FR2903882A1 - Insert for cotyloidal implant, has hemispherical outer surface with centre separated with respect to centre of hemispherical inner surface along axis of revolution of outer surface in direction of opening of insert - Google Patents

Abstract

The insert (1) has a hemispherical outer surface (2) for mounting the insert in an articulated manner, where the insert is arranged in a cup (5) fixed in a cotyloidal cavity of a patient. A hemispherical inner surface (3) delimits a cavity intended to mounting of a prosthetic femoral head in an articulated manner. A centre of the surface (2) is separated with respect to centre of the surface (3) along an axis of revolution of the surface (2) in direction of an opening (9) of the insert.

Description

The invention relates to an insert for cotyloidal implant with double

  mobility, a corresponding acetabular implant and a corresponding hip prosthesis. The dual mobility prostheses generally comprise: a metal cup, intended to be fixed on the iliac bone, in the patient's acetabular cavity, having a substantially hemispherical cavity, a polyethylene acetabular insert, mounted in an articulated manner in the cup cavity, having a substantially hemispherical shaped cavity - a femoral stem equipped with a femoral head, to be hingedly mounted in the cavity of the insert. The acetabular tip generally has an outer surface of substantially hemispherical shape and whose center coincides with that of the inner surface defining the cavity. During the movement of the femur, in particular during the abduction movement, that is to say, of separation from the medial sagittal plane, and during the adduction movement, that is to say of approximation by relative to this same plane, the femoral stem comes into contact with the insert, thereby causing it to rotate relative to the cup. Once the insert has moved, it remains in this position when the patient is in a standing position, because of the coincidence of the center of rotation of the insert in the cup, defined by the center of the outer surface of the the insert, with the center of rotation of the femoral head in the insert, defined by the center of the inner surface of the insert. The insert, which is not returned to its original position, can then be placed in an unfavorable position during the movement of the joint, increasing the risk of dislocation and wear by contact between the stem and the insert. The prior art proposes a dual mobility acetabular implant insert comprising: an outer surface of substantially hemispherical shape, intended for articulately mounting the insert in a cup fixed in an acetabular cavity of a patient; an inner surface of substantially hemispherical shape 35 delimiting a cavity for articulately mounting a prosthetic femoral head, the center of the outer surface being offset from the center of the inner surface along the axis of revolution of the surface external, towards the opening of the insert. Such an insert allows the offset of the center of rotation of the insert 5 in the cup relative to the center of rotation of the femoral head in the insert, so that once the patient in a standing position, when the femur is positioned along the vertical axis of the body, the forces exerted on the prosthetic head, in its center, create a pair of forces causing rotation of the cup until it is in equilibrium position.

  This equilibrium position corresponds to the position in which the two aforementioned centers of rotation are aligned on the axis along which the force is applied. This insert of the prior art then tends to be positioned horizontally when the patient is in a standing position.

