Abstract:
A method of implanting a glenoid component includes selecting a metaglene component having a body portion and an augment extending medially from the body based upon a defect in a scapula, inserting the selected metaglene component into the scapula, inserting a portion of a first fastener through a body fastener hole of the body portion into a void defined by the body portion and a portion of the augment, inserting the portion of the first fastener into a first augment fastener hole extending through the augment and aligned with the body fastener hole, and inserting the portion of the first fastener into the scapula.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of U.S. patent application Ser. No. 14/152,311, filed on Jan. 10, 2014 (now U.S. Pat. No. 9,114,017, issued on Aug. 25, 2015), which is a divisional of U.S. patent application Ser. No. 13/468,171, filed on May 10, 2012 (now U.S. Pat. No. 8,632,597, issued on Jan. 21, 2014), which is a continuation-in-part of U.S. patent application Ser. No. 12/343,272 entitled “Shoulder Prosthesis Having Augmented Metaglene Component for Use in Rotator Cuff Deficient Shoulder”, which was filed on Dec. 23, 2008, the entire contents of which are each incorporated herein by reference. 
    
    
     BACKGROUND 
     The present disclosure relates generally to shoulder prostheses, and more particularly to shoulder prostheses configured for use in rotator cuff deficient shoulders. 
     The rotator cuff is made up of a group of tendons and muscles which includes the deltoid, the supraspinatus, the infraspinatus, the infrascapular, and the smaller round. When massive rupture occurs of the rotator cuff, only the deltoid muscle remains functional which is insufficient to enable proper operation of the shoulder joint. Moreover, improper operation of the shoulder joint due to massive rotator cuff rupture when left untreated will cause erosion or other defects in the subchondral surface of the glenoid. Thus, it is common that a patient who is being treated for a rotator cuff deficiency will also have erosion or other defects of the subchondral surface of the glenoid. 
     Certain procedures have been used to treat rotator cuff deficient shoulders which have the above described glenoid erosion or defects. For example, the bone of the glenoid may be asymmetrically prepared to create an appropriately configured support to receive a typical metaglene component of a shoulder prosthesis. Asymmetric preparation of bone involves removing more bone from one side of the glenoid in comparison to another in order to create an even support surface for receipt of the metaglene component. In another example, a bone graft is utilized in conjunction with implantation of a standard metaglene component, the bone graft being configured to fill the eroded or defected area of the glenoid so that the implanted metaglene component is appropriately supported. Yet another example involves interposition shoulder arthroplasty in which new tissue is placed between the damaged surfaces of the joint. In interposition shoulder arthroplasty, a tissue-type graft is sutured over the eroded or defected area of the glenoid so as to ease the pain of the damaged joint while allowing the shoulder joint to retain some function. Interposition shoulder arthroplasty is typically a temporary solution to shoulder joint deficiency, and standard shoulder reconstruction will typically follow after several months. 
     Each of these treatments has significant drawbacks. For example, implanting a metaglene component in bone that has been asymmetrically prepared results in healthy bone stock being sacrificed. Use of a bone graft in conjunction with a metaglene component may have complications due to graft non-union and not all patients have adequate bone stock available for such a procedure. Interposition shoulder arthroplasty tends to be a short term solution that masks the shoulder joint deficiency, only to be followed some time later by more invasive conventional shoulder reconstruction in which humeral and glenoid components are implanted. This two step process results in more risk and inconvenience to the patient since two surgical procedures are involved. 
     What is needed therefore is an improved shoulder prosthesis for use in a rotator cuff deficient shoulder that involves glenoid erosion or defects. What is also needed is a shoulder prosthesis for use in a rotator cuff deficient shoulder that involves glenoid erosion or defects that conserves healthy bone stock. What is further needed is a shoulder prosthesis for use in a rotator cuff deficient shoulder that involves glenoid erosion or defects that does not necessitate a bone graft to be implanted in conjunction with the shoulder prosthesis. What is additionally needed is a shoulder prosthesis for use in a rotator cuff deficient shoulder that involves glenoid erosion or defects which does not promote a two stage surgical approach to restoring proper function of the shoulder joint. 
