Abstract:
A humeral head prosthetic device including a chassis and a head attached or attachable to the chassis. In the preferred embodiment, the chassis includes a tapered and multifaceted anchor element attached to and projecting distally from a base element, the configuration of the tapered and multifaceted anchor element adapted to counter rotation of the chassis once it is impacted into the humeral head. The preferred embodiment of humeral head prosthetic device also includes one or more blind holes each of the blind holes or slots being defined in part by a penetrable wall, each of the blind holes including a wall that may be readily penetrated in order permit insertion of a tool to aid in removal of the prosthesis where such removal is required.

Description:
[0001]    This application claims the benefit of the filing date of a prior-filed Provisional Application Ser. No. 61/589,243 entitled Humeral Head Prosthesis, filed Jan. 20, 2012, which is incorporated by reference herein. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to devices and methods for repairing the shoulder joint and more specifically to shoulder prostheses and methods of performing a shoulder arthroplasty. 
         [0004]    2. Background 
         [0005]    Until relatively recently, a total repair of the shoulder joint, or shoulder arthroplasty, required the removal of the entire head of the humerus bone, commonly at or below the anatomic neck, in order to accommodate the insertion of an elongated shaft of the device into the diaphysis of the bone. An articulation surface attached or attachable to the proximal end of the shaft and cooperates with a second articulation surface attached to the boney portion of the scapula. A relatively recent advance in total shoulder repair has been the introduction of the humeral head prosthesis, a device that mounts or attaches to a prepared surface of the humeral head. These devices also include a joint head having an articulation surface typically formed as a spherical segment configured to articulate against a cooperating surface attached to the boney portion of the scapula. The joint head is mounted to a mounting fixture which, according to the present state of the art, includes a variety of configurations. The mounting fixture is attached to the humeral head at a site located substantially at and coplanar to a distal margin of the anatomical head that has been modified by sawing, shaping and/or drilling to accommodate attachment of the mounting fixture to the modified humeral head. 
         [0006]    In U.S. Published Patent Application 2009/0292364 by Linares, a shoulder joint implant assembly is described that includes a plastic ball secured to a first bone end face and a plastic receiver secured to a second bone end face. A fastener is secured to the first bone end face and over which is mounted the plastic ball. The receiver is anchored by a pair of inwardly extending mounting tabs that extend into cavities machined in the first bone. 
         [0007]    U.S. Pat. No. 7,648,530 to Habermeyer, et al., describes a humeral head prosthesis including a joint head including a nearly spherical joint surface. A hollow screw fixes a mounting disk to a planed surface of the bone. The hollow screw is driven into the bone through a medial hole located in a collar formed on the proximal surface of the mounting disk. A cone shaped receiver is formed within the joint head and is suitably configured to receive the collar in a press fit. 
         [0008]    U.S. Pat. No. 7,611,539 to Bouttens, et al., describes a shoulder prosthesis that includes a mounting plate having a central tubular mounting bushing. A joint head including an articulation surface formed as a spherical segment having an axial screw is fit over the mounting plate and the axial screw is screwed into the tubular mounting bushing. 
         [0009]    U.S. Pat. No. 7,608,109 to Dalla Pria, describes a first articulation element associated with the top of the humerus that includes a two piece support member the first piece including a threaded stud for insertion into the humeral head, a second piece having a post that inserts into the core of the stud, the second piece also including several tabs that extend over the surface of the proximal end of the bone with screws that attach to the bone through the tabs. A joint head including an articulation surface formed as a spherical segment is attachable to the support structure. 
         [0010]    In U.S. Pat. No. 6,969,406 to Tornier, a multi-piece shoulder prosthesis is described that has at least four principal assembled components including:
       a) an anchor member having a tubular anchor extending from a base element,   b) a screw having a first external thread for threadedly engaging an internal thread located in the tubular anchor,   c) a bushing having an internal thread configured to threadedly engage a second external thread formed on the screw, and   d) a joint head including an articulation surface formed as a semi-spherical segment that includes a recess formed on an underside or the joint head. The recess includes an internal thread for engaging an external thread of the bushing. The recess of the joint head is configured such that as the internal thread of the joint head is advanced against the external thread of the bushing an inner surface of the recess seats against an outer annular surface of the base element.       
