WO2004012634A2 - Intersomatic implant - Google Patents

Abstract

Disclosed is an intersomatic implant which is inserted between two consecutive bodies of vertebrae and receives an osseous graft or replacement part within the volume that said implant defines. The inventive implant comprises a cage (1), one of the lateral walls of which is open so as to define an upper branch (2) and a lower branch (3) that enter in contact with the lower end-plate of the upper body of vertebrae and the upper end-plate of the lower body of vertebrae, respectively. By default, i.e. in the absence of an external constraint, said two branches (2, 3) form a reduced convergent angle relative to the junction zones (4) thereof. Both the upper (2) and lower branch (3) are provided with an internal threading that is oriented according to the principal dimension of the branches and cooperates with a screw (12) so as to space the branches apart at a desired angle.

Description

IMPLANT INTER-SQMATIQTJE.

The invention relates to an inter-somatic implant, more particularly intended to be inserted between the vertebral bodies of two consecutive vertebrae, in particular at the cervical level or at the lumbar level, with a view to achieving the fusion of the vertebral bodies at this level.

It has long been known to carry out the fusion of the vertebral bodies, in order to relieve the pain of patients, inherent in chronic pathologies affecting one or more cervical or lumbar intervertebral discs, among which one can cite major disc sagging with foraminal stenosis, iatrogenic disc diseases, chronic mono- or oligo- segmental disco-ligament dysfunctions, herniated discs, spondylolisthesis, and generally vertebral instabilities.

Among the technical solutions envisaged to result in the fusion of the vertebral bodies, it has been suggested to insert between the two consecutive vertebral bodies concerned, an inter-somatic cage, which, traditionally, constitutes a wedge inserted between the screw plates with respect to the two vertebral bodies concerned, defining a volume inside which is placed one or more bone grafts, in particular spongy, so as to produce an inter-somatic vertebral graft.

To this end, the walls in particular upper and lower of the cage in question have through lumens, to allow the bone graft to take.

If, on the theoretical level, this technical solution appears attractive, experience shows that at the practical level the fusion occurs in an unsatisfactory way between the two consecutive vertebral bodies concerned.

The unsatisfactory nature of this merger is due to various factors. First of all, an anatomical factor, insofar as the inter-somatic cages of the prior art, have a generally parallelepiped or cylindrical profile, not corresponding to the particular anatomical profile of the intervertebral plates. In this way, there are no real constraints at the level of the cage, necessary for the development of bone grafting, and therefore leading to the fusion of the vertebral bodies. In addition, this absence of shape adapted to the anatomy explains the micro-movements of the implant between the vertebral plates, which involve risks of non-union, and the retraction of the implant, if the latter is not stabilized. by a complementary posterior osteosynthesis.

In order to overcome these drawbacks, it has been proposed, for example in French patent FR-A-2 813 519, a flexible inter-somatic implant, capable of deforming elastically under the pressure force generated by the vertebral bodies, in order to favor the contact of the graft with the overlying and underlying vertebral bodies.

However, such a flexible implant does not allow the setting function, also sought by this type of implant.

What is more, it is not possible with such an implant to provide a differential setting, that is to say of desired amplitude and orientation, depending on the pathology diagnosed by the practitioner.

The object of the present invention aims to overcome these various drawbacks. To this end, it proposes an inter-somatic implant, allowing both an anatomical adaptation of the implant to the vertebral bodies at the level of which it is intended to be implanted, without requiring any associated posterior osteosynthesis, and other part, to ensure the timing function, in a differential orientation.

This inter-somatic implant, intended to be inserted between two consecutive vertebral bodies, and to receive a bone graft or a bone substitute in the volume which it defines, consists of a cage, one of the side walls of which is open. , thus defining an upper branch and a lower branch, respectively intended to come into contact with the lower plate of the upper vertebral body, and the upper plate of the lower vertebral body.

This implant is characterized in that by default, the two branches form between them a reduced convergent angle with respect to their junction zones, and in that each of the two upper and lower branches is provided with an internal thread or an internal chute. , oriented along the main dimension of the branches, and intended to cooperate with a screw, to result in the spacing of the branches, at a desired angle. In other outfits, the invention provides a rigid inter-somatic cage, with dynamic effect, said effect being selected by the practitioner during the surgical intervention for placing the implant, by actuating a screw whose degree screwing induces a greater or lesser divergence of the upper and lower branches, constituting the cage.

In doing so, it becomes possible, with the inter-somatic implant according to the invention, to result in a setting in kyphosis or in lordosis, depending on the pathology diagnosed, said cage being kyphogenic by default, and likely to become lordosing progressively, typically between - 5 ° to + 8 ° relative to the mean parallel direction defined by the two vertebral plates concerned.

According to a characteristic of the invention, the thread formed at the level of the upper and lower branches is capable of being destroyed, or simply deformed by means of an appropriate tool, after positioning the screw according to the desired degree of screwing. , itself dependent on the desired orientation of the branches

According to another characteristic of the invention, the upper and lower branches have a curved profile, in the main direction of the branches on the one hand, and in the direction perpendicular to the latter on the other hand.

