EP2136743A1

EP2136743A1 - Intervertebral implant for the human or animal body

Info

Publication number: EP2136743A1
Application number: EP08787792A
Authority: EP
Inventors: Philippe Vincent-Prestigiacomo; Nicolas Roth
Original assignee: CREASPINE
Current assignee: CREASPINE
Priority date: 2007-04-13
Filing date: 2008-03-14
Publication date: 2009-12-30
Also published as: WO2008142220A1; KR20100016503A; FR2914843A1; US20100161059A1; AU2008252819A1; JP2010523245A; FR2914843B1; ZA200906348B; CA2680250A1

Abstract

This intervertebral implant (17) for the human or animal body, suitable for an anterior or posterior location, comprising two relatively rigid pillars (19, 20) connected to each other only by at least two bearing portions (21, 22) able to interact with respective vertebral endplates (7) of the spine, at least one of said bearing portions (21, 22) comprising at least one relatively flexible zone allowing this bearing portion to at least partially conform to the shape of the associated vertebral endplate (7) when said implant (17) is positioned between said two endplates.

Description

Intervertebral implant for the human or animal body

The present invention relates to the field of spinal surgery of the human or animal body, and more particularly to intervertebral implants.

There are classically two categories of intervertebral implants:

the first category relates to so-called intervertebral implants, intended to replace the intervertebral discs, and therefore to be placed between two adjacent vertebrae;

- the second category concerns VBR ("Vertebral Body Replacement") type implants intended to partially or totally replace one or more vertebrae.

All these implants, which are generally associated with bone grafts, allow the fusion of the vertebral bodies with which they cooperate, and thus to remedy various pathologies of the spine.

A first type of intervertebral implant 1 of the state of the art is shown diagrammatically in FIG.

This implant, which may be made of a biocompatible plastic material such as PEEK (polyether ether ketone) or a metallic material such as a titanium alloy, has a substantially parallelepipedal shape, and is provided with orifices 3 allowing the placement of bone graft and the contact of this graft with the host bone.

FIG. 2 shows a vertebra 5 resting on this implant: as can be seen in this figure, the vertebral plate 7 of this vertebra which cooperates with this implant has a certain concavity.

Thus, the support of the vertebra 5 actually takes place only on the edges

8, 9 of the implant 1: this punctual support causes very significant stresses on the vertebral plateau 7 and in the adjacent vertebral body 11, which can ultimately lead to embrittlement or even collapse of the vertebra 5.

This concentration of stress on the edges of the implant is illustrated by the graph of FIG.

In this graph, the abscissa corresponds to the curvilinear abscissa on the vertebral plateau measured in mm along the x axis of FIG. 2, and the ordinate indicates the pressure exerted on the vertebra 5 by the implant 1, expressed in stress of Von Mises in Mpa: the two stress peaks 12a, 12b visible on this graph correspond to the zones of support of the edges 8, 9 of the implant 1 on the vertebral plate 7.

To overcome this drawback, it has been imagined, in the state of the art, to manufacture implants whose faces intended to abut against the vertebral endplates have a convexity complementary to the concavity of these trays.

An example of such an implant 13 is shown in FIG.

In practice, no vertebra has the same concavity: thus, the implant of Figure 4 will fit correctly the shape of some vertebrae, but will not be suitable for others.

Specifically, this means that for some vertebrae, we will find ourselves in the situation shown in Figure 5, where the contact between the implant 13 and the vertebral plateau 7 is punctual, resulting in a stress peak in the center of the vertebral plateau, as this is visible in Figure 6 at 15.

One finds oneself then again in an unfavorable configuration likely to lead to the embrittlement, even to the collapse of the vertebra 5. To remedy these drawbacks, it was proposed, in the documents US2004 / 267367, WO2004 / 064693 and WO2006 / 127849, intervertebral implants comprising the bearing portions adapted to cooperate with respective vertebral trays of the spine, having a certain flexibility. Thanks to this flexibility, it is possible to obtain a distribution of the bearing forces of the implant on each associated vertebral plateau, and thus to avoid the concentrations of stresses likely to damage the vertebra.

However, these intervertebral implants with soft bearing areas of the prior art have the disadvantage of not allowing optimal revascularization and bone fusion.

The present invention is intended to overcome this disadvantage.