 
         [0015]    While the devices and methods discussed above resolve some of the challenges related to providing a humeral head prosthesis, still a need exists to provide increasingly simplified humeral head prosthetic devices and systems. Additionally, a need exists to refine and improve upon the means by which the prosthesis is located on and secured to a prepared site located on the proximal humerus bone. In addition there is a need to provide a prosthetic device and system that includes improved means and features that allow for easier removal of the device in cases where such removal is indicated. Another issue left unaddressed by the current state of the art is the osteolysis that tends to occur in regions where there is no growth of the bone into the implant. Additionally, osteolysis is known to occur at the calcar region in patients who receive a prosthetic shoulder that includes a shaft that extends into the diaphysis of the bone. Other improvements may be seen in a humeral head prosthetic device by the addition of means for attaching a suture to the prosthesis so that the prosthesis may be utilized as an anchor for sutures that are used to re-attach connective tissue to the bone following installation of the prosthesis. 
         [0016]    Therefore one object of the present invention is to provide a humeral head resurfacing prosthetic device. Another object of the present invention is to provide a prosthetic device and system that includes improved means and features that allow for easier removal of the device in cases where such removal is indicated. Yet another object of the present invention is to provide a modular system for repair of the humeral head that includes a variety of device anchors having a range of diameters and lengths and a variety of prosthetic heads having a range of head sizes and diameters. Another object of the present invention is to provide an improved methodology for locating the humeral head prosthetic device with respect to a modified humeral head. Another object of the present invention is to provide a prosthetic device for a long bone that reduces the tendency of osteolysis that has been observed in connection with the use of some prosthetic implants. Another object of the present invention is to provide a humeral head prosthetic device that includes one or more apertures through which a suture may be passed, the apertures adapted and optimized to facilitate the use of sutures for augmenting soft tissue connection. An additional object of the present invention is to provide a humeral head prosthetic device that has been optimized for removal in the event that such removal is indicated. 
       SUMMARY OF THE INVENTION 
       [0017]    The present invention is directed to a humeral head prosthetic device includes a chassis having a base element from which a tapered and multifaceted anchor element projects distally. The tapered and multifaceted anchor element is fixed to or formed upon or attachable to an articulation surface. In the preferred embodiment the humeral head prosthetic device the articulation surface is formed as a semi-spherical segment that is removably attachable to the chassis. 
         [0018]    In one embodiment the humeral head prosthetic device is configured as a unitary prosthesis wherein the articulation surface is permanently fixed to or formed at the proximal end of the chassis and a contact surface includes a configuration that is suitable for mounting against a prepared surface of the humeral head. In one embodiment of the unitary prosthesis, the tapered and multifaceted anchor element is fixed or formed against an inner concave surface of the semi-spherical segment such that the inner concave surface becomes the contact surface and the outer convex surface serves as the articulation surface. This embodiment is intended for resurfacing, as opposed to replacing, the humeral head. In another embodiment, the joint head is separable from the chassis. Whether the prosthetic device is configured for resurfacing the joint or replacing the humeral head, the device includes a multifaceted anchor element fixed to or formed on the distal surface of the articulation surface. As for the unitary humeral head prosthetic device, the advantages of this configuration lie in part in its unitary construction and therefore the potential that it has to reduce costs associated with shoulder arthroplasty hardware and procedures. 
