Patent Publication Number: US-2023149176-A1

Title: Multi-Direction Fixation for Shoulder Prosthesis

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims the benefit of the filing date of U.S. Provisional Application No. 63/279,711, filed on Nov. 16, 2021, the disclosure of which is hereby incorporated herein by reference. 
    
    
     FIELD OF THE DISCLOSURE 
     The present application generally relates to a shoulder prosthesis and a method of implantation of a shoulder prosthesis, although the concepts described herein are applicable to other joint prostheses. 
     BACKGROUND OF THE DISCLOSURE 
     Over time and through repeated use, bones and joints can become damaged or worn. For example, repetitive strain on bones and joints (e.g., through athletic activity), traumatic events, and certain diseases (e.g., arthritis) can cause cartilage in joint areas, for example, which normally provides a cushioning effect, to wear down. When the cartilage wears down, fluid can accumulate in the joint areas, resulting in pain, stiffness, and decreased mobility. The same can happen in cases where tendons in a joint become lax or soft tissues in or adjacent the joint become damaged or worn. 
     Arthroplasty procedures can be used to repair such damaged joints. During a typical arthroplasty procedure, an arthritic or otherwise dysfunctional joint can be remodeled or realigned. A prosthesis or prostheses can be implanted to repair the damaged region(s). Arthroplasty procedures may take place in any of a number of different regions of the body, such as the knees, hips, shoulders, or elbows, for example. One type of arthroplasty procedure is a shoulder arthroplasty, in which a damaged shoulder joint may be replaced with prosthetic implants. The shoulder joint may have been damaged by, for example, arthritis (e.g., severe osteoarthritis or degenerative arthritis), trauma, or a destructive joint disease. 
     Shoulder prostheses may take the form of anatomic or reverse implants. In anatomic shoulder implants, the native humeral head is replaced with a prosthetic humeral head, and/or the native glenoid is replaced with a prosthetic glenoid. In a reverse shoulder implant, the native humeral head is replaced with a prosthetic cup or socket component, and the native glenoid is replaced with a prosthetic ball component (e.g. a glenosphere). As the name suggests, a reverse prosthetic shoulder system reverses the positions of the ball and socket components of the joint relative to the native positions of those components. 
     Prostheses that are implanted into a damaged region may provide support and structure to the damaged region, and may help to restore the damaged region, thereby enhancing its functionality. Prior to implantation of a prosthesis in a damaged region, the damaged region may be prepared to receive the prosthesis. In the case of a shoulder arthroplasty procedure, one or more of the bones in the shoulder area, such as the humerus and/or glenoid, may be treated (e.g., cut, drilled, reamed, and/or resurfaced) to provide one or more surfaces that can align with the implant and thereby accommodate the implant. 
     The fixation of an implant component into the bone is typically an important features of the implant system. Joint implants are frequently under loads of varying amounts and in varying positions. If an implant component becomes loose, it can become ineffective and even need to be removed and replaced with a new implant. Thus, fixation is an important feature of joint implant systems. For stemless humeral implants, fixation can be particularly important because stemless humeral implants typically have less structure than corresponding stemmed humeral implants, which may make proper fixation more difficult to achieve. However, proper fixation is important for all joint implants, including both stemmed and stemless humeral implants. 
     BRIEF SUMMARY OF THE DISCLOSURE 
     According to one aspect of the disclosure, a prosthetic implant system includes a first articulation component, a base, and a second anchor. The base may have a proximal portion and a first anchor extending in a distal direction along a longitudinal first anchor axis. The proximal portion of the base may be configured to couple to the first articulation component. The second anchor may be formed separately from the base and may extend along a longitudinal second anchor axis. The base may include a channel extending from a first opening in the proximal portion of the base through a second opening in a distal portion of the first anchor. The channel may be sized and shaped to receive the second anchor therethrough. When the second anchor is received within the channel, the longitudinal first anchor axis may be oblique to the longitudinal second anchor axis. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a view of bones of a shoulder joint. 
         FIG.  2    is a view of the bones of the shoulder joint of  FIG.  1    along with representations of the subscapularis muscle and the supraspinatus muscle. 
         FIGS.  3 A-C  are cross-sections of different steps of implanting a base of a prosthetic humeral implant into a humerus. 
         FIG.  3 D  is a cross-section of a base and secondary anchor implanted into a humerus, the secondary anchor being elongated relative to that shown in  FIGS.  3 A-C . 
         FIG.  4 A  is a perspective view of the base of the prosthetic humeral implant, and secondary anchor, shown in  FIGS.  3 A-C  but provided with additional detail. 
         FIG.  4 B  is a side view of the base illustrated in  FIG.  4 A . 
         FIG.  4 C  is a cross-section of base of  FIG.  4 B  taken along the section line  4 C- 4 C of  FIG.  4 B . 