     SUMMARY 
     In accordance with one embodiment of the disclosure, there is provided a metaglene assembly for use in a shoulder prosthesis. The metaglene assembly includes a metaglene body, an augment, a void, at least one fastener hole, and at least one fastener. The metaglene body has a lateral, prosthesis-facing side, and a medial, bone-facing side. The augment extends medially from the medial, bone-facing side of the metaglene body. The void is defined by a portion of the medial, bone-facing side of the metaglene body and a lateral portion of the augment. The fastener hole extends from the void through the augment. The fastener is configured to extend within the fastener hole. 
     Pursuant to another embodiment of the disclosure, there is provided a shoulder prosthesis kit. The shoulder prosthesis includes a plurality of metaglene components and a plurality of bearing components. Each of the metaglene components has a body, an augment extending from the body, and a void defined by a portion of the body and a portion of the augment. At least two of the metaglene components&#39; bodies have outermost diameters that are different from one another. At least two of the bearing components have innermost diameters that are slightly larger than the outermost diameters of respective metaglene components. 
     In yet another embodiment, a shoulder prosthesis kit includes at least one metaglene component including (i) a metaglene body having a lateral, prosthesis-facing side, and a medial, bone-facing side, the metaglene body defining an outer body perimeter which when projected onto a plane perpendicular to a longitudinal axis of the metaglene body is circularly shaped, (ii) an augment extending medially from the medial, bone-facing side of the metaglene body, the augment defining an outer augment perimeter which when projected onto the plane is semi-circularly shaped, and the projected augment perimeter coincides with at least a portion of the projected metaglene body perimeter, (iii) a void defined by a portion of the medial, bone-facing side of the metaglene body and a lateral facing portion of the augment, and (iv) at least one augment fastener hole extending from the void through the augment, a plurality of bearing components, each of the plurality of bearing components defining a cavity configured to couple with the metaglene body, and having a bearing surface that is sized differently from the size of another of the plurality of bearing components, and at least one fastener configured to be inserted into the at least one augment fastener hole. 
     In a further embodiment, a metaglene assembly kit for use in a shoulder prosthesis includes a metaglene component including (i) a lateral, prosthesis-facing side, and a medial, bone-facing side, (ii) an augment extending medially from the medial, bone-facing side of the metaglene body, (iii) a void defined by a portion of the medial, bone-facing side of the metaglene body and a lateral facing portion of the augment, (iv) a first fastener hole extending from the void through the augment and defining a first fastener hole axis; and (v) a second fastener hole extending through the metaglene body and defining a second fastener hole axis, the second fastener hole axis aligned with the first fastener hole axis, and a plurality of bearing components, each of the plurality of bearing components defining a cavity configured to couple with the metaglene component, and having a bearing surface that is sized differently from the size of another of the plurality of bearing components. 
     In one embodiment, a method of implanting a glenoid component includes selecting a metaglene component having a body portion and an augment extending medially from the body based upon a defect in a scapula, inserting the selected metaglene component into the scapula, inserting a portion of a first fastener through a body fastener hole of the body portion into a void defined by the body portion and a portion of the augment, inserting the portion of the first fastener into a first augment fastener hole extending through the augment and aligned with the body fastener hole, and inserting the portion of the first fastener into the scapula. 
     A method of implanting a glenoid component in some embodiments includes selecting a glenoid bearing component, positioning the body portion within a cavity of the selected glenoid bearing, and forming a Morse taper connection between the body portion and the cavity. 
     A method of implanting a glenoid component in some embodiments includes attaching the selected glenoid bearing component to the body portion using a second fastener. 