This object of the invention is achieved with an intervertebral implant for the human or animal body, adapted for anterior or posterior placement, comprising two relatively rigid pillars connected to each other only by at least two bearing parts adapted to cooperate with of the respective vertebral trays of the spine, at least one of said bearing portions comprising at least a relatively flexible area allowing this bearing portion to at least partially marry the shape of the associated vertebral plateau when said implant is positioned between said two trays. Thanks to this structure of pillars interconnected by support portions, the vertebral implant with flexible support zones according to the invention defines a cavity conducive to bone fusion and revascularization. This cavity allows in particular the establishment of bone grafts.

This particular structure distinguishes the implant according to the invention from those of the prior art, which are solid and thus form a screen against bone fusion and revascularization.

The fact that the two pillars are connected to each other only by two support parts gives the implant a particularly simple structure.

Surprisingly, it has been realized that the fact of providing a cavity in the implant was compatible with the fact of envisaging flexible support zones: with appropriate sizing, within the reach of the skilled person Having conventional rules of resistance of materials, it was found that one could reconcile flexibility and cavity without exposing the implant to a risk of crushing by the adjacent vertebrae. Until the present invention, it was thought that it was necessary for an implant with soft bearing areas to be massive to resist crushing.

According to other optional features of the implant according to the invention:

said support portions comprise at least two relatively flexible plates interconnecting said pillars with one another: this embodiment makes it possible to obtain the desired flexibility by configuring the plate bearing parts, that is to say in fact playing on the shape and the thickness of the material forming the implant, and thus on its intrinsic elasticity;

said support portions comprise support zones integral with said pillars and a relatively rigid plate connected to said pillars by relatively flexible arms: this is a variant of the previous embodiment, in which the desired flexibility is provided by the connecting means of the plates to the body;

said body and said plates define an external volume and an oblong internal cavity: this particular configuration makes it possible to obtain an implant that adapts particularly well to the different concavities of the vertebral endplates of the vertebrae;

said plates are provided with vascularization orifices: these orifices make it possible to reconstitute vascular networks in the zone of the implant;

said support portions comprise retention grooves: these grooves contribute to the immobilization of the implant between the associated vertebral endplates;

this implant is formed of a block made of a biocompatible metallic material such as TiAl 4 V (titanium alloy) or a biocompatible polymer such as PEEK, PLLA or PGA: this embodiment in one block is particularly simple, and can be respectively obtained by machining the metal alloy or by molding the polymers; these materials are very commonly used in the field of surgical implants. Other features and advantages of the present invention will appear in the light of the reading of the description which follows and the examination of the appended figures in which:

FIG. 1 is a perspective view of a first implant of the prior art, described above; FIG. 2 is a view of this implant cooperating with a vertebra;

FIG. 3 is a graph representing the stresses transmitted by the implant to the vertebra,

FIGS. 4 to 6 are views similar to those of FIGS. 1 to 3 for a second implant of the state of the art, described above,

FIG. 7 is a perspective view of an implant according to the invention,

FIG. 8 is a view of this implant cooperating with a vertebra, in the absence of compression, FIG. 9 is a view of this implant cooperating with a vertebra subjected to a compressive force,

FIG. 10 is a graph representing the stresses transmitted by the implant 17 to the vertebra 5 in a compression situation,

FIG. 11 is a front view of a variant of the implant according to the invention, and

- Figure 12 is a perspective view of this variant. Referring now to Figure 7, on which it can be seen that an implant according to the invention may comprise two pillars 19, 20 interconnected by two plates 21, 22.

The two pillars 19, 20, which form the body of the implant 17, have a high resistance to vertical forces, that is to say to the forces oriented along the line Z of FIG. 7.

The plates 21, 22 form for their support parts offering relative flexibility with respect to the pillars 19, 20: the ratio of elastic deformations, under a given load, between the rigid pillars and the flexible plates is typically of the order of 1 to 10.

Preferably, as shown, the pillars 19, 20 and the plates 21, 22 define an external volume on the one hand and an inner cavity 24 on the other hand of oblong and preferably elliptical sections with coinciding axes. In addition, a plurality of vasculature orifices 26, 28 are provided on the plates 21, 22.

It is also possible that these plates 21, 22 are provided with retaining streaks (not shown) on their outer surfaces.

Advantageously, the implant 7 may be formed of a single block in a material such as PEEK (polyether-ether ketone), PLLA (polylactic acid) or PGA (propylene glycol alginate). In this case, the implant 17 can be obtained for example by molding or by machining.

