Abstract:
A total shoulder prosthesis includes a glenoidal component a substantially hemispherical convex articular surface and of which a center of curvature is adapted, when the prosthesis is implanted, to be located in the glenoid cavity or in the immediate vicinity thereof, and a humeral component defining a concave articular surface adapted to cooperate with the convex articular surface of the glenoidal component. The concave humeral articular surface is defined by a metallic part of the humeral component to thereby reduce a space requirement of the prosthesis.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a shoulder prosthesis and, more specifically, to a shoulder prosthesis whose compactness can be improved with respect to those of the state of the art. 
     2. Brief Description of the Related Art 
     In the domain of shoulder prostheses, it is known, for example from EP-A-0 299 889, to constitute a so-called “inverted” prosthesis in which a convex articular surface implanted within a glenoid cavity and a concave articular surface implanted within a humerus, cooperate in order to recreate a joint at the shoulder, with a center of rotation located in the glenoid cavity. In this type of prosthesis, the convex articular surface is often made of metal, while a cup made of synthetic material, for example polyethylene, is shaped so as to create the concave humeral surface of articulation. In order to withstand the efforts to which it is subjected, such a cup must have a relatively great thickness, this causing a lateral space requirement of the prosthesis which may sometimes inhibit the patient, particularly during movements of abduction. 
     It is a more particular object of the present invention to overcome these drawbacks by proposing a novel total shoulder prosthesis of inverted type in which there is less risk of the lateral space requirement inhibiting the patient than the prostheses of the state of the art. 
     SUMMARY OF THE INVENTION 
     In that spirit, the invention relates to a total shoulder prosthesis comprising a glenoidal component, defining a substantially hemispherical convex articular surface of which the center of curvature is located in the glenoid cavity or in the immediate vicinity of the glenoid cavity, and a humeral component defining a concave articular surface adapted to cooperate with the convex articular surface of the glenoidal component, characterized in that the concave articular surface is defined by a metallic part of the humeral component. 
     With the invention, the lateral space requirement for implant of the prosthesis can be optimized, while conserving the functional character of the humeral articular surface. 
     According to advantageous but non-obligatory aspects of the invention, a total shoulder prosthesis of inverted type may incorporate one or more of the characteristics set forth below, taken in any technically admissible combination.
         The convex articular surface is defined in a metallic part of the glenoidal component. Surprisingly, a prosthesis of inverted type in which the two articular surfaces are made of metal has proved to allow a patient to move easily, while the fact of dispensing with polyethylene allows a better compactness of the prosthesis, particularly a reduction in its lateral space requirement.   The metallic parts in which the articular surfaces are formed are made of titanium or a chromium-cobalt alloy.   According to a first embodiment, the humeral component comprises a one-piece metaphyseal part which defines the concave articular surface.   According to another embodiment, the humeral component comprises a two-piece metaphyseal part formed by a body on which is mounted a metallic insert defining the concave articular surface. In this case, the insert is advantageously immobilized on the body by cooperation of shapes. In addition, this body may be provided to be adapted to receive different implants which define articular surfaces which are different and/or positioned differently with respect to the body, this making it possible to adapt, to a certain extent, the prosthesis to its site of implantation.   Whatever the embodiment considered, the metaphyseal part of the humeral component may be in one piece with, or added on, a stem for anchorage of the component in the humerus.   The humeral component is entirely metallic.       

    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be more readily understood and other advantages thereof will appear more clearly in the light of the following description of two forms of embodiment of a prosthesis in accordance with its principle, given solely by way of example and made with reference to the accompanying drawings, in which: 
         FIG. 1  schematically shows a prosthesis according to the invention implanted in a patient&#39;s shoulder. 
         FIG. 2  is a view in perspective of the humeral component of the prosthesis of  FIG. 1 . 
         FIG. 3  is a side view of a part of the humeral component and of the glenoidal component of the prosthesis of  FIG. 1 , in configuration separated from each other. 
         FIG. 4  is a view in perspective of the humeral component of a prosthesis according to a second form of embodiment of the invention. 
         FIG. 5  is a view similar to  FIG. 3  for the prosthesis of which the humeral element is shown in  FIG. 4 . 
