WO2001062190A1

WO2001062190A1 - Intervertebral implant with rigid body and support surfaces

Info

Publication number: WO2001062190A1
Application number: PCT/FR2001/000515
Authority: WO
Inventors: Frédéric HANSEN
Original assignee: Stryker Spine Sa
Priority date: 2000-02-24
Filing date: 2001-02-22
Publication date: 2001-08-30
Also published as: AU2001235741A1; FR2805457A1; FR2805457B1

Abstract

The invention concerns an intervertebral implant comprising a rigid body having two support surfaces on the end-plates of two adjacent and elastically deformable vertebrae, enabling to bring the two support surfaces closer together, and a cavity for receiving a block of material.

Description

INTERVERTEBRAL IMPLANT WITH RIGID BODY AND SUPPORTS

The present invention relates to vertebral link systems. During disc pathologies, a therapy often used essentially consists in carrying out an osteosynthesis by the use of rigid cages comprising an open cavity towards the upper and lower vertebrae, capable of receiving bone graft or any other substance promoting bone regrowth. On the other hand, it is recognized that the bone regrowth allowing the desired fusion to be obtained is stimulated and accelerated in proportion to the stresses suffered by the graft. However, beyond a certain limit, the constraints become too great and therefore cause an opposite effect on the quality of bone regrowth, or even necrosis of bone tissue. Currently existing cages absorb almost all of the stresses without deformation due to their high rigidity. Thus, the graft is hardly stimulated, which does not allow to have the best conditions for obtaining a fusion. This is the case of the implant described in document WO97 / 37620. This document describes a cage-plate having a rigid open body of generally parallelepipedal or ovoid shape intended to receive the graft thanks to open upper and lower faces. The materials used for the manufacture of such implants do not allow optimization of the fusion.

On the other hand, this type of implantable cage does not leave the surgeon the possibility of choosing the restoration of a certain mobility between the two instrumented vertebrae, in place of the fusion. Indeed, in certain cases, it is more judicious to restore a mobility to the pathological vertebral stage than to carry out the arthrodesis. This is the case for young patients and / or having vertebral bodies in excellent condition, where subsequent reintervention is certain on the stages adjacent to the instrumented stage, if a fusion is carried out. An object of the present invention is to provide an implant ensuring optimized bone fusion and to allow the choice between this fusion and a restoration of mobility.

With a view to achieving this goal, an intervertebral implant is provided according to the present invention comprising a rigid body having two bearing faces on the plates of two adjacent vertebrae and elastically deformable before receiving the block, allowing the two faces to be brought together support each other, and a cavity for receiving a block of material.

Thus, in the case of a fusion, the deformability of the body allows a better fusion because the stresses will be better distributed between the structure and the graft. In the case of a restoration of mobility, the deformability of the body allows the implant to ensure it.

Advantageously, the body is in one piece. Advantageously, the body comprises a folded blade forming the bearing faces.

Advantageously, the blade has a non-uniform thickness along the blade. Thus, the deformation of the body is optimized for the use of the implant and for the desired deformation.

Advantageously, the blade at least partially defines the cavity.

Advantageously, the body has a zone for joining the bearing faces.

Advantageously, the junction zone and the bearing faces give the body a “U” profile. Advantageously, at least one of the bearing faces has a profile adapted and complementary to the profile of the vertebral plateau with which it is intended to come into contact.

Advantageously, the body comprises means for anchoring to one face of the vertebrae contiguous to the vertebral plateau.

Advantageously, the body comprises at least two anchoring lugs to the respective vertebrae, each lug extending in continuity of material with only one of the bearing faces.

Advantageously, each leg extends in continuity of material with the bearing face intended to be in abutment on the plate of the vertebra associated with this leg. Advantageously, each leg extends in continuity of material with the bearing face intended to be in abutment on the vertebral plate associated with the other leg.

Advantageously, each fixing lug comprises at least one orifice intended to receive a bone screw. Advantageously, the body comprises a block of non-rigid material.

Advantageously, the block includes bone graft and / or any substance promoting bone regrowth.

Thus the implant can achieve a fusion. Advantageously, the block comprises biocompatible polymer (s) and / or any other biocompatible viscoelastic material. Thus, the implant acts as a disc prosthesis allowing the restoration of mobility.

There is also provided a method of implantation implant comprising an approach to the spine in an anterior way, a discectomy, a sharpening of the upper and lower plates of the disc space, a verification of the dimensions of the disc space, the choice of the type of block depending on whether a fusion or a restoration of mobility is desired, insertion of the implant into the prepared disc space, anchoring of the implant to the vertebral bodies, closure of the way first.

Other characteristics and advantages of the invention will become apparent from the following description of a preferred embodiment and of a variant given by way of nonlimiting examples. In the accompanying drawings:

- Figure la is a perspective view of the implant according to the invention according to a first embodiment;

- Figure lb is a top view of the implant according to the first embodiment;

- Figure 2 is a perspective view of one of the bone screws of Figure 1; - Figure 3 is a perspective view of a block according to the first embodiment;

- Figure 4 is a perspective view of the body according to the first embodiment; - Figure 5 is a side view of the body according to the first embodiment;

- Figure 6 is a perspective view of the body according to a second embodiment;

- Figure 7 is a side view of the body according to the second embodiment;

- Figure 8 is a side view in a sagittal plane of a cervical vertebra.