Referring now to Figure 8, which shows the implant 17 according to the invention in contact with the vertebral plate 7 of a vertebra 5 before compression, that is to say before be subject to the efforts transmitted by the spine.

As can be seen in this figure, the type of contact between the implant 17 and the vertebral plate 7 of the vertebra 5 is of the same nature as that shown in Figure 5: this contact is substantially punctual. Referring now to Figure 9, on which the implant 17 can be seen in a compression situation, that is to say when it is placed in the spine and subjected to the forces transmitted by the latter.

As can be seen in this figure, the two relatively flexible plates 21, 22 have deformed so as to approach one another, which considerably increases the contact surface of these plates with the vertebral plates. adjacent. In this way it is possible to obtain an optimal distribution of the stresses transmitted by the implant 17 to the vertebra 5 as illustrated by the flat zone 30 of the graph of FIG. 10.

In this way, the strong point constraints that can damage or ruin the vertebra are removed.

It will be noted that despite this flexibility of the plates 21, 22, the implant 17 continues to retain its structural function thanks to the relatively rigid pillars 19, 20.

Note also that the relative flexibility of the plates 21 and 22 allows the implant 17 according to the invention to adapt to virtually any degree of concavity of the vertebral endplates of the vertebrae.

Thus, the number of different implants adaptable to all the vertebrae can be considerably reduced.

The orifices 26, 28 formed in the relatively flexible plates 21, 22 allow rapid reconstitution of the vascular network between the vertebrae.

The inner cavity 24 allows the establishment of a bone graft, recommended for fusion or arthrodesis.

It will also be noted that the relative flexibility of the plates 21 and 22 makes it possible to stress the surfaces of the associated vertebral plates, and thus to promote the regrowth of the bone, according to Wolff's law, which is well known to those skilled in the art.

It will also be noted that the shape of the implant represented in FIGS. 7 to 9 is in no way limiting. Thus, while a symmetrical shape as shown in these figures is suitable for anterior-type placement (i.e., the front of the patient's body), an asymmetrical shape might be suitable for posterior position (that is, behind the patient's body).

Of course, other variants of the implant according to the invention could be envisaged.

For example, it is possible to envisage the implant variant 117 shown in FIGS. 11 and 12, in which the support portions against the vertebral plates are formed on the one hand by support zones 131a. , 131b and 132a, 132b secured to the relatively rigid pillars 119, 120 forming the body of this implant, and secondly by two plates relatively rigid 141, 142 connected to these pillars by relatively flexible arms 151a, 151b and 152a, 152b.

Claims

1. Intervertebral implant (17; 117) for the human or animal body, adapted for anterior or posterior placement, comprising two relatively rigid pillars (19, 20; 119, 120) interconnected by at least two parts only bearing (21, 22; 121, 122) adapted to cooperate with respective vertebral end plates (7) of the spine, at least one of said bearing portions (21, 22; 121, 122) comprising at least one relatively flexible zone allowing said bearing portion to at least partially conform to the shape of the associated vertebral plateau (7) when said implant (17; 117) is positioned between said two trays.

2. Implant (17) according to claim 1, characterized in that said bearing portions comprise at least two relatively flexible plates (21, 22) interconnecting said pillars (19, 20).

3. Implant (117) according to claim 1, characterized in that said bearing portions (121, 122) each comprise bearing zones (131a, 131b and 132a, 132b) integral with said pillars (119, 120). and a relatively rigid plate (141, 142) connected to said pillars by relatively flexible arms (151a, 151b and 152a, 152b).

4. Implant (17; 117) according to one of claims 2 or 3, characterized in that said body (19, 20; 119, 120) and said plates (21, 22; 121, 122) define an external volume and an inner cavity (24; 124) oblong.

5. Implant (17; 117) according to any one of claims 2 to 4, characterized in that said plates (21, 22; 141, 142) are provided with vascularization orifices (26, 28; 126, 128). .

6. Implant (17; 117) according to any one of the preceding claims, characterized in that said bearing portions comprise holding streaks.

7. Implant (17; 117) according to any one of the preceding claims, characterized in that it is formed of a block in a metal biocompatible material such as Ti6AI4V or a biocompatible polymer such as PEEK, PLLA or the PGA.