         [0019]    In the embodiment wherein the joint head is separable from the chassis, the joint head is held against the base element by means of a cooperating press fit between a tapered post and socket. In one embodiment the post and socket each include a cooperating Morse taper. One advantage of this configuration lies in allowing the surgeon to select a chassis of having a size that is most appropriate for the size of the humeral head being repaired and a head including an articulation surface that cooperates best with the patient&#39;s glenoid. Another advantage of this configuration lies in creating an option of placing auxiliary anchors through the base element into the humeral head which results in a more stable placement of the prosthesis in the bone, particularly immediately post surgery, before boney in-growth between the bone and the central stem member has had time to progress. Another advantage of this configuration lies in creating an option of replacement of the joint head where a condition allowing for such a repair presents itself 
         [0020]    The tapered and multifaceted anchor element of the humeral head prosthesis is defined by an inner wall surface and an outer wall surface. The wall of the anchor element has a tapering cross-section that diminishes in thickness as the distance from the base element increases, (distally converging). The surface of the inner wall of the anchor element is relatively featureless. The surface of the outer wall of the anchor element includes a series interconnected fins, each fin comprising a pair of converging wall segments or facets that taper distally as a distance from the base element increases, (distally converging). Apertures are formed through the wall of the anchor element to promote bone growth and revascularization. In alternate embodiments, the tapered and multifaceted anchor element may be formed as a single tubular element or it may be formed as a plurality of tubular segments. 
         [0021]    In a preferred embodiment, the invention, the converging wall segments formed on the outer wall of the anchor element converge or truncate at a distance proximal to a distal lip of the anchor element. A series of circular or oval apertures are formed through the wall of the anchor element just proximal to the distal lip. These apertures are provided to accommodate a method of the invention discussed herein below. In order to prevent surface abrasion against sutures that may be guided through the apertures, the region of the wall of the anchor element just proximal to the distal lip through which these apertures are formed may include a polished finish with the annular edges of the apertures being radiused and polished as well. 
         [0022]    At least a portion of both the inner wall and the outer wall of the region of the anchor element proximal to the polished region, as well as the contact surface of the base element exhibit a roughened surface. For instance the surfaces may be coated with a porous coating adapted to encourage bone in-growth, and hence enhanced mechanical properties at the site of impaction. Alternately, surfaces may be roughened by a process, such as grit blasting or machining, for example. 
         [0023]    In one embodiment, the humeral head prosthetic device includes a plurality of anchors that are adapted for placement through and engagement with the base element of the chassis. Preferably, two anchors are set into the greater tuberosity and one anchor is set into the calcar region. Once the anchors are set, and due to that fact that the three anchors diverge from one another and the primary axis of the device, the placement of the device with respect to the bone has become remarkably stable resisting both pull-out and rotational forces. It is particularly important that any humeral head prosthetic device remain stable and have good resistance to pull out particularly just following implantation and before the bony in-growth that follows surgery has occurred. 
         [0024]    Several characteristics of bony anatomy are addressed by the configuration of the humeral head prosthetic device of the present invention. First, the head of a bone is composed of an open-celled latticed material called trabecular bone encased in a sheath of cortical bone. Trabecular bone is adapted to absorb loads at the joint. In furtherance of this adaptation, trabecular bone exhibits a latticed structure that gives it a sponge-like appearance. As an individual ages, the size of a cavernous or osteopenic region of the bone increases from the inside towards the outside of the bone, decreasing the mass and density of the trabecular bone. 
         [0025]    A second observation about bony anatomy is stated by Wolff&#39;s law which observes that where loading on bone increases, the bone remodels itself over time to become stronger in order to resist the load. Of particular note, and consistent with Wolff&#39;s law, is the observation that internal architecture of the trabecular bone undergoes adaptive change when subjected to stress. Wolff&#39;s law also recognizes that where loading on a bone decreases, the bone will become weaker. This phenomenon has been identified at least in part for the occurrence of osteolysis at the calcar region of the humerus in patients who receive a prosthetic shoulder that includes a shaft that extends into the diaphysis of the bone, thereby relieving much of the normal stress seen at this region due simply to anatomical configuration and load bearing at the joint. 
