Patent Publication Number: US-2022211510-A1

Title: Reverse shoulder orthopaedic implant having an elliptical glenosphere component

Description:
This application is a continuation application of U.S. patent application Ser. No. 16/390,475, now U.S. Pat. No. 11,278,418, which was filed on Apr. 22, 2019, which is a continuation application of U.S. patent application Ser. No. 14/560,654, now U.S. Pat. No. 10,265,184, which was filed on Dec. 4, 2014 and which is a divisional application of U.S. patent application Ser. No. 13/431,416, which was filed on Mar. 27, 2012, each of which is expressly incorporated herein by reference. 
     CROSS-REFERENCE TO RELATED U.S. PATENT APPLICATION 
     Cross reference is made to U.S. patent application Ser. No. 13/431,406, now U.S. Pat. No. 8,945,229, entitled “REVERSE SHOULDER ORTHOPAEDIC IMPLANT HAVING A METAGLENE COMPONENT WITH A SCREW LOCKING CAP” by Kyle Lappin, which is assigned to the same assignee as the present invention. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates generally to orthopaedic implants, and more particularly to reverse shoulder orthopaedic implants. 
     BACKGROUND 
     During the lifetime of a patient, it may be necessary to perform a total shoulder replacement procedure on the patient as a result of, for example, disease or trauma. In a total shoulder replacement procedure, a humeral prosthesis is used to replace the natural head of the patient&#39;s humerus. The humeral prosthesis typically includes an elongated stem component that is implanted into the intramedullary canal of the patient&#39;s humerus and a hemispherically-shaped prosthetic head component that is secured to the stem component. In such a total shoulder replacement procedure, the natural glenoid surface of the scapula is resurfaced or otherwise replaced with a glenoid component that provides a bearing surface upon which the prosthetic head component of the humeral prosthesis articulates. 
     However, in some cases the patient&#39;s natural shoulder, including its soft tissue, has degenerated to a severe degree of joint instability and pain. In many such cases, it may be necessary to change the mechanics of the shoulder. Reverse shoulder implants are used to do so. As its name suggests, a reverse shoulder implant reverses the anatomy, or structure, of the healthy shoulder. In particular, a reverse shoulder implant is designed such that the prosthetic head (i.e., the “ball” in the ball-and-socket joint) known as a glenosphere component is secured to the patient&#39;s scapula, with the corresponding concave bearing (i.e., the “socket” in the ball-and-socket joint) known as a humeral cup being secured to the patient&#39;s humerus. Such a reverse configuration allows the patient&#39;s deltoid muscle, which is one of the larger and stronger shoulder muscles, to raise the arm. 
     SUMMARY 
     According to one aspect, a reverse shoulder orthopaedic implant includes a glenosphere component having a curved lateral bearing surface configured to articulate with a humeral cup of a humeral prosthesis, and a medial surface having a tapered bore formed therein. The glenosphere component has an anterior/posterior width defined by the distance between an anterior-most point of the lateral bearing surface and a posterior-most point of the lateral bearing surface, and a superior/inferior width defined by the distance between a superior-most point of the lateral bearing surface and an inferior-most point of the lateral bearing surface. The anterior/posterior width of the glenosphere component is greater than its superior/inferior width. 
     The lateral bearing surface of the glenosphere component may be hemi-ellipsoidal in shape. The glenosphere component may be metallic. 
     An imaginary line segment extends from a superior-most point of the medial surface to an inferior-most point of the medial surface. The center of the tapered bore may be positioned between the midpoint of the imaginary line segment and the superior-most point of the medial surface. Alternatively, the center of the tapered bore may be positioned at the midpoint of the imaginary line segment. 
     The reverse shoulder orthopaedic implant may also include a metaglene component having an annular-shaped platform with an elongated stem extending outwardly from a medial surface thereof. A tapered outer surface of the annular-shaped platform may be taper locked in the tapered bore of the glenosphere component. 
     According to another aspect, a reverse shoulder orthopaedic implant includes a glenosphere component having a curved lateral bearing surface configured to articulate with a humeral cup of a humeral prosthesis, and a medial surface having a bore formed therein to receive a metaglene component. The glenosphere component has an anterior/posterior width defined by the distance between an anterior-most point of the glenosphere component and a posterior-most point of the glenosphere component, and a superior/inferior width defined by the distance between a superior-most point of the glenosphere component and an inferior-most point of the glenosphere component. The anterior/posterior width of the glenosphere component is greater than the superior/inferior width of the glenosphere component. 
     The lateral bearing surface of the glenosphere component may be hemi-ellipsoidal in shape. The glenosphere component may be metallic. 
     An imaginary line segment extends from a superior-most point of the medial surface to an inferior-most point of the medial surface. The center of the bore may be positioned between the midpoint of the imaginary line segment and the superior-most point of the medial surface. Alternatively, the center of the bore may be positioned at the midpoint of the imaginary line segment. 
     The reverse shoulder orthopaedic implant may also include a metaglene component having an annular-shaped platform with an elongated stem extending downwardly from a lower surface thereof. The bore formed in the glenosphere component may include a tapered bore, with a tapered outer surface of the annular-shaped platform being taper locked in such a tapered bore. 
