FR2799116A1 - Intervertebral implant comprises pure or alloyed pyrocarbon and is placed between two vertebrae and interacts by means of friction with at least one of them - Google Patents

Abstract

The implant comprises friction-resistant structure of pyrocarbon chip permitting flexing, extending and rotation movements . The implant (100) is positioned between two vertebrae (1, 2), in such way as to interact with at least one of them. It consists of base (110) comprising part (111) fixing the implant to lower vertebra (1) and plate (112) supporting a chip (120) made of pyrocarbon and interacting by friction with upper vertebra (2). The plate (112) is provided with external collar (112d) surrounding the chip (120). The plate (112) comprises a hollow (112a) of a shape complementary to that of chip (120), which is forced into this hollow to form one single piece with the base (110). The hollow (112a) has central opening (112b), engaging anchoring bit of chip (120). The implant has polished convex face (121) in contact with vertebral plate (2a) of upper vertebra (2). The fixing part (111) of base (110) is provided with two through-orifices for mounting two anchoring bolts in the body (1b) of lower vertebra (1). The baseplate (112) has, on its face turned toward the lower vertebra (1), projections anchoring it to the vertebral plate (1a) of lower vertebra (1). The plate (112) and fixing part (111) of base (110) are oriented at angle approximate 100 deg to each other and are joined by rounded joining section (110a). The base (110) is preferably made of titanium alloy and the faces of implant in contact with vertebrae have preferably surface coating of hydroxyapatite type, or of porous titanium, or of other ostheo-conductor or conductor material.

Description

The present invention relates to an intervertebral implant adapted to be interposed between two vertebrae.

The invention is advantageously used to treat various pathologies of the cervical intervertebral disk, such as disc herniations, whether or not related to disc degeneration, and disc degeneration leading to problems with spinal statics.

The intervertebral disc constitutes one of the two articulations located between two vertebral bodies of the spine in association with the unco- vertebral articulations. The set of intervertebral disks represents about 22% of the vertebral complex at the cervical level. The role of the intervertebral disc is to allow greater mobility between each vertebra, to evenly distribute the forces on each vertebral body but also to absorb a part.

The cervical intervertebral disc cooperates with both upper and lower vertebral bodies.

There are two types of cervical disc herniations, soft disc herniation and hard disc herniation.

 The soft disc hernia corresponds to a posterolateral disc protrusion. It is related to disc degeneration due to a decrease in the degree of hydration of the intervertebral disc.

 The hard disc hernia corresponds to an excrescence which also causes root compression.

In addition, the degeneration of the intervertebral disk can cause problems of spinal immobility. More particularly, the loss of disc height can cause a loss of cervical lordosis or a reversal of curvature.

Treatments for herniated discs, especially cervical disc herniations, consist of medical treatments or surgical treatments.

When the medical treatment is ineffective, it may be necessary to perform a surgical removal of the disc.

When it comes to a soft disc herniation, different types of surgical procedures can be performed. The posterior surgical procedure makes it possible to extract the fragment of the excluded disc. The anterior surgical procedure allows a direct approach to the damaged intervertebral disk and thus a complete excision of it with or without the addition of a bone graft allowing to find a normal height of intervertebral disk but completely eliminating the possibilities of mobility local spine.

The installation of an intervertebral implant as proposed the present invention may advantageously allow to restore the intervertebral space provided previously by the healthy disc and restore the relative movement between the two contiguous vertebrae.

More particularly, according to the invention, the intervertebral implant is made of pure or alloyed pyrocarbon and it cooperates by friction with at least one of said vertebrae.

Thus, the relative movement of the two vertebrae is ensured by the friction vertebral plateau of the vertebra on the implant made of pyrocarbon, a material extremely resistant to friction and whose mechanical properties are similar to those of the bone. The relative flexibility of the pyrocarbon vis-à-vis the cartilage vertebral plateau of said vertebra is advantageous vis-à-vis the cartilage wear.

Pyrocarbon is an artificial carbon obtained cracked with hydrocarbons around 1450 C. It has the advantage of being hemocompatible, resistant, and to present after polishing a particularly smooth surface and resistant to friction and which does not produce premature wear of the cartilage cotyloidal opposite the implant.