         FIG.  5 A  is a perspective view of components of a humeral implant system according to another embodiment of the disclosure. 
         FIG.  5 B  is a cross-section of the base and secondary anchor of  FIG.  5 A  implanted into a humerus. 
         FIG.  6 A  is a perspective view of components of a humeral implant system according to a further embodiment of the disclosure. 
         FIG.  6 B  is a side view of the humeral implant system of  FIG.  6 A  assembled and implanted into a humerus. 
     
    
    
     DETAILED DESCRIPTION 
     As used herein, the term “proximal” refers to a location closer to an individual&#39;s heart, and the term “distal” refers to a location farther away from the individual&#39;s heart. When used in the context of an implant, the terms “proximal” and “distal” refer to locations on the implant closer to, or farther away from, the heart when the implant is implanted in an intended manner. As used herein, the term “medial” refers to a location closer to the midline of an individual, while the term “lateral” refers to allocation farther away from the midline of the individual. Further, it should be understood that although the term “stemless implant” is used herein, the term does not indicate that a stemless implant fully lacks any anchor, but rather a stemless implant may include an anchor that is significantly smaller and/or shorter than stems of typical known stemmed implants. 
       FIG.  1    illustrates bones of a right shoulder joint as viewed anteriorly (from the front of a patient). Generally, the bones of the shoulder joint include humerus  10 , a proximal end of which includes a head or ball of the ball-and-socket joint, and scapula  20 , which includes the glenoid cavity  22  that forms the socket of the ball-and-socket joint. The acromion  30  and coracoid process  40  are also illustrated in  FIG.  1   .  FIG.  2    illustrates the bones of  FIG.  1    but also provides representations of the subscapularis muscle  50  and the supraspinatus muscle  60 . Generally, the subscapularis muscle  50  is attached to the lesser tubercle of the humerus  10 , and the supraspinatus muscle  60  is attached to the greater tubercle of the humerus  10 . The subscapularis muscle  50  and supraspinatus muscle  60  form two of the four muscles forming the rotator cuff. As shown in  FIG.  2   , a generally triangular space is formed between (i) the tendons of the subscapularis muscle  50 , (ii) the tendons of the supraspinatus muscle  60 , and (iii) the base of the coracoid process  40 . This triangular space is known as the rotator cuff interval  70 . It should be understood that  FIG.  2    is not intended to be a complete representation of all soft tissue pertinent in a shoulder joint. 
     One aspect of a shoulder arthroplasty may include removal of the head of the humerus  10  and replacement of the humeral head with a prosthetic humeral head (in an anatomic shoulder implant) or a prosthetic cup (in a reverse shoulder implant). For example,  FIGS.  3 A-C  illustrate different steps of implanting a base  100  of a prosthetic humeral implant. It should be understood that the base  100  may be configured to receive a prosthetic humeral head for an anatomic shoulder replacement, a prosthetic cup for a reverse shoulder replacement, or otherwise any suitable component of an anatomic or reverse shoulder replacement. 
     In  FIG.  3 A , the native humeral head has already been cut to provide a generally planar surface in which base  100  will be received. Generally, base  100  may include a collar  110  and an anchor  120 . The collar  110  may be generally circular, although it may take other shapes, such as a triangular shape, oblong shape, or a shield-shape. The proximal surface of the collar  110  is preferably planar, and when implanted, the proximal planar surface of the collar  110  may substantially align with the proximal planar resected surface of the humerus, although in other embodiments the surface of the collar need not directly align with the surface of the proximal humeral resection. The anchor  120  extends distally from the collar  110  and generally serves to provide an amount of fixation between the base  100  and the humerus  10 . In the illustrated embodiment, the anchor  120  is illustrated in a simplified format, but the anchor  120  may take various shapes. In some embodiments, the anchor  120  extends distally from the collar  110  along a central longitudinal axis that is substantially perpendicular to the proximal surface of the collar  110 . After making the proximal humeral resection, the base  100  may be implanted into the humerus  10  by any suit able method. In some embodiments, the proximal humerus may be further prepared, e.g. via drilling pilot holes or via punch mechanisms to provide complementary or guiding shapes to receive the base  100 . In other embodiments, the base  100  may be implanted without further preparation, for example by driving the base  100  into the proximal humerus the desired distance, for example until the proximal surface of the collar  110  is about flush with the proximal humeral resection. In the embodiment shown in  FIG.  3 A , the base  100  is driven in direction D 1 , which may be generally parallel the longitudinal axis of the anchor  120  and/or perpendicular the proximal resected surface of the humerus  10  (and/or perpendicular the proximal surface of the collar  110 ), until the base  100  is positioned at the desired depth and angle, as shown in  FIG.  3 B . 