     According to another aspect, a reverse shoulder orthopaedic implant includes a glenosphere component having a lateral bearing surface configured to articulate with a humeral cup of a humeral prosthesis. The lateral bearing surface is hemi-ellipsoidal in shape with its longitudinal axis extending in the anterior/posterior direction. The reverse shoulder orthopaedic implant also includes a metaglene component secured to the glenosphere component. 
     An anterior/posterior width of the glenosphere component may be defined by the distance between an anterior-most point of the lateral bearing surface and a posterior-most point of the lateral bearing surface, with its superior/inferior width being defined by the distance between a superior-most point of the lateral bearing surface and an inferior-most point of the lateral bearing surface. The anterior/posterior width of the glenosphere component is greater than the superior/inferior width of the glenosphere component. 
     A tapered bore may be formed in the medial surface of the glenosphere component, with a tapered outer surface of the metaglene component being taper locked therein. 
     An imaginary line segment extends from a superior-most point of the medial surface to an inferior-most point of the medial surface. The center of the tapered bore may be positioned between the midpoint of the imaginary line segment and the superior-most point of the medial surface. Alternatively, the center of the tapered bore may be positioned at the midpoint of the imaginary line segment. 
     Both the glenosphere component and the metaglene component may be metallic. 
     The platform of the metaglene component may include a number of screw holes extending therethrough. 
     According to another aspect, a reverse shoulder orthopaedic implant includes a metaglene component having a platform with a number of screw holes extending therethrough, and an elongated stem extending downwardly from a medial surface thereof. The elongated stem is configured to be implanted into the scapula of a patient. The elongated stem has a bore formed therein. The reverse shoulder orthopaedic implant also includes a screw cap having a shaft positioned in the bore of the metaglene component, and a locking flange extending outwardly from the shaft so as to at least partially cover each of the number of screw holes of the metaglene component. 
     Each of the number of screw holes defines a circumference. An outer edge of the locking flange of the screw cap overlaps at least a portion of the circumference of each of the number of screw holes of the metaglene component. 
     The bore formed in the elongated stem of the metaglene component may be embodied as a threaded bore and the shaft of the screw cap may be embodied as a threaded shaft that is threaded into the threaded bore of the metaglene component. 
     The locking flange may be annular shaped, with the shaft extending outwardly from a lower surface of the locking flange. A drive socket may be formed in the upper surface of the locking flange. 
     The reverse shoulder orthopaedic implant may also include a glenosphere component having a bore formed therein, with the screw cap being captured in the bore of the glenosphere component. 
     The reverse shoulder orthopaedic implant may also include a retaining ring secured within the bore of the glenosphere component so as to retain the screw cap therein. 
     The reverse shoulder orthopaedic implant may further include a number of compression screws positioned in the number of screw holes of the metaglene component. Each of such compression screws has a screw head having a round outer edge, with an outer edge of the locking flange of the screw cap overlapping at least a portion of the round outer edge of each of the number of screw holes of the metaglene component. 
     According to another aspect, a reverse shoulder orthopaedic implant includes a metaglene component having a platform with a number of screw holes extending therethrough, and an elongated stem extending downwardly from a medial surface thereof. The elongated stem has a bore formed therein. The reverse shoulder orthopaedic implant also includes a glenosphere component having a bore formed therein and a screw cap captured in the bore of the glenosphere component. The screw cap is rotatable relative to the glenosphere component. The screw cap has a shaft positioned in the bore of the metaglene component, and a locking flange extending outwardly from the shaft so as to at least partially cover each of the number of screw holes of the metaglene component. 
     The locking flange of the screw cap may include an annular-shaped beveled surface. 
     The screw cap may also include a cylindrically-shaped surface extending upwardly from the annular-shaped beveled surface, and a retaining flange extending outwardly from the cylindrically-shaped surface. A retaining ring may be positioned around the cylindrically-shaped surface of the screw cap and secured to the sidewalls of the glenosphere defining the bore. The diameter of the retaining flange of the screw cap is larger than the inner diameter of the retaining ring and smaller than the outer diameter of the retaining ring. 
     A drive socket is formed in an upper surface of the retaining flange of the screw cap. 
     The retaining ring may be press fit within the bore of the glenosphere component so as to retain the screw cap therein. 
     Each of the number of screw holes defines a circumference. An outer edge of the locking flange of the screw cap overlaps at least a portion of the circumference of each of the number of screw holes of the metaglene component. 
     The bore formed in the elongated stem of the metaglene component may be embodied as a threaded bore and the shaft of the screw cap may be embodied as a threaded shaft that is threaded into the threaded bore of the metaglene component. 
     The reverse shoulder orthopaedic implant may also include a number of compression screws positioned in the number of screw holes of the metaglene component. The locking flange of the screw cap may include an annular-shaped beveled surface, with each of the number of compression screws has a screw head having a round outer edge. The beveled surface of the locking flange of the screw cap contacts the round outer edge of each of the number of screw holes of the metaglene component. 
