Abstract:
A prosthetic glenoid component for attachment to a glenoid surface of a scapula to replace a natural socket of a shoulder and to provide a bearing surface for a head portion of an arm bone or humerus. The glenoid component has a metal back with integrally formed attachment legs which are cemented into corresponding holes formed in the glenoid surface, and also has an opening for receiving a hollow metal cage which is screwed into the glenoid surface.

Description:
This application claims the benefit of U.S. Provisional Application No. 60/403,429, filed Aug. 15, 2002. 

   FIELD OF THE INVENTION 
   The present invention relates to the field of prosthetic devices and, in particular, to a prosthetic glenoid component for attachment to a glenoid surface of a scapula to replace a natural socket of a shoulder and to provide a bearing surface for a head portion of an arm bone or humerus. 
   BACKGROUND OF THE INVENTION 
   It is known in the prior art to provide glenoid components for replacing a glenoid surface which have a two piece construction and comprise plastic inserts which slide into or are otherwise coupled to metal backings. The metal backings are used to secure the plastic inserts to the glenoid surface. The backings are typically made from titanium or other suitable metals, and are typically attached to the glenoid surface using metal fixation screws or cages, such as disclosed in U.S. Pat. No. 4,865,605 and EP 0 538 895 A2. Other glenoid components known in the art use a plurality of attachment pegs for penetrating the glenoid to secure the glenoid to the glenoid surface. See, e.g., U.S. Pat. No. 5,080,673. 
   There is needed, therefore, a new glenoid prosthesis device and a method of affixing the glenoid prosthesis device to a resected surface of a scapula more securely than provided in the prior art. 
   SUMMARY OF THE INVENTION 
   The present invention provides a prosthetic glenoid component which attaches to a glenoid surface of a scapula to replace a natural socket of a shoulder and provides a bearing surface for a head portion of an arm bone or humerus. More particularly, the present invention provides a metal back glenoid component having integrally formed attachment legs which are cemented into corresponding holes formed in the glenoid surface, and also having an opening for receiving a hollow, threaded cage which is screwed into the glenoid surface. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other features and advantages of the invention will be better understood from the following detailed description, which is provided in connection with the accompanying drawings. 
       FIG. 1  is a close-up view of a glenoid prosthesis comprising pegs constructed in accordance with an embodiment of the present invention. 
       FIG. 2  is a side sectional view of an exemplary metal cage screw that is used in conjunction with the glenoid prosthesis of  FIG. 1  constructed in accordance with an embodiment of the present invention. 
       FIG. 3  is a top-side view of the exemplary metal cage screw of  FIG. 2 . 
       FIG. 4  is an assembly drawing of a glenoid prosthesis and an insert constructed in accordance with the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   In the following detailed description, reference is made to various specific embodiments of the invention. These embodiments are described with sufficient detail to enable those skilled in the art to practice the invention. It is to be understood that other embodiments may be employed, and that various structural, logical and electrical changes may be made without departing from the spirit or scope of the invention. 
   The invention will now be described with reference to  FIGS. 1–4  illustrating a metal back glenoid constructed in accordance with the invention. 
   The glenoid component  2  of the present invention is designed for use in a total shoulder replacement procedure. In a total shoulder replacement procedure, a humeral component having a head portion is used to replace the natural head portion of the humerus. The humeral component typically has an elongated intramedullary stem to secure the humeral component to the humerus. The glenoid portion of the scapula is resurfaced with a glenoid component which provides a bearing surface for the head portion of the humeral component. For instance, the glenoid prosthesis  2  can be positioned in a resected portion of the head of the scapula. 
   Referring now to  FIG. 1 , the glenoid prosthesis  2  used is preferably a metal back glenoid prosthesis  2 . The metal back glenoid prosthesis  2  preferably comprises titanium metal. The metal back glenoid prosthesis  2  consists of a lateral surface  3 , flat sidewalls  5 , a substantially flat medial surface  7 , and at least two pegs  4  extending medially from the flat medial surface  7 . The glenoid prosthesis  2  is formed to be approximately the same shape as a natural glenoid cavity. 