It is therefore particularly advantageous to constitute the friction surface of such an acetabular implant.

According to a preferred embodiment of the invention, the intervertebral implant comprises a base comprising a fastening lug to a lower vertebra and a plate supporting a pyrolytic pellet cooperating by friction with an upper vertebra, said plate being provided with a outer flange surrounding said pellet. The intervertebral space is restored by the intervertebral implant according to the invention, the total height of the assembly of the base and the pellet of pyrocarbon substantially corresponds to the intervertebral height to be reinstated.

The shape and the friction-resistant structure of the pyrolytic pellet notably allow the upper vertebra the following movements: bending, extension, rotation and the combined movements of the three aforementioned movements.

The material used for the pellet of the intervertebral implant according to the invention is a biomaterial which does not cause premature wear of the vertebral plateau of the upper vertebra and which does not wear too quickly.

In addition, the outer flange is an elliptical base that advantageously avoids lateral bone growth.

The following description with reference to the accompanying drawings, given by way of non-limiting examples, will make it clear what the invention consists of and how it can be achieved.

In the accompanying drawings - FIG. 1 is a diagrammatic perspective view of three quarters of the intervertebral implant according to the invention, before assembly of the pellet and the base, FIG. 2 is a diagrammatic perspective view from above of embodiment of the intervertebral implant according to the invention after assembly of the pellet and the base, - Figure 3 is a bottom view of the vertebral implant of Figure 2, and - Figures 4a and 4b show schematically seen from above and from below, a preferred embodiment of the vertebral implant according to the invention.

FIGS. 1 to 4b show a unipolar intervertebral implant 100 which comprises a base 110 comprising a fixing lug 111 to a lower vertebra 1 and a plate 112 supporting a pellet 120 made of pyrocarbon and cooperating by friction with an upper vertebra 2.

The plate 112 of the base 110 has a housing 112a of a shape generally complementary to that of the pellet 120 and wherein said pellet is force-fitted to form with the base 110 a single piece.

The assembly of the base and the pellet is advantageously made in the factory to form a single piece easily used by the surgeon.

The housing 112a of the plate 112 of the base comprises a central orifice 112b in which is engaged an anchor pin (not shown) of the patch 120. According to a variant not shown, the orifice may be eccentric. This eccentricity of the orifice of the housing of the plate makes it possible to gain space in the implant.

The pellet 120 made of pure or alloyed pyrocarbon has a dimension corresponding to the dimensions of the vertebral plateau of the upper vertebra. It has for this purpose a diameter of the order of 15 mm preferably between 13 and 16 mm. The pellet 120 has a polished domed face 121 which when the pellet is mounted in the housing 112a of the plate 112 of the base 110, protrudes slightly outwardly of said plate. This polished convex face 121 comes into contact with vertebral plateau 2a of upper vertebra 2.

The bracket. 111 of the base 110 is provided with two orifices 111a, 111b passing through for the mounting of two anchoring screws (not shown) in the vertebral body 1b of the lower vertebra 1.

In addition, advantageously, the plate 112 of the base 110 includes on the face 112c facing the lower vertebra 1 of the protrusions in commas 113 for anchoring in the vertebral plate 1a of the lower vertebra 1. These projections in comma allow to strengthen the primary fixation of the intervertebral implant to the lower vertebra 1.

According to the variant shown in Figures 4a and 4b, the plate 112 of the base 110 does not include projections on its lower surface.

The plate 112 and the bracket 111 of the base 110 are oriented relative to each other at about 100 degrees and are connected by rounded connection portion 110a.

The rounded connection portion 110a is an integral part of the bracket and has a radius of curvature best adapted to the morphology of the vertebra concerned.

The rounded connection portion 110a extends between the plate and the central portion of the upper edge of the bracket 111.