     A method of implanting a glenoid component in some embodiments includes inserting a portion of a third fastener into a second augment fastener hole extending through the augment without first inserting the portion of the third fastener through the body portion, and inserting the portion of the third fastener into the scapula. 
     A method of implanting a glenoid component in some embodiments includes abutting a spherically shaped portion of the third fastener with a concave bearing seat of the second augment fastener hole. 
     In some embodiments, the second augment fastener hole defines a fastener hole axis, and the third fastener is not aligned with the fastener hole axis when the portion of the third fastener is inserted into the scapula. 
     In some embodiments selecting the metaglene component includes selecting the metaglene component from a kit comprising a plurality of metaglene components, each of the plurality of metaglene components having a metaglene body thickness different from a metaglene body thickness of each of the other of the plurality of metaglene components, wherein the selected metaglene component has a desired metaglene body thickness. 
     In some embodiments each of the plurality of metaglene components includes an augment extending at an angle relative to the metaglene body different from an angle at which the augments of each of the other of the plurality of metaglene components extend from their respective bodies, and the selected metaglene component has an augment extending at a desired angle relative to the metaglene body. 
     In some embodiments each of the plurality of metaglene components includes an augment displacement different from an augment displacement of each of the other of the plurality of metaglene components, and the selected metaglene component has a desired augment displacement. 
     In some embodiments each of the plurality of metaglene components includes an augment radius with a respective length different from an augment radius length of each of the other of the plurality of metaglene components, and the selected metaglene component has a desired augment radius length. 
     The above described features and advantages, as well as others, will become more readily apparent to those of ordinary skill in the art by reference to the following detailed description and accompanying drawings. While it would be desirable to provide a metaglene assembly for use in a shoulder prosthesis or a shoulder prosthesis kit that includes one or more of these advantageous features, the teachings disclosed herein extend to those embodiments which fall within the scope of the appended claims, regardless of whether they accomplish one or more of the above-mentioned advantages. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a shoulder prosthesis implanted in a scapula and a humerus of a patient to form a joint therebetween; 
         FIG. 2  is a cross sectional view of a glenoid component of the shoulder prosthesis of  FIG. 1 ; 
         FIG. 3  is an exploded cross sectional view of the glenoid component of  FIG. 2 , shown with the fasteners removed for clarity of description; 
         FIG. 4  is a side perspective view of a metaglene assembly of the present disclosure that can be used in the glenoid component of the shoulder prosthesis of  FIGS. 1-3 ; 
         FIG. 5  is a side perspective view of the metaglene component of the metaglene assembly of  FIG. 4 ; 
         FIG. 6  is a schematic diagram of a side projection of a portion of the metaglene component of  FIG. 5 ; 
         FIG. 7  is a bottom view of the metaglene component of  FIG. 5 ; 
         FIG. 8  is a side elevational view of the metaglene component of  FIG. 5 ; 
         FIG. 9  is an alternative embodiment of a metaglene component configured for use in the metaglene assembly of  FIG. 4 ; and 
         FIG. 10  is yet another alternative embodiment of a metaglene component configured for use in the metaglene assembly of  FIG. 4 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     While the shoulder prosthesis described herein is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that there is no intent to limit the shoulder prosthesis to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims. 
     As used herein, the terms “medial” and “lateral” are anatomical directional terms referring to positioning relative to the center of the body receiving the shoulder prosthesis. The term “medial” means closer to the center of the body. The term “lateral” means farther from the center of the body. 
     Referring to  FIG. 1 , there is shown a shoulder prosthesis  10  that includes a glenoid component  12  and a humeral component  14  that are configured to cooperate with each other to form a shoulder joint. The glenoid component  12  is configured to be attached to a glenoid of a scapula  16 , while the humeral component  14  is configured to be implanted in an intramedullary canal  18  of a humerus  20  as shown in  FIG. 1 . 