   The lateral articulating surface  3  of the glenoid prosthesis  2  provides a bearing surface for the head portion of the humeral component. In a preferred embodiment, an insert  12  can be provided that slides into grooves on the lateral articulating surface  3  to form a substantially spherical contact from which the head portion of the humeral component will rest against. 
   The glenoid prosthesis  2  is attached to the resected portion of the scapula. Portions of the scapula are resected such that a relatively flat surface is provided to which the glenoid prosthesis  2  will become affixed to. The amount of scapula that is resected will depend upon the thickness of the metal back glenoid prosthesis  2 . After a flat surface on the scapula has been obtained, at least two holes are drilled substantially perpendicular into the resected portion to provide cylindrical sidewalls and a flat end. Typically, the holes are drilled to be larger than the pegs  4  in order to allow cement to be provided therein, if desired. In a preferred embodiment, cement is provided into the provided peg holes and applied on the resected surface of the scapula. 
   The pegs  4  are then inserted into the peg holes and the medial surface  7  is positioned adjacent to the resected surface of the scapula. The cement then provides a continuous bond between the medial surface  7  and the resected surface of the scapula, and between the pegs  4  and peg holes formed in the scapula. The affixation of the medial surface  7  to the resected portion of the scapula prevents movement of the glenoid prosthesis  2  and the bone. The presence of cement enhances the affixation of the glenoid prosthesis  2  to the resected surface of the scapula. 
   In a preferred embodiment, the pegs  4  are provided with a plurality of circumferential grooves  13  that are disposed throughout the length of the pegs  4 . The circumferential grooves  13  increase the surface area of the pegs  4  to which cement can bond to. In essence, a stronger bond is achieved to which the pegs  4  can be strongly affixed within the peg holes of the scapula in which cement is provided therein. 
   As a result, the metal back glenoid component  2  of the present invention provides a unique combination of attachment means including a plurality of pegs  4  which are designed to be inserted and cemented into predrilled holes in the resected surface of the scapula. Metal back glenoid component  2  also includes a central aperture  6  for receiving a hollow metal cage screw  8  which is formed of titanium and can optionally be provided with fenestrations  10  ( FIG. 2 ) to promote bone growth. Metal cage screw  8  is received in a cavity formed by a coring reamer (not shown), and provides the primary fixation for the glenoid component, while pegs  4  provide additional fixation and prevent rotation. The lateral medial surface  7  of the glenoid prosthesis can also be cemented to the glenoid surface to provide even further adhesion. 
     FIG. 2  is a side-sectional view of metal cage screw  8 . As illustrated, a plurality of fenestrations  10  may extend through the cylindrically-shaped, hollow cage screw  8 . As the bone grows, it can grow through the fenestrations  10 , thus providing adhesion properties in addition to those provided above. For exemplary purposes, metal cage screw  8  is illustrated with a plurality of fenestrations  10  offset from each other. 
   The metal cage screw  8  is provided with circumferential threads  15  as illustrated in  FIG. 2 . The circumferential threads  15  are provided at an angle that ranges from about 40° to about 50° on the main shaft of the metal cage screw  8 .  FIG. 3  is a top-down view of metal cage screw  8 . 
   Referring now to  FIG. 4 , an assembly drawing of the invention is shown in which glenoid prosthesis  200  with metal cage screw  8  is shown with a polyethylene insert  100 , which provides a smooth bearing surface on the medial side of the prosthesis. Insert  100  has tapered edges  208  which slide into the indented raised edges  108  of the glenoid prosthesis  200  to couple the insert to the prosthesis. 
   The above description and drawings are only to be considered illustrative of exemplary embodiments which achieve the features and advantages of the invention. Although exemplary embodiments of the present invention have been described and illustrated herein, many modifications, even substitutions of materials, can be made without departing from the spirit or scope of the invention. Accordingly, the above description and accompanying drawings are only illustrative of exemplary embodiments that can achieve the features and advantages of the present invention. It is not intended that the invention be limited to the embodiments shown and described in detail herein. The invention is limited only by the scope of the appended claims.