     
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring now to the drawings, the prosthesis P shown in  FIG. 1  comprises a glenoidal component  1  which defines a convex articular surface S 1  of globally hemispherical shape and of which the center of curvature C 1  is located at the rear face of the component  1 , i.e. at the milled surface S G  of the glenoid cavity. As is more particularly visible in  FIG. 3 , the component  1  comprises a base  11  provided with an anchoring stem  12  and intended to be fixed on the glenoid cavity G by means of a plurality of screws (not shown). A metallic head  13  is provided to be mounted on the base  11  and shaped to define the surface S 1 . This glenoidal component may, for example, be in accordance with the technical teaching of French Patent 2 835 425. 
     The prosthesis P also comprises a humeral component  2  which is also metallic. The component  2  comprises a metaphyseal part  21  in one piece with a stem  22  for anchoring in the medullary canal M of the humerus H. The part  21  is hollowed out by machining and defines a concave surface S 2  in the form of a portion of sphere of radius substantially equal to that of the surface S 1 . 
     The surface S 2  is bordered by an annular and circular edge  23 . 
     When the prosthesis is implanted, as shown in  FIG. 1 , where the component  2  is shown in section while the component  1  is shown in outside view in order to render the drawing clearer, the surfaces S 1  and S 2  are in surface abutment against each other, this allowing the different shoulder movements which are sought after. 
     Taking into account the fact that the surface S 2  is formed by the part  21  itself, the distance d between the resectioned surface S G  of the glenoid cavity and the cut edge B of the resectioned humerus H is relatively small compared to the same distance for a known prosthesis. 
     The part  13  and the component  2  are advantageously made of a bio-compatible metal, for example titanium or an alloy based on chromium-cobalt. 
     According to an advantageous variant of the invention, the surface S 2  is not necessarily centered in the metaphyseal part  21 . For example, the component  2  may be selected from a set of components of which the surfaces S 2  are more or less eccentric with respect to their respective metaphyseal parts. 
     In the second form of embodiment of the invention shown in  FIGS. 4 and 5 , elements similar to those of the first embodiment bear identical references increased by 100. The glenoidal component  101  of this embodiment also comprises a base  111  of which the stem  112  allows anchoring in the glenoid cavity as well as a metallic head  113  defining a hemispherical, convex articular surface S 1 . 
     The humeral component  102  comprises a metaphyseal part  121  constituted by a body  124  and an insert  125 , both metallic. The insert and the body are advantageously made of the same metal or metallic alloy, for example titanium or an alloy based on chromium-cobalt. 
     The insert  125  is intended to be immobilized on the body  124  by cooperation of shapes, being partially engaged in the inner volume  126  of the body  124 , a peripheral edge  123  of the insert  125  coming into abutment on a peripheral edge  127  of the body  124 . 
     The insert  125  defines a concave hemispherical surface S 2  with the same geometry as that of the prosthesis of the first form of embodiment. 
     The insert  125  is provided with a notch  128  at the level of its edge  123 , while the body  124  bears a lug  129  on its edge  127 . The cooperation of elements  128  and  129  makes it possible to immobilize the insert  125  in rotation about an axis X 2 -X′ 2  of the surface S 2 . 
     Furthermore, the part  121  is added on an anchoring stem  122  intended to be immobilized in the humeral medullary canal. To that end, the body  124  is provided with an extension  124   a  intended to be introduced and wedged inside a housing  122   a  of corresponding shape provided in the stem  122 . 
     As previously, the fact of making the surfaces S 1  and S 2  in parts  113  and  125  which are metallic makes it possible to improve the compactness of the prosthesis, while allowing easy, high-amplitude movements of the patient&#39;s arm with respect to the glenoid cavity. 
     According to an aspect of the invention (not shown), inserts  125  of different shapes may be provided to be mounted on the body  124 , this making it possible to adapt the prosthesis to its site of implantation. For example, inserts  125  whose surfaces S 2  have different radii of curvature may be used, one of them being selected and mounted on the body  124  as a function of the geometry of the surface S 1  used for the glenoidal component. Similarly, inserts in which the surfaces S 2  are positioned differently with respect to the edge  123  may be used, one of them being selected, when installing the prosthesis, as a function of the patient&#39;s morphology. 
     The characteristics of the forms of embodiment described may be combined together within the scope of the present invention. In particular, a one-piece metaphyseal part, such as that of the first embodiment, may be added on an anchoring stem such as that of the second embodiment. Similarly, the body of the second embodiment may be in one piece with an anchoring stem, as in the first embodiment.