EP0793463A1

EP0793463A1 - Implant for the fusion of two adjacent bony bodies, particularly two consecutive vertebrae

Info

Publication number: EP0793463A1
Application number: EP95940320A
Authority: EP
Inventors: Joel Letendart; Philippe Chelius; Yves Der Sarkissian; Valéry Dehais; Alain Ducolombier
Original assignee: Objectif-Implants Belgique
Current assignee: Objectif-Implants Belgique
Priority date: 1994-11-16
Filing date: 1995-11-15
Publication date: 1997-09-10
Also published as: WO1996014809A1

Abstract

According to the invention, said implant (2) has a general U shape, in other words it is comprised of two side blades (10) connected to each other at one end by means of a heel (11), at least one of said blades being provided with a cutting edge (12) at its free end, the implant (2) being conformed so that it provides for the taking of a monoblock bone graft (16).

Description

IMPLANT ALLOWING THE FUSION OF TWO ADJACENT BONE BODIES, PARTICULARLY TWO CONSECUTIVE VERTEBRES

The present invention relates to an implant allowing the fusion of two adjacent bone bodies. This implant is mainly intended to be used to obtain the fusion of two consecutive vertebrae, but can also be used for arthrodeses under Astragalian or Tibio-Astragalian.

It is known to use intervertebral arthrodesis in cases of disc pathologies, in order to restore an adequate disc height, in cases of narrowing of the lumbar canal, in order to achieve the anterior stabilization of the vertebrae made necessary by the weakening of the posterior arch, or in cases of vertebral instabilities, in order to achieve the fusion of the vertebrae which have become unstable.

This arthrodesis is generally obtained by the establishment of a posterolateral bone graft, implanted on the articular processes, on the transverse processes and on the intervertebral blades. In the absence of the vertebral laminae as a result of laminectomy, the grafts are placed only in the posterolateral grooves, then a metallic stabilization material is implanted to immobilize the spine while the fusion takes place.

This technique has the drawback of being relatively complex and time-consuming to implement, taking into account the addition of this stabilization material, and of not making it possible to restore sufficient disc height.

It is also known to implant a bone graft in the intervertebral space, after complete excision of the damaged disc. However, obtaining a solid fusion is uncertain, due to the constraints exerted on the graft and on the graft-vertebra interfaces. These constraints frequently lead crushing and incorporating the graft into one or 1 • other of the vertebrae.

One technique consists of implanting intervertebral cages at the level of the affected disc, on either side of the axis of the spine.

These cages are cylindrical, hollow, externally threaded and include side windows. They receive a filling of bone particles taken from a cancellous bone, then are engaged by screwing in intervertebral housings previously drilled in the plates of the vertebrae to be fused.

Each cage must be positioned so that two opposite windows are in contact with the trays, in order to make possible bone growth inside the cage.

This technique has the disadvantage of involving the use of a means of temporary distraction of the vertebrae, which is fairly traumatic, during the time necessary for drilling the housings, filling and placing the cages.

In addition and above all, it appears that the stability of the fusion obtained by these cages is not guaranteed over time.

The duration of intervention is also important, which is hardly desirable for the patient.

It is also known from European patent EP 0 307 241 to produce a cage of parallelepiped shape, comprising upper, lower and side windows. The outside surfaces of this cage are rough, to allow the cage to be kept in its housing and to promote bone growth.

This cage is also intended to be furnished with pieces of cancellous bone, then is compacted in the intervertebral housings, previously arranged. The present invention aims to remedy the aforementioned drawbacks of the prior techniques. It provides an intervertebral implant allowing the perfect fusion of the vertebrae, with adequate enhancement of the intervertebral disc and guaranteed stability over time. This implant must be able to be placed posteriorly, without risk of nerve damage at the level of the hard mother or at the level of the roots, by a relatively simple and rapid technique of implementation. According to the invention, the implant has a general U-shape, that is to say is constituted by two lateral blades connected to each other, at one end, by a heel, at least one of which comprises a sharp edge at its free end, this implant being shaped to allow the removal of a one-piece bone graft itself.

Thus, the implant is not intended to be filled with spongy spongy bone particles, with the risk of inclusion of air bubbles, as may be the case with conventional intervertebral cages. On the contrary, it is itself used for the removal, preferably in the iliac crest of the patient, of a graft constituted by cancellous bone "of mass", clearly denser than an agglomeration of bone particles. This density corresponds substantially to that of the cancellous bone of the vertebrae.

The graft removed comes to completely fill the implant, and is maintained in the latter, so that it can be cut again if necessary. The upper and lower openings delimited by the blades have much larger dimensions than the windows in the existing cages, and allow large areas of contact of the graft with the cancellous bone of the vertebrae. In addition, the graft is held laterally in the intervertebral space by the implant blades. All of these factors allow obtaining a perfect fusion of the vertebrae and the graft, without crushing or inserting the graft into the cancellous bone. The fusion thus obtained gives any guarantee of stability over time.

In addition, the conventional operation of filling the implant is eliminated, which allows an appreciable gain in terms of the duration of intervention.

Advantageously, the blades have on their upper and / or lower edges teeth of the "harpoon" or "fir" type.

These teeth are intended to be inserted into the cancellous bone of the vertebral plates, and to prevent any possibility of movement of the implant backwards. In addition, their insertion into the bone allows compression of the graft, the latter having, thanks to direct sampling, a width which corresponds perfectly to the maximum width of the implant, including teeth. This compression ensures perfect application and total immobilization of the graft relative to the vertebrae, which is entirely favorable for good bone growth, and therefore for obtaining a perfect fusion. The penetration of the teeth inside the vertebrae also promotes the initiation of bone growth to achieve fusion.

