Abstract:
A modular humeral implant and associated kit and method for implantation into a humerus that includes a natural humeral shaft and a natural humeral head. The modular implant includes a humeral stem for implantation into the natural humeral shaft, and an adapter. The adapter includes an anchoring projection and is operable for coupling to the humeral stem. The anchoring projection is adapted for insertion into an underside of the natural humeral head.

Description:
INTRODUCTION 
     A humeral prosthesis for total shoulder joint replacement generally includes a prosthetic humeral stem and a prosthetic humeral head which replaces the natural humeral head and is disposed within the shoulder socket. For three and four-part humeral head split fractures in which the blood supply to the fragments is compromised, a hemiarthroplasty can be performed, also replacing the humeral head with a prosthetic head. 
     In some humeral fractures, however, blood supply to the head fragment may be adequate, such as, for example, when the head is still attached to one of the tuberosities. In such cases, repairing and salvaging the natural head is preferable to replacing it. Accordingly, prostheses that allow retention and/or repair of the natural humeral head are still desirable. 
     SUMMARY 
     Various aspects of the invention teach a modular humeral implant and associated kit and method for implantation into a humerus that includes a natural humeral shaft and a natural humeral head. The modular implant includes a humeral stem for implantation into the natural humeral shaft, and an adapter. The adapter includes an anchoring projection and is operable for coupling to the humeral stem. The anchoring projection is adapted for insertion into an underside of the natural humeral head. 
     The present teachings also provide a method for implanting a modular humeral prosthesis to repair a humeral fracture in which the natural humeral head is still attached to a portion of the natural humeral shaft. The method includes rotating the natural humeral head to expose the proximal surface of the natural humeral shaft without severing the attachment. A longitudinal bore is prepared into the humeral shaft. An adapter is coupled to one of the natural humeral head and a humeral stem, and the humeral stem is implanted into the longitudinal bore. The natural humeral head is rotated onto the natural humeral shaft such that the adapter is inserted into the other of the natural humeral head and the humeral stem, and the natural humeral head substantially contacts the natural humeral shaft. 
     The present teachings also provide a modular humeral implant for implantation into a humerus that includes a natural humeral shaft and a natural humeral head. The implant includes a humeral stem for implantation into the natural humeral shaft, and a plurality of fasteners fastening the natural humeral shaft through the humeral stem to the natural humeral head. 
     The present teachings also provide a method for implanting a modular humeral prosthesis to repair a humeral fracture in which the natural humeral head is still attached to a portion of the natural humeral shaft. The method includes rotating the natural humeral head to expose a proximal surface of the natural humeral shaft without severing the attachment, preparing a longitudinal bore into the natural humeral shaft; inserting the humeral stem into the bore, rotating the natural humeral head onto the proximal surface of the natural humeral shaft, drilling a plurality of angled bores extending from natural humeral shaft though the humeral stem to the natural humeral head, and inserting fasteners through the angled bores to attach the natural humeral shaft to the natural humeral head. 
     Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein: 
         FIG. 1  is an exploded view of a humeral implant according to the present teachings; 
         FIG. 1A  is an exploded view of a humeral implant according to the present teachings; 
         FIG. 1B  is an exploded view of a humeral implant according to the present teachings; 
         FIG. 1C  is a partially assembled environmental view of a humeral implant according to the present teachings; 
         FIG. 1D  is a partially assembled environmental view of a humeral implant according to the present teachings; 
         FIG. 1E  is an isometric environmental view of the adapter of  FIG. 1D ; 
         FIG. 1F  is an environmental isometric view of a humeral implant according to the present teachings; 
         FIG. 1G  is isometric view of a humeral implant according to the present teachings; 
         FIG. 2  is an exploded view of a humeral implant according to the present teachings; 
         FIG. 2A  is a partially assembled environmental view of a humeral implant according to the present teachings; 
         FIG. 2B  is a side view of a humeral implant according to the present teachings; 
         FIG. 2C  is an environmental sectional view of a humeral implant according to the present teachings; 
         FIG. 3  is an environmental view of the humeral implant of  FIG. 1 ; 
         FIG. 3A  is an environmental view of a humeral implant according to the present teachings; 
         FIG. 4  is an environmental view of the humeral implant of  FIG. 2 ; 
         FIG. 5  is kit of modular humeral components according to the present teachings. 
         FIGS. 6A-6C  illustrate a sequence of implantation procedures according to the present teachings; and 
         FIG. 6D  illustrates an alternative to the procedure of  FIG. 6B . 
     
    
    
     DETAILED DESCRIPTION 
     The following description of various embodiments is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. 