In addition, the top of the dome thus produced is substantially located at the junction of the posterior third and the anterior two thirds, measured with respect to the largest dimension of said branches, for the purpose of greater anatomical adaptation.

According to another characteristic of the invention, the implant has a reduced median surface, making it possible to obtain a predetermined and chosen contact surface, with a second symmetrical implant intended to be inserted also at the level of the space between vertebral. A left implant and a right implant are thus defined, the two implants being symmetrical to each other with respect to their lateral surface intended to come into contact with one another during the positioning of said implants.

Indeed, traditionally, two inter-somatic cages are put in place between two consecutive vertebral bodies, corresponding substantially to the two cups defined by said plates of the vertebral bodies. The manner in which the invention can be implemented and the advantages which ensue therefrom will emerge more clearly from the embodiment which follows, given by way of indication and not limiting in support of the appended figures.

Figure 1 is a schematic representation illustrating the inter-somatic implant according to the present invention, placed between two vertebral bodies of a spine.

FIG. 2 is a schematic perspective representation of the interbody implant according to the invention. Figure 3 is a schematic representation of the rear face of the inter-somatic implant according to the invention.

Figure 4 is a schematic front view of the inter-somatic implant according to the invention. Figure 5 is a partial view of Figure 2, showing in particular the lower branch of the inter-somatic implant.

Figure 6 is a schematic side representation of the inter-somatic implant according to the invention.

Figure 7 is a schematic representation illustrating the placement of implants according to the invention.

The inter-somatic implant according to the invention has been particularly shown in relation to Figure 2. It is intended to be inserted between the vertebral plates (15, 16) of two consecutive vertebrae (see Figure 1).

It is made of any material, in particular titanium, or even polyether-etherketone, sold under the brand PEEK. This material is well known for being stable and also radio-transparent, in particular making it possible to perfectly control the fusion when it has occurred. What is more, this material is also known to have an elasticity which is closest to the bone, thereby favoring the desired fusion phenomenon.

According to the invention, this inter-somatic implant consists of a rigid cage, defined by an upper branch (2), a lower branch (3), secured at one of their ends by a junction zone (4).

On the other hand, their other end is free, defining a slot (11), as can be seen in FIG. 2. In other words, the inter-somatic implant according to the invention has a closed slot at the junction zone (4).

According to a characteristic of the invention, in the absence of external constraints, the orientation of the slot from the junction zone (4) is convergent. In other outfits, the slot has a narrower width at the free end of the slot (11) than at the junction zone (4).

The objective is that in the absence of constraint, the inter-somatic implant produces a kyphogenic effect by default when it is put in place.

The cage thus produced defines an internal volume, into which is intended to be inserted one or more spongy bone grafts or a bone substitute, intended to allow effective fusion between the two vertebral bodies between which said implant is inserted.

To this end, the expansion of the cancellous bone takes place at the level of the entire periphery of the slot, except at the level of the through opening (5) defined at the level of the junction zone (4), where this opening is filled, at least in part by the screw (12) described below in more detail.

According to a characteristic of the invention, the two branches, respectively (2) and (3) have at their respective internal face, a partial thread (8) extending substantially over part of their length, and interrupting a slightly below their free end by forming a chute (14) therefore free of any thread, and only serving as a guide for a screw (12) described in more detail below.

This thus defined thread is intended to cooperate with a screw (12), of corresponding screw pitch. This screw (12) is inserted at the level of the opening (5) of the junction zone (4), after the inter-somatic implant has been placed at the desired inter-vertebral space. This screw therefore comes to bite into the thread (6) of the junction zone (4). The screw head is provided either with a slot, or with a cross, or else with a hexagonal volume (13), in order to be able to cooperate with a screwdriver or a hexagon key. It is easily understood that when this screw is screwed, also acting as a plug, it progresses on the partial thread (8), and is further guided by the chute (14), said screw (12) then having a terminal portion ( 15) free of any thread, in order to cooperate freely with the chute (14). As it progresses, it induces the progressive separation of the branches (2) and (3) from one another. In this way, the screwing of the screw at the level of this thread gradually transfers the kyphogenic action of the implant into lordosing action, typically in a range between -5 ° to + 8 ° relative to the average parallel defined by l orientation of the two plates at which the implant is inserted.

We can therefore see the whole point of the inter-somatic implant of the invention, insofar as depending on the pathology encountered, the surgeon is able to use a standard inter-somatic implant, which he adjusts depending on the desired action of said implant by simple more or less pronounced screwing of the screw within the thread (8).

In addition, in order to ensure that there is no modification of the adjustment desired by the practitioner, the thread (8) located upstream of the screw relative to the direction of screwing is destroyed, for example at using a sharp tool

In doing so, the screw can no longer move back. At the same time, it can no longer advance, given the pressure exerted by the two arms, respectively upper and lower, on the screw, and by its default kyphosic configuration.

According to the invention, the area (5) of the rear face of the cage is relatively small with regard to this rear face. In this way, during the placement of the implant, and especially during the screwing operation, the practitioner can visualize the progression of the cage in the inter-vertebral space without being hampered by the ancillary of placement , thus optimizing security conditions.

