FR2784291A1 - Intervertebral disc prosthesis has connecting pieces with through cells between plates and core - Google Patents

Abstract

The prosthesis, comprising two plates (6), a core (38) and connecting pieces (18), e.g. of titanium, between them that have through cells (30) lying in straight or oblique parallel lines. The cells can be circular in section or hexagonal, forming a honeycomb structure. Each connecting piece has a truncated conical surface (22) in contact with the core, which has an outer surface (37) in contact with the patient's body and a maximum dimension in contact with each plate.

Description

 The invention relates to intervertebral disc prostheses.

 Document EP-0 317 972 discloses an intervertebral disc prosthesis comprising two rigid plates, a core of deformable synthetic polymer material and two connecting members connecting the core to the respective plates, in the form of a mushroom flaring out. from the associated plateau towards the other plateau. This shape ensures good anchoring of the core to the plates. However, the compressive, bending and torsional stresses undergone by the core being very high, it is necessary to further improve the quality of the anchoring of the core to the plates.

 An object of the invention is to provide a disc prosthesis ensuring better anchoring of the core to the plates.

 In order to achieve this goal, there is provided according to the invention, an intervertebral disc prosthesis, comprising two plates, a core and connecting members connected to the respective plates and to the core, in which the connecting members have cells profiled.

 Thus, the profiled cells increase the contact surface between each connecting member and the core, and offer numerous facets oriented differently with respect to each other. These two factors improve the anchoring of the core to each connecting member, regardless of the general shape of the latter.

 Advantageously, each cell is profiled along a rectilinear axis.

 Thus, the cells are easy to produce.

 Advantageously, the axes of the cells are radial to an axis of the prosthesis extending from one to the other of the plates.

 Advantageously, the axes of the cells are parallel to each other.

 Advantageously, the axes of the cells are parallel to an axis of the prosthesis extending from one to the other of the plates.

 Advantageously, each cell has a closed profile in a plane transverse to an axis of the cell.

 Advantageously, the profile is circular.

 Advantageously, the cells form a honeycomb structure.

 Thus, this structure makes the connecting members particularly robust without requiring a large mass of material, the cells may have extremely thin walls.

 Advantageously, the connecting members are attached to the respective plates.

 Thus, the plates and the connecting members, produced separately, are easy and less expensive to produce.

 Alternatively, the connecting members are in one piece with the respective plates.

 Advantageously, each connecting member has a width, perpendicular to an axis of the prosthesis extending from one to the other of the plates, decreasing from the plate to which it is connected, in the direction of the other plate up to 'at one end of the connecting member.

 Thus, the shape of each connecting member offers a large contact surface with the core for a robust anchoring, while allowing a large range of relative movement between the plates, in particular in bending without requiring a large distance between the plates.

 Advantageously, each connecting member has a frustoconical external face in contact with the core.

On the other hand, it is known that in an intervertebral disc prosthesis such as that of document EP-0 317 972, the shape of the core of the prosthesis being cylindrical, its ability to support and hold in the vertebral bodies cannot be satisfactory. than in static load. In fact, as soon as it is loaded, the material used for the core of the prosthesis, due to its cylindrical shape, flows towards the outside of the two vertebral bodies. Consequently, this behavior can lead to the following risks:
compression of the roots;
-compression of the vertebral canal if the creep of the
material is too important;
- early degradation of the material;
- risk of implant loosening; and
- no possibility of rotation.

 In order to overcome this drawback, it is provided according to a preferred embodiment of the invention that the core has an external face capable of being in contact with the patient's body, the core having a width, perpendicular to an axis of the prosthesis extending from one to the other of the plates, decreasing from each plate in the direction of the other plate, the width being maximum at the level of each plate.

 Thus, at least under a moderate load, the core does not flow outwards from the plates. This tendency to creep will be all the more reduced, or even totally eliminated, as the width of the core will decrease rapidly towards its middle portion.

 Advantageously, one of the plates has an external face opposite to an external face of the other plate and inclined with respect to the latter.

