FR2919490A1 - Intervertebral implant i.e. intervertebral cage, for stabilizing cervical vertebrae, has posterior wall comprising concavity with surface parallel to axial direction, where bending radius of concavity is equal to radius of cervical part - Google Patents

Abstract

The implant has an implant body (1) made of biocompatible solid material and comprising parallelepiped structure delimited by upper and lower walls (2, 3), lateral walls (4, 5), anterior wall (6) and posterior wall (7). The upper and lower walls are convergent towards rear and spaced from each other along an axial direction (I-I). An internal cavity (9) emerges into the upper and lower walls. The posterior wall has a cylindrical concavity (12) with a surface parallel to the axial direction. The bending radius of the concavity is equal to the radius of a cervical part of a vertebral canal.

Description

The present invention relates to an implant

  intersomatic, and more particularly an intersomatic implant intended to be inserted anteroposteriorly between the cervical vertebrae of a patient. Such intersomatic implants are also known by the term intervertebral cage, because of the presence in their center of an inner cavity opening largely on the upper and lower walls. This cavity is generally intended to contain a bone graft to promote the joining of the vertebrae to one another by fusion through the intersomatic implant. The intersomatic implants are indeed used for the purpose of stabilizing the cervical vertebrae of the patient by being inserted between the trays of two adjacent cervical vertebrae, in the center of the trays in the frontal plane, in front of the cervical part of the spinal canal. The cervical portion of the spinal canal is located in the center of the cervical vertebra in the frontal plane and has a convex outer surface with a substantially circular section. In known manner, the intersomatic implants with anteroposterior insertion for stabilization of adjacent cervical vertebrae of a patient comprise an implant body of biocompatible solid material having a parallelepipedal general structure.

  The implants thus have a general structure limited by two upper and lower walls slightly converging towards the rear, two side walls, an anterior wall and a posterior wall. A problem of known intersomatic implants is that, when they are inserted between two adjacent cervical vertebrae anteroposteriorly or during their use before the vertebrae are joined to one another through the implant, it can happen that the implant either inserted or moves too far towards the spinous process and comes to damage the spinal cord of the cervical part of the spinal canal. The risk of spinal cord injury is exacerbated by the fact that the general structure of known intersomatic cages (or implants) easily penetrates the spinal cord from the onset of contact between the implant and the spinal cord. A first problem proposed by the invention is to limit the risk of injury to the spinal cord of a patient during the insertion of an intersomatic implant or during its use before joining the adjacent vertebrae through the implant. . According to a second aspect, the invention aims to design an implant with a low penetration capacity in the spinal cord. To achieve these and other objects, the invention provides an intersomatic implant with anteroposterior insertion for stabilizing adjacent cervical vertebrae of a patient, comprising an implant body of biocompatible solid material having a parallelepipedal general structure limited by two upper and lower walls slightly converging towards the rear and disposed apart from each other in an axial direction, two side walls, an anterior wall and a posterior wall, with an inner cavity 10 opening largely on the walls; upper and lower, and wherein the posterior wall of the implant has a generally cylindrical concavity generatrix parallel or approximately parallel to the axial direction. Such an implant, when accidentally brought into contact with the spinal cord during its insertion or use, comes into contact with the spinal cord in a larger area than the known implants and avoids the creation of surface areas. pressure concentration, thanks to the shape of this contact, and this from the beginning of contact. This effectively limits the risk of injury to the spinal cord by penetration of the intervertebral cage therein. The insertion force is indeed distributed over a larger area and in a regular manner, unlike known interbody implants with rectilinear anterior wall which, at the entrance of the contact between the implant and the spinal cord, concentrate the force of insertion on a small surface and cause the section of the spinal cord and at least one notch therein. Preferably, the concavity of the posterior wall may comprise a curvature whose radius is substantially equal to the radius of the spinal canal of the patient. The surface in which the implant comes into contact with the spinal cord is thus maximum, resulting in the lowest possible surface contact pressure: the implant thus has a lower penetration capacity in the spinal cord than conventional implants. . Advantageously, the concavity of the posterior wall may comprise a curvature whose radius is between about 3 mm and 8 mm, in order to be as close as possible to the radius of the cross section of the spinal cord in the cervical part of the spinal canal.

  Because the radius of the cross-section may vary over the height of the cervical vertebrae of a patient, it can be advantageously provided that the concavity of the posterior wall has a curvature having a radius of about 5 mm. There is thus an implant whose radius of concavity of the posterior wall is substantially equal to the average diameter of the spinal cord in the cervical part of the spinal canal of a patient, achieving a good compromise allowing the use of a single implant throughout the cervical spine area. Advantageously, the concave posterior wall may be connected to the side walls by rounded convex connection sections.