     The humeral component  14  includes a stem  22  that is configured to be received in the intramedullary canal  18  as shown in  FIG. 1 . The humeral component  14  further includes a humeral bearing component  24  that has a humeral bearing surface  26 . 
     The glenoid component  12  of the shoulder prostheses  10  is shown in more detail in  FIGS. 2-3 . In particular, as shown in  FIG. 2 , the glenoid component  12  includes a metaglene assembly  13  and a glenoid bearing component  32 . The metaglene assembly  13  includes a metaglene component  30  and a plurality of fasteners  34 . The metaglene component  30  is configured to be attached to the glenoid of the scapula  16  (shown in  FIG. 1 ) with the fasteners  34 , while the glenoid bearing component  32  is configured to be coupled to the metaglene component  30  as shown in  FIGS. 2 and 3 . 
     As shown in  FIG. 3 , the metaglene component  30  includes a metaglene body  36  having a lateral, prosthesis-facing side  38  and a medial, bone-facing side  39 . The lateral, prosthesis-facing side  38  defines a lateral metaglene plane  90 . The lateral, prosthesis-facing side  38  of the metaglene body  36  is substantially circularly shaped and defines a metaglene body center (not shown). The metaglene body  36  further has an external peripheral wall surface  44  having an outermost diameter  94  that defines an external coupling surface that extends between the lateral, prosthesis-facing side  38  and the medial, bone-facing side  39 . The external peripheral wall surface  44  tapers slightly outwardly from the lateral, prosthesis-facing side  38  to the medial, bone-facing side  39  such that the metaglene body  36  is slightly larger at the medial, bone-facing side  39  than at the lateral, prosthesis-facing side  38 . The external peripheral wall surface  44  extends completely (i.e. 360 degrees) around the periphery of the metaglene component  30 . The metaglene body  36  has defined therein a plurality of metaglene body fastener holes  37 A,  37 B, and two other metaglene body fastener holes (not shown). The metaglene body fastener holes  37 A,  37 B are defined, in part, by walls having concave bearing seats  50 . 
     The metaglene component  30  also includes a post  46  extending from the metaglene body  36 . The post  46  defines a post axis  92  that is perpendicular to the lateral metaglene plane  90  and passes through the metaglene body center. The post  46  is attached to the metaglene body  36  by being integrally formed therewith. A plurality of ribs  49  are defined on the post  46 . The post  46  has defined therein a central passage  48 . The central passage  48  extends through the metaglene body  36  as shown in  FIGS. 2-3 . The post  46  also includes an internally threaded wall portion  52 . 
     As stated above, the metaglene assembly  13  further includes metaglene body fasteners  34 A,  34 B, and two other metaglene body fasteners (not shown). Each of the metaglene body fasteners  34 A-D includes a head having a convex surface to be matingly received by a respective concave bearing seat  50  of a respective metaglene body fastener hole  37 A-D, as shown in  FIGS. 2-3 , such that the metaglene body fasteners  34 A-D do not extend above the concave bearing seats  50 . Additionally, each of the metaglene body fasteners  34 A-D is configured to be adjustable to any one of a variety of angles with respect to the metaglene body  36  due to the spherical shape of both the fastener heads and the concave bearing seats  50 . 
     Two of the metaglene body fasteners can be locking fasteners wherein advancement of an expander (not shown) into a head recess (not shown) of its respective head causes the fastener head to expand thereby locking the head and thus the metaglene body fastener to the metaglene body  36 . Alternatively, more or fewer than two of the metaglene body fasteners can be locking fasteners. 
     As is shown in  FIGS. 2-3 , the glenoid bearing component  32  includes a substantially hemispherical glenoid bearing surface  60  that defines an axis “X”. The glenoid bearing surface  60  has an access opening  61  defined therein. The glenoid bearing surface  60  is configured to mate with the humeral bearing surface  26  of the humeral bearing component  24  as shown in  FIG. 1 . In particular, the glenoid bearing surface  60  defines a convex surface and the humeral bearing surface  26  defines a concave surface which is configured to receive the convex glenoid bearing surface  60 . Alternatively, the glenoid bearing surface  60  may be configured to define a concave surface and the humeral bearing surface  26  may be configured to define a convex surface which is configured to receive the alternative concave glenoid bearing surface  60 . 