     According to another aspect, a reverse shoulder orthopaedic implant includes a metaglene component configured to be implanted into the scapula of a patient. The metaglene component has a platform with a number of screw holes extending therethrough. A number of compression screws are positioned in the number of screw holes of the metaglene component. Each of the number of compression screws has a screw head with a round outer edge. A screw cap is secured to the metaglene component. The screw cap has a locking flange that includes an outer edge that overlaps at least a portion of the round outer edge of each of the number of screw holes of the metaglene component. 
     Each of the number of screw holes defines a circumference, with the outer edge of the locking flange of the screw cap overlapping at least a portion of the circumference of each of the number of screw holes of the metaglene component. 
     The platform of the metaglene component may include an elongated stem with a threaded bore formed therein, with the screw cap having a threaded shaft extending downwardly for a lower surface of the locking flange. The threaded shaft of the screw cap may be threaded into the threaded bore of the metaglene component. 
     A drive socket may be formed in an upper surface of the screw cap. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The detailed description particularly refers to the following figures, in which: 
         FIG. 1  is an anterior elevational view showing a reverse shoulder orthopaedic implant that has been implanted into the shoulder of a patient; 
         FIG. 2  is a lateral elevational view showing the elliptical glenosphere component of the reverse shoulder orthopaedic implant of  FIG. 1  implanted on the scapula of a patient; 
         FIG. 3  is an elevational view of the lateral bearing surface of the elliptical glenosphere component of  FIG. 2 ; 
         FIG. 4  is a cross sectional view of the elliptical glenosphere component taken along the line  4 - 4  of  FIG. 3 , as viewed in the direction of the arrows; 
         FIG. 5  is a medial elevational view of the elliptical glenosphere component of  FIG. 3  showing the tapered bore positioned in a centered position; 
         FIG. 6  is a view similar to  FIG. 5 , but showing the tapered bore positioned in an offset position; 
         FIG. 7  is a cross sectional view showing the elliptical glenosphere component of  FIG. 3  implanted on the scapula of a patient; 
         FIG. 8  is an exploded perspective view showing a screw cap used to lock the compression screws within a metaglene component; 
         FIG. 9  is a cross sectional view showing the compression screws and screw cap installed on the metaglene component; 
         FIG. 10  is a plan view showing the compression screws and screw cap installed on the metaglene component; 
         FIG. 11  is an exploded perspective view showing a screw cap that is captured in a glenosphere component and used to lock the compression screws within a metaglene component; 
         FIG. 12  is an assembled cross sectional view showing the screw cap captured in the glenosphere component by the retaining ring; and 
         FIG. 13  is a view similar to  FIG. 12 , but showing the glenosphere component secured to the metaglene component. 
     
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
     While the concepts of the present disclosure are susceptible to various modifications and alternative forms, specific exemplary 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 concepts of the present disclosure 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. 
     Terms representing anatomical references, such as anterior, posterior, medial, lateral, superior, inferior, etcetera, may be used throughout this disclosure in reference to both the orthopaedic implants described herein and a patient&#39;s natural anatomy. Such terms have well-understood meanings in both the study of anatomy and the field of orthopaedics. Use of such anatomical reference terms in the specification and claims is intended to be consistent with their well-understood meanings unless noted otherwise. 
     Referring now to  FIGS. 1-6 , there is shown a reverse shoulder orthopaedic implant  10  for replacing the natural shoulder joint of a patient. The reverse shoulder orthopaedic implant  10  includes an elliptical glenosphere component  12  that is secured to the glenoid surface  20  of the patient&#39;s scapula  22  by a metaglene component  14  implanted in the bone tissue of the scapula  22 . The elliptical glenosphere component  12  articulates on the bearing surface  24  of a humeral cup  26  of a humeral prosthesis. As can be seen in  FIG. 1 , the humeral cup  26  is secured to a humeral stem component  28  that is implanted in the intramedullary canal of a patient&#39;s humerus (not shown). 
     The elliptical glenosphere component  12  includes a body  32  having a curved lateral surface  34 . The curved lateral surface  34  of the body  32  provides a smooth bearing surface upon which the bearing surface  24  of the humeral cup  26  articulates. As can be seen in  FIG. 2-4 , the lateral bearing surface  34  is hemi-ellipsoidal in shape. That is, the lateral bearing surface  34  defines the general shape of ellipsoid sliced in half along its longitudinal plane. 
     The elliptical glenosphere component  12  also includes a substantially flat medial surface  36  opposite its lateral bearing surface  34 . The medial surface  36  has a tapered bore  38  formed therein. The tapered sidewalls  40  defining the bore  38  extend laterally away from the medial surface  36  to a bottom wall  42 . As will be discussed below in more detail, an annular-shaped tapered surface of the metaglene component  14  may be inserted into the tapered bore to engage the sidewalls  40  thereby taper locking the elliptical glenosphere component  12  to the metaglene component  14 . 
     As can be seen in  FIG. 4 , one end of an installation hole  44  opens into the bottom wall  42  of the tapered bore  38 , with the other end of the installation hole  44  opening into the lateral bearing surface  34 . As will be discussed below in greater detail, a surgical instrument, such as a hex head driver, may be passed through the installation hole  44  during a surgical procedure to implant the elliptical glenosphere component  12 . 
