface of said anterior flange; wherein said anterior cover is configured to lock said articulating surface component to said base portion, such that when said anterior cover is mounted to said anterior flange, said articulating surface component is locked to said base portion.

Description:
REFERENCE TO PENDING PRIOR PATENT APPLICATION 
       [0001]    This patent application claims benefit of pending prior U.S. Provisional Patent Application Ser. No. 61/906,227, filed Nov. 19, 2013 by Barry T. Bickley et al. for METHOD AND APPARATUS FOR RESTORING A SHOULDER JOINT (Attorney&#39;s Docket No. SIM-9 PROV), which patent application is hereby incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    This invention relates to medical procedures and apparatus in general, and more particularly to medical procedures and apparatus for restoring a shoulder joint and/or another joint. 
       BACKGROUND OF THE INVENTION 
       [0003]    The shoulder joint is formed at the convergence of the proximal humerus and the glenoid. More particularly, and looking now at  FIGS. 1-3 , the proximal humerus comprises a protrusion (or “head”), and the lateral glenoid comprises a recess (or “socket”) for receiving the protrusion (or head) of the proximal humerus. Soft tissue (e.g., ligaments, tendons, muscles, etc.) stabilize the joint and permit the proximal humerus to articulate through a range of motion with respect to the glenoid. 
         [0004]    Shoulder joint replacement surgery seeks to replace one or more of the operative elements of the shoulder joint with prosthetic components so as to provide long-lasting function and pain-free mobility. By way of example but not limitation, in a “standard” shoulder joint replacement surgery, the proximal humerus may be replaced by a prosthetic ball-and-stem, the lateral glenoid may be replaced by a prosthetic socket, or both. By way of further example but not limitation, in a “reverse” shoulder joint replacement surgery, the proximal humerus may be provided with a prosthetic socket and the lateral glenoid may be provided with a prosthetic protrusion. 
       SUMMARY OF THE INVENTION 
       [0005]    The present invention is directed to situations where the lateral glenoid is to be replaced by a prosthesis. 
         [0006]    In one form of the invention, the glenoid prosthesis comprises a socket which mimics the natural socket of the glenoid. 
         [0007]    In another form of the invention, the glenoid prosthesis comprises a protrusion for interaction with a prosthetic socket formed in the lateral humerus, in a so-called “reverse” shoulder replacement. 
         [0008]    Significantly, the glenoid prosthesis is constructed so as to allow a surgeon to switch from a standard shoulder replacement procedure to a reverse shoulder replacement procedure, or vice-versa, either during surgery or at a later date. 
         [0009]    While the present invention is specifically intended for use in the glenoid, the prosthesis of the present invention may also be adapted for use in a variety of other joints within the body, e.g., the hip, knee, elbow, wrist, ankle, etc. 
         [0010]    In one preferred form of the invention, there is provided apparatus for repairing a shoulder joint, said apparatus comprising:
       a baseplate for mounting to a glenoid, said baseplate comprising:
           a base portion comprising a medially-facing surface and a laterally-facing surface, and at least one opening passing through said medially-facing surface and said laterally-facing surface for receiving at least one base portion screw; and   an anterior flange carried by said base portion, said anterior flange comprising an anteriorly-facing surface and a posteriorly-facing surface, said anterior flange extending away from, and perpendicular to, said medially-facing surface of said base portion, said anterior flange further comprising at least one opening passing through said anteriorly-facing surface and said posteriorly-facing surface for accepting at least one flange screw;   
           an articulating surface component for mounting to said laterally-facing surface of said base portion so as to substantially cover said laterally-facing surface of said base portion; and   an anterior cover for mounting to said anteriorly-facing surface of said anterior flange;   wherein said anterior cover is configured to lock said articulating surface component to said base portion, such that when said anterior cover is mounted to said anterior flange, said articulating surface component is locked to said base portion.       