     In addition, the glenoid bearing component  32  defines a cavity  62 . The cavity  62  defines an internal wall surface  64  having an innermost diameter  65  that defines an internal coupling surface. The internal wall surface  64  extends completely (i.e. 360 degrees) around the cavity  62 . The innermost diameter  65  is sized slightly larger than the outermost diameter  94  of the external peripheral wall surface  44  of the metaglene body  36 , and the external peripheral wall surface  44  is positioned in contact with the internal wall surface  64  to form a friction fit connection between the glenoid bearing component  32  and the metaglene component  30  as shown in  FIGS. 2-3 . In order to facilitate the friction fit connection, both the external peripheral wall surface  44  and the internal wall surface  64  are tapered so that the surfaces  44 ,  64  when joined together form a Morse taper connection. 
     The glenoid bearing component  32  further includes a screw  66  that is aligned with the axis X. As shown in  FIG. 2 , the glenoid bearing component  32  further defines a space  68  in which a head  69  of the screw  66  is retained by a washer  70 . In particular, the glenoid bearing component  32  further defines an internally threaded wall  72  which meshes with external threads  73  of the washer  70 . So retained, the screw  66  is free to rotate in relation to the bearing surface  60 . The screw  66  includes a longitudinal axial channel  76  as shown in  FIGS. 2-4 . The screw  66  also includes an externally threaded portion  78  that is configured to meshingly engage the internally threaded portion  52  of the post as shown in  FIGS. 2 and 3 . Further structure and operation of the screw and related components may be understood with reference to similar structure disclosed in U.S. Pat. No. 6,953,478 issued to Bouttens et al., the disclosure of which is herein incorporated by reference in its entirety. 
       FIG. 4  depicts a metaglene assembly  113  of the present disclosure which can be used in the glenoid component  12  of  FIGS. 1-3  in place of the metaglene assembly  13 . The metaglene assembly  113  includes a metaglene component  130  and fasteners  156  and  158 .  FIG. 5  shows the metaglene component  130  in more detail. The metaglene component  130  is configured and used in substantially the same manner as the metaglene component  30  described hereinabove. The metaglene component  130 , however, includes additional features described below which provide additional advantages over the metaglene component  30  of  FIGS. 1-3 . 
     As shown in  FIG. 5 , the metaglene component  130  includes a metaglene body  136 , a post  146 , an augment  140 , and a void  180 . The metaglene body  136  has a lateral, prosthesis-facing side  138  and a medial, bone-facing side  139 . The lateral, prosthesis-facing side  138  of the metaglene body  136  defines a lateral metaglene plane  190  having a metaglene body center  191 . The post  146  defines a post axis  192  extending longitudinally through the post  146  perpendicularly to the metaglene plane  190 . The metaglene component  130  is arranged substantially radially around the post axis  192 . Thus, features of the metaglene component  130  can be referred to as being closer to or farther from the post axis  192  regardless of the orientation of the metaglene component  130 . 
     The augment  140  is attached to the medial, bone-facing side  139  of the metaglene body  136 . The augment  140  is attached to the metaglene body  136  by being integrally formed therewith. Alternatively, the augment  140  can be removably attached to the metaglene body  136  by a coupling mechanism (not shown). For example, the coupling mechanism may include a post (not shown) attached to the augment and a recess (not shown) formed in the metaglene body  136 , in which the post and recess mate in a friction fit manner to secure the augment  140  to the metaglene body  136 . 
