Abstract:
A shoulder prosthesis and/or prosthesis sizing system, especially for treatment of degenerative arthritis or trauma, has an articulating head component. The shoulder prosthesis includes a humeral stem and a series of humeral heads. The heads are attached to the humeral stem by means of a locking connector. The locking connector allows the humeral head to be oriented in multiple positions of version, varus/valgus angulation, eccentricity and head height, while providing rigid securing of the humeral head to the humeral stem in the selected position relative to the humeral stem. In one form, the locking connector includes an expansion collar that provides radially outward expansion for humeral head position locking. The present shoulder prosthesis provides a means to anatomically position the humeral head relative to the humeral stem and rigidly secure the humeral head in the selected position relative to the humeral stem. This is accomplished by a minimum of components.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to prosthetic systems for the replacement of limbs or portions thereof. More particularly, the invention concerns a modular shoulder prosthesis system that can be used in the extremities that have experienced bone loss or significant, irreparable bone trauma.  
           [0002]    For treatment of various problems with the shoulder such as degenerative arthritis and trauma of the shoulder, one method of providing relief to a patient is to replace the articulating surfaces of the shoulder, i.e. the humerus and glenoid articulating surfaces. In such replacement, pin relief, increased motion and anatomic reconstruction of the shoulder joint are goals of the orthopaedic surgeon. With multiple variations in human anatomy, prosthetic systems need to accurately replicated human anatomy with minimal component inventory.  
           [0003]    Artificial or prosthetic joints for the extremities are well-known. Many of prosthetic joints are modular, meaning that they include a selection of different components to account for differences in patient anatomy or surgical procedures. For example, U.S. Patent No. 5,314,479, owned by the assignee of the present invention, discloses a modular shoulder prosthesis that includes an array of selectable stems, bodies, collars and head members. The modular prosthesis of the &#39;479 Patent allows the orthopaedic surgeon to assemble a custom prosthetic joint by selecting different sizes, shapes and orientations of the individual joint components.  
           [0004]    As indicated above, current modular prostheses consist of a series of humeral stems and heads for replacement of articulating surfaces. The stems are offered with various metaphysis and diaphysis sizes. Humeral heads are offered in various radiuses of curvature, diameters, and heights. Any locking member used to rigidly attach the humeral head to the humeral stem has a fixed position, offering no means for positional adjustment of version, varus/valgus angulation.  
           [0005]    Eccentricity can be addressed using humeral heads with the attachment feature placed off center from the articulating exterior spherical surface. However, the eccentric position of the humeral head is only adjustable about the fixed central axis of the locking member located on the humeral stem. More importantly, version, varus/valgus angulation adjustments are not possible with these embodiments.  
           [0006]    In view of the above-noted shortcomings, modular shoulder prostheses have been developed that allow orienting the humeral head in multiple angular positions. Each of these embodiments, however, is deficient in design, and thus each is considered a sub-optimal solution. In U.S. Pat. No. 6,197,062 issued to Fenlin provides a modular shoulder prosthesis that utilizes an offset male taper member. The offset male taper member is rotated about the connecting axis of the humeral stem thus changing the angular position of the humeral head. Some of the problems associated with this particular embodiment include having to completely remove the humeral head to make positional adjustments, and version and varus/valgus angulation adjustments are not independent of one another.  
           [0007]    In EP 0712617, a modular shoulder prosthesis is provided that allows positional adjustments of the humeral head. This prosthesis utilizes a split spherical ball and locking set screw to rigidly secure the humeral head in the selected position. While independent adjustment of humeral head position is possible with this prosthesis, such adjustments to humeral head position can only be made when the humeral stem is removed from the humeral canal because of the location of the locking set screw.  
           [0008]    In U.S. Pat. No. 5,741,335 and EP 0715836, a shoulder prosthesis is provided that has a locking member consisting of a split spherical ball and locking set screws. A humeral head with a spherical cavity receives the spherical ball. The locking set screws located on the lateral aspect of the humeral stem below the head resection plane advances a pusher that compresses the ball against the humeral head stem while locking the ball against the cavity to lock the humeral head in place. The location of the locking set screws make it impossible to remove the humeral head or make positional changes to the humeral head after the humeral stem is engaged in the bone.  