         [0026]    The configuration of the tapered and multifaceted anchor element of the present invention and the preferred method of implanting anchor is directed at avoiding these physical limitations of aging bony anatomy by maximizing anchor to bone surface area in order to take advantage of impacting the device in a manner that promotes bony in-growth between the anchor member and the trabecular bone. The interconnected fins formed on the outer wall of the anchor element project out and away, further towards the periphery, and further from the center of the bone. The combined configurations of the tapering cross-section of the wall of the anchor element and the configuration of the proximally diverging outer wall segments or facets against the substantially vertical walls of the circular cut made in the prepared end of the humerus create substantial hoop stresses between the anchor element and the matrix of exposed trabecular bone into which the anchor element is impacted, which creates stresses at the site of impaction which in turn stimulates bony in-growth and remodeling over time in order to resist the load. According to a preferred methodology of implanting the anchor member, the interior of the anchor member may be packed with bone graft material to accelerate and promote boney in-growth. Additionally, bone growth is stimulated where it comes in contact with the roughened surfaces of the anchor element and the entire contact surface of the base element. As such, once in-growth has progressed at the bone-to-prosthesis interface, the occurrence of osteolysis promoted by mechanical stress shielding or introduction of foreign matter such as polyethylene debris at the bone-to-prosthesis interface should reduce substantially. 
         [0027]    In the case where removal is required, several structural adaptations have been incorporated in the design of the humeral head prosthetic device of the present invention. For example, while a substantial portion of the anchor member of the prosthesis of the present invention includes a roughened surface or a surface coated with a porous coating, the porous surface extends only a portion of the length of the anchor member, so that bony growth is not promoted the full length of the anchor member towards the distal end of the prosthesis. 
         [0028]    Additionally, and in furtherance of the objective of facilitating removal of an implantable prosthesis in the event that removal is required, one or more of “blind” holes or slots may be formed in a surface of the implantable prosthesis that would be used to aid in the removal of the chassis from the bone once impacted. Each blind hole or slot includes a penetrable wall that in part defines the blind hole or slot. In a case where removal of an implanted prosthesis is indicated, a drill or osteotome may be used to penetrate the penetrable wall formed at the bottom of each “blind” hole or slot. The drill or osteotome may then continue through the bone to help separate the prosthesis from the bone in a controlled manner. A thin metal layer or a frangible wall composed of cement, for instance a polymethylmethacrolate cement, or plastic would serve as a barrier with the purpose of keeping foreign material, particularly polyethylene debris, from finding its way through the “blind” hole into the bone over time. The surface of the wall section that is oriented towards the bone would preferably include a roughened surface consistent with the surrounding surfaces of the base element to promote bony in-growth against the surface of the base element. Alternately a “blind” hole may be created simply by filling a portion of a hole or slot formed in the prosthesis with a cement or plastic thereby forming a penetrable wall which bony growth may readily occur. 
         [0029]    In a preferred embodiment, the device is to be manufactured and offered in a variety of sizes. In particular the diameter at the base of the joint head and the diameter of the base element are offered in increments through a range of diameters so that the device size can be matched as closely as reasonably possible to a particular patient&#39;s bone. Preferably, the diameter of the base element is the same as the diameter of the prepared site of the proximal humerus bone such that the base element&#39;s roughened surface contacts both the trabecular bone as well as the more dense cortical bone, thereby preventing subsidence of the device in the softer trabecular bone. The in-growth of the bone to the prosthesis that occurs at the periphery of the prepared bone should also serve as a barrier with the purpose of keeping foreign material, particularly polyethylene debris, from finding its way into the bone over time. 
