FR2951930A1 - Disc prosthesis for cervical vertebrae, to replace intervertebral disc, has cap and cup encircled peripherally by edges whose inclination angles are such that edges constitute stops to limit articulation clearance when cap is engaged in cup - Google Patents

Abstract

The prosthesis (1) has plates (2, 3) fixed on two successive vertebrae. The plates include inner faces respectively comprising a spherical cap (22) and a spherical cup (32). The cap and the cup are encircled peripherally by respective flat edges (23, 33) inclined from the cap and cup towards peripheral edges of the inner faces along certain angles with respect to general planes of the plates. The inclination angles of the flat edges are such that the flat edges constitute stops to limit articulation clearance when the spherical cap is engaged in the cup. Each of the plates includes anchoring unit made of metal.

Description

The present invention relates to a disc prosthesis for cervical vertebrae, intended to be implanted in place of an intervertebral disc. An intervertebral disc consists of a ring of fibrous cartilage interposed between two vertebrae, which contributes to the shock absorption and allows the movements of the spine. It can happen that a vertebral disc undergoes degradations that can lead to pain. To overcome this disadvantage, the disk is generally replaced by a prosthetic disc. Prosthetic implants must have different characteristics depending on the region of the spine considered. In certain regions, lumbar or dorsal, it is possible to remove a degraded disc and achieve the joining of the two vertebrae through arthrodesis, which has the disadvantage of a loss of mobility. On the other hand, in the cervical region, it is preferable to maintain a certain mobility, and articulated disc prostheses are thus used.

These prostheses generally comprise on the one hand two trays, intended to be fixed on the two successive vertebrae whose disk must be replaced, each comprising an outer face intended to be secured to the vertebral body of one of said vertebrae, and an inner face. extending facing the inner face of the other plate, and secondly a hinge means interposed between said inner faces, comprising a spherical cap adapted adapted to cooperatively pivotally congruent with a spherical cup.

According to the various embodiments, the hinge means may consist of one or more inserts, independent of the trays to which they are adaptable, and thus be in the form of inserts as is for example the case of the prostheses described in the documents FR 2 805 733 and FR 2 824 261.

These prostheses have certain drawbacks, in particular because the jointing means can move angularly with respect to the main axis, especially when these articulation means are also designed capable of a trim correction, by presenting asymmetrical profiles. . In addition, such a prosthesis, in the particular case of the cervical region, must allow articulation movements with a limited deflection, all being of a reduced total thickness. However, none of the currently known prostheses does not achieve all these objectives. The present invention aims to provide a disc prosthesis for cervical vertebrae to remedy this deficiency. The disc prosthesis for cervical vertebrae, intended to be implanted as a replacement for an intervertebral disc according to the invention, comprises on the one hand two trays intended to be fixed on the two successive vertebrae of which the disc must be replaced, each comprising a outer face intended to be secured to the vertebral body of one of said vertebrae, and an inner face extending facing the inner face of the other plate, and on the other hand a hinge means interposed between said inner faces, comprising a spherical cap adapted adapted to cooperate in pivoting congruently with a spherical cup, the disk prosthesis is essentially characterized in that the inner face of one of the trays comprises said spherical cap which is peripherally bordered by a flat rim inclined at a certain angle, with respect to the general plane of said plate, from said cap to the edge peripheral of said inner face, while the inner face of the other plate comprises said cup which is peripherally bordered by a plane rim inclined at an angle, relative to the general plane of said plate, from said cup to the peripheral edge of said inner face, in that the height of said spherical cap is less than the depth of said cup, and in that said angles are such that when the two plates are assembled to each other, that is to say when said spherical cap is engaged in said cup, said planar flanges constitute abutments which limit the articulation deflection.

According to an additional feature of the disk prosthesis according to the invention, in equilibrium, that is to say when the two plates are parallel to each other, the two flat edges make between them angle between 6 and 10 °, preferably 8 °.

According to an additional characteristic of the disk prosthesis according to the invention, the angle of inclination of the plane rim of a plate is different from that of the other plate. According to another additional characteristic of the disk prosthesis according to the invention, the angle of inclination of the plane edge of a plate is equal to that of the other plate. According to another additional feature of the disc prosthesis according to the invention, the outer face of each of the trays has anchoring means in the bone material.