     Referring to  FIGS. 1-4 , a modular humeral implant  100  includes a humeral stem  102  and an adapter  104 . The humeral stem  102  is adapted to be inserted into a natural humeral shaft  80 , which can be prepared to receive the humeral stem  102  using methods known in the art, such as reaming, drilling, etc. The humeral stem  102  can be integral or modular, including two or more separate components, and can be provided in variable lengths and shapes. The adapter  104  functions to connect, the implanted humeral stem  102  and the natural humeral head  84 . The natural humeral head  84  can be intact or reconstructed from fracture fragments by methods known in the art. The natural humeral head  84  can be still attached to a portion of the natural humeral shaft  80 , such as, for example, one of the tuberosities  82 . Because the natural humeral head  84  remains attached to the tuberosity  82 , blood supply to the natural humeral head  84  can be preserved, thus improving the therapeutic outcome relative to the risk of localized necrosis. The humeral implant  100  can be implanted without severing the attachment of the natural humeral head  84  to the tuberosity  82 , as is discussed below. 
     Referring to  FIG. 1 , the humeral stem  102  can include a proximal tapered recess  106  that is adapted to taper lock with a tapered projection  108  of the adapter  104 . Alternatively, as shown in  FIG. 1A , the humeral stem  102  can include a tapered projection  306  that interlocks with a mating tapered recess  308  of the adaptor  104 . The angle α between a longitudinal axis A of the adapter  104  and a proximal end surface  101  of the humeral stem  102  can be 90° or any other angle as desired under particular circumstances. The adapter  104  includes an anchoring projection  113  which is adapted for insertion into an underside surface  120  of the natural humeral head  84 . The anchoring projection  113  can be a ribbed projection or threaded screw  112 , as illustrated in  FIGS. 2 and 4 , or a bulbous projection  110  that defines a convex surface  118 , as illustrated in  FIGS. 1 and 3 . The bulbous projection  110  can be a ball or a portion of a sphere or ellipsoid or a polyhedral three-dimensional shape, or any other suitable three-dimensional shape. The bulbous projection  110  can be bioabsorbable or metallic with an attachment device  111  that includes a porous-coating to promote bone ongrowth and ingrowth. The attachment device  111  of the bulbous projection  110  can also define barbs, spikes, threads, grooves or other devices. Instead of a taper-lock, the bulbous projection  110  can also be coupled to the humeral stem  102  using any other means, such as a threaded screw  109  that is threaded from the humeral stem  102  into the bulbous projection  110 , as shown in  FIG. 1B , or vice-versa. 
     The threaded screw  112  can be directly threaded into cancellous bone through the underside surface  120  of the natural humeral head  84 . To receive the bulbous projection  110 , the natural humeral head  84  can be prepared by removing, if necessary, cancellous bone from the underside surface  120  of the natural humeral head  84  to create a snugly-fitting recess  122 . Alternatively, a cancellous bone impactor (not shown) can be used to define a recess  122  that snugly matches the bulbous projection  110 . 
     Referring to  FIG. 3A , one or more fasteners  132  inserted into corresponding angled bores  130  can be used to re-attach the natural humeral head  84  either exclusively or in conjunction with the projection  110 . The fasteners  132  could be placed through the natural humeral shaft  80  and the humeral stem  102  after the humeral head  84  is impacted onto the projection  110  to provide initial stability to the natural humeral head  84 . For proper placement, the angled bores  130  can be drilled through the natural humeral shaft  80  and/or tuberority  82  after the humeral stem  102  is inserted into the humeral canal. The fasteners  132  could be made of resorbable polylactide, polyglycolide, or combination thereof, or calcium phosphate, bone morphogenetic protein, allograft, etc., or any other biocompatible material. 
     Referring to  FIG. 1C , the bulbous projection  110  of the adaptor  104  can include guiding bores  152  through which anchoring wires  154  pass to be embedded in the natural humeral head  84 . The anchoring wires  154  can be attached to a base plate  161  at the base of the bulbous projection  110 , and are pushed into the natural humeral head  84  by a set screw or other fastener  160 , which is inserted through the tapered projection  108  and pushes against the base plate  161 . The anchoring wires  154  can be made of nitinol or other biocompatible material and can have barbs  156 . 