           [0009]    With the above shoulder prostheses, once the shoulder prosthesis has been inserted into the patient&#39;s bone, the angular position of the humeral head cannot be changed without removing the humeral stem. Misalignment caused by such factors as incorrect resection are not readily correctable with respect to humeral head alignment.  
           [0010]    Consequently, there is a need for a modular shoulder system that can accommodate differences in patient anatomy, particularly with respect to angular positioning of the humeral head with respect to the humeral stem. There is a further need for a shoulder prosthesis that provides version and varus/valgus angulation/positioning that is easily set and reset.  
         SUMMARY OF THE INVENTION  
         [0011]    In order to address these needs, the present invention provides a shoulder prosthesis designed to meet the challenges of shoulder replacement surgery. In one embodiment, shoulder prosthesis comprises at least three components, namely a humeral stem, a humeral head, and an adjustment and/or humeral head locking device.  
           [0012]    In one form, the subject invention provides a shoulder prosthesis. The shoulder prosthesis includes a humeral stem adapted to be implanted into a humerus and including an expansion receptor, a humeral head defining an articulation surface and a mounting cavity, and an expansion device cooperating with the mounting cavity and the expansion receptor to couple the humeral head to the humeral stem, the expansion device allowing angular positioning of the humeral head relative to the humeral stem and locking of a selected angular position of the humeral head relative to the humeral stem by expansion of the expansion device relative to the expansion receptor.  
           [0013]    In another form, the subject invention provides a shoulder prosthesis. The shoulder prosthesis includes a humeral stem having a proximal end and a distal end, the proximal end having a post extending therefrom, the post having tapered threads extending essentially from said proximal end of the humeral stem to an end of said post, a humeral head having an articulation surface and a bottom surface, and a mounting cavity in the bottom surface, and an expansion member configured to be received in the mounting cavity and having a threaded bore adapted to be received on the threaded post, the expansion member allowing humeral head angulation and fixing of a selected humeral head position when the expansion member is advanced onto the threaded bore such that expansion member expands.  
           [0014]    In yet another form, the subject invention provides a shoulder prosthesis. The shoulder prosthesis includes a humeral stem having a proximal end and a distal end, the proximal end having an expansion cavity therein, a humeral head having an articulation surface and a bottom surface, and a mounting cavity in the bottom surface, and an expansion device configured to be received in the expansion cavity, the expansion device having an expansion member with a threaded bore and a mounting expander, the mounting expander having a head adapted to receive the mounting cavity of the humeral head and a threaded body adapted to receive the expansion member, the expansion device allowing humeral head angulation and fixing of a selected humeral head position when the mounting expander is advanced onto the threaded bore such that expansion member expands.  
       
    
    
     DESCRIPTION OF THE FIGURES  
       [0015]    [0015]FIG. 1 is an exploded side view of a proximal humeral replacement or prosthesis assembled from components constituting a comprehensive modular limb preservation system in accordance with one embodiment of the present invention, some of the components of which are depicted in cross-section.  
         [0016]    [0016]FIG. 2 is a side view of a humeral stem component of the humeral prosthesis of FIG. 1.  
         [0017]    [0017]FIG. 3 is an enlarged bottom perspective view of a humeral head component of the humeral prosthesis of FIG. 1.  
         [0018]    [0018]FIG. 4 is an enlarged top view of the humeral head component of FIG. 3.  
         [0019]    [0019]FIG. 5 is an enlarged bottom view of the humeral head component of FIG. 3.  
         [0020]    [0020]FIG. 6 is an enlarged top perspective view of an expansion collar component of the humeral prosthesis of FIG. 1.  
         [0021]    [0021]FIG. 7 is an enlarged top view of the expansion collar of FIG. 6.  
