FR2617040A1 - Acetabular prosthesis - Google Patents

Abstract

This prosthesis comprises, in combination, a cup 2 made of a synthetic material such as polyethylene, of general hemispherical shape, and whose internal surface 3 is used for the articulation of the spherical part of the head of the prosthesis, and a metal cap 10 integral with the cup 2, covering its outer face, from the outer surface of which project fingers 15 which are regularly distributed. Application to making hip prostheses.

Description

COTYLOIDIAN PROSTHESIS
The present invention relates to an acetabular prosthesis.

 In the event of deterioration of the head of the femur, or of the acetabular cavity, inside which it is mounted, it is common to proceed with the implantation of a prosthesis.

 The implantation of a prosthesis is carried out by sawing the neck of the femur or upper part thereof and by replacing it with a part which includes a tail intended to be engaged in the medullary canal, terminated by a shaped head. general spherical engagement in the acetabulum.

 Depending on the state of this cavity, it may or may not be fitted with a cup of generally hemispherical shape inside which the head of the prosthesis is articulated.

 Such a cup, made of polyethylene, is fixed in the acetabular cavity by sealing with cement, after enlarging the cavity by milling. The outer surface of the cup frequently has grooves favoring the attachment of the cement.

 In practice, after the cavity has been lined with cement, the cup is engaged in it. During this positioning, and taking into account the profiled shape of the cup, the cement tends to be expelled from the bottom of the cup towards the edge of the latter, so that it is difficult to dispose of a constant thickness of cement, this thickness tending to be smaller at the top of the cup than in the areas located near the edge thereof.

 However, it is precisely on the top of the cup that the main reaction forces of the head of the prosthesis are exerted when it is in use. This results in a deformation of the cup by creep of the synthetic material, which in the long term results in a loosening of the cup with degradation of the bone, requiring a new intervention with the installation of a ring of support, prior to the implantation of a new prosthesis.

 The present invention aims to remedy these drawbacks.

 To this end, the acetabular prosthesis which it concerns comprises, in combination, a cup made of synthetic material such as polyethylene, of general hemispherical shape, and the inner surface of which serves to articulate the spherical part of the head. of the prosthesis, and a metal cap integral with the cup, covering the outer face of the latter, and the outer surface of which project regularly distributed fingers.

 Such a prosthesis, intended to be used in the case where it is not necessary to carry out a bone reconstitution, has numerous advantages compared to known prostheses constituted by simple cups.

 When mounting the prosthesis in the acetabular cavity, the fingers protruding from the outer surface of the cap, bear against the bone wall of the cavity and constitute as many points of contact with it through which the lines of force pass. due to the reaction of the head of the prosthesis, in conditions of use thereof.

 The lines of force being regularly distributed over the surface of the prosthesis, the risks of deformations are therefore less significant than in the case of a traditional cup in which the lines of force pass through the sole top of the prosthesis.

 In addition, pressing the fingers against the bone wall of the cavity ensures a regularity of the thickness of the sealing cement which is equal to the length of the fingers.

 Finally, the metal cap of the cup, which is for example made of titanium, mechanically reinforces the latter by preventing the creep of polyethylene.

 According to another characteristic of the invention, the metal cap has regularly distributed openings. These openings increase the modulus of elasticity of the cap, which favors the possibilities of adaptation of the latter to the cavity, and also constitute areas for anchoring the cement.

 Advantageously, the metal cap has a central opening opening into its bottom and a plurality of elongated slots oriented from its bottom towards its edge.

 According to another characteristic of the invention, the plastic cup has a plurality of profiled teeth facing outwards and formed near its edge and the cap comprises, at its edge, a return towards the inside. , behind which the teeth are intended to come to bear in the nested position of the cup inside the cap.

 The mounting of the cup in the cap is therefore carried out simply and quickly by snap-fastening.