 
         [0017]    In another preferred form of the invention, there is provided a method for restoring a shoulder joint, said method comprising: 
         [0018]    providing apparatus for repairing a shoulder joint, said apparatus comprising:
       a baseplate for mounting to a glenoid, said baseplate comprising:
           a base portion comprising a medially-facing surface and a laterally-facing surface, and at least one opening passing through said medially-facing surface and said laterally-facing surface for receiving at least one base portion screw; and   an anterior flange carried by said base portion, said anterior flange comprising an anteriorly-facing surface and a posteriorly-facing surface, said anterior flange extending away from, and perpendicular to, said medially-facing surface of said base portion, said anterior flange further comprising at least one opening passing through said anteriorly-facing surface and said posteriorly-facing surface for accepting at least one flange screw;   
           an articulating surface component for mounting to said laterally-facing surface of said base portion so as to substantially cover said laterally-facing surface of said base portion; and   an anterior cover for mounting to said anteriorly-facing surface of said anterior flange;   wherein said anterior cover is configured to lock said articulating surface component to said base portion, such that when said anterior cover is mounted to said anterior flange, said articulating surface component is locked to said base portion;       
 
         [0025]    mounting said baseplate to the glenoid by positioning said baseplate against the glenoid and passing at least one base portion screw through said at least one opening in said base portion, and by passing at least one flange screw through said at least one opening in said flange; 
         [0026]    mounting said articulating surface component to said base portion, such that said at least one base portion screw is covered by said articulating surface component; and 
         [0027]    mounting said anterior cover to said anterior flange, such that said articulating surface component is locked to said base portion and said at least one flange screw is covered by said anterior cover. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0028]    These and other objects and features of the present invention will be more fully disclosed or rendered obvious by the following detailed description of the preferred embodiments of the invention, which is to be considered together with the accompanying drawings wherein like numbers refer to like parts, and further wherein: 
           [0029]      FIG. 1  is a schematic view showing the skeletal structure of the upper half of a human torso; 
           [0030]      FIG. 2  is a schematic view showing a right shoulder joint; 
           [0031]      FIG. 3  is a schematic view showing a right glenoid; 
           [0032]      FIGS. 4-7  are schematic views showing a novel glenoid prosthesis formed in accordance with the present invention; 
           [0033]      FIGS. 8-10  are schematic views showing the baseplate of the novel glenoid prosthesis shown in  FIGS. 4-7 ; 
           [0034]      FIGS. 11-14  are schematic views of the articulating surface component of the novel glenoid prosthesis shown in  FIGS. 4-7 ; 
           [0035]      FIGS. 15-18  are schematic views of the anterior cover of the novel glenoid prosthesis shown in  FIGS. 4-7 ; 
           [0036]      FIGS. 19 and 20  are schematic views showing the novel glenoid prosthesis of  FIGS. 4-7  secured in position to a resected glenoid; 
           [0037]      FIGS. 21-38  are schematic views showing another novel glenoid prosthesis formed in accordance with the present invention; and 
           [0038]      FIGS. 39-41  are schematic views showing a glenoid prosthesis which may be used in a so-called “reverse” shoulder replacement surgery. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0039]    The present invention comprises a new shoulder joint prosthesis for replacing the lateral glenoid. 
         [0040]    In one form of the invention, the glenoid prosthesis comprises a socket which mimics the natural socket of the glenoid. 
         [0041]    In another form of the invention, the glenoid prosthesis comprises a protrusion for interaction with a prosthetic socket formed in the lateral humerus, in a so-called “reverse” shoulder replacement. 
         [0042]    Significantly, the glenoid prosthesis is constructed so as to allow a surgeon to switch from a standard shoulder replacement procedure to a reverse shoulder replacement procedure, or vice-versa, either during surgery or at a later date. 
         [0043]    In order to simplify description of the present invention, the new glenoid prosthesis will first be discussed in the context of providing a socket which mimics the natural socket of the glenoid. Thereafter, the new glenoid prosthesis will be discussed in the context of providing a protrusion for interaction with a prosthetic socket formed in the lateral humerus, in a so-called “reverse” shoulder replacement. 
       Glenoid Prosthesis Comprising a Socket which Mimics the Natural Socket of the Glenoid 
       [0044]    Looking first at  FIGS. 4-7 , there is shown a novel glenoid prosthesis  5  formed in accordance with the present invention. Glenoid prosthesis  5  generally comprises a baseplate  10 , an articulating surface component  15  and an anterior cover  20 . 