         [0022]    [0022]FIG. 8 is an enlarged sectional view of the expansion collar of FIG. 6 taken along line  8 - 8  of FIG. 7.  
         [0023]    [0023]FIG. 9 is a side view of the proximal humeral prosthesis of FIG. 1 assembled, with the humeral head component of which is depicted in cross-section to better illustrate and/or understand the manner of articulation and expansion locking of the humeral head component relative to the humeral stem component.  
         [0024]    [0024]FIG. 10 is an enlarged cross sectional view of the humeral head component mounted onto the expansion collar and humeral stem component taken along line  10 - 10  of FIG. 9.  
         [0025]    [0025]FIG. 11 is can enlarged cross-sectional view of the humeral head component and the expansion collar of the present invention illustrating a neutral position regarding a manner and degree of articulation by the humeral head component.  
         [0026]    [0026]FIG. 12 an enlarged cross-sectional view of the humeral head component and the expansion collar of the present invention illustrating the manner and degree of articulation by the humeral head component relative to a right side of the humeral head component in a down position.  
         [0027]    [0027]FIG. 13 an enlarged cross-sectional view of the humeral head component and the expansion collar of the present invention illustrating the manner and degree of articulation by the humeral head component relative to a left side of the humeral head component in a down position.  
         [0028]    [0028]FIG. 14 is an exploded side view of a proximal humeral replacement or prosthesis assembled from components constituting a comprehensive modular limb preservation system in accordance with another embodiment of the present invention, some or a portion of the components of which are depicted in cross-section.  
         [0029]    [0029]FIG. 15 is a side view of a humeral stem component of the humeral prosthesis of FIG. 14.  
         [0030]    [0030]FIG. 16 is an enlarged side view of an integral locking and humeral head seating component of the humeral prosthesis of FIG. 14.  
         [0031]    [0031]FIG. 17 is a top view of the integral locking and humeral head seating component of FIG. 16.  
         [0032]    [0032]FIG. 18 is a partially exploded side view of the humeral prosthesis of FIG. 14 illustrating compression fixation of the integral locking and humeral head seating component before placement of the humeral head thereon.  
         [0033]    [0033]FIG. 19 is a side view of the proximal humeral prosthesis of FIG. 14 assembled, with the humeral head and stem components of which are depicted at least in partial cross-section to better illustrate and/or understand the manner of articulation and expansion locking of the humeral head component relative to the humeral stem component.  
         [0034]    [0034]FIG. 20 is a side view of the proximal humeral prosthesis of FIG. 14 assembled, with the humeral head and stem components of which are depicted at least in partial cross-section to better illustrate and/or understand the manner of articulation and expansion locking of the humeral head component relative to the humeral stem component. 
     
    
       [0035]    Corresponding reference characters indicated corresponding parts throughout the figures.  
       DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0036]    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.  
         [0037]    The present invention contemplates a limb preservation system that includes a comprehensive set of modular implants capable of addressing a wide range of orthopaedic conditions. Components of the system can be combined in a variety of ways to account for variations in patient anatomy and differences in bone or limb trauma. For instance, the comprehensive modular implant system of the present invention can be employed as a replacement for the proximal humerus. The particular modular components can be selected after consideration of the limb trauma, and more specifically in view of the degree and type of bone loss involved, such as might occur due to tumor, end-stage revision or trauma. Additionally, patient anatomy is utilized as a reference or model for selection of the particular size of components.  
         [0038]    Referring to FIG. 1, there is depicted one embodiment of the subject invention. Particularly, there is depicted a shoulder prosthesis generally designated  30 . It should be understood that the principles of the subject invention as described herein are applicable to prostheses for joints other than the shoulder, particularly for articulating surface joints similar to the shoulder. The shoulder prosthesis  30  includes a stem  32  configured, operable and/or adapted to be received in a humerus of a patient. The humeral stem  32  is implanted into a humerus such as is known in the art. The shoulder prosthesis  30  also includes a humeral head  34  that is receivable on the humeral stem  32 . According to an aspect of the present invention, the humeral head  34  is selectively positionable regarding angular orientation with respect to the humeral stem  32 , both in the version and varus/valgus angulation orientations. More particularly, the humeral head  34  is positionable in almost infinitely variable angular positions with respect to the humeral stem  32 , whether the humeral stem  32  is implanted in the humerus or not.  