Referring to Figures la to 5, the implant 1 comprises a body 2 resiliently deformable, a block 3 included within the body 2 and bone screws 4 for fixing.

The body 2 is formed by a blade describing a path resembling an "α". The loop of the "α" includes a lower bearing face 10, a rear wall 11 connecting the face 10 to an upper bearing face 12, the assembly describing a "U" shape. The bearing faces 10,12 are opposite to each other and generally extend in two planes parallel to each other. This loop is generally parallelipipedic to fill the disc space as much as possible. This loop delimits a cavity 20 which is suitable for receiving block 3. This block 3 may be made up either of bone graft or of any other substance which promotes bone regrowth such as bone substitutes, or of a biocompatible polymer or of any other biocompatible viscoelastic material. In the first case, the implant 1 will be used in order to obtain a fusion between the two instrumented vertebrae. The elastic deformability of the blade in “α” makes it possible to obtain a distribution of the stresses between the body 2 and the block 3 consisting of bone graft. Thus the constraints supported by the graft allow the latter to produce a better quality bone for fusion. In the second case, the implant 1 will be used with the aim of restoring mobility between the two instrumented vertebrae. The elastic deformability of the blade in “α” associated with the viscoelasticity of block 3 makes it possible to reproduce the mechanical reactions of the healthy natural vertebral disc replaced by the implant 1. The branches of the profile in “α” of the body 2 include two legs 13 extending the lower support face 10 at right angles thereto and allowing the implant 1 to be fixed on the body of the upper vertebra, and a lug 14 extending the upper support face 12 at right angles to it ci and allowing the fixation of the implant on the body of the lower vertebra. In top view, as shown in Figure lb, the legs 13,14 are inclined relative to each other to be oriented so as to follow the curvature of the anterior wall of the vertebral bodies to which they are fixed. Each of the legs 13,14 comprises at least one orifice 15 which is capable of receiving a bone screw 4 with a head 5 for fixing in the vertebral body. The orifice 15, preferably of generally circular section, has a surface 18 capable of receiving the head 5 of the bone screw 4. The surface 18 is substantially complementary to the surface 7 of the head 5 of the bone screw 4 contiguous to the threaded rod. On the other hand, each of the bone screws 4 comprises implementing means 8 in the form of a hollow imprint of hexagonal section, a bone thread 6 and a notch 9 located at the opposite end of the head. 5, along the axis of the screw which allows the self-tapping of the screw in the vertebral body.

The parts of the blade acting as lower 10 and upper 12 bearing faces are shaped to conform as much as possible to the shape of the vertebral plates with which they are in contact. Thus the implant is better stabilized in the disc space. In the embodiment presented in FIGS. an upper plate with a face 43 and a lower plate with a face 42. In section along the median sagittal plane in FIG. 8, the upper plate 43 of the vertebra has a substantially rectilinear horizontal profile while the lower plate 42 has a profile concave in airplane wing complementary to that convex of the upper plate 12 of the body 2 as described below. The lower bearing face 10 of the body 2 is able to come into contact with the plate 43 of the vertebra 40. As a result, the lower bearing face 10 has a substantially rectilinear horizontal profile in the sagittal plane. The upper bearing face 12 of the body 2 is able to come into contact with the plate 42 of the vertebra 40. As a result, the upper bearing face 12 has a profile consisting of two generally rectilinear sections 16,17 inclined with respect to each other to give this profile a convex shape. The rear section 16 is the longer of the two sections. It extends, in the sagittal plane, over approximately 80% of the length of the body 2. The section 16 is slightly inclined towards the rear of the body 2. It is therefore slightly inclined relative to the lower bearing face 10 The section 17 is inclined towards the front of the body more strongly than the inclination of the rear section 16 towards the rear. Its length is approximately equal to a quarter of that of the rear section 16. The two sections 16, 17 give the upper bearing face 12 a profile close to that of an airplane wing. The bearing faces 10,12 comprise at least one orifice 30 passing through the thickness of the blade, of preferably circular section. This orifice 30 connects the internal cavity 20 to the structure 2 with the bearing face 12 or the bearing face 10. In the case of the choice of a fusion, this orifice 30 allows the progression of the fusion towards the trays 42,43 of the adjacent vertebrae. In the case of the choice of a restoration of mobility, this orifice 30 allows a strengthening of the anchoring, because there is bone regrowth within the orifice 30 which will fill it up again over the thickness of the blade. Preferably, the bearing faces 10,12 comprise a multitude of orifices 30 of circular section and uniformly distributed on the bearing faces 10,12. The deformation of the body 2 is controlled by the variations in the thickness of the blade along the profile described by the bearing face 12, the rear wall 11 and the bearing face 10. Thus, the distribution of stresses between the body 2 and the block 3 is optimized.