         [0030]    Preferably, the device is manufactured having dimensions within the following ranges: 
         [0031]    Head diameter=35-55 mm 
         [0032]    Head height=12-28 mm 
         [0033]    Anchor length=12-22 mm 
         [0034]    Anchor element outer diameter distal end=20-30 mm 
         [0035]    Anchor element outer diameter at base element=22-34 mm 
         [0036]    In one embodiment, the device is manufactured having the following dimensions: 
         [0037]    Head diameter=50 mm 
         [0038]    Head height=19 mm 
         [0039]    Anchor length=17 mm 
         [0040]    Anchor element inner diameter distal end=24 mm 
         [0041]    Anchor element inner diameter at base element=23 mm 
         [0042]    Anchor element outer diameter distal end=28 mm 
         [0043]    Anchor element outer diameter at base element=30 mm 
         [0044]    Fin height at base element=2.5 mm tapering distally 
         [0045]    Fin width at base element=2.0 mm tapering distally 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0046]      FIG. 1  is a representative isometric view of a multi-piece humeral head prosthesis according to the present invention; 
           [0047]      FIG. 2  is a representative isometric exploded view of a multi-piece humeral head prosthesis according to the present invention; 
           [0048]      FIG. 3  is a representative side cutaway view of a multi-piece humeral head prosthesis according to the present invention; 
           [0049]      FIG. 4  is a representative bottom view of a multi-piece humeral head prosthesis according to the present invention; 
           [0050]      FIG. 5  is a representative isometric exploded view of a multi-piece humeral head prosthesis according to the present invention; 
           [0051]      FIG. 6  is a representative bottom view of a multi-piece humeral head prosthesis according to the present invention; 
           [0052]      FIG. 7  is a representative side cutaway view of a single piece humeral head prosthesis according to the present invention; 
           [0053]      FIG. 8  is a representative isometric view of a single piece humeral head prosthesis according to the present invention; 
           [0054]      FIG. 9  is a representative isometric view of a single piece humeral head prosthesis according to the present invention; 
           [0055]      FIG. 10  is a representative side cutaway view a single piece humeral head prosthesis according to the present invention; 
           [0056]      FIG. 11  is a representative side view of a humeral head; 
           [0057]      FIG. 12  is a representative side view of a humeral head; 
           [0058]      FIG. 13  is a representative side view of a multi-piece humeral head prosthesis according to the present invention; 
           [0059]      FIG. 14  is a representative side view of a multi-piece humeral head prosthesis according to the present invention; 
           [0060]      FIG. 15  is a representative side view of a chassis of a humeral head prosthesis according to the present invention. 
       
    
    
     DETAILED DESCRIPTION  
       [0061]    Referring to  FIGS. 1 through 4 , a preferred embodiment of humeral head prosthesis  10  is shown configured as a two-piece prosthesis.  FIGS. 1 through 3  show humeral head prosthesis  10  including chassis  11  and head  12  having articulation surface  13  formed as a spherical segment. Chassis  11  is formed having anchor element  14  that projects distally below head  12 . A plurality of suture anchor apertures  18  are formed near distal end  16  of anchor element  14 . Suture anchor apertures  18  are configured to permit the passage of a suture according to a method of the invention discussed herein below. Distal end  16  of anchor element  14 , and an inner edge defining each of the suture anchor apertures  18  includes a polished surface  17  adapted to prevent surface abrasion between a suture that may be guided through any one of the plurality of suture anchor apertures  18 . 
         [0062]    Referring to  FIGS. 2 and 3 , head  12  includes coupling aperture  19  formed in a distal face  32  of head  12  that cooperates with post  20  that extends from base element  28  to secure head  12  to chassis  11 . In the preferred embodiment, coupling aperture  19  and post  20  include cooperating Morse tapers. 
         [0063]    Referring to  FIGS. 3 and 4 , chassis  11  includes anchor element  14  having tapering cross-section  15  that diminishes in thickness as a distance from base element  28  increases, (distally converging). As seen in  FIG. 4 , inner surface  21  of anchor element  14  is relatively featureless. Outer surface  22  of anchor element  14  includes a plurality of fins  23 , each fin  23  comprising a pair of converging wall segments  24  and  25  that taper distally as a distance from head  12  increases, (distally converging). The plurality of fins  23  create a multifaceted outer surface  22  that counters rotation of chassis  11  once impacted into the humeral head. Revascularization apertures  26 , shown in  FIG. 3  are formed through anchor element  14  from inner surface  21  to outer surface  22  to promote bone growth and revascularization both inside and outside anchor element  14 . 