     The augment  140  has a lateral augment surface  181 , a medial augment surface  182 , a lateral portion  141 , and a medial portion  142  and defines an external sidewall  143  that extends between the lateral augment surface  181  and the medial augment surface  182  and extends along both the lateral portion  141  and the medial portion  142 . The void  180  is formed between the lateral augment surface  181  of the augment  140  and the medial, bone-facing side  139  of the metaglene body  136 . The intersection between the external sidewall  143  and the medial augment surface  182  forms an augment edge  184 . 
     To clarify the arrangement and configuration of the features of the metaglene component  130 ,  FIG. 6  depicts a projection of a side of the metaglene body  136  and the augment  140  onto a plane. As seen in  FIG. 6 , when viewed from a side perspective, the augment edge  184  (formed at the intersection of the external sidewall  143  and the medial augment surface  182 ) forms an augment arc  185  that extends along a portion of an augment circle  186 . The augment circle  186  has an augment radius  187  that extends from the augment edge  184  to the center of the augment circle  186 . The augment edge  184  departs from the augment circle  186  near the intersection of the augment  140  with the metaglene body  136 . A medial augment line  188  indicates where the augment edge  184  departs from the augment circle  186 . The medial augment line  188  is parallel to the post axis  192  (shown in  FIG. 4 ). Also shown most clearly in  FIG. 6 , the metaglene body  136  has a thickness  193 . 
       FIG. 7  depicts an end view of the metaglene component  130  having an outermost diameter  194 . The outermost diameter  194  is sized slightly smaller than the innermost diameter  65  of the glenoid bearing component  32  (shown in  FIGS. 2-3 ) to form a frictional fit in a glenoid component as described above with relation to the glenoid component  12  of  FIGS. 1-3 . The external sidewall  143  of the augment  140  aligns with a portion of the external peripheral wall surface  144  of the metaglene body  136 . In other words, the perimeter of the augment  140  coincides with a portion of the perimeter of the metaglene body  136 . In the embodiment of the metaglene component  130  shown in  FIG. 7 , the external sidewall  143  of the augment  140  extends circumferentially for approximately a half of the extent of the external coupling surface  144  of the metaglene body  136 . In other words, the external sidewall  143  of the augment  140  extends circumferentially for approximately  180  degrees around the periphery of the metaglene body  136 . In other embodiments, however, the external sidewall of the augment can extend circumferentially for more than or less than a half of the extent of the external coupling surface of the metaglene body. 
     As shown in  FIGS. 5 and 7 , the metaglene component  130  has defined therein a plurality of metaglene body fastener holes  137 A-D like the metaglene body fastener holes  37 A-D described above with reference to the metaglene component  30  (shown in  FIGS. 2-3 ). Additionally, the augment  140  of the metaglene component  130  has defined therein a plurality of augment fastener holes  145 A,  145 B, and  145 C. The augment fastener holes  145 A,  145 B, and  145 C are defined, in part, by walls having concave bearing seats  150  (shown in  FIG. 5 ) like those of the metaglene body fastener holes  137 A-D. 
     As can be seen in  FIGS. 5 and 7 , the augment fastener hole  145 A aligns with the metaglene body fastener hole  137 A. As used herein, when holes “align” they are oriented such that a fastener extending through a first hole can also extend through a second hole without changing angle. In contrast, the augment fastener holes  145 B and  145 C do not align with metaglene body fastener holes. Additionally, the augment fastener holes  145 B and  145 C extend through the metaglene component  130  at angles different than the angles at which the augment fastener hole  145 A and the metaglene body fastener holes  137 A,  137 B,  137 C, and  137 D extend through the metaglene component  130 . As shown in  FIG. 6 , the augment fastener holes  145 A,  145 B, and  145 C can be accessed through the void  180 . Due to the placement and the angle of the augment fastener holes  145 B and  145 C, lateral end openings  147  of augment fastener holes  145 B and  145 C are partially defined in the external side wall  143 . 