         [0039]    The shoulder prosthesis  30  also includes a position locking mechanism  36  here embodied as a collar, ring or the like. As described below, the collar  36  cooperates with the humeral stem  32  and the humeral head  34  to provide a substantially universal joint for angular orientation of the humeral head  34  relative to the humeral stem  32  and for fixing or locking the selected angular orientation/position of the humeral head  34  relative to the humeral stem  32 .  
         [0040]    Referring now to FIG. 2, there is shown the humeral stem  32  of the shoulder prosthesis  30  of FIG. 1 and such will be described with more particularity. The humeral stem  32  is characterized by a body  40  having a distal end  42  and a proximal end  44 . The body  40  is dimensioned to extend into the humeral canal of the patient&#39;s humerus. Particularly, the distal end  42  is inserted into a preferably previously reamed or bored humeral canal of the humerus (not shown). The body  40  also has an end surface  46  that is preferably substantially flat and provided at an angle relative to a longitudinal axis of the humeral stem  32 . The angle of the end  46  is designed to match an angle of resection of the humerus. Note that the humeral stem  32  has no collar adjacent or proximate to the end  46 . The humeral stem  32  is adapted to extend into the humeral canal such that the end  46  is flush with the resected surface of the humerus.  
         [0041]    The humeral stem  32  also includes a hub, post, boss or the like  48  that extends from the end  46 . As such, the humeral stem  32  may be considered a male component of the shoulder prosthesis  30 . The post  48  includes threads  50  on an outer surface thereof. The post  48  is tapered inwardly as it extends outwardly from the end  46  and, as such, the threads  50  are tapered. In one form, the taper is of the same configuration as a Morse taper. The post  48  is preferably integral with the body  40 .  
         [0042]    Referring to FIGS.  3 - 5 , there is shown the humeral head  34  of the shoulder prosthesis  30  of FIG. 1 and such will be described with more particularity. The humeral head  34  is characterized by a body  54  having an articulation surface  56  and a bottom surface  58 . The articulation surface  56  is essentially hemispherically oblong in shape and/or a shape that closely matches the natural anatomy of the natural humerus head. The body  54  also includes a cavity  60  that extends into the body  54  from the bottom surface  58 . The cavity  60  is essentially spherical and thus has an essentially spherical surface  62 . While the cavity  60  is shown essentially centered in the body  54 , it should be appreciated, and it is contemplated, that the cavity  60  may be provided in various locations or positions in the body  54 . This permits the present invention to allow for eccentricity correction and/or compliance with respect to a patient&#39;s anatomy. By providing the cavity  60  in off center positions in the body  54 , various eccentricities may be taken into account. The humeral head  34  comes in various dimensions with various cavity  60  locations.  
         [0043]    The cavity  60  includes a key, rotation driver, angular adjustment guide and/or the like  64 . The key  64  extends from the bottom surface  58  and along the spherical surface  62  to a point within the cavity  60 . The length of the key  64  may be determined by the amount of angular displacement the humeral head  34  may undergo before bottoming out against the humeral stem  32 , particularly the end surface  46  thereof. As developed more fully below, the key  34  in conjunction with the collar  36  provides a manner of adjusting the angular position or orientation (angulation) of the humeral head  34  relative to the humeral stem  32  and a manner of fixing or locking the humeral head  34  through rotation of the humeral head  34  in a manner described below. As an introduction, rotation of the humeral head  34  rotates the collar  36  which expands inside of the cavity  60  in connection with the advancing of the collar  36  upon the threaded, tapered post  48 . Expansion of the collar  36  inside of the cavity  60  fixes the humeral head  34  from further angulation relative to the humeral stem  32 .  