     Now referring to  FIG.  3 B , after the base  100  has been implanted, a secondary anchor  130  may be implanted into the humerus  10  and engaged with the base  100 , for example through the anchor  120 . In the particular embodiment illustrated in  FIG.  3 B , anchor  120  includes a channel  122  sized to accept the secondary anchor  130  therethrough. For example, the channel  122  may extend in a direction so that, when the base  100  is implanted, the channel  122  is substantially parallel with (or even generally coaxial with) a longitudinal axis of the intramedullary canal of the humerus  10 . However, it should be understood that other relative angles may also be suitable. Preferably, the channel  122  is formed so that structure of the anchor  120  circumscribes the channel  122  fully, although in other embodiments a less-than-complete circumscription may be suitable. The cross-sectional shape of the channel  122  preferably matches the cross-sectional shape of the secondary anchor  130 . For example, if the secondary anchor  130  is cylindrical (with a circular cross-section), the channel  122  is preferably cylindrical (with a circular cross-section). The cross-sections of the channel  122  and the secondary anchor  130  may be other than circular, including oblong, triangular, rectangular, square, etc. Preferably, the dimensions of the channel  122  match or are slightly larger than those of the secondary anchor  130  so that the secondary anchor  130  has a tight fit with the channel. In some embodiments, locking features may be provided, such as matching threading between the channel  122  and the secondary anchor  130  so that the secondary anchor  130  may be screwed into and through the channel  122 . As shown in  FIG.  3 B , the secondary anchor  130  may be driven into the humerus  10  and through the channel  122  in a direction D 2  to further secure the base  100  within the humerus  10 . In the particular illustrated embodiment, the direction D 2  is substantially parallel to (or even coaxial with) the intramedullary canal of the humerus  10 . 
       FIG.  3 C  illustrates the secondary anchor  130  having been implanted into the humerus  10  after the base  100  has been implanted into the humerus. As noted above, secondary anchor  130  is implanted through a channel  122  in the anchor  120 . In the illustrated embodiment, another channel  124  is provided in the collar  110 . The channel  124  may be generally similar to the channel  122 , and preferably (but not necessarily) is fully circumscribed by the collar  110 . A central longitudinal axis that passes through channel  122  also preferably passes through the center of channel  124 , so that channels  122  and  124  are coaxial. Thus, in order to implant secondary anchor  130  after base  100  is implanted, channel  124  in collar  110  may be used as a guide. Because the proximal surface of the collar  110  is exposed after implantation, the surgeon may be able to directly visualize the opening that leads to channel  124 . The secondary anchor  130  may be passed through channel  124 , with the secondary anchor  130  advancing distally and being guided into channel  122  by virtue of the alignment between channels  122 ,  124 . In some embodiments, it may be possible to omit channel  124 , although in such circumstances, guiding the secondary anchor  130  into the channel  122  may be more difficult and require guidance, such as via imaging. 
     Still referring to  FIG.  3 C , the combination of anchor  120  and secondary anchor  130  may help increase fixation and resist the tendency of the base  100  to pull out or otherwise loosen, particularly in the directions D 3  and D 4 . Direction D 3  is generally along the center longitudinal axis of the anchor  120 , the opposite of D 1 , while D 4  is generally along (or parallel to) the longitudinal axis of the humerus  10  (or the humeral intramedullary canal), the opposite of D 2 . If any forces in the direction of D 3  are applied to the base  100 , the secondary anchor  130  may particularly resist motion in that direction. And if any forces in the direction of D 4  are applied to the base, the anchor  120  may particularly resist motion in that direction. Because the secondary anchor  130  is coupled to the base  100  (e.g. via collar  110  and/or anchor  120 ), the assembled construct of base  100  and secondary anchor  130  will be particularly effective in resisting any tendency to loosen or otherwise be pulled out of the bone after implantation. It should be understood then, that in order to remove the assembled construct (e.g. in preparation for a future joint replacement procedure), it may be necessary or at least desirable to first remove the secondary anchor  130 , and only afterwards remove the base  100 . 
     Although in the text above, the order of implantation is described as being the base  100  being implanted first, and the secondary anchor  130  being implanted second, in some embodiments the secondary anchor  130  may be implanted first, followed by the base  100 . In that embodiment, it may be preferable to have channel  122  not fully circumscribed by anchor  120 , or otherwise a different connecting mechanism between the anchor  120  and the secondary anchor  130  than is shown in connection with  FIGS.  3 A-C . 