  This limits the risk of tilting the insert in an unfavorable position, reducing the risk of dislocation. However, wear due to contact between the insert and the rod is increased. Indeed, such a shift generates a torque tending to bring the insert in the horizontal position and therefore in the position of contact with the rod. The invention aims to solve this problem by providing an insert capable of being placed in a position in which the risk of luxation of the hip and the wear of the insert are minimal. To this end, the invention relates to a dual mobility acetabular implant insert comprising: an outer surface of substantially hemispherical shape, intended for the articulated mounting of the insert in a cup fixed in an acetabular cavity of a patient; an inner surface of substantially hemispherical shape defining a cavity intended for articulately mounting a prosthetic femoral head, the center of the outer surface being offset relative to the center of the inner surface along the axis of revolution of the outer surface, towards the opening of the insert, characterized in that the center of the outer surface is further offset from the center of the inner surface along an axis perpendicular to the axis of revolution of the outer surface. Such a structure makes it possible to position the insert angularly with respect to the cup and the femoral stem, in a position capable of combating dislocation and less unfavorable with regard to the wear of the insert by contact with the stem. especially with the collar. According to a feature of the invention, the axis passing through the center of the outer surface and that of the inner surface forms an angle of about 45 with the axis of revolution of the outer surface. This offset allows the positioning of the insert in equilibrium position of the acetabulum. Advantageously, the axis of revolution of the inner surface forms an angle with the axis of revolution of the outer surface. This offset makes it possible to delay the contact between the insert and the femoral stem. It also allows to generate larger contact areas and therefore more resistant to wear. The invention also relates to a cotyloid implant with dual mobility intended to be formed in an acetabulum of a patient, characterized in that it comprises: a cup, intended to be fixed on the iliac bone, in the cavity cotyloid of the patient, having a substantially hemispherical cavity, and an acetabular insert according to the invention, mounted in an articulated manner in the cavity of the cup. The invention further relates to a hip prosthesis, characterized in that it comprises: - an acetabular implant according to the invention, - a femoral stem comprising a neck and equipped with a femoral head fixed on the cervix at the level of its free end. In any case, the invention will be better understood from the description which follows, with reference to the appended schematic drawing showing, by way of non-limiting example, two embodiments of this insert. Figure 1 is a sectional view of an insert of the prior art along its axis of revolution; Figure 2 is a front partial sectional view of a prosthesis of the prior art in a first position on a patient; Figures 3 and 4 are views corresponding to Figure 2 of the prosthesis in a second and third consecutive position; Figure 5 is a sectional view of a cotyloid implant of the prior art in a first position of the insert; Figure 6 is a view corresponding to Figure 7 of the implant in equilibrium position; 7 and 8 are views respectively corresponding to FIGS. 5 and 6 of a first embodiment of an implant according to the invention. FIGS. 9 and 10 are views respectively corresponding to FIGS. 5 and 6 of a second embodiment of FIG. embodiment of an implant according to the invention. 11 is a partial frontal sectional view of a prosthesis according to the invention in a first abduction position, FIGS. 12 and 13 are views corresponding to FIG. 11, respectively of a second position of equilibrium and FIG. a third position of adduction of the prosthesis. Figure 1 shows an acetabular implant insert of the prior art. It has external surfaces 2 and internal 3 of substantially hemispherical shape, and whose centers are coincident. The inner surface 3 of the insert defines a cavity for articulately mounting a prosthetic femoral head 4, as shown in particular in FIG. 2. This figure shows a hip prosthesis in a first position corresponding to the standing position. of the patient, the axis of the femur (not shown) being substantially vertical. The prosthesis has a cup 5 of substantially hemispherical shape, fixed in an acetabulum cavity of the patient's pelvic bone. The cup 5 comprises a cavity intended for articulately mounting the insert 1, the femoral head 4 being mounted in the cavity of the latter. The prosthesis further comprises a femoral stem 7 attached to the femur 35 at the diaphyseal and metaphyseal portion of the stem. The stem comprises, at its proximal end, a neck 8 at the end of which is formed a frustoconical portion 9 allowing a press fitting into a complementary housing formed in the prosthetic femoral head 4. In this first position, the plane defined by the open end face of the insert, forms an angle of about 45 with the sagittal medial plane of the patient. As shown in FIG. 3, during the adduction movement, the insert 1 comes into contact with the neck 8 of the rod 7, the latter also coming into contact with the cup 5. The continuity of the adduction movement, possible thanks to the dual mobility, will not be detailed here. Figure 4 shows a third position following that shown in Figure 3, in which the patient is in a standing position. In this case, the femoral stem 7 is again located substantially in the vertical, while the insert 1 remains, in turn, in a position of equilibrium corresponding to that shown in Figure 3. The position of the insert 1 has been represented here for a displacement following an abduction movement. However, the insert 1 could also be moved following contact between the neck 8 of the rod 7 and the insert 1, during an abduction movement, or by friction of the prosthetic head 4 on the insert 1 during successive movements of the rod 7. Note that this type of prosthesis does not control the equilibrium position of the insert, the latter may tip in a position that may cause contact of the neck with the insert likely to cause premature wear, and therefore the destruction of the part avoiding dislocation. An insert 1 of the prior art for limiting this risk is represented with the corresponding cup 5 in FIG. 5, in a first position at 45 corresponding to the position of the insert 1 in FIG.

  The center of the outer surface 2, corresponding to the center of rotation of the insert 1 in the cup 5, is offset relative to the center of the inner surface 3, corresponding to the center of rotation of the prosthetic head 4 in the insert 1 , along the axis of revolution of the outer surface 2 towards the opening 9 of the insert 1.