According to another additional characteristic of the disk prosthesis according to the invention, the outer face of each of the plates comprises, at least peripherally on the lateral edges, teeth. According to another additional feature of the disc prosthesis according to the invention, the outer face of each of the trays comprises, in its central region, peaks. According to another additional feature of the disk prosthesis according to the invention, the outer face of each of the plates comprises in the transverse direction of the profile ribs sawtooth. According to another additional feature of the disk prosthesis according to the invention, the plates, at least their inner part which comprises for one the spherical cap and the other for the spherical cup, are made of "PEEK".

According to another additional feature of the disk prosthesis according to the invention, the anchoring means are made of metal. The advantages and characteristics of the disk prosthesis according to the invention will become more clearly apparent from the description which follows and which refers to the appended drawing, which represents several non-limiting embodiments thereof. In the accompanying drawing: - Figure 1 shows a schematic perspective view of a prior disc prosthesis for cervical vertebrae according to the invention. FIG. 2 represents a schematic view in posterior perspective of the same disk prosthesis for cervical vertebrae. Figure 3 is a diagrammatic elevational view of the same disc prosthesis for cervical vertebrae. FIG. 4 represents a diagrammatic sectional view along the axis XX 'of FIG. 3. FIG. 5 is a schematic perspective and exploded view of a variant of the disc prosthesis for cervical vertebrae. With reference to FIGS. 1, 2, 3 and 4, it can be seen that a disc prosthesis 1 for cervical vertebrae according to the invention comprises two plates 2 and 3, generally shaped like that of a natural disc, c that is to say, convex on the anterior side, and slightly concave on the posterior side. The plate 2 has an outer face 20 intended to be secured to the vertebral body of one of the two vertebrae to be equipped, in this case the upper vertebra, and an inner face 21 comprising in its central region a spherical cap 22, visible in FIG. 4. The spherical cap 22 is peripherally bordered by a plane rim 23 inclined at an angle to the general plane of the plate 2, from the spherical cap 22 towards the peripheral edge 24, to form a frustoconical segment of which protrudes the spherical cap 22.

The plate 3 comprises an outer face 30 intended to be secured to the vertebral body of one of the two vertebrae to be equipped, in this case the lower vertebra, and an inner face 31 comprising in its central region a spherical cup 32, visible on FIG. 4, of radius equal to that of the spherical cap 22, and of depth less than the height of the spherical cap 22. The spherical cup 32 is bordered peripherally by a plane rim 33 inclined at an angle to the plane general of the plate 3, from the spherical cup 32 to the peripheral edge 34, to form a frustoconical segment at the top of which is formed the spherical cup 32. When the two plates 2 and 3 are assembled, that is to say when the spherical cap 22 is engaged in the spherical cup 32, the difference in height of the spherical cap 22 with the depth of the spherical cup 32 allows pivoting in all the directions of the plate 2 relative to the plate 3, while because of the taper of the plane flanges 23 and 33 these constitute stops which ensure the limits of this pivoting. Note that the radius of curvature of the spherical cap 22 and the cup 32 is relatively large, it is thus substantially equivalent to the width, in the anteroposterior direction, of the plates 2 and 3.

When the two plates 2 and 3 are in equilibrium position, that is to say when they are parallel to each other, the two plane flanges 23 and 33 form between them an angle α which in Figures 3 and 4 is 8 °. It will be noted that with regard to the disk prosthesis 1 shown in the figures, the angle α is obtained by adding the slope angles of the plane flanges 23 and 33 which are equal, therefore 4 °, knowing that it is perfectly possible to envisage trays 22 and 3 where these angles would not be equal while maintaining a total difference of 8 °.