     As alluded to above, unlike conventional hemispherically-shaped components, the glenosphere component  12  described herein is hemi-ellipsoidal in shape. As can be seen in  FIGS. 2 and 3 , the glenosphere component  12  is wider in the anterior/posterior direction than it is in the superior/inferior direction. Specifically, as can best be seen in  FIG. 2 , the longitudinal axis  46  of the glenosphere component  12  extends in the anterior/posterior direction, with its shorter lateral axis  48  extending in the superior/inferior direction. This is demonstrated geometrically in the elevational view of the glenosphere component&#39;s lateral bearing surface  34  shown in  FIG. 3  where both the anterior/posterior and the widths of the glenosphere component  12  are shown as a pair of imaginary line segments extending through the glenosphere component  12  in their respective directions. In particular, an imaginary line segment  52  extends between an anterior-most point  54  of the glenosphere component  12  (i.e., the anterior-most point on the glenosphere component&#39;s lateral bearing surface  34 ) and a posterior-most point  56  (i.e., the posterior-most point on the glenosphere component&#39;s lateral bearing surface  34 ) of the glenosphere component  12 . The length of the imaginary line segment  52  defines the anterior/posterior width of the glenosphere component  12 . As can be seen in  FIG. 3 , in the illustrative embodiment described herein, the line segment  52  extends orthogonally between an imaginary tangent line  58  passing through the anterior-most point  54  of the glenosphere component  12  and an imaginary tangent line  60  passing through the posterior-most point  56  of the glenosphere component  12 . Similarly, an imaginary line segment  62  extends between a superior-most point  64  of the glenosphere component  12  (i.e., the superior-most point on the glenosphere component&#39;s lateral bearing surface  34 ) and an inferior-most point  66  of the glenosphere component  12  (i.e., the inferior-most point on the glenosphere component&#39;s lateral bearing surface  34 ). As can be seen in  FIG. 3 , in the illustrative embodiment described herein, the line segment  62  extends orthogonally between an imaginary tangent line  68  passing through the superior-most point  64  of the glenosphere component  12  and an imaginary tangent line  70  passing through the inferior-most point  66  of the glenosphere component  12 . The length of the imaginary line segment  62  defines the superior/inferior width of the glenosphere component  12 . Because the glenosphere component  12  is wider in the anterior/posterior direction than it is in the superior/inferior direction, the imaginary line segment  52  is longer than the imaginary line segment  62 . 
     It should be appreciated that such an arrangement in which the glenosphere component  12  is wider in the anterior/posterior direction than it is in the superior/inferior direction may reduce the occurrences of notching in some patients. In particular, depending on the anatomy of a specific patient, a glenosphere component that is wider in the anterior/posterior direction than it is in the superior/inferior direction may reduce the occasions in which the medial side of the glenosphere component contacts the scapula relative to a hemispherically-shaped glenosphere component. 
     As can be seen in the elevational views of the glenosphere component&#39;s medial surface  36  shown in  FIGS. 5 and 6 , the glenosphere component&#39;s tapered bore  38  may be centered in the superior/inferior direction (see  FIG. 6 ) or offset superiorly in the superior/inferior direction (see  FIG. 7 ). In particular, the central axis  72  of the tapered bore  38  may be positioned at the center of the superior/inferior width of the elliptical glenosphere component  12 , or it may be positioned superiorly of the center of the superior/inferior width of the elliptical glenosphere component  12 . The is demonstrated in the elevational views of the glenosphere component&#39;s medial surface  36  shown in  FIGS. 5 and 6  where the position of the central axis  72  of the tapered bore  38  is shown relative to a midpoint  74  that bisects the imaginary line segment  62  defining the superior/inferior width of the glenosphere component  12 . As can be seen in  FIG. 5 , in the case of a centered glenosphere component  10 , the central axis  72  of the tapered bore  38  is positioned on the midpoint  74  of the imaginary line segment  62  defining the superior/inferior width of the glenosphere component  12 . However, as can be seen in  FIG. 6 , in the case of an offset glenosphere component  10 , the central axis  72  of the tapered bore  38  is still positioned on the imaginary line segment  62  defining the superior/inferior width of the glenosphere component  12 , but is spaced apart from its midpoint  74  in the superior direction. In other words, in the case of an offset glenosphere component  10 , the central axis  72  of the tapered bore  38  is positioned on the imaginary line segment  62  at a location between its midpoint  74  and the superior-most point  64 . 
     Such offset of the tapered bore  38  in the superior direction offsets the glenosphere component  12  in the inferior direction when it is secured to the metaglene component  14  implanted in the patient&#39;s glenoid surface. Such an implanted offset glenosphere component  12  is shown in  FIG. 2 . It should be appreciated that such an inferior offset of the glenosphere component  12  may reduce the occurrences of notching in some patients. In particular, depending on the anatomy of a specific patient, a glenosphere component offset inferiorly may reduce the occasions in which the medial side of the glenosphere component contacts the scapula relative to a centered glenosphere component. 