         [0064]      FIG. 3  also shows post  20  formed on proximal face  31  of base element  28  inserted into  19  formed in distal face  32  of head  12 . Also shown in to  FIGS. 3 and 4  are a plurality of blind holes  29 . Blind holes  29  are formed in base element  28  of chassis  11 . Each blind hole  29  includes a penetrable wall  27  that may be readily pierced or drilled through to accommodate insertion of an osteotome or other tool to assist in removal of chassis  11  from the bone where such removal has become necessary. 
         [0065]    Referring to  FIGS. 5 through 7  an alternate embodiment of humeral head prosthesis  50  is shown configured as a two-piece prosthesis. Humeral head prosthesis  50  includes chassis  51  and head  52  that includes articulation surface  53  formed as a spherical segment. Chassis  51  is formed including anchor element  54  that projects distally below head base element  68 . A plurality of suture anchor apertures  58  are formed near distal end  56  of anchor element  54 . As with the preferred embodiment described above, suture anchor apertures  58  are configured to permit passage of suture according to a method of the invention discussed below. Distal end  56  of anchor element  54 , and an inner edge defining each of the suture anchor apertures  58  includes a polished surface  57  adapted to prevent surface abrasion between a suture that may be guided through any one of the plurality of suture anchor apertures  58 . As seen in  FIG. 5 , head  52  includes post  60  that extends proximally from a distal surface of head  52 . 
         [0066]    Referring to  FIG. 6 , coupling socket  59  is formed in chassis  51  and extends distally from base element  68 . Post  60  and socket  59  have a cooperating fit configured to secure head  52  to chassis  51 .  FIG. 6  also shows chassis  51  configured having anchor element  54  having tapering cross-section  55  that diminishes in thickness as a distance from base element  68  increases, (distally converging). As seen in  FIG. 6 , inner surface  61  of anchor element  54  is relatively featureless. Outer surface  62  of anchor element  54  includes a series of fins  63 , each fin comprising a pair of converging wall segments  64  and  65  that taper distally as a distance from head  12  increases, (distally converging). Revascularization apertures  66 , shown in  FIG. 5  are formed through anchor element  54  from inner surface  61  to outer surface  62  to promote bone growth and revascularization both inside and outside anchor element  54 . 
         [0067]    Referring to  FIG. 6  a plurality of blind holes  69  are formed in base element  68  of chassis  51 . Each blind hole  69  includes a penetrable wall  67  that may be readily fractured, pierced or drilled through to accommodate insertion of an osteotome or other tool to assist in removal of chassis  51  from the bone where such removal has become necessary. 
         [0068]      FIGS. 5 through 7  show bone anchors  71 ,  72 , (shown in  FIGS. 5 and 6 ), and  73  arranged preferably so that on installation of humeral head prosthesis  50 , anchors  71  and  72  are oriented so as to be set into the greater tuberosity GT and anchor  73  is oriented so as to be set into the calcar region CR of humeral head HH. As seen in  FIG. 6 , each of the bone anchors  71 ,  72  and  73  are adapted for insertion through and threaded engagement with one of the plurality of bone anchor apertures  33  formed through base element  68 . 
         [0069]      FIG. 8  shows unitary humeral head prosthesis  100  an alternate embodiment that has as one advantage a lowered cost of manufacture as compared to the multi-piece embodiments previously discussed. Humeral head prosthesis  100  includes chassis  101  to which head  102  is integrally formed. Head  102  includes articulation surface  103  formed as a spherical segment. Chassis  101  includes anchor element  104  which extends from base element  115 . Anchor element  104  includes a plurality of distally converging fins  105 . A plurality of revascularization apertures  110  are formed one between each of the plurality of distally converging fins  105 . Distal end  106  of anchor element  104  includes polished surface  107 . A plurality of suture anchor apertures  108  are formed proximate to distal end  106 . As shown in  FIG. 8 , the face of base element  115  and a substantial portion of anchor element  104  include textured surface  114 . 