     In some embodiments, no additional locking or fixation mechanism between secondary anchor  130  and base  100  is required beyond simply passing the secondary anchor  130  through channel  122  and/or  124 . However, in other embodiments, alternative or additional locking mechanisms may be used. For example, tapered connections or press-fit relations between the secondary anchor  130  and the base  100  may provide fixation between the two components. Additionally or alternatively, adhesives such as biocompatible glue may help fix base  100  to secondary anchor  130 . In other embodiments, threading may be provided to create a screw-type mechanism to fix the secondary anchor  130  to the base  100 . For example, the secondary anchor  130  may include external threads and the channel  122  and/or  124  may include corresponding internal threads so that the secondary anchor  130  may be screwed into the base  100 . 
     While secondary anchor  130  is illustrated as a relatively short member in  FIGS.  3 A-C , it should be understood that secondary anchor  130  may extend farther into humerus  10 . For example,  FIG.  3 D  illustrates secondary anchor  130  having a greater length than as shown in connection with  FIGS.  3 A-C . As shown in  FIG.  3 D , secondary anchor  130  may extend a significant length into the canal of the humerus  10 , and including one or more apertures to receive fasteners  140  therethrough. For example, secondary anchor  130  may include one or more threaded holes that can received bones screws  140  therethrough, the bone screws being passed through the cortical shell of the humerus  10  and laterally (e.g. transverse the longitudinal axis of the intramedullary canal of the humerus  10 ) to provide additional fixation of the secondary anchor  130 . If such a feature is utilized, it may be preferable to use a targeting device and/or image guidance to allow for the fasteners  140  to be passed into the humerus  10  in the desired position and trajectory in order to be received within the corresponding apertures of the elongated secondary anchor  130 . It should be understood that fasteners  140  may provide even further fixation of the construct of the base  100  and the secondary anchor  130 . In some embodiments, elongated secondary anchor  130  may be further fixed into the humerus  10  with the use of a cement mantle around the elongated secondary anchor  130 . In fact, whether elongated or not, and whether fasteners  140  are provided, the secondary anchor  130  may be fixed to the humerus  10  with the use of bone cement or similar material. 
     It should be understood that both the base  100  and the secondary anchor  130  illustrated in  FIGS.  3 A-D  are shown as simplified components. The base  100  may take various shapes, including those shown and described in U.S. Patent Application Publication No. 2018/0271667 and U.S. patent application Ser. No. 17/308,107, the disclosures of which are hereby incorporated by reference herein, with modifications to provide for the desired interaction with the secondary anchor  130 . For example,  FIGS.  4 A-C  illustrate an embodiment of base  100  and secondary anchor  130  that provides additional specific details. 
     Referring to  FIG.  4 A , base  100  is illustrated, along with secondary anchor  130 , the proximal end of humerus  10 , and a prosthetic humeral head  150  to be coupled to base  100 . Prosthetic humeral head  150  may include a convex surface  152  intended for articulation with a native or prosthetic glenoid. Prosthetic humeral head  150  may also include a connector  154  to be received within base  100 . In the illustrated example, connector  154  includes a taper, such as a Morse taper, that is received within a corresponding tapered hole  112  in the collar  110  of base  100 .  FIG.  4 A  illustrates an opening in the collar  110  that leads to channel  122 . In the illustrated embodiment, channel  122  may be continuous with channel  124  in anchor  120 . In other words, channels  122  and  124  are not separate channels in  FIG.  4 A , but rather a single continuous channel that extends along an axis X 1 , the distal end of the channel  122  opening at anchor  120 . As described above, the axis X 1  of the channel  122  may be coaxial with, or parallel to, the intramedullary canal upon implantation of the base  100  into the humerus  10 . 
     In the embodiment illustrated in  FIG.  4 A , the tapered hole  112  is in fluid communication with channel  122 , as described in greater detail below. The secondary anchor  130  is illustrated as being generally cylindrical with a circular cross-section, and thus channel  122  may also be generally cylindrical with a circular cross-section. As noted above, however, secondary anchor  130  may have other shapes, including an oval or rectangular cross-section, with channel  122  having a corresponding cross-section. Depending on the cross-sectional shape of the secondary anchor  130  and the channel  122 , the secondary anchor  130  may only fit into channel  122  in one, or a limited number of, rotational orientations. This alternative cross-sectional shape may also prevent rotation of the secondary anchor  130  relative to the base  100  after the components are assembled, which may be desirable. The secondary anchor  130  may include a cut-out or recessed section  132 , as well as an angled proximal face  134 . In one embodiment, the base  100  is first implanted into humerus  10  (with or without earlier preparation of the resected proximal humerus  10 ). With the base  100  implanted, both the tapered hole  112  and proximal opening of the channel  122  in the collar  110  are able to be directly visualized by the surgeon. The secondary anchor  130  may then be implanted into the humerus  10 , for example into the intramedullary canal of the humerus  10 , by passing the secondary anchor  130  through the channel  122 . In some embodiments, the humeral canal may first be prepared to receive the secondary anchor  130 , although such preparation is not required. The secondary anchor  130  is inserted until the proximal face  134  is substantially flush with the proximal face of collar  110 . However, in other embodiments, the proximal face  134  of the secondary anchor  130  may extend a depth into the base  100 . When the secondary anchor  130  is at the desired depth, the recessed portion  132  aligns with the tapered hole  112  so that, when the connector  154  of the prosthetic humeral head  150  is inserted into the tapered hole  112 , the body of the secondary anchor  130  does not interfere with such insertion. Although tapered hole  112  is described as having a Morse taper to correspond to connector  154 , it should be understood that in some embodiments, tapered hole  112  may be a non-tapered hole. 