         [0045]    More particularly and looking now at  FIGS. 8-10 , baseplate  10  comprises a substantially flat base portion  25  for seating against the surface of the resected glenoid. Base portion  25  comprises a plurality of holes  30  passing therethrough for receiving bone screws  35  therein (see  FIGS. 19 and 20 ), whereby to secure base portion  25  (and hence baseplate  10 ) to the surface of the resected glenoid, as will hereinafter be discussed. Baseplate  10  further comprises a plurality of protrusions  40  extending outwardly from base portion  25  of baseplate  10 , wherein each protrusion  40  comprises a groove  45  for securing articulating surface component  15  to baseplate  10 , as will hereinafter be discussed. An anterior flange  50  extends medially and substantially perpendicular to the plane of base portion  25 . Anterior flange  50  comprises a plurality of holes  55  passing therethrough for receiving bone screws  60  therein ( FIG. 20 ), whereby to secure anterior flange  50  (and hence baseplate  10 ) to the surface of the resected glenoid, as will also hereinafter be discussed. Anterior flange  50  further comprises a plurality of grooves  65  for securing anterior cover  20  to baseplate  10 , as will hereinafter be discussed. 
         [0046]    Looking next at  FIGS. 11-14 , articulating surface component  15  comprises a concave laterally-facing surface  70  and a planar medially-facing surface  75 . A plurality of grooves  80  are disposed around the perimeter of articulating surface component  15  intermediate laterally-facing surface  70  and medially-facing surface  75 , whereby to form a plurality of tabs  85  out of portions of the perimeter of medially-facing surface  75 . Tabs  85  are sized to be received in grooves  45  of baseplate  10 , whereby to secure articulating surface component  15  to baseplate  10  (e.g., by a friction fit, a snap fit, etc.). By way of example but not limitation, articulating surface component  15  may be formed out of polyethylene so as to provide a smooth articulating surface. Concave laterally-facing surface  70  preferably has a surface profile approximating the surface profile of the native lateral glenoid. 
         [0047]    Looking next at  FIGS. 15-18 , anterior cover  20  comprises a smooth anteriorly-facing surface  90 , a protrusion  95  located along one side of anterior cover  20 , and two tabs  100  sized to be slidably received in slots  65  of anterior flange  50  of baseplate  10 . 
         [0048]    In use, the native bone (i.e., the native lateral glenoid) is first surgically resected so as to provide a seat for receiving glenoid prosthesis  5  (i.e., the lateral glenoid is resected so as to provide a surface for seating base portion  25  and flange  50  of baseplate  10  against the bone). Then baseplate  10  is positioned against the resected lateral glenoid, and a plurality of bone screws  35  are advanced through holes  30  of base portion  25  into the resected lateral glenoid, whereby to secure base portion  25  to the resected bone ( FIGS. 19 and 20 ). Next, a plurality of bone screws  60  are advanced through holes  55  of flange  50  into the lateral glenoid ( FIG. 20 ), whereby to secure flange  50  to the resected lateral glenoid. It should be appreciated that by having bone screws  60  disposed substantially perpendicular to bone screws  35 , baseplate  10  of glenoid prosthesis  5  is securely fastened to the native bone via a multi-planar fixation. 
         [0049]    Next, articulating surface component  15  is secured to baseplate  10  by sliding tabs  85  of articulating surface component  15  into grooves  45  of baseplate  10 . Note that articulating surface component  15  overlies bone screws  35 , thereby preventing bone screws  35  from backing out of the resected lateral glenoid. 
         [0050]    Finally, anterior cover  20  is secured to anterior flange  50  (and hence, to baseplate  10 ) by sliding tabs  100  of anterior cover  20  into grooves  65  of anterior flange  50  until protrusion  95  of anterior cover  20  engages the perimeter of medially-facing surface  75  of articulating surface component  15 . Note that anterior cover  20  overlies bone screws  60 , thereby preventing bone screws  60  from backing out of the resected lateral glenoid. It should be appreciated that after anterior cover  20  is secured to baseplate  10  in this fashion, anterior cover  20  “locks” articulating surface component  15  to baseplate  10 , thereby preventing articulating surface component  15  from being removed from baseplate  10  without first removing anterior cover  20 . 