         [0044]    With reference to FIGS.  6 - 8 , there is shown the collar  36  of the shoulder prosthesis  30  of FIG. 1 and such will be described with more particularity. The collar  36  is characterized by a body  68  defining an essentially annular ring having a bore  70  and an opening or gap  72 . The collar  36  may be characterized as a non-overlapping split ring. The bore  70  is threaded with threading of the same dimensions as the threading  50  of the post  48  of the humeral stem  32  so as to threadedly mate with the threads  50 . The gap  72  is sized to receive the key  64  therein and allow essentially arcuate movement of the key  64  therethrough.  
         [0045]    As best seen in FIG. 8, the collar  36  has an outer, essentially annular surface  74  that has a radius of curvature extending from an arbitrary top  75  of the body  68  to an arbitrary bottom  77  of the body  68  of the collar  36  that matches the radius of curvature of the spherical cavity  60  of the humeral head  34 . This allows the collar  36  to be received in the cavity  60 . This also allows the collar  36  to angle in all directions with respect to an axis of rotation of the collar  36  (i.e. an axial axis through the bore  70 ) while within the cavity  60 . As explained more fully below, since the collar  36  is fixed in position, the cooperating shapes of the cavity  60  and the outer surface  74  of the collar  36  allows the humeral head  34  to be angularly positionable about the collar  36 .  
         [0046]    Referring to FIG. 9, there is depicted the shoulder prosthesis  30  in an assembled state. The collar  36  is threadedly received on the threads  50  of the post  48  to provide a locking and angular adjustment mechanism  76 . Because the threads  50  are tapered from smaller diameter threads at the top of the post  48  to larger diameter threads proximate the end  46 , the collar  36  is first threadedly situated at the top of the post  48 . The humeral head  34  is received over the collar  36 . Particularly, the humeral head  34  is positioned such that the collar  36  is received in the cavity  60  and the side  74  of the collar  36  is in contact or immediately adjacent/congruent with the cavity surface  62  to the extent of the side  74 . Additionally, the humeral head  34  is initially rotationally positioned such that the key  64  is received in the gap  72 .  
         [0047]    As illustrated by the arrows about the fixed axis  78  of the post  48 , the humeral head  34  is free to perform version and varus/valgus angulation with respect to the humeral stem  32 , and particularly with respect to the post  48  and/or the end surface  46  of the humeral stem  32 . The double-headed arrow  80  indicates the movement of the humeral head  34  as the humeral head  34  is changed in angular orientation as constrained by the key  64  in the gap  72 . The key  64  thus provides an angulation guide for the humeral head  34 .  
         [0048]    As depicted in FIG. 10, with reference being made thereto, the key  64  also provides a rotation driver for the collar  36  once the angulation of the humeral head  34  is complete. Rotational motion of the body  54  of the humeral head  34  in either direction, as indicated by the double-headed arrow  81 , rotates the key  64  that engages a side of the gap  72  causing the collar  36  to rotate in the same direction of rotation as indicated by the double-headed arrow  83 . Particularly, engagement of the key  64  with either end of the gap  72  rotates the collar  36  either advancing the collar  36  downward onto the post  48  or upwards off of the post  48 . During advancement of the collar  36  downward onto the post  48 , the taper of the post  48  radially outwardly pushes against the collar  36  (as indicated by the radially outward directed arrows). At a certain point of advancement of the collar  36  downward onto the post  48 , the collar  36  is radially expanded outward wherein the side  74  of the collar  36  abuts the surface  62  of the cavity  60 . Expansion of the collar  36  fixes the collar  36  within the cavity  60  and against movement with respect to the key  64 . The humeral head  34  is then fixed in angular position. This can be accomplished by a strap wrench (not shown). To unfix the humeral head  34 , the humeral head  34  is rotated in the opposite direction to the point where the radial outward expansion of the collar  36  eases from abutting the cavity surface  62 . This can be accomplished either before or after implantation of the humeral stem  32 . The present system thus allows the angular position of the humeral head  34  to be changed even after implantation, and as often as one desires.  
