WO2005032430A1

WO2005032430A1 - Humeral insert for an inverted shoulder prosthesis

Info

Publication number: WO2005032430A1
Application number: PCT/FR2004/002499
Authority: WO
Inventors: Denis Katz; Philippe Sauzieres; Philippe Valenti
Original assignee: Implants Industrie
Priority date: 2003-10-03
Filing date: 2004-10-04
Publication date: 2005-04-14
Also published as: EP1670395A1; FR2860427A1; FR2860427B1

Abstract

The humeral insert (3), which can be engaged on a humeral rod (2) and can receive a glenosphere (4), comprises means on the posterior surface thereof for fixing to the humeral rod (2), and an articular concave surface (9) on the anterior surface (8) thereof. The posterior surface (6) and the anterior surface (8) are joined by means of an enclosing wall (10). According to the invention, the enclosing wall (10) contains a recess (12).

Description

The present invention relates to a humeral insert for an inverted shoulder prosthesis. As part of a reconstruction of the humeral joint, it is well known to place a total shoulder prosthesis. When the cap is badly damaged, a so-called inverted prosthesis can be placed. This type of prosthesis includes a humeral subset and a scapular subset. The humeral subset is composed of a humeral rod which is engaged in the medullary canal of the humerus and an insert which is fixed on the head of the humeral rod. This insert has a concave outer face and is generally made of polyethylene. The scapular subset is composed of a glenosphere fixed on the scapular part of the joint to be reconstructed. The glenosphere is fixed by means of a metal base anchored in the scapular bone. Clinical experience has revealed a significant drawback of this type of prosthesis. Practitioners have noticed that a notch appears in the pillar of the scapula, that is to say the part located under the glenoid cavity of the scapula. This bone notch is due to a conflict between the humeral implant and the abutment of the scapula. Indeed, during an adduction movement of the arm, and in particular at the end of this movement, a collision can occur between the humeral insert and the pillar of the scapula, which can then create this bone notch. This phenomenon is even more marked in patients in whom the pillar of the scapula is vertical. This notch generally stabilizes but, in certain cases, can progress towards a greater necrosis, due in particular to the polyethylene debris resulting from the friction of the glenosphere on the insert. Although these cases are not the majority, it is very undesirable to allow a notch to form in a bone, since the latter, even when stabilized, remains a zone of weakness of the bone. An object of the invention is therefore to propose a humeral insert which minimizes the formation of a bone notch. To this end, the present invention relates to a humeral insert which can be engaged on a humeral rod and which can receive a glenosphere, comprising means for fixing to the humeral rod on its posterior face, and a concave articular surface on its anterior wall, the face posterior and the anterior face being connected by a belt wall, characterized in that it has a recess in its belt wall. Thus, the presence of a recess in the belt wall of the insert makes it possible, by orienting the recess facing the pillar of the scapula, to avoid a conflict between the insert and the pillar of the scapula. According to an advantageous embodiment, the recess is intersecting with the concave articular surface, which makes it possible to maintain a reduced bulk of the insert, without however adversely affecting the holding of the glenosphere in the concave articular surface. According to an advantageous possibility, the belt wall is substantially trapezoidal, the recess being formed in its large base. Preferably, the recess has a cylindrical surface, which allows the recess to be produced by a milling operation. In addition, the surface of the recess forms, with the belt face, an acute angle. In one embodiment, the recess extends over a part of the belt face adjacent to the front face. To avoid a conflict between a base fixed in the scapular bone receiving the glenosphere and the humeral insert, a chamfer is formed at each of the connection zones between the recess and the anterior face. A variant may provide that the insert has a conical pin protruding from its rear face by its attachment to a humeral rod. For a good understanding, the invention is described with reference to the attached drawing showing by way of nonlimiting example an embodiment of a humeral insert according to it. Figures 1 to 3 show respectively in side view and in perspective in two orientations a humeral insert according to the invention cooperating with a glenosphere of a total shoulder prosthesis. Figure 4 shows a total shoulder prosthesis incorporating the humeral insert according to the invention. FIG. 4 represents the usual components of a shoulder prosthesis, namely a humeral rod 2 intended to be anchored in the medullary canal of a humerus, a humeral insert 3 which engages in the metaphyseal part of the humeral rod 2, a glenosphere 4 and a base 5 fixed to the scapular part of the joint to be reconstructed. Referring to Figures 1 to 3, we can see that the humeral insert 3 has a rear face 6 of which protrudes from a conical pin 7. This conical pin 7 allows attachment to the humeral rod. It is also noted that the rear face 6 has a peripheral rib. The front face 8 of the insert has a concave articular surface 9 which, in the example shown, has perfect congruence with the glenosphere 4. The belt face 10 connecting the front and rear faces has a trapezoidal shape, which prevents the rotation of the humeral insert 3 when it is mounted on the humeral rod 2. The insert can usually be made of polyethylene. As shown in the figures, a recess 12 is made in the belt face of the insert. The recess 12 is made in the large base of the belt and cuts the concave articular surface 9. The recess 12 has a cylindrical surface which is inclined relative to the belt surface by an angle of inclination up to at about 50 °. We also note that the recess 12 is not made over the entire height of the belt face 10, but is hollowed out only on the part of the belt wall 10 located on the side of the front face 8. It is also note that, at each of the connection zones of the recess and the front face, two chamfers 14 are produced. Thus, when a total shoulder prosthesis comprising an insert

3 is posed, we can see by referring to Figure 3 that, at the end of the adduction movement, the humeral insert 3 forms with the glenosphere an angle which would cause a conflict between the pillar of the scapula and the insert will smell, if it were not formed in the latter, I recess 12. The insert humerai 3 is of course oriented in such a way that the recess 12 is in the supply plane. It should be noted that the chamfers 14 also participate in the proper functioning of the prosthesis by avoiding a conflict between the humeral insert 3 and the metal base 5 (also called glenoid back metal), during an internal rotation movement of the arms. The invention thus provides a humeral insert which prevents the formation of a bone notch in the pillar of the scapula. Of course, the invention is not limited to the embodiment described above by way of nonlimiting example, but on the contrary embraces all of the embodiments thereof. Thus, the humeral insert could be generally circular and not trapezoidal.

Claims

CLAIMS 1. Humeral insert (3) which can be engaged on a humeral stem

(2) and capable of receiving a glenosphere (4), comprising means for fixing to the humeral stem (2) on its posterior face (6), and a concave articular surface (9) on its anterior face (8), the face rear face (6) and the front face (8) being connected by a belt wall (10), characterized in that it has a recess (12) in its belt wall (10). 2. Humeral insert according to claim 1, characterized in that the recess (12) intersects with the concave articular surface (9).

3. Humeral insert according to claim 1 or claim 2, characterized in that the belt wall (10) is substantially trapezoidal, the recess (12) being formed in its large base.

4. Humeral insert according to one of claims 1 to 3, characterized in that the recess (12) has a cylindrical surface.

5. Humeral insert according to claim 4, characterized in that the surface of the recess (12) forms, with the belt wall (10), an acute angle.

6. Humeral insert according to claim 4 or claim 5, characterized in that the recess (12) extends over a part of the belt face (10) adjacent to the anterior face (8).

7. Humeral insert according to one of claims 2 to 6, characterized in that a chamfer (14) is formed at each of the connection zones between the recess (12) and the front face (8).

8. Humeral insert according to one of claims 1 to 7, characterized in that it has a conical pin (7) projecting from its rear face (6).