         [0051]    Note that novel glenoid prosthesis  5  is “universal”, in the sense that the same glenoid prosthesis may be used to reconstruct either the right shoulder of the patient or the left shoulder of the patient. Thus, while the glenoid prosthesis  5  shown in  FIGS. 4-18  is shown oriented for a right shoulder reconstruction, and while the glenoid prosthesis  5  is shown in  FIGS. 19 and 20  as being used in a right shoulder reconstruction, the same glenoid prosthesis  5  may be used for a left shoulder reconstruction, i.e., by simply rotating the orientation of the glenoid prosthesis  5  by 180 degrees. 
         [0052]      FIGS. 21-38  show another novel glenoid prosthesis  5 A formed in accordance with the present invention. The novel glenoid prosthesis  5 A shown in  FIGS. 21-38  is generally similar to the novel glenoid prosthesis  5  shown in  FIGS. 4-20 , except that the geometry and/or size of several of the elements comprising novel glenoid prosthesis  5 A vary from the geometry and/or size of their counterpart elements comprising novel glenoid prosthesis  5 . It will be appreciated that  FIGS. 21-25  show novel glenoid prosthesis  5 A in its assembled form;  FIGS. 26-29  show baseplate  10 A of novel glenoid prosthesis  5 A;  FIGS. 30-33  show articulating surface component  15 A of novel glenoid prosthesis  5 A; and  FIGS. 34-38  show anterior cover  20 A of novel glenoid prosthesis  5 A. 
       Glenoid Prosthesis Comprising a Protrusion for Interaction with a Prosthetic Socket Formed in the Lateral Humerus 
       [0053]    In the foregoing description, glenoid prosthesis  5  is discussed in the context of providing a concave articulating surface to approximate the socket geometry of the native glenoid. However, it should also be appreciated that, if desired, articulating surface component  15  can comprise a substantially convex laterally-facing surface (i.e., a protruding element), rather than the aforementioned concave laterally-facing surface  70  (or concave laterally-facing surface  70 A), whereby to provide a so-called “reverse” shoulder replacement prosthesis. By way of example but not limitation, and looking now at  FIGS. 39-41 , glenoid prosthesis  5  may comprise an articulating surface component  15 ′ having a convex laterally-facing surface  70 ′, whereby to provide the “protrusion” portion of the shoulder joint (rather than the “socket” portion of the shoulder joint) and which can engage the “socket” portion of another bone structure or another prosthesis so as to provide an articulating joint. 
       Some Significant Aspects of the Invention 
       [0054]    Significantly, as discussed above, the glenoid prosthesis of the present invention provides a baseplate that can be used as a foundation for either a “standard” shoulder replacement procedure or a “reverse” shoulder replacement procedure. The glenoid prosthesis of the present invention allows a surgeon to easily switch from one procedure to the other procedure (i.e., from a “standard” shoulder replacement procedure to a “reverse” shoulder replacement procedure, or vice-versa) either intra-operatively or at a later date, if it is decided that one or the other procedure is more appropriate, such as in the scenario where a patient has a standard prosthesis placed for arthritis but, at a later date, develops a rotator cuff tear and there is a need to revise the standard prosthesis to a reverse shoulder replacement so as to improve his/her function. In such a case, with the present invention, the surgeon can simply exchange the articulating surface component  15  that is fitted to the baseplate  10  and not have to revise the entire glenoid component, which could potentially jeopardize the somewhat limited bone stock at the natural glenoid on the scapula. In other words, where it is desired to revise the standard prosthesis to a reverse prosthesis, the surgeon can simply exchange the standard articulating surface component  15  (having a concave laterally-facing surface  70 ) with the reverse articulating surface component  15 ′ (having a convex laterally-facing surface  70 ′) without ever having to remove baseplate  10  from the resected glenoid. 