         [0049]    Referring to FIGS.  11 - 13 , there is illustrated a neutral angulation positioning of the humeral head  34  as well as various extremes of angulation positioning of the humeral head  34  with respect to the collar  36 . As indicated above, since the collar  36  is essentially fixed in position, the collar  36  may be considered fixed in position (while still free to rotate).  
         [0050]    In FIG. 11, the collar  36  is in a neutral position. The humeral head  34  is oriented with respect to the collar  36  such that an axial axis of the humeral head  34  is coincident with the axial axis  78  of the collar  36 .  
         [0051]    In FIG. 12, the humeral head  34  is oriented with respect to the collar  36  such that an axial axis  79  of the humeral head  34  is offset by an angle φ from the collar axis  78 . This illustrates angulation with respect to one direction.  
         [0052]    In FIG. 13 the humeral head  34  is oriented with respect to the collar  36  such that the axial axis  79  of the humeral head  34  is offset by an angle Θ from the collar axis  78 . This illustrates angulation with respect to another direction. The humeral head  34  is thus essentially infinitely variable within the angulation range. The collar  36  cooperates with the cavity  60  to provide an essential universal joint for angulation.  
         [0053]    With reference now to FIG. 14, there is depicted another embodiment of a modular shoulder prosthesis generally designated  90 . The shoulder prosthesis  90  includes a stem  92  configured, operable and/or adapted to be received in a humerus of a patient. The humeral stem  92  is implanted into a humerus such as is known in the art. The shoulder prosthesis  90  also includes a humeral head  94  that is receivable on the humeral stem  92 . According to an aspect of the present invention, the humeral head  94  is selectively positionable regarding angular orientation with respect to the humeral stem  92 , both in the version and varus/valgus angulation orientations. More particularly, the humeral head  94  is positionable in almost infinitely variable angular positions with respect to the humeral stem  92 , whether the humeral stem  92  is implanted in the humerus or not.  
         [0054]    The shoulder prosthesis  90  also includes a position locking mechanism  96  here embodied as a threaded post and a collar, ring or the like  36 . As described below, the collar  36  cooperates with the adjustment hub or post  124 , the humeral stem  92  and the humeral head  94  to provide a substantially universal joint for angular orientation of the humeral head  94  relative to the humeral stem  92  and for fixing or locking the selected angular orientation/position of the humeral head  94  relative to the humeral stem  92 .  
         [0055]    Referring now to FIG. 15, there is shown the humeral stem  92  of the shoulder prosthesis  90  of FIG. 14 and such will be described with more particularity. The humeral stem  92  is characterized by a body  110  having a distal end  112  and a proximal end  114 . The body  110  is dimensioned to extend into the humeral canal of the patient&#39;s humerus. Particularly, the distal end  112  is inserted into a preferably previously reamed or bored humeral canal of the humerus (not shown). The body  110  also has an end surface  116  that is preferably substantially flat and provided at an angle relative to a longitudinal axis of the humeral stem  92 . The angle of the end  116  is designed to match an angle of resection of the humerus. Note that the humeral stem  92  has no collar adjacent or proximate to the end  116 . The humeral stem  92  is adapted to extend into the humeral canal such that the end  1   16  is flush with the resected surface of the humerus.  
         [0056]    The humeral stem  92  also includes a recess or cavity that extends into the end  116 . As such, the humeral stem  92  may be considered a female component of the shoulder prosthesis  90 . The cavity  118  is substantially spherical in shape defined by an interior surface  120 .  
         [0057]    Referring back to FIG. 14 the humeral head  94  is characterized by a body  98  having an articulation surface  100  and a bottom surface  102 . The articulation surface  100  is essentially hemispherically oblong in shape and/or a shape that closely matches the natural anatomy of the natural humerus head. The body  98  also includes a cavity or recess  104  that extends into the body  98  from the bottom surface  102 . The cavity  104  is essentially frusto-conical and thus has an essentially frustoconical surface  106 . Stated another way, the cavity  104  is cylindrically tapered into the body  98 , preferably with a Morse type taper. While the cavity  104  is shown essentially centered in the body  98 , it should be appreciated, and it is contemplated, that the cavity  104  may be provided in various locations or positions in the body  98 . This permits the present invention to allow for eccentricity correction and/or compliance with respect to a patient&#39;s anatomy. By providing the cavity  104  in off center positions in the body  98 , various eccentricities may be taken into account. The humeral head  94  comes in various dimensions with various cavity  104  locations.  