The cavity 20 is suitable for receiving the block 3. The choice of the composition of the block 3 depends on the will of the surgeon to obtain either a fusion between the two vertebrae within the framework of an arthrodesis, or to restore mobility between the two vertebrae. In the first case, block 3 will consist of bone graft and / or any other substance promoting bone regrowth. In the second case, the block 3 will consist of one or more biocompatible polymers or any other biocompatible viscoelastic material. The block 3 has an external surface complementary to that of the cavity for a perfect match with the shape of the cavity 20 which is delimited by the profile of the blade of the body 2: the surface 10a is complementary to the lower bearing face 10 of the body 2. The surface 12a is complementary to the upper bearing face 12 of the body 2 and consists of two sections 16a, 17a complementary to the sections 16, 17 of the bearing face 12. Similarly, the surface 11a is complementary to the internal face of the posterior wall 11 of the body 2. The implant 1 is placed in the patient's body via an anterior approach which allows direct access to the vertebral bodies, and this, on their front side. The practitioner performs a discectomy of the damaged intervertebral disc then sharpens the lower trays of the upper vertebra, and the upper of the lower vertebra delimiting the disc space. After having checked the size of this disc space thus cleared, the practitioner prepares the implant 1 for implantation: if the practitioner decides to perform a fusion, he introduces into the cavity 20 a block 3 of graft and / or any other substance promoting bone regrowth; if the practitioner decides to restore mobility, he introduces into the cavity 20 a block 3 consisting of biocompatible polymer (s) or any other biocompatible viscoelastic material. Once prepared, the practitioner sets up the implant 1 which he fixes with the bone screws 4 to the vertebral bodies, through the orifices 15 in the fixing lugs 13, 14. He then closes the lane first.

In a second embodiment illustrated in Figures 6 and 7, the body 102 of the implant is always formed of a blade which describes a path resembling a "U". It always has a lower bearing face 110 similar to the previous bearing face 10, a rear wall 111 similar to the previous wall 11, an upper bearing face 112 similar to the upper upper bearing face 12. The attachment to the overlying vertebra is effected by a fixing lug 113 extending the upper support face 112. The attachment to the underlying vertebra is effected by two fixing lugs 114 extending the lower support face 110. The anchoring means are identical to those of the previous embodiment. The blade here has a "U" shape and no longer an "α" shape so that the two branches of "U" do not cross, as in the previous mode. The U-shaped blade of the body 112 delimits an identical cavity 20 capable of receiving the block 3. The installation of this second embodiment does not differ from the implementation of the first embodiment.

The blade can be replaced by a helical spring capable of receiving a block of biomaterials at its core.

The bone screws may include a blocking mechanism vis-à-vis the fixing lugs to prevent their recoil.

The bone screws can be polyaxial with respect to the fixing lugs.

Claims

claims

1. Intervertebral implant comprising a rigid body (2; 102) having two bearing faces on the plates of two adjacent vertebrae and a cavity (20) for receiving a block (3) of material, characterized in that the body is elastically deformable before reception of the block, allowing the two bearing faces to be brought closer to one another.

2. Implant according to claim 1 characterized in that the body is in one piece.

3. Implant according to claim 1 or 2 characterized in that the body comprises a folded blade forming the bearing faces.

4. Implant according to claim 3 characterized in that the blade has a non-uniform thickness along the blade.

5. Implant according to claim 3 or 4 characterized in that the blade at least partially defines the cavity.

6. Implant according to one of claims 1 to 5 characterized in that the body has a junction area of the bearing faces.

7. Implant according to claim 6 characterized in that the junction zone and the bearing faces give the body a "U" profile.

8. Implant according to one of claims 1 to 7 characterized in that at least one of the bearing faces has a profile adapted and complementary to the profile of the vertebral plate with which it is intended to come into contact.

9. Implant according to one of claims 1 to 8 characterized in that the body comprises means for anchoring to a face of the vertebrae contiguous to the vertebral plateau.

10. Implant according to one of claims 1 to 9 characterized in that the body comprises at least two anchoring lugs to the respective vertebrae, each lug extending in continuity of material with only one of the bearing faces

11. Implant according to claim 10 characterized in that each lug extends in continuity of material with the bearing face intended to be in abutment on the plate of the vertebra associated with this lug.

12. Implant according to claim 10 characterized in that each leg extends in continuity of material with the bearing face intended to be supported on the vertebral plate associated with the other leg.

13. Implant according to one of claims 10 to 12 characterized in that each fixing lug comprises at least one orifice intended to receive a bone screw.

14. Implant according to one of claims 1 to 13 characterized in that it comprises a block of non-rigid material.

15. Implant according to claim 14 characterized in that the block includes bone graft and / or any substance promoting bone regrowth

16. Implant according to claim 14 characterized in that the block comprises biocompatible polymer (s) and / or any other biocompatible viscoelastic material.