     Although additional fixation of the secondary anchor  130  is not specifically required, it should be understood that fixation of the secondary anchor  130  may be achieved by bone cement, additional fasteners such as fasteners  140  illustrated in  FIG.  3 D , and/or via other locking mechanisms such as a threaded connection between the secondary anchor  130  and the base  100  as described above. 
       FIG.  4 B  is a side view of base  100 , illustrating suture passages  126 ,  128 .  FIG.  4 C  is a cross-section of base  100  taken along the section line  4 C- 4 C of  FIG.  4 B .  FIGS.  4 B-C  illustrate optional suture passages  126 ,  128  passing through the base  100 . As shown in  FIG.  4 B , each suture passage  126 ,  128  general opens to the outside of the base  100  at a position on anchor  120  just distal to the collar  110 , although other positions relative to the collar  110  may be appropriate. As best shown in  FIG.  4 C , suture passage  126  is relatively straight extending mostly in a single direction transverse to the longitudinal axis of the anchor  120 , whereas suture passage  128  has more curvature compared to suture passage  126 . It should be understood that although two suture passages  126 ,  128  with specific trajectories are illustrated, suture passages may be omitted, or the base  100  may be provided with one, or more than two, suture passages. Further, any suture passages that are provided by have shapes and trajectories similar to, or different than, those shown in  FIG.  4 C . 
     Following implantation of base  100 , sutures may be passed from outside the cortical shell of the humerus  10  through one of the suture passages  126 ,  128 , until the suture passes through the opposite end of the suture passage  126 ,  128  and passes through the humerus  10  on the opposite side. A targeting device (similar to that used with fasteners  140 ) or other guiding (such as imaging) may be used to ensure that the sutures are positioned in the correct location and advanced with the desired trajectory to enter the suture passages  126 ,  128 . The sutures that extend through the passages  126 ,  128  and outside the humerus  10  may be tied or otherwise fixed to provide enhanced fixation of the base  100  within the humerus  10 , as well as to help prevent rotation of the base  100  relative to the humerus  10  after implantation. Although the term sutures is used, it should be understood that other materials, such as relatively rigid pins (e.g. strands of a metal or metal alloy such as nitinol) may be used with the suture passages  126 ,  128 . The suture passages  126 ,  128  may also be used to help secure fractured portions of the humerus  10  to the base  100  and/or to the remaining portion(s) of the humerus  10 . The curvature (or lack thereof) of the suture passages  126 ,  128  may be based on preference. For example, if a needle or other leading member attached to the sutures has a curvature, such a needle may more easily pass through suture channel  128  compared to suture channel  126 . 
     It should also be noted that the cross-section of  FIG.  4 C  illustrates the communication between the tapered hole  112  and the channel  122  described above. 
       FIGS.  5 A-B  illustrate another embodiment of a humeral implant system, including prosthetic humeral head  150 , base  100   a,  and secondary anchor  130   a.  As with other embodiments described herein, although the base  100   a  is illustrated as coupling with a prosthetic humeral head  150 , the base  100   a  may also be used with a reverse shoulder implant system, in which case the base  100   a  may couple with a prosthetic cup (or tray) instead of a prosthetic humeral head  150 . Prosthetic humeral head  150  may be identical to that described in connection with  FIG.  4 A  and is thus not described again here. 
     Base  100   a  may include a collar  110   a  that is generally similar to collar  110  described above. For example, collar  110   a  may be a short cylinder with a circular cross-section, although other shapes may be suitable. The proximal face of collar  110   a,  when implanted into the humerus (for example as shown in  FIG.  5 B ), is preferably substantially flush with the resected proximal surface of the humerus  10 . The collar  110   a  may include an aperture  112   a,  for example near a center of the collar  110   a,  that extends from the proximal face through the distal face. Aperture  112   a  may be generally cylindrical, although other shapes may be suitable. Aperture  112   a  need not be tapered, but in some embodiments it may be tapered. 