     It should be appreciated that the tapered bore  38  of the elliptical glenosphere component  12  may also be offset in other directions. For example, the tapered bore  38  of the elliptical glenosphere component  12  may be offset anteriorly or posteriorly relative to the center of the glenosphere component&#39;s medial surface  36  (i.e., it may be offset anteriorly or superiorly relative to the midpoint  74  that bisects the imaginary line segment  62 ). Moreover, the tapered bore  38  of the elliptical glenosphere component  12  may be offset inferiorly relative to the center of the glenosphere component&#39;s medial surface  36 . Yet, further, the tapered bore  38  of the elliptical glenosphere component  12  may be offset in a combination of directions relative to the center of the glenosphere component&#39;s medial surface  36 . For example, the tapered bore  38  of the elliptical glenosphere component  12  may be offset both superiorly and anteriorly (or superiorly and posteriorly) relative to the center of the glenosphere component&#39;s medial surface  36 . 
     The glenosphere component  12  may be constructed with an implant-grade biocompatible metal, although other materials may also be used. Examples of such metals include cobalt, including cobalt alloys such as a cobalt chrome alloy, titanium, including titanium alloys such as a Ti6Al4V alloy, and stainless steel. The lateral bearing surface  34  of such a metallic glenosphere component  12  may be polished or otherwise treated to enhance its smooth bearing surface. 
     The glenosphere component  12  may be provided in various different configurations to provide the flexibility necessary to conform to varying anatomies from patient to patient. For example, the glenosphere component  12  may be provided in various superior/inferior diameters to match the needs of a given patient. For example, in one illustrative embodiment, the glenosphere component  12  may be provided in two different superior/inferior diameters—38 mm and 42 mm. 
     As shown in  FIG. 7 , the glenosphere component  12  is installed on the metaglene component  14  implanted in the bone tissue of the glenoid surface  20  of the patient&#39;s scapula  22 . To do so, the surgeon first aligns the glenosphere component  12  relative to the implanted metaglene component  14  such that its tapered bore  38  is aligned with the an annular-shaped tapered outer surface  108  of the metaglene component  14 . The surgeon then advances the glenosphere component  12  such that the tapered outer surface  108  of the metaglene component  14  is inserted into the tapered bore  38  of the glenosphere component  12 . The surgeon then strikes the glenosphere component  12  (or a head impaction tool positioned thereon) with a surgical mallet, sledge, or other impaction tool to drive the glenosphere component  12  medially so as to urge the sidewalls  40  defining the glenosphere component&#39;s tapered bore  38  into contact with the tapered outer surface  108  of the metaglene component  14  thereby taper locking the glenosphere component  12  to the implanted metaglene component  14 . Such final assembly of the glenosphere component  12  to the implanted metaglene component  14  is shown in  FIGS. 2 and 7 . 
     Referring now to  FIGS. 8-10 , there is shown the metaglene component  14  in more detail. The metaglene component  14  includes a platform  102  having a stem  104  extending outwardly from its medial surface  106 . The metaglene component&#39;s stem  104  is configured to be implanted into the surgically-prepared bone tissue of the glenoid surface  20  of the patient&#39;s scapula  22 . As described above, the glenosphere component  12  is securable to metaglene component  14 . In particular, the outer annular surface  108  of the metaglene component&#39;s platform is tapered. As described in detail above, the glenosphere component  12  may be installed on the metaglene component  14  such that the tapered outer surface  108  of the metaglene component  14  is inserted into the tapered bore  38  of the glenosphere component  12 . So positioned, the glenosphere component  12  may be driven or otherwise urged toward the metaglene component  14  such that the sidewalls  40  defining the glenosphere component&#39;s tapered bore  38  are urged into contact with the tapered outer surface  108  of the metaglene component  14  thereby taper locking the glenosphere component  12  to the metaglene component  14 . 
     As best seen in  FIGS. 8 and 9 , the metaglene component&#39;s stem  104  has a threaded bore  110  formed therein. The threaded bore  110  extends through the entire length of the stem  104 , although it could be embodied as a blind bore. A number of threads  112  are formed in the sidewall that defines the threaded bore  110 . The threads  112  are sized to match, and hence threadingly receive, the threads of a screw cap  140  and a retraction tool (not shown). 
     As can be seen in  FIGS. 8-10 , the metaglene component&#39;s platform  102  has a number of screw holes  114  extending therethrough. One end of each of the screw holes  114  opens into the medial surface  106  of the platform  102 , with its other end opening into the platform&#39;s opposite lateral surface  116 . As can be seen best in  FIG. 9 , each of the screw holes  114  is counterbored to accommodate the screw heads of the compression screws used to secure the metaglene component  12  to the bone tissue of the patient&#39;s scapula  22 . As such, the upper end of the screw holes  114  has a larger diameter than does the lower end of the screw holes  114 . Each of the screw holes  114  is located in one of the four quadrants of the metaglene component&#39;s platform  102 . As such, each of the screw holes  114  is positioned about 90° from one another. 