 Other characteristics and advantages of the invention will appear in the following description of several preferred embodiments given by way of nonlimiting examples in the appended drawings: FIG. 1 is a partial side view of a spine showing 1 ' location of the prosthesis according to the invention; FIG. 2 is a view in axial section of a disc prosthesis according to a first embodiment of the invention; FIG. 3 is a partial view in cross section along the plane III-III of one of the connecting members in FIG. 2; FIGS. 4 and 5 are views in axial section of the second and third embodiments of the connecting members; FIG. 6 is a partial perspective view of a fourth embodiment of the connecting members; and FIG. 7 is a simplified view in axial section of an alternative embodiment.

 With reference to FIG. 1, the intervertebral disc prosthesis 2 according to the invention is intended to be received between two vertebral plates of two vertebrae 4 of a spine.

With reference to FIGS. 2 and 3, the prosthesis 2 comprises two upper and lower plates 6, of flat shape, with upper 8 and lower faces 10. The faces of each plate may be parallel to one another. Alternatively, the two faces of each tray may be slightly inclined one to the other, as illustrated in an exaggerated manner in FIG. 7. Each tray 6 has in plan a general shape of a bean, known in itself. Each tray is extended beyond its outer, upper 8 for the upper and lower 10 for the lower tray, by two tabs 12 extending to the edges 36 of the tray and having an orifice capable of receiving a screw 14 intended to be anchored in the associated vertebra 4 in a manner known per se. The prosthesis is thus arranged so that the external face of each plate is in surface contact with the vertebral plate of the associated vertebra, with, in addition, interposition between the vertebra and the prosthesis of a layer 16 of a coating.
PAH (hydroxyapatite) known per se, promoting bone growth and further improving anchoring. The two plates 6 generally extend parallel to one another, at a distance from each other and with their edges 36 in coincidence. They define an axis 19 of the prosthesis, extending from one to the other of the plates and passing through their center.

 The prosthesis 2 comprises two connecting members 18 having in this case a flat face 20 perpendicular to the axis 19 and a conical face 22 with rounded tip 24, of axis 19, and intended to be in contact with the core 38.

 Thus, each connecting member has a width 1 measured perpendicular to the axis 19 decreasing from the associated plate 6, to its rounded tip 24 in the direction of the other plate.

 Each connecting member 18 is attached to the plate 6 associated by means of a screw 26 introduced by the external face of the plate in a central orifice thereof and extending along the axis 19 in the connecting member 18 .

 The prosthesis comprises, for each connecting member 18 at least one pin 28, in this case two per connecting member, occupying a position distant from the axis 19 and each extending in both the plate 6 and 1 ' associated connecting member 18, to prevent their relative rotation about the axis 19.

 Each connecting member 18 has cells 30 each profiled along a rectilinear axis 32. The axes 32 are here parallel to each other and also parallel to the axis 19. The cells 30 here have a closed profile in cross section to the axis 32. The profile in this case is circular. The cells 30 open at their two axial ends respectively on the flat face 20 and the conical face 22 of the connecting member.

The connecting members 18 are arranged with their points 24 facing and at a distance from each other.

 The prosthesis comprises a core 38 or intermediate body made of a deformable biocompatible material, for example based on silicone and known per se. The core 38 extends continuously from the internal lower face 10 of the upper plate 6 to the internal upper face 8 of the lower plate 6. The core 38 extends in contact with the conical face 22 of each connecting member 18 and inside each cell 30 which it completely fills. The core 38 extends from one to the other of the peripheral edges 36 of the plates. It has an external face 37 capable of being in contact with the patient's body and thus not covered by another element of the prosthesis.

 The core 38 has a width L, measured perpendicular to the axis 19, going from each plate directly from the other plate to a middle portion 39 of the core extending between the two connecting members 18. The width L is maximum at the level of each plate 6. The external face 37 of the core here has a concave shape, curve in radial section, substantially symmetrical of revolution around the axis 19 and giving the core a diabolo shape.

 This prosthesis can be compressed along the axis 19, flexed around any axis perpendicular to the axis 19, or twisted around this axis 19 without threatening the anchoring of the core 38 to the connecting members 18 and without creep of the core outside the perimeter of the plates 6. It can absorb shocks and return to its original position and shape without deformation. The plate 6 and the connecting members 18 can be made of titanium or of a biocompatible titanium alloy. The lower face 10 of the upper plate and the upper face 8 of the lower plate will preferably be parallel to each other. In this case, the two faces of each plate may have the aforementioned relative inclination, the plates being oriented so that this inclination is doubled between the upper face 8 of the upper plate and the lower face 10 of the lower plate, as is see in FIG. 7. Alternatively, the two faces of each plate may be parallel to each other. These different possibilities depend on the stage of the instrumented spine, the state of the vertebral endplates adjacent to the prosthesis and the patient's pathology.