     A main difference between base  100  and base  100   a  is the shape and position of the anchor  120  compared to the anchor  120   a.  As best shown in  FIG.  5 A , anchor  120   a  may have a proximal end that is attached to (or near) an outer circumference of the collar  110   a.  When the base  100   a  is implanted into the humerus  10 , the proximal end of the anchor  120   a  may be positioned laterally (although in other embodiments other positioning including medial positioning may be suitable). The anchor  120   a  is a generally flat elongate member and may include a small thickness (in the medial-to-lateral direction) relative to its width (in the anterior-to-posterior direction). The anchor  120   a  may extend from its proximal point of attachment to collar  110   a  to a free distal end, such that the anchor  120   a  extends at an oblique angle relative to the proximal and distal faces of the collar  110   a  to form a general “V”-shape with the collar  110   a.  In some embodiments, the anchor  120   a  may include an aperture  122   a,  which may receive a component such as secondary anchor  130   a,  described in greater detail below. 
     In use, the collar  110   a  may be implanted into the humerus  10  first, with the distal or free end of the anchor  120   a  leading the implant, until the proximal face of the collar  110   a  is substantially flush with the proximal resection of the humerus  10 . As best shown in  FIG.  5 B , the “V”-shape of the collar  110   a  and anchor  120   a  construct results in a volume of native bone being positioned between the two components. In fact, as the anchor  120   a  drives into the humerus  10 , a volume of native humeral bone (e.g. cancellous bone) may compress between the anchor  120   a  and the collar  110   a.  The native volume of bone of the humerus  10  trapped between the anchor  120   a  and the collar  110   a  may provide significant resistance against the base  100   a  pulling out of the humerus  10 , particularly in a direction orthogonal to the proximal face of the collar  110   a.  In order to position the anchor  120   a  within the humerus  10 , a corresponding cavity may be created in the bone using a reamer, punch, or other suitable bone preparation tool. 
     After the base  110   a  is implanted, the secondary anchor  130   a  may be implanted. The secondary anchor  130   a  may be a generally cylindrical member, and the distal or leading end may be passed through aperture  112   a  of the collar  110   a,  until the distal or leading end of the secondary anchor  130   a  is received within aperture  122   a  of anchor  120   a,  as best shown in  FIG.  5 B . The proximal or trailing end of the secondary anchor  130   a  may include an aperture, such as tapered hole  136   a,  which may receive the connector  154  of the prosthetic humeral head  150 . As noted above, the tapering may be a Morse taper to help secure the prosthetic humeral head  150  to the assembled base  100   a  and secondary anchor  130   a.  Preferably, the secondary anchor  130   a  is inserted in a direction orthogonal to the proximal face of the collar  110   a.  When implanted and assembled as shown in  FIG.  5 B , the anchor  120   a  may be particularly helpful in resisting pull-out of the base  100   a  in a direction orthogonal to the proximal face of the collar  110   a,  while the secondary anchor  130   a  may be particularly helpful in resisting pull-out of the base  100   a  in a direction parallel to the intramedullary canal of the humerus  10 . 
     The anchor  120   a  may be formed monolithically (or integrally) with the collar  110   a.  However, in other embodiments, the anchor  120   a  and collar  110   a  may be formed separately, implanted separately, and only coupled during/after implantation. For example, the anchor  120   a  may be provided as a separate member implanted first, and the collar  110   a  may be implanted next, with mating features provided to couple the collar  110   a  to the anchor  120   a.  In other embodiments, the collar  110   a  and anchor  120   a  may be coupled to each other in any suitable fashion, such as via adhesives, during or after implantation. 
     The fixation of the base  100   a  may be increased by providing for an amount of flexion of the anchor  120   a  to compress native bone between the anchor  120   a  and the collar  110   a.  For example, if the aperture  122   a  is provided with a taper (such as a Morse taper), and the outer surface of the secondary anchor  130   a  is provided with a corresponding taper, the secondary anchor  130   a  may be driven farther through aperture  122   a  to cause flexing (e.g. “pulling”) of the anchor  120   a  toward the collar  110   a  as the secondary anchor  130   a  is driven farther through the aperture  122   a.  Additionally or alternatively, the anchor  120   a  may be flexed in one direction (or provided with bias otherwise) and implanted while flexed/biased, so that the anchor  120   a  tends to revert to a non-biased condition. The tendency to revert to the non-biased condition may cause native bone to compress farther. For example, the anchor  120   a  may be flexed laterally during implantation, and then attempt to “unflex” medially after implantation to cause compression of bone between the anchor  120   a  and the collar  110   a,  which may provide for additional fixation of the base  100   a  within the humerus  10 . 