     In the illustrative embodiment described herein, each of the screw holes  114  is spaced radially outwardly from the center of the metaglene component&#39;s platform  102  at a position between the threaded bore  110  and the outer annular edge  118  where the platform&#39;s lateral surface  116  meets its tapered outer surface  108 . As can be seen in  FIGS. 8 and 9 , the lateral surface  116  of the metaglene component&#39;s platform  102  has a countersunk surface  120  formed therein. As can be seen in  FIG. 8 , each of the screw holes  114  opens partially into the countersunk surface  120  of the metaglene component&#39;s platform  102 . In particular, as can be seen from the elevational view of the metaglene component&#39;s lateral surface  116  shown in  FIG. 10 , the external boundary or perimeter of each of the screw holes  114  defines a circumference  122 . An inner section  124  of the circumference  122  of each of the screw holes  114  (i.e., a section positioned near the center of the metaglene component&#39;s platform  102 ) is positioned within the countersunk surface  120 . 
     The metaglene component  14  may be constructed with an implant-grade biocompatible metal, although other materials may also be used. Examples of such metals include cobalt, including cobalt alloys such as a cobalt chrome alloy, titanium, including titanium alloys such as a Ti6Al4V alloy, and stainless steel. Such a metallic metaglene component  14  may also be coated with a surface treatment, such as hyaluronic acid (HA), to enhance biocompatibility. Moreover, the surfaces of the metaglene component  14  that engage the natural bone, such as the medial surface  106  of platform  102  and the outer surfaces of the stem  104  may be textured to facilitate securing the component to the bone. Such surfaces may also be porous coated to promote bone ingrowth for permanent fixation. 
     Unlike the glenosphere component  12  that may be provided in various sizes to provide the flexibility necessary to conform to varying anatomies from patient to patient, in the illustrative embodiment described herein, the metaglene component  14  may be provided in a single, “universal” size that accommodates glenosphere components of various sizes. For example, in one illustrative embodiment, a metaglene component  14  may be provided in a single size to accommodate both a 38 mm glenosphere component  12  and a 42 mm glenosphere component  12 . 
     As can be seen in  FIGS. 8-10 , a compression screw  130  may be positioned in some or all of the screw holes  114  to secure the metaglene component  12  to the bone tissue of the patient&#39;s scapula  22 . Each of the compression screws  130  includes a threaded shank  132  having a round screw head  134  on an end thereof. The diameter of the threaded shank  132  is smaller than the diameter of the lower end of the counterbored screw holes  114  of the metaglene component  12  so that the threaded shank  132  may pass through the entire length of the screw holes  114 . The screw head  134 , on the other hand, has a diameter smaller than the upper end of the counterbored screw holes  114 , but larger than the lower end of the counterbored screw holes  114 . As such, the screw heads  134  of the compression screws  130  are contained in the upper end of the counterbored screw holes  114  when installed in the metaglene component  12 . 
     Like the metaglene component  14 , the compression screws  130  may be constructed with an implant-grade biocompatible metal, although other materials may also be used. Examples of such metals include cobalt, including cobalt alloys such as a cobalt chrome alloy, titanium, including titanium alloys such as a Ti6Al4V alloy, and stainless steel. 
     As can be seen in  FIGS. 8-10 , a screw cap  140  is secured to the metaglene component  14 . The screw cap  140  includes a locking flange  142  having a threaded shaft  144  extending away from its lower surface  146 . The screw cap&#39;s threaded shaft  144  may be threaded into the threaded bore  110  of the metaglene component&#39;s stem  104  to secure the screw cap  140  to the metaglene component. A drive socket  148 , such as a hex drive socket, is formed in an upper surface  150  of the screw cap&#39;s locking flange  142 . A drive tool, such as a hex driver (not shown), may be inserted into the drive socket  148  to drive (i.e., rotate) the screw cap  140  relative to the metaglene component  14 . Rotation in one direction (e.g., clockwise) may be used to tighten, and hence secure, the screw cap  140  to the metaglene component  14 , with rotation in the opposite direction (e.g., counterclockwise) being used to loosen, and hence, remove the screw cap  140  from the metaglene component  14 . 
     As can be seen in  FIG. 9 , the lower surface  146  of the screw cap&#39;s locking flange  142  defines a generally conical annular-shaped beveled surface  152 . The annular-shaped beveled surface  152  is sized and shaped to be received into and closely compliment the countersunk surface  120  of the metaglene component&#39;s platform  102 . In such a way, the locking flange  142  partially covers the metaglene component&#39;s screw holes  114  and hence the heads  134  of the compression screws  130  positioned therein. What is meant herein by “cover” in regard to the position of the locking flange  142  relative to the screw holes  114  of the metaglene component  14  and/or the heads  134  of the compression screws  130  is that the outer annular edge  154  overlays or overlaps at least a section of the circumference  122  of the screw holes  114  and/or the round outer edge  136  of the compression screws  130 . This is best demonstrated in the lateral elevational or plan view of  FIG. 10 . Specifically, when viewed laterally such as the case of  FIG. 10 , the outer annular edge  154  of the screw cap&#39;s locking flange  142  intersects, and hence overlaps, the circumference  122  of each of the screw holes  114  and the round outer edge  136  of each of the compression screws  130 . In such a way, the locking flange  142  prevents the compression screws  130  from backing out and escaping the screw holes  114 . 