         [0070]      FIGS. 9 and 10  show an alternate embodiment of humeral head resurfacing prosthesis  150  configured as a unitary prosthesis use where resurfacing of the humeral head is possible and indicated. Humeral head resurfacing prosthesis  150  includes chassis  151  to which head  152  is integrally formed. Head  152  includes articulation surface  153  formed as a spherical segment. Chassis  151  includes anchor element  154  which extends from base element  161 . Anchor element  154  includes a plurality of distally converging fins  163 . A plurality of revascularization apertures  160  are formed one between each of the plurality of distally converging fins  155 . Distal end  156  of anchor element  154  includes polished surface  157 . A plurality of suture anchor apertures  158  are formed proximate to distal end  156 . As seen in  FIG. 9 , anchor element  154  includes tapering cross-section  155 . As shown in  FIGS. 9 and 10 , head  152  includes partially concave surface  162  which is configured to cooperate with a prepared surface of the humeral head to be resurfaced. Concave surface  162  and a substantial portion of anchor element  154  include textured surface  164 . 
         [0071]    Referring to  FIG. 11  and according to a method of the present invention, humeral head HH is prepared for installation of humeral head prosthesis  10  shown in  FIGS. 1 through 4  by first removing anatomical head AH along cutline CL defining a plane that corresponds generally to anatomical neck AN.  FIG. 12  shows the next steps in the preparation including the drilling of pilot hole PH that lies substantially perpendicular to planar surface PS. Pilot hole PH is used to guide a hole saw, (not shown), for cutting circular cut CC having a diameter that is substantially equal to a diameter of distal end  16  of humeral head prosthesis  10  shown in  FIG. 1 . Also according to one methodology of the present invention bony plug BP may be harvested from anatomical head AH by means of a hole saw having a diameter substantially equal to an inside diameter of anchor element  14  of humeral head prosthesis  10  shown in  FIG. 1 . Bony plug BP may be used as bone graft material that is inserted into the interior of anchor element  14  in cases where there has been deterioration of the trabecular bone at the center of humeral head HH. 
         [0072]    Referring to  FIG. 15 , in the event that removal of humeral head prosthesis  10  is required, the surgeon removes head  12 , shown in  FIG. 2  and hole saw HS having a diameter slightly greater than a diameter of base element  28  is used to form removal cut RC. Chassis  11  is then worked free of underlying bone and removed together with bony head segment HS. 
         [0073]    Referring to  FIGS. 13 and 14 , sutures S 1 , S 2  and S 3  are passed through first, second and third tunnels T 1 , T 2  and T 3  formed through the cortical bone and terminating in circular cut CC. Distal end  16  of chassis  11  is then pressed into circular cut CC. Referring to  FIGS. 3 and 4 , tapering cross-section  15  creates a press fit as anchor member  14  is pressed into circular cut CC. Additionally, fins  23  counter rotation of chassis  11  once positioned in circular cut CC. As anchor member  14  is pressed further into circular cut CC, sutures S 1 , S 2  and S 3  are pulled tight and as shown in  FIG. 14  knotted across lesser tuberosity LT to secure the subscapularis tendon and/or the lesser tuberosity against humeral head HH. 
         [0074]    The description of the illustrated embodiments has been presented for purposes of illustration and description and is not intended to be exhaustive or to limit the invention to the precise form or to exemplary embodiment(s) and implementation(s) disclosed. Modifications and variations will be apparent to practitioners skilled in this art. Process steps described might be interchangeable with other steps in order to achieve the same result. At least one preferred embodiment was chosen and described in order to best explain the principles of the invention and a best mode of practical application, thereby to enable others skilled in the art to understand the invention and the various modifications that are suited to the particular use or implementation contemplated. The scope of the invention is defined by the claims appended hereto and their equivalents. Reference to an element in the singular is not intended to mean “one and only one” unless explicitly so stated, but rather means “one or more.” No claim element herein is to be construed under the provisions of 35 U.S.C. Sec.  112 , sixth paragraph unless the element is expressly recited using the phrase “means for . . . ”