As a corollary, in addition to the possible dynamic action of the implant, the invention also aims to optimize its anatomical profile.

Thus, the external faces of the upper and lower branches respectively are curved, in order to allow a better adaptation to the concave profile of the plates of the vertebral bodies at the level of which they are intended to exert pressure. More specifically, they have a double bending, that is to say both according to their main dimension, but also in a direction perpendicular thereto, as can be observed in relation to FIGS. 2 to 4 .

This bulging is slightly asymmetrical, and is more pronounced in the internal area of the implant. In this regard, the height of the implant in the internal zone is slightly greater than that in the external zone.

The top of the bulge is advantageously located at the junction of the posterior third and the front two thirds, respectively of the upper and lower faces of the upper and lower branches.

Furthermore, the convexity of the lower branch is slightly lower than that of the upper branch.

In doing so, the spacing of the branches (2, 3) resulting from the introduction of the screw (12) within the cage induces a support of said branches against the respective vertebral plates substantially at the level of their entire surface, respectively lower and superior, and not limited to their only end, thereby favoring the desired fusion phenomenon.

At the same time, given that this type of implant is called upon to operate in pairs, as shown in FIG. 7, that is to say an implant cooperating with each of the cavities of the plateau of the vertebral body, the one of the lateral faces has a reduced surface in the middle, making it possible to obtain a predetermined and chosen contact surface, with a second symmetrical implant intended to also be inserted at the level of the inter-vertebral space. A left implant and a right implant are thus defined, the two implants being symmetrical to each other with respect to their lateral surface intended to come into contact with one another during the positioning of said implants.

We thus have an intervertebral intervertebral implant combining both an anatomical and a dynamic function, simplifying the work of the practitioner, while operating from standard elements. More specifically, the particular shape of the implant confers on the invention, more particularly adapted to the anatomy of the vertebral plates, in order to increase the contact surface with these, to have a better distribution of the stresses, and therefore, lead to a better fusion.

In addition, due to this better anatomically adapted shape, the implant becomes self-supporting, and therefore does not require posterior stabilization osteosynthesis, which was not the case with implants of the prior art.

In addition, the dynamic nature of the implant gives the invention pennet in addition to better adaptation of it to the patient's pathology, also to reduce the risk of possible deformations such as kyphosis, hyperlordosis, scoliosis, spondylolisthesis.

Finally, due to its anatomy and dynamic nature, the implant of the invention provides a wedging function, according to a differentiated orientation, leading to intrinsic stability.

Claims

1. Inter-somatic implant, intended to be inserted between two consecutive vertebral bodies (16, 17), and to receive a bone graft or a bone substitute in the volume which it defines, consisting of a cage (1), of which one of the side walls is open, thus defining an upper branch (2) and a lower branch (3), respectively intended to come into contact with the lower plate of the upper vertebral body, and with the upper plate of the lower vertebral body, characterized in that by default, that is to say in the absence of external stress, the two branches (2, 3) darken between them a reduced angle converging with respect to their junction zones (4), and in that each of the two upper (2) and lower (3) branches is provided with an internal thread (8), oriented along the main dimension of the branches, and intended to cooperate with a screw (12), to result in the spacing of the branches, at a desired angle e. 2. inter-somatic implant according to claim 1, characterized in that the thread (8) formed at the level of the upper (2) and lower (3) branches is extended by an internal chute (14) for guiding the screw (12 ). 3. inter-somatic implant according to one of claims 1 and 2, characterized in that the thread (8) formed at the level of the upper (2) and lower (3) branches, is capable of being destroyed, after placing in place of the screw according to the desired degree of screwing, itself dependent on the desired orientation of the branches. 4. inter-somatic implant according to one of claims 1 to 3, characterized in that the screw (12) capable of progressing at the level of the thread (8) and the chute (14), is introduced within the implant at the junction zone (4) of the two upper (2) and lower (3) branches, said junction zone (4) being provided for this purpose with a through opening (5) within which is formed a thread (6) with the same characteristics as the thread (8) formed at the level of said branches. 5. inter-somatic implant according to one of claims 1 to 4, characterized in that the screw (12) also acts as a plug, aimed at opposing the progression of the spongy bone graft (s) inserted within of the cavity defined by the implant. 6. inter-somatic implant according to one of claims 1 to 5, characterized in that the upper (2) and lower (3) branches have a convex profile, in the main direction of the branches on the one hand, and according to the direction perpendicular to these on the other hand. 7. inter-somatic implant according to claim 6, characterized in that the apex of the dome thus produced is substantially located at the junction of the posterior third and the anterior two thirds respectively of the upper and lower faces of the upper and lower branches, measured relative to to the largest dimension of said branches. 8. inter-somatic implant according to one of claims 1 to 7, characterized in that it is not symmetrical, thus defining a left implant and a right implant. 9. inter-somatic implant according to claim 8, characterized in that it has a reduced median surface, making it possible to obtain a predetermined contact surface with a second symmetrical implant of the first, intended to be inserted also at the inter-vertebral space.