     As can be seen in  FIG. 9 , when the screw cap  140  is installed to the metaglene component  14 , the annular-shaped beveled surface  152  of the screw cap&#39;s locking flange  142  contacts or otherwise engages the round outer edge  136  of each screw head  134  of any of the compression screws  130  installed in the metaglene component  14 . 
     Such contact generates a clamping force to resist the compression screws  130  from backing out from the bone tissue of the patient&#39;s scapula  22 . 
     Like the metaglene component  14  and the compression screws  130 , the screw cap  140  may be constructed with an implant-grade biocompatible metal, although other materials may also be used. Examples of such metals include cobalt, including cobalt alloys such as a cobalt chrome alloy, titanium, including titanium alloys such as a Ti6Al4V alloy, and stainless steel. 
     As shown in  FIG. 7 , the metaglene component  14  may first be implanted into the surgically-prepared glenoid surface  20  of the patient&#39;s scapula  22  by positioning it at the desired location and orientation, and thereafter fixing it in place by inserting one or more compression screw(s)  130  through the screw holes  114  and driving them into the bone tissue. Once the compression screws  114  have been seated, the surgeon may then install the screw cap  140  by inserting its threaded shaft  144  into the threaded bore  110  of the metaglene component&#39;s stem  104  and thereafter rotating the screw cap  140  with a hex driver (not shown) inserted into the drive socket  148  formed in the upper surface  150  of the screw cap&#39;s locking flange  142 . Tightening of the screw cap  140  in such a manner urges the annular-shaped beveled surface  152  of the screw cap&#39;s locking flange  142  into contact with the round outer edge  136  of each screw head  134  of the compression screws  130  installed in the metaglene component  14  thereby asserting a clamping force on the screw heads  134  to resist the compression screws  130  from backing out the bone tissue of the patient&#39;s scapula  22 . Once the screw cap  140  has been installed, the surgeon may then taper lock the glenosphere component  12  to the implanted metaglene component  14  in the manner described above. 
     If the metaglene component  14  subsequently needs to be removed during, for example, a revision procedure, the surgeon may first remove the glenosphere component  12  from the implanted metaglene component  14  by breaking the taper lock connection between the two components and lifting the glenosphere component  12  away. Thereafter, the surgeon may insert a hex driver (not shown) into the drive socket  148  formed in the upper surface  150  of the screw cap&#39;s locking flange  142  and rotating the screw cap  140  in a direction opposite to the direction used to install the screw cap  140 . Loosening of the screw cap in such a manner moves the annular-shaped beveled surface  152  of the screw cap&#39;s locking flange  142  out of contact with the round outer edge  136  of each screw head  134  of the compression screws  130  installed in the metaglene component  14  thereby releasing the clamping force from the screw heads  134 . Continued loosening of the screw cap  140  allows its threaded shaft  144  to escape the threaded bore  110  of the metaglene component&#39;s stem  104  thereby allowing the screw cap  140  to be lifted away. Thereafter, the surgeon may use a drive tool (not shown) to remove the compression screws  130 . An extraction tool (not shown) may be threaded into the threaded bore  110  of the metaglene component&#39;s stem  104  and thereafter used to extract the metaglene component  14  from the bone tissue of the patient&#39;s scapula  22 . 
     Referring now to  FIGS. 11-13 , there is shown an embodiment in which the screw cap  140  is captured in the glenosphere component  14 . In such an embodiment, slight modification has been made to the glenosphere component  14  and the screw cap  140  as shown in  FIGS. 11-13 . The same reference numerals are used in  FIGS. 11-13  to designate components similar to those discussed above in regard to  FIGS. 1-10 . As can be seen in  FIG. 11 , the screw cap  140  is captured and retained in the tapered bore  38  of the glenosphere component  12  by a retaining ring  160 . To do so, the screw cap  140  of the design of  FIGS. 11-13  includes a cylindrically-shaped surface  162  that mates at one end with the annular-shaped beveled surface  152  of the screw cap&#39;s locking flange  142  and at its opposite end with an annular retaining flange  164 . The retaining ring  160  is captured on the cylindrically-shaped surface  162  of the screw cap  140 . That is, the cylindrically-shaped surface  162  of the screw cap  140  is positioned in the retaining ring&#39;s opening  166 . As can be seen in  FIGS. 11 and 12 , the inner diameter of the retaining ring  160  (i.e., the diameter of its opening  166 ) is greater than the diameter of the cylindrically-shaped surface  162  of the screw cap  140 , but less than the diameter of the screw cap&#39;s retaining flange  164 . The outer diameter of the retaining ring  160  (i.e., the diameter of its outer surface  168 ) is greater than the diameter of the screw cap&#39;s retaining flange  16  and is sized and configured to be press fit, welded (or press fit and welded), or taper locked to the tapered sidewalls  40  defining the glenosphere component&#39;s tapered bore  38 . As such, when assembled, the retaining ring  160  captures the screw cap  140  in the glenosphere component&#39;s tapered bore  38 . So captured, both free rotation and limited linear movement of the screw cap  140  relative to the glenosphere component  12  are allowed, but it is prevented from escaping the glenosphere component&#39;s tapered bore  38 . 
