WO2009024730A2 - Intervertebral stabilisation assembly for arthrodesis including a damping member - Google Patents

Abstract

The invention relates to an intervertebral stabilisation device for connecting two pedicular screws extending into two adjacent vertebrae, that comprises two rigid members (10, 20) to be hinged relative to the two pedicular screws, a dampening member (30) connected to the rigid members so as to be attached to the latter both in compression and extension, and at least one wall (40) axially extending from a first rigid member (10) in the vicinity of the periphery of the dampening member (30) and in the direction of the other rigid member (20) in order to form both an abutment in compression as well as centring means for preventing any axis deviation of the two rigid members.

Description

 INTERVERTEBRAL STABILIZATION DEVICE FOR ARTHRODESIS, COMPRISING A DAMAGING ELEMENT

The present invention relates to an intervertebral stabilization device for arthrodesis, comprising a damping element.

The invention is in the field of arthrodesis, namely bone fusion between at least two adjacent vertebrae. It will be recalled that the arthrodesis aims to allow only micro-movements between the vertebrae, as well as damping vibrations. These micro-movements allow, among other things, the patient, once again bipedal after the operation, to adjust his balance as best as possible before taking the bone graft. These micromovements also allow the assembly according to the invention not to oppose after the bone fusion to plastic adaptations, which are one of the fundamental characteristics of the evolution of the spine during life of the patient.

Typically, an extra-discal assembly for arthrodesis within the meaning of the invention allows an amplitude of movement between two vertebrae, viewed from the side, which is equal to at most about 10% of the natural physiological amplitude. In other words, if there is a maximum natural amplitude of 10 ° in rotation between two given adjacent vertebrae, the stabilization assembly according to the invention is capable of allowing, at most, a clearance of 1 ° between these two vertebrae.

It should be noted that it is essential to make a distinction between, on the one hand, a prosthesis which is designed to recreate the intervertebral movement and, on the other hand, the assembly according to the invention whose primary purpose is to get a bone fusion between two vertebrae. In this respect, it will be recalled that there are substantial structural and functional differences between a prosthesis and an osteosynthesis device, so that a prosthesis can not provide bone fusion and that, similarly, a set for arthrodesis can provide a prosthesis function.

A stabilization device as targeted by the invention comprises two rigid members, each of which is adapted to cooperate with a corresponding pedicle screw, while these two screws are implanted in two vertebrae adjacent. There is further provided a damping element, reported against the walls opposite these two rigid bodies.

Such a device is for example proposed by the company MEDTRONIC under the commercial reference AGILE. The damping element, which has a form of buffer, is reported against end plates of the rigid bodies, in particular by hot vulcanization. Under these conditions, this damping element can not only be compressed, but also be stretched while remaining integral with these two bodies, thanks to the presence of this connection.

This AGILE stabilization device further comprises centering means, intended to prevent the two rigid members from offsetting, particularly during bending movements. For this purpose, use is made of a cable secured to one of the two rigid members, which passes through the damping pad and extends into the interior volume of the hollow rigid member opposite.

This known solution, however, has certain disadvantages. In particular, the AGILE stabilization assembly tends to work much too flexibly, which reduces its efficiency and life.

Note also that this object, which was originally designed as a prosthesis accompanying the vertebral movement, was transformed into an osteosynthesis device, because of the administrative constraints on the US territory. Such a transformation has been implemented without structural modification of this object in order to restrain the movement, which highlights its impossibility to obtain an arthrodesis, since this object allows a much greater amount of movement.

That being said, the invention aims to provide an alternative to this intervertebral stabilization device, which overcomes these disadvantages.

For this purpose, it relates to an intervertebral stabilization device according to claim 1 attached. Advantageous features of the invention are the subject of the subclaims.

The invention will be described below, with reference to the accompanying drawings, given solely by way of non-limiting example, in which Figures 1 to 3 are longitudinal sectional views, illustrating a stabilization device according to the invention. in respective positions of rest, compression and extension. The stabilization device according to the invention, which is shown in Figure 1, comprises firstly a first rigid member 10, and a first pedicle screw 110, which cooperate mutually. Thus, this rigid member and pedicle screw are articulated relative to each other, namely that they have three degrees of freedom in rotation relative to each other. It will also be noted that this rigid member and this screw may either be mutually integral in translation or have at least one degree of mutual freedom in translation.

The articulated cooperation of the rigid member 10 and the pedicle screw 110 can be made according to a ball-type connection, having a single center of rotation. In particular, it may be an "equatorial catch" connection, in particular in accordance with the teaching of FR-A-2 812 535.

Such an equatorial catch is also represented in FIG. 1, on which the screw 110 has a shank 112 implanted in the vertebral body, as well as a head 114 comprising an inclined equatorial flat 116, namely that it is not not perpendicular to the main axis of the screw. In addition, the rigid member 10 is terminated by a cup 11 defining a housing 11 'in which can be introduced the head 114 above, according to the principle of equatorial capture described in FR-A-2812535.

However, it can provide articulated cooperation between the rigid member and the pedicle screw, in a connection involving more than a single center of rotation, or a cloud of centers of rotation. In this regard, it can be provided that the screw or rigid member is provided with an eyelet whose walls define an orifice, while the rigid member or the screw has a clean end to penetrate into this orifice, with a possibility deflection in at least one direction of the plane of this orifice. This cooperation between the rigid member and the screw can thus be in accordance with the teaching of the French patent application filed May 6, 2008 under the number 08 02508, in the name of the same Applicant, whose content is incorporated herein by reference.