Advantageously, the faces of the intervertebral implant 100 shown in the figures, in contact with the vertebrae may be covered with a coating of hydroxyapatite, porous titanium or any other osteoconductive or conductive coating. This makes it possible to obtain good osseointegration of the implant in the patient's spine. It can be provided alternatively that only one face of the implant in contact with the vertebra is covered with such a coating. In this case, it is preferable that this face is the face of the plate of the base coming into contact with the vertebral plate of the lower vertebra.

The base 110 is advantageously made of titanium alloy which is a biocompatible material with a long service life.

According to a variant shown in Figure 4a, it is expected that the plate <B> 11 </ B> is provided with an outer flange 112d surrounding the pellet 120. This outer flange advantageously avoids lateral bone growth.

total height of the intervertebral implant is of the order of 4 or 6 mm. Such an implant can restore the intervertebral height available when the intervertebral disc is healthy.

Fixing screws are of the standard type for a cervical plate, for example spongy diameter 4 and self-tapping.

The intervertebral implant 100 according to the invention is set up as follows.

After having approached the spine of a patient by the antero-lateral route, the surgeon proceeds to the excision of the damaged intervertebral disc. He practices a revitalizing vertebral plateau of the lower vertebra, where the intervertebral implant will be supported by means of the lower face of the plate supporting the friction pad. The surgeon revives the entire vertebral plateau concerned but respects the apophyses unciform. It proceeds as a result of the establishment of the intervertebral implant according to the invention by previously choosing the most appropriate implant size, that is to say the size of the base bearing friction pad and the height of the implant. He permanently fixes the implant in the lower vertebra using the two fixation screws. When the implant is fixed, the polished convex face of the pyrolytic pellet is in contact with the vertebral plateau of the upper vertebra and cooperates with it by friction.

relative movement of the two vertebrae is then ensured by the friction of the vertebral plateau of the upper vertebra on the polished convex face of the implant pyrolytic pellet, a material extremely resistant to friction and whose mechanical properties are close to those of the bone. The intervertebral space is ensured by the total height of the implant. The limitations of amplitude movement of the vertebrae are not ensured by the implant but the capsulo-ligamentary system of the vertebrae which is preserved to the maximum, in particular the peripheral fibers of the implant.

 The present invention is not limited to the embodiment described, but those skilled in the art will be able to make any variant within its spirit.

Claims (1)

<U> CLAIMS </ U> 9. Invertebral implant (100) interposed between two vertebrae (1,2), characterized in that it is made of pure or alloyed pyrocarbon and in that it cooperates by friction with at least one of said vertebrae. Intervertebral implant (100) according to claim 1, characterized in that it comprises a base (110) comprising a bracket (111) to a lower vertebra (1) and a plate (112) supporting a patch (1 made of pyrocarbon cooperating by friction with an upper vertebra (2), said plate 12) being provided with an outer flange (112d) surrounding said wafer (120). Implant according to claim 2, characterized in that said plate (112) of the base (110) comprises a housing (112a) of complementary shape to that of said wafer (120) and in which the latter is forcibly mounted to form with the base (110) one piece. Implant according to claim 3, characterized in that the housing (112a) of said plate (112) comprises a central orifice (112b) in which is engaged an anchor stud carried by said wafer (120). Implant according to one of claims 1 to 4, characterized in that it has a polished convex face (121) in contact with the vertebral plate (2a) of the upper vertebra (2). Implant according to one of claims 2 to 5, characterized in that the bracket (111) of the base (110) is provided with two through holes for mounting two anchor screws in the vertebral body (1b ) the lower vertebra (1). Implant according to one of claims 2 to 6, characterized in that the plate 12) of the base comprises on its face facing the lower vertebra (1) comma projections (113) for anchoring in the vertebral plate (1a) of said lower vertebra (1). Implant according to one of claims 2 to 7, characterized in that the plate (12) and the fixing lug (111) of the base (110) are oriented with respect to about 100 degrees and are connected by a rounded connection part Oa). Implant according to one of claims 2 to 8, characterized in that the base 10) is made of titanium alloy. 10. Implant according to one of the preceding claims, characterized in that the faces of the implant in contact with the vertebrae include surface coating such as hydroxylapatite coating, porous titanium, any other osteoconductive or conductive coating.