According to a preferred embodiment of the invention, the length of the blades is uneven, in order to facilitate the removal of the graft.

The blades can be rectangular, trapezoidal, or in the shape of a parallelogram.

At least one of the two blades may include a lateral lumen, to also allow bone growth in this lateral direction. Advantageously, the heel connecting the two blades is pierced with a threaded hole allowing the mounting of the implant on the end of an impacting tool, for the removal of the graft then for the placement of the implant in its intervertebral housing.

Preferably, the distance separating the blades is determined so that the area occupied by the bone graft at the upper and lower faces of the implant represents at least 50% of the total area of these faces.

For a good understanding, the invention is again described below with reference to the appended diagrammatic drawing representing, by way of nonlimiting example, a preferred embodiment of the intervertebral implant which it concerns.

Figure 1 is a perspective view; Figure 2 is a side view, after removal of the graft intended to garnish it; Figure 3 is a top view; Figure 4 is an end view, on the rear side; Figure 5 is a rear view of two implants placed in an intervertebral space, and Figure 6 is a side view of one of the two implants, after placement in an intervertebral space.

The figures represent, from different angles, an implant 2 making it possible to obtain the fusion of two consecutive vertebrae 3,4, at the level of an intervertebral disc 5.

This implant 2 has a general U shape, that is to say is constituted by two rectangular lateral blades 10, connected to each other, at one end, by a heel 11. The blades 10 have a length uneven and have sharp edges 12 at their ends free, delimited by their internal faces and by beveled end faces.

The blades 10 include teeth 13 of the "harpoon" or "fir" type on their upper and lower edges, and lateral slots 14.

The heel 11 connecting the two blades 10 is pierced with a threaded hole 15 allowing the mounting of the implant 2 on the end of an impaction tool (not shown).

The implant 2, once mounted on this tool, allows direct removal of a monobloc bone graft 16 consisting of cancellous bone "of mass", preferably originating from the iliac crest of the patient.

The unequal length of the blades 10 facilitates the removal of the graft 16. It appears in FIGS. 2 to 4 that the graft 16 thus obtained completely fills the space delimited by the blades 10 and the heel 11, and that it has a corresponding width at the maximum width of the implant 2, teeth 13 included. The graft 16 is perfectly maintained in the implant 2 and can be resized if necessary.

In practice, as shown in FIGS. 5 and 6, intervertebral housings are drilled in the plates of the vertebrae 3 and 4 to be fused, on either side of the axis of the spine, to receive two implants 2 provided with a plugin 16.

These implants 2 are impacted in the housings by means of the aforementioned tool. When they are fully inserted into the housings, the tool is removed. The teeth 13 are inserted into the cancellous bone of the vertebral plates, and prevent any possibility of movement of the implants 2 backwards.

This insertion causes the grafts 16 to compress over a height corresponding to that of the teeth 13, that is to say approximately 2 millimeters for each row of teeth. This compression allows perfect application and total immobilization of the grafts 16 relative to the vertebrae 3,4, which is entirely favorable for obtaining good bone growth, and therefore perfect fusion. .

In addition, the penetration of the teeth 13 inside the vertebrae promotes the initiation of bone growth from which the fusion takes place.

The density of the grafts 16 corresponds substantially to that of the cancellous bone of the vertebrae 3,4, and the grafts 16 are held in place laterally by the blades 10 in the intervertebral housings.

It appears from the figures that the distance separating the blades 10 is determined so that the surface occupied by the graft 16 at the level of the upper and lower faces of the implant 2 represents at least 50% of the total surface of these faces. The upper and lower openings delimited by these blades 10 thus allow wide contact surfaces of the graft 16 and of the cancellous bone of the vertebrae 3,4.

The lateral lights also allow bone growth in this lateral direction.

The invention thus provides an intervertebral implant making it possible to obtain perfect fusion of the vertebrae, with adequate enhancement of the intervertebral disc and guarantee of stability over time, this implant being able to be placed by posterior route, according to a relatively simple technique. and quick to implement.

Claims

1 - Implant allowing the fusion of two adjacent bone bodies, in particular of two consecutive vertebrae, characterized in that it has a general U-shape, that is to say is constituted by two lateral blades (10) connected to the one to the other, at one end, by a heel (11), at least one of which has a cutting edge (12) at its free end, this implant (2) being shaped to allow the removal of a monobloc bone graft (16).

2 - Implant according to claim 1, characterized in that the blades (10) have on their upper and / or lower edges teeth (13) of the "harpoon" or "fir" type. 3 - Implant according to claim 1 or claim 2, characterized in that the length of the blades (10) is uneven.

4 - Implant according to one of claims 1 to 3, characterized in that the blades (10) can be rectangular, trapezoidal, or in the form of a parallelogram.

5 - Implant according to one of claims 1 to 4, characterized in that at least one of the blades (10) comprises a lateral lumen (14). 6 - Implant according to one of claims 1 to 5, characterized in that the heel connecting the blades (10) is pierced with a threaded hole (15) allowing the mounting of the implant on the end of a tool of impaction.

7 - Implant according to one of claims 1 to 6, characterized in that the distance separating the blades (10) is determined so that the surface occupied by the bone graft (16) at the upper and lower faces of the implant (2) represents at least 50% of the total surface of these faces.