As a further alternative, it can be provided that the rigid member and the screw cooperate according to the teaching of the French patent application filed on

August 14, 2008 under the title "Extra-discal intervertebral stabilization set for arthrodesis" and under number 08 55574, in the name of the same Applicant, the contents of which are incorporated herein by reference. In this case, the rigid member is example prolonged by two terminal slides, supporting a pair of jaws that cooperate with the pedicle screw. At least one jaw is then slidable along the slides, while there is provided return means of each movable jaw in contact with the screw. The rigid member 10 firstly comprises an axial rod 12, which is provided with the end cup 11 cooperating with the pedicle screw 110 in the manner described above. This rod 12 is extended by an end plate 14, extending radially in the manner of a disc.

The device of the invention further comprises a second rigid member 20 and a second pedicle screw 120, which are respectively analogous to the mechanical elements 10 and 110. In addition, the member 20 and the pedicle screw 120 are articulated by Equatorial capture, similarly to what has been described above with reference to the first pair 10 and 110. However, by way of a variant, it is possible to provide that these members 10, 20 and / or the screws 110, 120 have different structures.

The device according to the invention further comprises an intermediate buffer 30, made of any suitable material having a damping character, such as an elastomer. Since, as we have seen above, the present invention is in the field of arthrodesis, a relatively rigid material will be chosen in order to allow maximum micro-movements.

This buffer is fixed on the opposite faces of the end plates 14 and 24, for example by hot vulcanization, as in the case of the device marketed by the company MEDTRONIC under the reference AGILE. It will be noted that the first plate 14 has a diameter slightly greater than that of the buffer 30, as well as that of the second plate 24.

This first plate 14 is associated with at least one wall 40, which extends from the outer periphery of this plate in an axial direction, with reference to the longitudinal principal axis A of the device. In the illustrated example, this wall extends over the entire periphery of the pad 30, namely that it forms a cylindrical barrel. However, it is possible, alternatively, to use several axial branches, for example distributed at regular angular spacings. The shaft 40 is terminated by a radial flange 42, which is reentrant so as to form a covering zone with the plate 24 opposite. Under these conditions, this flange 42 is capable of forming a stop for the plate 24, as will be seen in more detail in the following. At rest, as illustrated in Figure 1, the shaft 40 defines, with the outer wall of the buffer 30, an annular spacer space, denoted e. In addition, the walls facing the flange 42 and the plate 24 define an axial spacing space noted e '.

During a compressive force exerted on the device (FIG. 2), the members 10 and 20 come closer to one another. Under these conditions, the buffer 30 has a tendency to occupy the intermediate space e, until it is blocked radially by the peripheral wall 40. It will therefore be noted that the latter forms a compression abutment means, as well as a means of centering, insofar as this wall 40 prevents the two members 10 and 20 to offset to a sensitive extent.

On the contrary, FIG. 3 illustrates an extension phase of the device, in which the members 10 and 20 tend to move away. Under these conditions, the plate 24 abuts against the flange 42, so that the latter limits the extension movement. In addition, the presence of the barrel 40 prevents any significant shearing effort.

The stabilization device according to the invention, which has a simple structure, further has stop means for limiting the amplitude in compression and, advantageously, also in extension. In addition, the compression abutment means provide an additional centering function, which prevents the two rigid bodies from offsetting.

In this respect, it will be noted that it is possible to adjust the characteristics of the buffer 30 and / or the resting dimensions of the interspace spaces e and e ', in order to adjust the amplitude of the authorized displacements while remaining in the range of the arthrodesis. It will also be noted that the buffer 30 is advantageously full, namely that it does not have a central orifice such as that of the AGILE device presented above. This is advantageous in terms of ease of implementation, as well as overall life. Finally, it is particularly advantageous to provide rigid members, each of which is hingedly connected to a corresponding pedicle screw. In fact, in service, all the forces that are not exerted along the longitudinal axis of the device, in particular the bending forces, are absorbed by the presence of the two joints. Under these conditions, the only residual forces to which the device is subjected, are axial type, namely stretching and compression. This makes it possible to extend the life of this device substantially, in particular by comparison with the prior art AGILE, which works substantially in flexion.

Claims

An intervertebral stabilization device for arthrodesis, for connecting two adjacent vertebrae, comprising: two pedicular screws (110, 120), each of which is intended to be implanted in the vertebral body of a corresponding vertebra; two rigid members (10, 20), each of which is intended to be articulated with respect to a corresponding pedicle screw; - A damping element (30) attached to these rigid members, so as to be secured to them in both compression and extension, the device further comprising at least one wall (40) extending axially from a first rigid member (10), in the vicinity of the periphery of the damping element (30) and in the direction of the other rigid member (20), so as to form both a compression abutment and means of centering to avoid misalignment of these two rigid bodies. 2. intervertebral stabilization device according to claim 1, characterized in that each rigid member (10, 20) comprises a radial plate (14, 24) on which is fixed the damping element (30), and the or each axial wall extends from the periphery of the plate (14) of the first rigid member (10). 3. intervertebral stabilization device according to claim 1 or 2, characterized in that the axial wall (40) is extended by a radial collar (42) intended to form an extension stop for the second rigid member (20). 4. intervertebral stabilization device according to any one of the preceding claims, characterized in that the damping element (30) is full. Intervertebral stabilization device according to one of the preceding claims, characterized in that a single wall is provided axial, forming a cylindrical barrel (40) extending at the periphery of the damping element (30). 6. intervertebral stabilization device according to one of claims 1 to 4, characterized in that there is provided a plurality of axial branches extending at the periphery of the damping element.