     Returning now to  FIG. 4 , the metaglene assembly  113  further includes metaglene body fasteners  156  and augment fasteners  158 . For simplicity, only two metaglene body fasteners  156  and one augment fastener  158  are shown. The metaglene body fasteners  156  can be identical to or different from the augment fasteners  158 . The metaglene body fasteners  156  are configured to extend through the metaglene body fastener holes  137 A,  137 B,  137 C, and  137 D (shown in  FIG. 5 ), and the augment fasteners  158  are configured to extend through the augment fastener holes  145 B and  145 C (shown in  FIG. 5 ). The metaglene body fastener  156  that extends through the augment fastener hole  145 A (shown in  FIG. 5 ) is configured to additionally extend through metaglene body fastener hole  137 A (shown in  FIG. 5 ). However, as shown in  FIG. 4 , the metaglene body fastener  156  that extends through augment fastener hole  145 A (shown in  FIG. 5 ) does not necessarily extend through metaglene body fastener hole  137 A (shown in  FIG. 5 ). 
     Each of the metaglene body fasteners  156  includes a head having a convex surface configured to be matingly received by a respective concave bearing seat  150  of the respective metaglene body fastener hole  137 A-D. Each of the metaglene body fasteners  156  is configured to be adjustable to any one of a variety of angles with respect to the metaglene body  136  due to the spherical shape of both the fastener heads and the concave bearing seats  150 . Accordingly, depending on the angle at which a metaglene body fastener  156  is inserted through a metaglene body fastener hole  137 , the metaglene body fastener  156  does not necessarily extend laterally beyond the plane  190  (shown in  FIG. 5 ). Similarly, each of the augment fasteners  158  includes a head having a convex surface configured to be matingly received by a respective concave bearing seat  150  of the respective augment fastener hole  145 A-D. Each of the augment fasteners  158  is configured to be adjustable to any one of a variety of angles with respect to the metaglene body  136  due to the spherical shape of both the fastener heads and the concave bearing seats  150 . Accordingly, the augment fastener  158  does not typically extend into the void  180 , although a portion of it may extend into the void  180  depending on the angle at which an augment fastener  158  is inserted through an augment fastener hole  145 . 
     When a shoulder prosthesis is implanted into a body, the appropriate metaglene component for use in the metaglene assembly is selected based on the properties of the defect(s) in the bones of the shoulder joint. To most effectively compensate for the defect(s) in the shoulder, the best metaglene component has a metaglene body with the appropriate metaglene body thickness, an augment and metaglene body extending for an appropriate length relative to the post, and an augment extending at an appropriate angle relative to the metaglene body. These factors, among others, influence the particular size and shape of the metaglene component. Because, as noted above, the metaglene component is arranged substantially radially around the post, the metaglene component can be rotated and inserted at any angle appropriate to compensate for the defect(s) in the shoulder. 
     As shown in  FIG. 8 , the particular size and shape of the metaglene component  130  are dictated by the length of the augment radius  187 , the metaglene body thickness  193 , and the distance between the medial augment line  188  and the post axis  192 , this distance being referred to as the augment displacement  189 . Modifications of the particular size and shape of the metaglene component  130  include, for example, lengthening the augment radius  187  without changing the metaglene body thickness  193  or the augment displacement  189 . This results in the augment and the metaglene body extending for a longer length relative to the post  146 . The size of the void  180  is selected based on the size and shape of the metaglene component  130  such that the void  180  allows for optimized visualization of the lateral augment surface  181  and optimized access to the augment fastener holes  145 . 