Note also that it may be expected that the prosthesis 1 may include regions where the angle is different, it is possible to provide a lower angle in the posterior region. The outer faces 20 and 30 comprise anchoring means which consist of ribs, respectively 25 and 35, of serrated profile directed towards the anterior side, so that the prosthesis 1 can be introduced in the anteroposterior direction, without being able to escape in the opposite direction. The anchoring means 25 and 35 also make it possible to immobilize the plates 2 and 3 on their respective vertebral bodies, in order to allow axial pivoting of one with respect to the other. Note the presence of the anterior side of the plates 2 and 3, gripping impressions, respectively 26 and 36, which allow to maintain assembled and indexed the two plates 2 and 3, during the establishment of the prosthesis 1. L association of the spherical cap 22 and the spherical cup which have a relatively large radius of curvature, and flanges 23 and 33 which allow limited clearance, allows controlled mobility of the vertebrae equipped, relative to each other , mobility close to natural mobility. In the embodiment shown in these figures 1, 2, 3 and 4, each of the trays 2 and 3 is obtained by assembling two parts, namely on the one hand an inner part, respectively 27 and 37, made of "PEEK" , and essentially comprising the body of the plate, 2 and 3, and the spherical cap 22 for one and the spherical cup 32 for the other, and on the other hand an external part, respectively 28 and 38, made of metal, preferably titanium, and comprising the outer face, 20 and 30, and its anchoring means 25 and 35. The assembly is carried out mechanically, for example by interlocking or sliding, through concordant impressions, tail dovetail for example. Referring now to Figure 5, we can see a variant of the disc prosthesis, where most of the trays 2 and 3 is made of "PEEK", while the anchoring in the vertebral bodies is ensured, besides by peripheral teeth, respectively 29 and 39, by means of metal peaks, respectively 25 'and 35', which project from the external faces, respectively 20 and 30.5

Claims (10)

CLAIMS1) Disc prosthesis (1) for cervical vertebrae, intended to be implanted as a replacement for an intervertebral disc, comprising on the one hand two plates (2, 3) intended to be fixed on the two successive vertebrae whose replacement must be replaced disc, each having an outer face (20, 30) to be secured to the vertebral body of one of said vertebrae, and an inner face (21, 31) extending opposite the inner face of the other tray, and on the other hand a hinge means interposed between said inner faces (21, 31), comprising a spherical cap (22) provided adapted to cooperate in pivoting congruently with a spherical cup (32), characterized in that the face interior (21) of one of the plates (2, 3) comprises said spherical cap (22) which is peripherally bordered by a plane flange (23) inclined at an angle to the general plane of said plate (2), dep uis said cap (22) towards the peripheral edge (24) of said inner face, while the inner face (31) of the other plate (3) comprises said cup (32) which is peripherally bordered by a flat flange ( 33) inclined at an angle to the general plane of said plate (3), from said cup (32) to the peripheral edge (34) of said inner face (31), in that the height of said spherical cap (22) ) is less than the depth of said cup (32), and in that said angles are such that when the two plates (2, 3) are assembled to each other, that is to say when said spherical cap (22) is engaged in said cup (32), said flat flanges (23, 33) constitute stops which limit the articulation travel. 2) disc prosthesis (1) according to claim 1, characterized in that, at equilibrium, that is to say when the two plates (2, 3) are parallel to each other, the two plane flanges (23, 33) are between them an angle (a) between 6 and 10 °, preferably 8 °. 3) disc prosthesis (1) according to claim 1 or claim 2, characterized in that the angle of inclination of the plane flange (23, 33) of a plate (2, 3) is different from that of the other tray (2, 3). 4) disk prosthesis according to claim 1 or claim 2, characterized in that the angle of inclination of the plane flange (23, 33) of a plate (2, 3) is equal to that of the other plate (2, 3). 5) disc prosthesis (1) according to any one of the preceding claims, characterized in that the outer face (20, 30) of each of the trays (2, 3) has means (25, 35; 25 ', 35). anchoring in the bone material. 6) disk prosthesis (1) according to any one of the preceding claims, characterized in that the outer face (20, 30) of each of the plates (2, 3) comprises, at least peripherally on the lateral edges, teeth (28, 38). 7) disc prosthesis (1) according to any one of the preceding claims, characterized in that the outer face (20, 330) of each of the trays (2, 3) comprises, in its central region, peaks (25 '). , 35 '). 8) disc prosthesis (1) according to any one of claims 1 to 5, characterized in that the outer face (20, 30) of each of the plates (2, 3) comprises in the transverse direction ribs (25, 35) in sawtooth profile. 9) disk prosthesis (1) according to any one of the preceding claims, characterized in that the plates (2, 3), at least their inner portion (26, 36) which comprises for one the spherical cap (22). ) and for the other the spherical cup (32), are made of "PEEK". 10) disk prosthesis (1) according to any one of the preceding claims, characterized in that the anchoring means (25, 35; 25 ', 35') are made of metal.