The intersomatic implant thus has no acute angles (acute or obtuse) likely to easily damage the spinal cord. Other objects, features and advantages of the present invention will become apparent from the following description of particular embodiments, with reference to the accompanying drawings, in which: FIG. 1 is a perspective view of an embodiment; intersomatic implant according to the invention; FIG. 2 is a side view of the interbody implant of FIG. 1; and FIG. 3 is a view from above of the interbody implant of FIG. 1. The intersomatic implant of FIG. 1 comprises an implant body 1 with a generally parallelepipedal general structure limited by two upper and lower walls. , two lateral walls 4 and 5, an anterior wall 6 and a posterior wall 7. The anterior wall 6 is provided with a threaded hole 8 making it possible to fix the intersomatic implant at the end of a gripper by means of which the surgeon operates the implant during its anteroposterior insertion between two adjacent cervical vertebrae. Fig. 2 shows that the upper and lower walls 3 are slightly rearwardly convergent (i.e. in the direction of the rear wall 7) and arranged one away from the other in an axial direction 1-I.

The implant has an interior cavity 9 opening largely on the upper and lower walls 2 and 3. This cavity 9 may contain a bone graft so that the two adjacent cervical vertebrae, between which the implant is inserted, are solidary with one another. the other through the implant body 1. The upper and lower walls 3 and 3 are provided with oblique teeth 35 giving the cage, in side view (FIG. 2), a fishbone configuration. The teeth 10 thus oppose an anterior expulsion of the implant by a movement of direction and direction defined by the arrow 11 once it is inserted between two adjacent cervical vertebrae. FIG. 3 shows more particularly that the posterior wall 7 of the implant has a generally cylindrical concavity with a generator II-II 5 parallel to or approximately parallel to the axial direction 1-1. The concavity 12 has a curvature of radius R substantially constant, the radius R may advantageously be chosen substantially equal to the radius of the cervical portion of the spinal canal of a patient. Thus, in the case of accidental contact between the implant and the spinal cord, this contact is made in as large a surface as possible and regularly distributes the pressure possibly exerted by the implant against the spinal cord. Since the cross section of the cervical channels is not the same for all individuals, and this section evolves somewhat between the first and the last cervical vertebra, a good compromise has been obtained by choosing a radius R between 3 and 8 mm. about, and preferably about 5 mm. In the embodiment illustrated in FIGS. 1 to 3, the concave posterior wall 7 is connected to the side walls 4 and 5 by rounded convex connecting sections 13 and 14 with generally cylindrical walls with generatrices parallel or approximately parallel to the axial direction. 1-1.

These rounded connecting sections 13 and 14 avoid the presence of sharp edges and angles (acute or obtuse) which could also attack the spinal cord and easily cause serious lesions therein. To effectively limit this risk of injury, the convex connecting sections 13 and 14 may have a radius of curvature R 'which is between 1.5 and 5 mm, and preferably about 3 mm. The present invention is not limited to the embodiments which have been explicitly described, but it includes the various variants and generalizations thereof within the scope of the claims below.

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Claims (6)

  1 - An intersomatic implant with anteroposterior insertion for stabilizing adjacent cervical vertebrae of a patient, comprising a body (1) of biocompatible solid material implant having a parallelepipedal general structure limited by two upper (2) and lower (3) walls slightly converging rearwards and disposed apart from each other in an axial direction (1-I), two side walls (4, 5), an anterior wall (6) and a rear wall (7) , with an inner cavity (9) opening largely on the upper (2) and lower (3) walls, characterized in that the posterior wall (7) of the implant has a generally cylindrical concavity (12) with a parallel generator or approximately parallel to the axial direction (1-1). 2 - intersomatic implant according to claim 1, characterized in that the concavity (12) of the posterior wall (7) comprises a curvature whose radius (R) is substantially equal to the radius of the cervical portion of the spinal canal of the patient. 3 - intersomatic implant according to one of claims 1 or 2, characterized in that the concavity (12) of the rear wall (7) has a curvature whose radius (R) is between 3 mm and 8 mm. 4 - intersomatic implant according to any one of claims 1 to 3, characterized in that the concavity (12) of the posterior wall (7) has a curvature whose radius (R) is about 5 mm. 5 - intersomatic implant according to any one of claims 1 to 4, characterized in that the concave posterior wall (7) is connected to the side walls (4, 5) by convex connection sections (13, 14) rounded to 25 generally cylindrical walls with generatrices parallel or approximately parallel to the axial direction (II). 6 - intersomatic implant according to claim 5, characterized in that the rounded convex connecting sections (13, 14) comprise a curvature whose radius (R ') is between approximately 1.5 and 5 mm, and preferably equal to about 3 mm.