     The design of  FIGS. 11-13  may be installed in a similar manner to as described above in regard to the design of  FIGS. 8-10 . In particular, the metaglene component  14  may first be implanted into the surgically-prepared glenoid surface  20  of the patient&#39;s scapula  22  by positioning it at the desired location and orientation, and thereafter fixing it in place by inserting one or more compression screw(s)  130  through the screw holes  114  and driving them into the bone tissue. Once the compression screws  114  have been seated, the surgeon may then install the glenosphere component  12 , and hence the screw cap  140  captured therein, by inserting the screw cap&#39;s threaded shaft  144  into the threaded bore  110  of the metaglene component&#39;s stem  104 . Thereafter, the drive tip of a hex driver (not shown) may be advanced through the glenosphere component&#39;s installation hole  44  and into the screw cap&#39;s drive socket  148 . The surgeon then rotates the screw cap  140  with the hex driver. Such tightening of the screw cap  140  urges the annular-shaped beveled surface  152  of the screw cap&#39;s locking flange  142  into contact with the round outer edge  136  of each screw head  134  of the compression screws  130  installed in the metaglene component  14  thereby asserting a clamping force on the screw heads  134  to resist the compression screws  130  from backing out of the bone tissue of the patient&#39;s scapula  22 . Once the screw cap  140  has been installed, the surgeon may then taper lock the glenosphere component  12  to the implanted metaglene component  14  in the manner described above. 
     If the metaglene component  14  subsequently needs to be removed during, for example, a revision procedure, the surgeon may first remove the glenosphere component  12 , and hence the captured screw cap  140 , from the implanted metaglene component  14  by inserting the drive tip of a hex driver through the glenosphere component&#39;s installation hole  44  and into the screw cap&#39;s drive socket  148 . The surgeon then rotates the screw cap  140  with the hex driver in a direction opposite to the direction used to install the screw cap  140 . Loosening of the screw cap in such a manner moves the annular-shaped beveled surface  152  of the screw cap&#39;s locking flange  142  out of contact with the round outer edge  136  of each screw head  134  of the compression screws  130  installed in the metaglene component  14  thereby releasing the clamping force from the screw heads  134 . The surgeon may then break the taper lock connection between the glenosphere component  12  and the metaglene component  14  and continue loosening the screw cap  140  until its threaded shaft  144  escapes the threaded bore  110  of the metaglene component&#39;s stem  104  thereby allowing the glenosphere component  12 , and hence the screw cap  140  captured therein, to be lifted away from the metaglene component  14 . Thereafter, the surgeon may use a drive tool (not shown) to remove the compression screws  130 . An extraction tool (not shown) may be threaded into the threaded bore  110  of the metaglene component&#39;s stem  104  and thereafter used to extract the metaglene component  14  from the bone tissue of the patient&#39;s scapula  22 . 
     It should be appreciated that the screw caps  140  described above in regard to  FIGS. 8-13  provide efficiency during a surgical procedure to implant the metaglene component  14 . For example, the screw caps  140  allow for implantation of the metaglene component  14  without the use of self-locking surgical screws. Surgical installation of self-locking surgical screws requires the use of a guide wire and other surgical considerations. By providing a locking function, the screw cap  140  allows compression screws, which are much easier to surgically install, to be used in lieu of self-locking surgical screws. 
     It should be appreciated that the concepts and features disclosed herein may be used in various combinations with one another or independently of one another. For example, the elliptical glenosphere component  12  of  FIGS. 1-6  may be used in combination with either the metaglene component  14  of  FIGS. 8-10  or the metaglene component  14  of  FIGS. 11-13 . Moreover, the elliptical glenosphere component  12  of  FIGS. 1-6  may be used in combination with other metaglene components, including metaglene components without the screw caps  140  described herein. Similarly, the metaglene component  14  of  FIGS. 8-10  may be used in combination with the elliptical glenosphere component  12  of  FIGS. 1-6 , or, alternatively, may be used with a conventional hemispherically-shaped or other type of glenosphere component. Along the same line, the metaglene component  14  of  FIGS. 11-13  may be used in combination with the elliptical glenosphere component  12  of  FIGS. 1-6 , or, alternatively, may be used with a conventional hemispherically-shaped or other type of glenosphere component. 
     While the disclosure has been illustrated and described in detail in the drawings and foregoing description, such an illustration and description is to be considered as exemplary and not restrictive in character, it being understood that only illustrative embodiments have been shown and described and that all changes and modifications that come within the spirit of the disclosure are desired to be protected. 
     There are a plurality of advantages of the present disclosure arising from the various features of the apparatus, system, and method described herein. It will be noted that alternative embodiments of the apparatus, system, and method of the present disclosure 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 apparatus, system, and method that incorporate one or more of the features of the present invention and fall within the spirit and scope of the present disclosure as defined by the appended claims.