     The angle between the anchor  120   a  and the collar  110   a  may be provided as a single angle, or a group of bases  100   a  may be provided, each with a different angle between the proximal face of the collar  110   a  and the extension direction of the anchor  120   a.  Having a set of bases  100   a  with different angles may allow a user to choose the best angle for achieving the best fixation for a particular patient. In other embodiments, the angle between the collar  110   a  and the anchor  120   a  may be patient-specific, either based on a single individual patient&#39;s anatomy, or based on a set of patient data. The length of the anchor  120   a  may be similarly provided as a single value, different values within a kit of bases  100   a,  or specific to a single patient or specific based on analysis of a group of patients. For example, a particular patient&#39;s humerus  10  may be scanned (e.g. via CT or MRI imaging) to determine the geometry of the bone, as well as the quality of the bone. For example, the imaging may help to distinguish the density of the bone at different locations (e.g. based on the brightness of the pixels in the imaging). Based on the patient&#39;s imaging results, the length and/or angle of the anchor  120   a  may be customized so that the anchor  120   a  is located in the best bone quality for providing anchoring, and while ensuring that the anchor  120   a  is not at risk of penetrating through the cortical shell of the bone upon implantation. While individual patient imaging may be suitable for designing a patient-specific base  100   a,  a database may also be used. For example, the Stryker Orthopaedic Modeling and Analytics (“SOMA”) database may be leveraged to determine, across a patient population, optimal lengths and/or angles of the anchor  120   a  for achieving optimal fixation without penetrating the cortical shell of the humerus  10 . 
     Although secondary anchor  130   a  is described as having a tapered fit with aperture  122   a,  other fits may be suitable. In one example, secondary anchor  130   a  may be have external threading and aperture  122   a  may have internal threading to allow for a screw-type connection between secondary anchor  130  and anchor  120   a.  In some embodiments, secondary anchor  130   a  may have a proximal flange or shoulder that limits the depth that he secondary anchor  130   a  may be inserted through aperture  112   a.  In such embodiments, additional screwing of secondary anchor  130   a  into aperture  122   a  may tend to pull the anchor  120   a  toward the collar  110   a,  compressing bone between the anchor  120   a  and the collar  110   a.    
       FIGS.  6 A-B  illustrate another embodiment of a humeral implant system, including prosthetic humeral head  150  and base  100   b.  As with other embodiments described herein, although the base  100   b  is illustrated as coupling with a prosthetic humeral head  150 , the base  100   b  may also be used with a reverse shoulder implant system, in which case the base  100   b  may couple with a prosthetic cup (or tray) instead of a prosthetic humeral head. Prosthetic humeral head  150  may be similar or identical to that described in connection with  FIG.  4 A  and is thus not described again here. 
     Base  100   b  may include a collar  110   b  that is generally similar to collars  110 ,  110   a  described above. For example, collar  110   b  may be a short cylinder with a circular cross-section, although other shapes may be suitable. The distal face of collar  110   b,  when implanted into the humerus (for example as shown in  FIG.  6 B ), is preferably substantially flush with the resected proximal surface of the humerus  10 . In other words, whereas collar  110   a  of base  100   a  is preferably flush with the resected proximal surface of the humerus  10 , collar  110   b  of base  100   b  may effectively rest atop the proximal surface of the humerus  10 . With this approach, minimal bone may be removed from the proximal humeral resection compared with other embodiments described here. 
     The collar  110   b  may include an aperture  112   b,  for example near a center of the collar  110   b,  that extends from the proximal face through the distal face. Aperture  112   b  is preferably, but need not be, tapered. The connector  154  of the prosthetic humeral head  150  may include a male taper (e.g. a Morse taper) that fits with a complementary taper in aperture  112   b  to help lock the prosthetic humeral head  150  to the base  100   b.    
     Base  100   b  may include an anchor  120   b.  In the illustrated embodiment, anchor  120   b  includes a generally cylindrical main body and extends to a blunted terminal end. In use, the anchor  120   b  is implanted into, and generally coaxial with, the intramedullary canal of the humerus  10 . In some embodiments, the anchor  120   b  may be configured to have a press-fit engagement with the intramedullary canal without additional fixation. However, in other embodiments, additional or alternative fixation modalities may be used. For example, the anchor  120   b  may be fixed within the intramedullary canal of the humerus  10  with cement or other suitable adhesive. Other options, such as the fasteners  140  described in connection with  FIG.  3 D , may additionally or alternatively used with anchor  120   b.  It should be understood that if fasteners  140  are utilized, corresponding apertures would be provided within anchor  120   b.    
     Preferably, the anchor  120   b  and the collar  110   b  are formed as a single integral or monolithic construct. However, in other embodiments, the anchor  120   b  and the collar  110   b  may be formed as separate members and attached to each other prior to, or during, implantation. 