In any case, the invention will be clearly understood with the aid of the description which follows, with reference to the appended diagrammatic drawing representing, by way of nonlimiting example, an embodiment of this prosthesis
Figure l is a perspective view in the mounted position
Figure 2 is a longitudinal sectional view in exploded position;
Figure 3 is a longitudinal sectional view in the mounted position
Figure 4 is a view of this prosthesis in position implanted in an acetabular cavity, part of which has been cut away.

 The prosthesis, shown in the drawing, comprises a cup 2 made of synthetic material, such as polyethylene, comprising an interior surface 3 of generally hemispherical shape intended for the articulation of the head of the femoral part of the prosthesis not shown in the drawing.

 The edge 4 of the cup 2 has a peripheral shoulder 5 facing outwards, from which protrude a number of teeth 6, regularly distributed around its periphery, oriented parallel to the axis of the cup.

 Each tooth has a face 7 inclined from the bottom of the cup towards the edge of the latter and from the inside to the outside, the part of large section of each tooth being delimited by a return 8 of orientation parallel to the plane from the edge 4 of the cup.

 Each tooth 6 is separated from the cup by a slot 9, which provides the teeth with a possibility of radial bending.

 This prosthesis further comprises a metal cap 10 for example made of titanium, having an internal profile 12 complementary to the external profile of the cup 2. This cap 12 has an edge 13 having a return 14 towards the interior, this return being intended to allow, in the mounted position of the cup 2 in the cap 10, the support of the teeth 6 as shown in FIG. 3.

 From the outer face of the cap 10 project fingers 15 regularly distributed. In addition, the cap 10 has a central opening 16 at its bottom and a certain number of openings 17 in the form of slots oriented from the bottom towards the edge 13.

 In practice, the mounting of the cup 2 in the cap 10 is carried out by interlocking, at the end of which an elastic snap occurs.

 After the acetabular cavity 18, shown in FIG. 4, has been filled with cement 19, the prosthesis is put in place, the support of the fingers 15 against the bone wall of the cavity guaranteeing a constant thickness of cement.

 In addition, these contact points serve to pass the lines of force resulting from the reaction of the head of the prosthesis, thus ensuring a distribution of the lines of force over the entire surface of the prosthesis.

 Finally, the penetration of cement into the openings 16 and 17 of the cap promotes the anchoring of the prosthesis.

 As is apparent from the above, the invention brings a great improvement to the existing technique by providing an acetabular prosthesis of simple design, easy to set up, the anchoring of which is carried out in excellent conditions, and the cup of which does not deform under conditions of use, thus avoiding the risk of bone deterioration.

 It goes without saying that the invention is not limited to the sole embodiment of this prosthesis, described above by way of example; on the contrary, it embraces all of its variant embodiments.

 It is thus in particular that the means for securing the cup and the cap could be different, that the material constituting the cap could be different or even that the shape and the number of the openings could vary without being sorted out for as much within the scope of the invention.

Claims (4)

 1. - acetabular prosthesis, characterized in that it comprises, in combination, a cup (2) made of synthetic material such as polyethylene, generally hemispherical in shape, and the inner surface (3) of which is used for articulation of the spherical part of the head of the prosthesis, and a metal cap (10) integral with the cup (2), covering the outer face of the latter, and the outer surface of which project fingers (15) regularly distributed.  2. - Prosthesis according to claim 1, characterized in that the metal cap (10) has openings (16, 17) regularly distributed.  3. - Prosthesis according to claim 2, characterized in that the metal cap (10) has a central opening (16) opening into its bottom and a plurality of elongated slots (17) oriented from its bottom towards its edge (13).  4. - Prosthesis according to any one of claims 1 to 3, characterized in that the cup (2) in synthetic material comprises a plurality of profiled teeth (6) turned outwards, and formed near its edge ( 4) and the cap (10) comprises, at its edge (13), a return (14) inwards, behind which the teeth (6) are intended to come to bear in the nested position of the cup (2 ) inside the cap (10).