     Referring to  FIGS. 1D and 1E , the adapter  104  can include a disk-shaped projection  170 , which can be integrally or modularly attached to the tapered projection  108 . The disk-shaped projection  170  has peripheral suturing holes  172  to allow suturing to the natural humeral head  84 . The disk-shaped projection  170  can be circular or polygonal or have any other flat shape and can be recessed into the natural humeral head  84 , such that the disk-shaped projection  170  is flush with the underside surface  120  of the natural humeral head  84 . In another aspect, illustrated in  FIG. 1F , the adapter  104  can be replaced with an adapter-stem combination  104 ′, such that the disk-shaped projection  170  is directly coupled to a humeral stem  108 ′. It will be appreciated that the humeral stem  108 ′ can be selected from any suitable stems including a Copeland-style stem  108 ′ illustrated in  FIG. 1F , a short hip-style stem  108 ′ illustrated in  FIG. 1G , etc. The stem  108 ′ can be porous coated and can include suturing holes  105 . 
     Referring to  FIG. 2A , the adapter  104  can be modular and include a tapered projection  108  and an expandable tubular sleeve  164  that is received in the natural humeral head  84 . A plug  162  extends from the tapered projection  108 . The plug  162  is inserted into the sleeve  164  causing to expand and lock into the natural humeral head  84 . In another aspect, illustrated in  FIG. 2C , the adapter  104  is replaced with an adapter-stem combination  104 ′, such that the plug  162  is directly coupled to a humeral stem  108 ′, such as a short hip stem. In yet another aspect illustrated in  FIG. 2B , the anchoring projection  113  is also directly coupled to a humeral stem  108 ′, such as a short hip stem. 
     Referring to  FIG. 5 , separate adapters  104  having differently shaped and sized anchoring projections  113 , and humeral stems  102  of different shapes and sizes can be assembled together as a kit  200  and made available to the operating surgeon for optimal intraoperative selection depending on the particular patient and condition encountered during reconstructive surgery. Various size fasteners  132  (shown in  FIG. 3A ) can also be included in the kit. Although not specifically shown in  FIG. 5 , the kit  200  can also include adapter/stem combinations  108 ′ using a variety of anchoring portions and humeral stems portions, including any of those described above. 
     In operation and with reference to  FIGS. 6A-6C , the natural humeral head  84 , while still attached to the tuberosity  82 , is rotated relative to the tuberosity  82  to be examined, exposing the proximal surface  103  of the natural humeral shaft  80  at the proximal end  86 . A humeral stem  102  can be selected depending on the condition and size of the natural humeral shaft  80 . A longitudinal bore  88  is prepared in the natural humeral shaft  80  to receive the humeral stem  102 , as shown in  FIG. 6A . Other existing natural shaft fractures can also be repaired, using, if necessary, fixation screws, pins and the like. Depending on the condition of the fracture, the size and robustness of the natural humeral shaft  80  and natural humeral head  84 , one of the adapters  104  can be selected from the kit  200  for anchoring into the natural humeral head  84 . 
     When the selected adapter  104  has a bulbous projection  110 , the adapter  104  can be first taper-locked with the humeral stem  102 , which is then inserted into the longitudinal bore  88 , as shown in  FIG. 6B , with the bulbous projection  110  exposed above the proximal surface  103  of the natural humeral shaft  80 . The natural humeral head  84  can be prepared for receiving the bulbous projection  110  by optionally creating a recess  122  using, for example, an impactor or reamer. The natural humeral head  84  can then be rotated back toward the natural humeral shaft  80  and pressed against the bulbous projection  110  until a snug fit is obtained and the underside surface  120  of the natural humeral head substantially contacts the proximal surface  103  of the natural humeral shaft  82 . The natural humeral head is sutured to the humeral shaft  80  and to the tuberosities  82 . Alternatively, the adapter  104  can be first anchored into the natural humeral head  84 , and then taper-locked into the humeral stem  102 . 
     When the selected adapter  104  has an anchoring projection  113  of the threaded screw  112  type, the adapter  104  can be first threaded into the underside surface  120  of the natural humeral head  84 , which is then taper-locked with the humeral stem  102 , after the humeral stem  102  has been inserted into the longitudinal bore  88 , as shown in  FIG. 6D . The natural humeral head  84  can be sutured to the humeral shaft  80  and to the tuberosities  82 . Other fractures proximal humerus can be repaired and rebuilt, as necessary, using methods known in the art for three-part and four-part fractures of the proximal humerus. 
     The humeral stem  102  and the adapter  104  can be manufactured from a variety of biocompatible materials such as, for example, Ti6Al4V or CoCrMo. The adapter  104  can also be a hybrid combination of titanium or cobalt chromium with bioabsorbable materials, such as polylactides, plyglycolides, calcium phosphate, hydroxyapatite, etc. 
     The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.