         [0055]    Securing a glenoid prosthesis to the native lateral glenoid so as to avoid loosening, given the shape and size of the bone structure, is a well-known problem for surgeons. Baseplate  10  of the present invention is mounted to the glenoid by first preparing a bone surface (i.e., by resecting the lateral glenoid) so as to accommodate baseplate  10  of glenoid prosthesis  5  (or baseplate  10 A of glenoid prosthesis  5 A). Baseplate  10  of glenoid prosthesis  5  (or baseplate  10 A of glenoid prosthesis  5 A) is then mounted to the resected glenoid and secured in place by screws  35  (or pins) that go through baseplate  10  (or baseplate  10 A) perpendicular to the face of the resected lateral glenoid. However, a unique feature in the glenoid prosthesis of the present invention is the provision of additional screw fixation that is placed from the anterior aspect of the baseplate, i.e., through anterior flange  50  (or anterior flange  50 A). These screws (i.e., screws  60 ) go into the native glenoid at an angle and provide fixation from a different plane than the screws (i.e., screws  35 ) going perpendicular to the plane of the glenoid face. This multi-planar fixation of baseplate  10  (or baseplate  10 A) is different than the standard method of glenoid fixation and provides greater strength and durability to the glenoid prosthesis. No other glenoid prosthesis provides this feature. 
         [0056]    Screws  35  passing through substantially flat base portion  25  of baseplate  10  (or through substantially flat base portion  25 A of baseplate  10 A), and/or screws  60  passing through anterior flange  50  of baseplate  10  (or flange  50 A of baseplate  10 A), can be locking, i.e., screws  35  can tighten into threaded holes  30  in baseplate  10  (or threaded holes  30 A in baseplate  10 A) that correspond to threads on the screw head, so as to couple the screws and baseplate together), and/or screws  60  can tighten into threaded holes  55  in anterior flange  50  (or threaded holes  55 A in anterior flange  50 A) so as to couple the screws and anterior flange together. Or screws  35  and/or screws  60  can be non-locking, i.e., traditional smooth-headed screws  35  that go through the baseplate  10  (or baseplate  10 A) but do not mechanically lock the screws to the baseplate, and/or traditional smooth-headed screws  60  that go through anterior flange  50  (or anterior flange  50 A) but do not mechanically lock the screws to the anterior flange. 
         [0057]    Additionally, one or more of holes  30  in baseplate  10  (or holes  30 A in baseplate  10 A) can be replaced by slots. These slots can allow greater options in placing screws  35 . If desired, these slots may have offset edges that act as a thread that corresponds to a thread on the screw head, so as to provide a mechanical lock between screws  35  and baseplate  10 . Furthermore, one or more of holes  55  in anterior flange  50  (or holes  55 A in anterior flange  50 A) can be replaced by slots. These slots can allow greater options in placing screws  60 . If desired, these slots may have offset edges that act as a thread that corresponds to a thread on the screw head, so as to provide a mechanical lock between screws  60  and anterior flange  50 . 
         [0058]    As noted above, screws  35  on the face of baseplate  10  (or baseplate  10 A) are prevented from backing out by the articulating surface component  15  (or by the articulating surface component  15 A, or by the articulating surface component  15 ′) that is mounted to baseplate  10  (or baseplate  10 A). 
         [0059]    As also noted above, screws  60  extending through anterior flange  50  (or anterior flange  50 A) are covered by a separate cover plate (i.e., anterior cover  20  or anterior cover  20 A) that acts as a “door” to allow the standard articulating surface component  50  (or articulating surface component  50 A), or the reverse articulating surface component  50 ′, to be slid into baseplate  10  (or baseplate  10 A). Note that as the articulating surface component is slid into place on the baseplate, the articulating surface component is caught by grooves  45  on baseplate  10  (or grooves  45 A on baseplate  10 A) so that the articulating surface component cannot move in a plane perpendicular to the face of the baseplate. Note also that the articulating surface component will be unable to move anterior/posterior, inasmuch as the articulating surface component is bound posteriorly by a protrusion  40  of baseplate  10  (or a protrusion  40 A of baseplate  10 A) and anteriorly by the anterior cover (which is mounted in place after positioning of the articulating surface component). With the desired articulating surface component slid into place on the baseplate, the final step is to slide the anterior cover along the anterior flange of the baseplate, in the grooves in the anterior flange that accommodate the anterior cover. The anterior cover will catch on the baseplate and/or the articulating surface component when the anterior cover is fully seated, thereby providing a snap fit. There is no force on the anterior cover to back out, as there is no movement of the articulating surface component on the baseplate in the plane perpendicular to the face of the implant, and the anterior cover is further secured by catching on the articulating surface component and grooves on the baseplate. The anterior cover also covers the anterior screws (i.e., screws  60 ) so they cannot loosen and back out and, in effect, this construct locks all the components together as one unit so as to minimize the risk of the entire glenoid baseplate loosening over time. 