     In use, the anchor  120   b  is first implanted into the intramedullary canal of the humerus  10 , either with or without additional fixation mechanisms such as cement. After positioning the anchor  120   b,  the collar  110   b  is positioned to rest on the plane of the proximal resection of the humerus  10 . If anchor  120   b  and collar  110   b  are monolithic, these pieces are implanted simultaneously. If anchor  120   b  and collar  110   b  are separate pieces, they may either be coupled together first and then implanted together, or the anchor  120   b  may be implanted first, and then the collar  110   b  may be positioned and coupled to the anchor  120   b.    
     In some embodiments, the collar  110   b  may be separately fixed to the humerus, for example using fasteners such as screws or cross-pins, adhesives such as cement, and/or a press-fit with the humeral bone. However, in other embodiments, additional fixation of the collar  110   b  is not required. 
     After the base  100   b  is in the desired position, prosthetic humeral head  150  (or a humeral cup or tray for a reverse shoulder arthroplasty procedure), may be coupled to the collar  110   b  by inserting connector  154  through aperture  112   b.  As shown in  FIG.  6 B , connector  154  may extend beyond the distal end of the collar  110   b  and extend directly into the bone of the humerus  10 . In other embodiments, the connector  154  (or a connector of a humeral cup or tray component) may be elongated so that, upon insertion through aperture  112   b,  the connector  154  may engage with the anchor  120   b.  For example, the anchor  120   b  may be provided with an aperture or other mating feature, which may be similar to the aperture  122   a  of anchor  120   a  of base  100   a,  so that the connector  154  may directly lock into anchor  120   b,  providing even further fixation. 
     As shown in  FIG.  6 B , when base  100   b  is implanted, the collar  110   b  is positioned generally parallel to the proximal resection of the humerus  10 , while the anchor  120   b  is positioned generally parallel to (and/or coaxial with) the axis of the intramedullary canal of the humerus  10 . This positioning results in the anchor  120   b  having an oblique angle relative to the proximal and/or distal faces of the collar  110   b.  This angle, and the fact that the base  110   b  and anchor  120   b  are not able to move relative to each other, helps to minimize the risk of subsiding of the base  100   b  and/or micromotion of the base  100   b  after implantation. 
     As described for all of the embodiments above, although the bases of the humeral implant system are shown as engaging with a prosthetic humeral head, the bases could be used (with or without modification) to engage with components of a reverse shoulder arthroplasty system, such as a tray or a cup intended to interact with a glenoid implant, such as a glenosphere. But it should be further understood that the bases described herein are not limited to use in the humerus or in shoulder implants. For example, the bases described herein may be implanted into any suitable long bone for a joint replacement procedure, such as the femur for a hip replacement. 
     Further, although the structure of various bases have been described herein, it should be understood that the bases may be provided with additional features as desired. Any structure of the bases described herein, particularly those that will be in direct contact with bone, may be provide with features to enhance the fixation with the bone. For example, surfaces that will be in direct contact with bone may be provided with roughened surfaces, for example a porous metal surface, in order to enhance bone ingrowth into those surfaces to achieve better fixation over time. Similarly, structures such as flutes, serrations, or pegs may also be provided on surfaces that will engage bone to provide for increased fixation where desired and appropriate. 
     Some of the benefits of the implant systems described herein have already been described above, including the enhanced fixation provided by the bases. However, other benefits may also be achieved. For example, while good fixation is generally important for all prosthetic joint devices, reverse shoulder arthroplasty procedures may represent some of the worst case implants in terms of loading conditions. For example, a humeral component of a reverse shoulder arthroplasty system may generally experience more compression and higher sheer stresses compared to a humeral component of a total shoulder arthroplasty system. The bases described herein may provide high levels of resistance to both pull-out and torque-out of the humeral component, which may be especially desirable for a reverse shoulder arthroplasty procedure. 
     Still further, the humeral base component described herein may be well-suited for use in patients with very poor bone quality (e.g. lower than normal bone density), with little or no cancellous bone, and/or in revision cases in which a prior implant must be explanted and significant bone stock is missing after the explantation. The bases described herein may provide enhanced fixation and resulting better stability, even if the condition of the bone is poor. In these scenarios, the bases described herein may also increase the likelihood of achieving suitable fixation without the use of bone cement or other adhesives, which may be a desirable result. 
     For all of the bases described herein, any necessary bone preparation may be performed manually or with the help of either semi-autonomous or autonomous robotics. The use of a robotic system, such as the MAKO robot, may provide additional benefits in preparing the bone to receive the bases described herein, as the preparation of any desired bone cavity or recess may be performed with extreme precision to provide an exact match of implant geometry and bone shape. However, in some scenarios, little or no bone preparation may be needed once the initial resection (e.g. the proximal humeral resection in a shoulder arthroplasty) is performed. 
     Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims. For example, features described in connection with one embodiment may be combined, if suitable, with features described in connection with other embodiments.