     To facilitate selection of the best components for implantation of a prosthetic shoulder, a kit can be formed including components having a variety of shapes and sizes. The kit can include more than one glenoid bearing component  32  having a variety of dimensions. For example, at least one glenoid bearing component  32  can have a larger innermost diameter  65  than another glenoid bearing component  32 . The kit can also include more than one metaglene component  30  having a variety of dimensions. For example, at least one metaglene component  30  can have a larger outermost diameter  94  than another metaglene component  30 . The kit can also include more than one metaglene component  130  having a variety of dimensions. For example, at least one metaglene component  130  can have a larger augment radius  187  than another metaglene component  130 . Additionally, at least one metaglene component  130  can have a larger metaglene body thickness  193  than another metaglene component  130 . Additionally, at least one metaglene component  130  can have a larger augment displacement  189  than another metaglene component  130 . The kit can also include more than one type of fastener to be used as metaglene body fasteners  156  and as augment fasteners  158 . 
     Using such a kit allows a doctor to select the best combination of components based on a patient&#39;s particular bone geometry and defect(s). For example, the doctor could select a glenoid bearing component  32  having a smaller innermost diameter  65  for a patient having a smaller shoulder. The doctor could select a shorter fastener to be used as a metaglene body fastener  156  or augment fastener  158  for a patient having a thinner depth of bone into which the implant is to be fastened. The doctor could also select a metaglene component  130  having the particular combination of larger metaglene body thickness  193 , smaller augment displacement  189 , and larger augment radius  187  to compensate for a bone defect having a particular depth, width and angle relative to the remaining bone. To further optimize the compensation of the implant and the fixation of the implant into the shoulder bones, the selected metaglene components can be inserted at any degree of rotation and the fasteners can be inserted through the metaglene components and into the bone at a range of angles. 
     In other embodiments discussed below, the particular size and shape of the metaglene components and voids can be different than those of the embodiment shown in  FIGS. 4-8 . Each alternative embodiment is suited for a different bone defect in the shoulder and, thus, each has particular benefits. 
     By way of example,  FIG. 9  shows an alternative embodiment of a metaglene component  230  that is configured and used in substantially the same manner as the metaglene component  130  described hereinabove. The metaglene component  230  differs from the metaglene component  130 , however, in size and configuration of the metaglene component and the void. In particular, the augment displacement  289  is smaller than the augment displacement  189  (shown in  FIG. 8 ). Additionally, the augment displacement  289  is in the opposite direction relative to the void  280  than the augment displacement  189  relative to the void  180  (shown in  FIG. 8 ). The augment radius  287  is larger than the augment radius  187  (shown in  FIG. 8 ). Accordingly, the augment  240  and the void  280  shown in  FIG. 9  have different shapes and configurations in relation to the metaglene component  230  than the augment  140  and the void  180  in relation to the metaglene component  130  shown in  FIG. 8 . 
     Turning now to  FIG. 10 , there is shown yet another alternative embodiment of a metaglene component  330  that is configured and used in substantially the same manner as the metaglene component  130  described hereinabove. The metaglene component  330  differs from the metaglene component  130 , however, in size and configuration of the metaglene component and the void. In particular, the augment displacement  389  is smaller than the augment displacement  189  (shown in  FIG. 8 ). Additionally, the augment radius  387  is larger than the augment radius  187  (shown in  FIG. 8 ). Accordingly, the augment  340  and the void  380  shown in  FIG. 10  have different shapes and configurations in relation to the metaglene component  330  than the augment  140  and the void  180  in relation to the metaglene component  130  shown in  FIG. 8 . 
     Although not specifically depicted, additional alternative embodiments can include any combination of augment displacement, augment radius, and metaglene body thickness that results in a functional metaglene component. Additionally, an alternative embodiment can have a combination of an augment displacement and an augment radius such that the post is attached only to the metaglene body or only the augment rather than to both the metaglene body and augment. 
     There is a plurality of advantages arising from the various features of each of the embodiments of the shoulder prosthesis described herein. It will be noted that alternative embodiments of the shoulder prosthesis may not include all of the features described yet still benefit from at least some of the advantages of such features. Those of ordinary skill in the art may readily devise their own implementations of the shoulder prosthesis that incorporates one or more of the features and fall within the spirit and scope of the present invention as defined by the appended claims.