  In this way, when the patient is in a standing position, a vertical force F appears, the latter being directed upwards from the center of the internal cavity of the insert 1. This force creates a rotational torque due to the lever of length d, the latter corresponding to the horizontal projection of the offset between the two centers. The pair thus created brings back, as indicated by the arrow, the insert 1 5 in horizontal equilibrium position, shown in FIG. 6. However, as previously seen, this position promotes the wear of the insert 1 due to the contact between it and the neck 8 of the rod 7 (not shown). FIG. 7 represents a first embodiment of the insert 10 1 according to the invention, mounted in a cup 5. The insert 1 according to the invention is made of polyethylene, the cup 5 being metallic, so as to obtain a low coefficient of friction between these two elements. The insert 1 has an offset of the center of the outer surface 2 relative to the center of the inner surface 3, both along the axis of revolution of the outer surface, but also along the axis perpendicular thereto. . The axis passing through each of the two centers forms an angle of 45 with respect to the axis of revolution of the outer surface 2. In this way, the torque generated by the presence of the force F 20 makes it possible to bring back the insert 1 in an equilibrium position in which the plane defined by the open end of the insert forms an angle of approximately 45 relative to the sagittal medial plane of the patient. This equilibrium position is particularly favorable since it makes it possible to avoid the dislocation of the hip as much as the contacts 25 between the insert 1 and the neck 8 of the stem 7, during the movements of the prosthesis. Another embodiment of the invention is shown in FIG. 9. In this second embodiment, the axis of revolution of the inner surface 3 forms an angle α with the axis of revolution of the outer surface 2. FIG. angle α can be between 1 and 20. It is preferably equal to 5. The centers are, as in the case of the first embodiment, located on an axis forming an angle of 45 with the axis of revolution of the outer surface 2.

Because of the arrangement of the surfaces, a thick zone 10 is formed at the region of the insert 1 in contact with the rod 7 during the abduction movement. In the same manner as above, a pair of forces 5 makes it possible to bring the insert 1 back to equilibrium position, as represented in FIG. 10. FIG. 11 represents a prosthesis according to the invention when the cup 5 and the neck 8 of the stem 7, during the abduction movement.

It should be noted that this figure does not represent the position of the prosthesis corresponding to the maximum amplitude. Indeed, the structure of the prosthesis offers a double mobility thereof, allowing a greater amplitude. This principle of dual mobility will not be detailed here, it being known per se.

As shown in FIG. 11, the neck 8 of the stem 7 has a posterior face 11, coming into contact with the cup 5 during the abduction movement, and an anterior face 12, coming into contact with the cup 5 during of the adduction movement, as shown in FIG. 13.

The neck 8 further comprises a cone 9 in known manner at its end fitted on the prosthetic head. Figure 12 shows the prosthesis in equilibrium position, when the patient is in a standing position. In this position, the centers of the inner 3 and outer 2 surfaces of the insert are aligned on the vertical direction axis C-C of the force. The insert 1 is then in equilibrium position in the acetabular cavity. FIG. 13 represents the prosthesis during the contact between the neck 8 of the rod 7, more precisely of its anterior face 12, and the insert 1, during the adduction movement.

As is obvious, the invention is not limited to the embodiments of this system, described above by way of example, but it embraces all variants. Thus, in particular, the fixation of the femoral head on the stem could be carried out differently or that the materials of the insert and the cup could be different.

Claims (5)

  1. Insert (1) for a dual mobility acetabular implant comprising: an outer surface (2) of substantially hemispherical shape for articulately mounting the insert (1) in a cup (5) fixed in an acetabulum cavity of a patient, - an inner surface (3) of substantially hemispherical shape delimiting a cavity for articulately mounting a prosthetic femoral head (4), the center of the outer surface (2) being offset from the center of the inner surface (3) along the axis of revolution of the outer surface (2) towards the opening (9) of the insert (1), characterized in that the center of the outer surface ( 2) is further offset from the center of the inner surface (3) along an axis perpendicular to the axis of revolution of the outer surface (2).   2. Insert according to claim 1, characterized in that the axis passing through the center of the outer surface (2) and that of the inner surface (3) forms an angle of approximately 45 with the axis of revolution of the outer surface (2). 20   3. Insert according to one of claims 1 to 2 characterized in that the axis of revolution of the inner surface (3) forms an angle (a) with the axis of revolution of the outer surface (2).   4. Cotyloid implant with dual mobility intended to be formed in an acetabular cavity of a patient, characterized in that it comprises: a cup (5), intended to be fixed on the iliac bone (6), in the acetabulum of the patient, having a substantially hemispherical cavity, and an acetabular insert (1) according to one of claims 1 to 3, mounted in an articulated manner in the cavity of the cup (5). 30   5. Hip prosthesis, characterized in that it comprises: - an acetabular implant according to claim 4, - a femoral stem (7) comprising a neck (8) and equipped with a femoral head (4) fixed on the neck (8) at its free end.