         [0060]    It should be appreciated that if the articulating surface component should become worn and require replacement, the articulating surface component can be replaced without dismounting the baseplate from the resected glenoid, thereby preserving the fusion which has been established between the baseplate and the bone. More particularly, where the articulating surface component has become worn and requires replacement, the anterior cover is removed, the worn articulating surface component is dismounted from the baseplate, the new articulating surface component is installed on the baseplate, and then the anterior cover is replaced. 
         [0061]    If it is desired to revise the prosthesis, e.g., to convert the glenoid prosthesis from a socket-type prosthesis to a protrusion-type prosthesis, the anterior cover  20  (or the anterior cover  20 A) can easily be removed as the catching mechanism (i.e., the snap fit of the anterior cover with the articulating surface component) is easily overcome by inserting a separate flat tool (such as a flat screw driver, not shown) in the groove at the lateral-most aspect of the anterior cover, and then twisting the tool. This action slides the anterior cover medially in the grooves  65  (or grooves  65 A) that the anterior cover sits in, and begins the disassembly process. With the anterior cover removed, the articulating surface component on the base plate can then be slid out anteriorly and exchanged for a reverse (dome-shaped) articulating surface component (i.e., articulating surface component  15 ′), allowing for easy revision to a reverse prosthesis. The reverse (dome-shaped) articulating surface component  15 ′ is then secured in place by replacing the anterior cover, whereupon the revision is complete, without ever needing to affect the security and fixation of the baseplate to the resected lateral glenoid. 
         [0062]    If it is desired to remove the entire glenoid prosthesis, e.g., such as in the case of a significant infection, then the components are disassembled in a similar fashion. The anterior cover is removed, which exposes the anterior screws  60  and allows for removal of the articulating surface component from the baseplate. Removal of the articulating surface component exposes the screws  35  extending through the baseplate. All screws can then be removed, with no scar or fibrous ingrowth in the screw heads inasmuch as the screw heads have been covered previously during the life of the implant. 
         [0063]    Thus it will be seen that the novel glenoid prosthesis of the present invention allows the surgeon to mount a baseplate to the resected glenoid, and then add components to the baseplate, so that a worn component of the system can be easily replaced, or the shoulder reconstruction can be easily revised from standard reconstruction to a reverse reconstruction, without ever disrupting attachment of the baseplate to the resected glenoid. 
         [0064]    It will also be seen that the novel glenoid prosthesis provides a unique multi-planar fixation feature to the baseplate, so as to allow better fixation of the glenoid prosthesis to the resected glenoid. 
         [0065]    And it will be seen that the manner in which the various components of the novel glenoid prosthesis fit together ensures that when they are assembled, the components together prevent any of the individual components from loosening or coming apart. However, when desired, a portion of the construct can be disassembled so as to allow replacement of the articulating surface component (either because the articulating surface component has become worn, or because the shoulder reconstruction is to be revised from a standard glenoid insert to a reverse glenosphere insert); or the construct can be completely disassembled and removed if needed, e.g., such as in the case of a significant infection. 
       Applicable Joints 
       [0066]    While the present invention is specifically intended for use in the glenoid, it will be appreciated that the prosthesis of the present invention may be adapted for use in a variety of other joints within the body, e.g., the hip, knee, elbow, wrist, ankle, etc. In this respect it should be appreciated that inasmuch as the articulating surface component of the new prosthesis can have various profiles according to the articulating surface it is to replace, the prosthesis can be used in a wide range of joint reconstructions. 
       MODIFICATIONS OF THE PREFERRED EMBODIMENTS 
       [0067]    It should be understood that many additional changes in the details, materials, steps and arrangements of parts, which have been herein described and illustrated in order to explain the nature of the present invention, may be made by those skilled in the art while still remaining within the principles and scope of the invention.