 In the embodiment of FIG. 4, the cells 30 are profiled along rectilinear axes 32 radial with respect to the axis 19. The cells extend in the direction of the axis 19 from the conical face 22 to the flat face 20 of the connecting member. The inclination of the axes 32 of the cells with respect to the axis 19 can be arbitrary or perpendicular to this axis.

 In the embodiment of FIG. 5, the rectilinear axes 32 of the profiled cells are parallel to each other and form any non-zero angle with respect to the axis 19.

 In the embodiment of Figure 6, the cells 30 have a hexagonal transverse profile and are arranged to form a honeycomb structure.

 Provision may be made for the connecting members 18, instead of being attached to the plates 6, to be formed in one piece with them.

 The screw connection of each connecting member 18 to the associated plate 6 may be replaced by another fixing means such as clipping.

 The external face 37 of the core may have a different shape and for example may have two frustoconical faces whose small sections alone are in mutual contact or are separated by a cylindrical middle part.

 The peripheral edge of each connecting member 18 can extend at a distance and inside the peripheral edge 36 of the associated plate 6 as in FIG. 2, or else coincide with this edge, the plates 6, the connecting members 18 and the core 38 then having the same maximum width.

 The face 22 of each connecting member may have a shape other than that illustrated, for example a convex spherical shape.

 The characteristics relating to the shape of the external face 37 of the core and to its position relative to the plates 6 may be implemented independently of the existence of the connecting members 18 and of the cells passing through them.

 The same applies to the characteristics concerning the shape of the face of the connecting members 18 in contact with the core 38.

Claims (14)

 1. Intervertebral disc prosthesis comprising two plates (6), a core (38) and connecting members (18) connected to the respective plates and to the core, characterized in that the connecting members (18) have profiled cells ( 30).  2. Prosthesis according to claim 1, characterized in that each socket is profiled along a rectilinear axis (32).  3. Prosthesis according to claim 2, characterized in that the axes (32) of the cells (30) are at an axis (19) of the prosthesis extending from one to the other of the plates (6).  4. Prosthesis according to claim 2, characterized in that the axes (32) of the cells (30) are mutually parallel.  5. Prosthesis according to any one of claims 2 or 4, characterized in that the axes (32) of the cells (30) are parallel to an axis (19) of the prosthesis extending from one to the other trays (6).  6. Prosthesis according to any one of claims 1 to 5, characterized in that each socket (30) has a closed profile in a plane transverse to an axis (32) of the socket.  7. Prosthesis according to claim 6, characterized in that the profile is circular.  8. Prosthesis according to any one of claims 1 to 7, characterized in that the cells (30) form a honeycomb structure.  9. Prosthesis according to any one of claims 1 to 8, characterized in that the connecting members (18) are attached to the respective plates (6).  10. Prosthesis according to any one of claims 1 to 8, characterized in that the connecting members (18) are in one piece with the respective plates (6).  11. Prosthesis according to any one of claims 1 to 10, characterized in that each connecting member (18) has a width, perpendicular to an axis (19) of the prosthesis extending from one to the other plates (6), decreasing from the plate to which it is connected, towards the other plate to one end of the connecting member (18).  12. Prosthesis according to any one of claims 1 to 11, characterized in that each connecting member (18) has a frustoconical face (22) in contact with the core (38).  13. Prosthesis according to any one of claims 1 to 12, characterized in that the core (38) has an external face (37) capable of being in contact with the patient's body, the core having a width, perpendicular to an axis (19) of the prosthesis extending from one to the other of the plates (6), decreasing from each plate in the direction of the other plate, the width being maximum at the level of each plate (6 ).  14. Prosthesis according to any one of claims 1 to 13, characterized in that one of the plates (6) has an external face (8) opposite to an external face (10) of the other plate (6) and inclined to it.