         [0058]    Referring to FIGS. 16 and 17, the hub  124  is shown in particular detail. The hub  124  is characterized by a frusto-conical or tapered head  126  in like manner to the cavity  104  of the humeral head  94 . This allows the humeral head  94  to be releasably mounted onto the hub  124 . The hub  124  further includes a tapered and threaded body  128 . The tapered and threaded body  128  is tapered opposite to the head  126 . As best seen in FIG. 17, the head  126  includes a keyed opening  128  particularly for a allen wrench or the like. As explained further below, the hub  124  is rotated in the collar  36  in order to expand the collar  36  within the cavity  118  of the humeral stem  92 . Expansion of the collar  36  provides locking of the collar  36  and hub  124  thus locking the humeral head  98 .  
         [0059]    Referring now to FIG. 18, there is depicted a manner of humeral head angulation positioning and/or locking thereof with respect to the shoulder prosthesis embodiment  90  of FIG. 14. It should initially be appreciated that the collar  32  operates in the same manner as that described above for the embodiment of FIG. 1. The collar  32  is situated in the cavity  118  such that the side of the collar  74  abuts and conforms to the spherical surface  120  of the cavity  118 . This allows the collar  32  to be angularly positioned in the cavity  118 . Once the angular position of the collar  32  is set (typically by temporarily placing the humeral head  94  onto the head  126 , then removing same), the hub  124  is rotated (screwed) into the collar  32 . Particularly, the threaded body  128  is received in the threaded bore  770  of the collar  32 . A wrench  130  has a head  132  that is receivable in the opening  128  of the head  126 . Rotation of the wrench  130  rotates the hub  124 . As the hub advances into the collar  32 , the taper of the threaded body  128  expands the collar  32 . Expansion of the collar  32  wedges or fixes the collar  32  against the surface  120  of the cavity  118 . Thereafter, the humeral head  94  is press fit onto the head  126  (i.e. the cavity  104  receives the head  126 ).  
         [0060]    [0060]FIG. 19 depicts an example of an angular orientation of the humeral head  94  with respect to the humeral stem  92  for the modular shoulder prosthesis  90 . In FIG. 19, the humeral head  94  is offset from an axis  134  of the cavity  118  of the humeral stem  92  as indicated by the axis line  136  for the humeral head  94 . The arrows depict the possible angulation of the humeral head  94 .  
         [0061]    [0061]FIG. 20 depicts another example of an angular orientation of the humeral head  94  with respect to the humeral stem  92  for the modular shoulder prosthesis  90 . In FIG. 20, the humeral head  94  is offset from an axis  134  of the cavity  118  of the humeral stem  92  as indicated by the axis line  136  for the humeral head  94 . The arrows depict the possible angulation of the humeral head  94 .  
         [0062]    The components of the shoulder prosthesis can be formed of conventional bio-compatible metals or suitably strong materials. For instance, the humeral stem  32 , humeral head  34  and the expansion ring  36  and/or the angular alignment locking mechanism can be formed of a titanium alloy. Such components may also be formed of a cobalt-chromium alloy.  
         [0063]    The humeral stem  32  and the humeral head  34  porous coated depending upon the preferred application. The humeral stem  32  can be offered in conventional lengths and diameters. The humeral head  34  In one preferred embodiment, the shoulder prosthesis is provided to the orthopaedic surgeon in a kit of various sizes/dimensions of stems and heads, the stems and/or heads having centered and off-centered angular alignment cavities depending on the embodiment. The kit can include all of the components necessary to perform any of the replacement surgeries described above. The components can be assembled in the operating room, if necessary.  
         [0064]    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.