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Veretebra stabilizing assembly

Veretebra stabilizing assembly description/claims

This application is a continuation of prior U.S. patent application Ser. No. 10/486,046, filed 2 Jul. 2004, which claims the benefit of PCT/FR02/02834, filed 8 Aug. 2002, which claims benefit of French application FR 01.10604, filed 8 Aug. 2001. The above referenced applications are incorporated herein by reference.

The present invention relates to an assembly for stabilizing vertebrae, in particular lumbar vertebrae. This assembly can be defined as a relief prosthesis having a dual effect, as will be appreciated below.

It is known that the mobility of two adjacent vertebrae, in particular in the lumbar region, is dependent on the intervertebral disc at the anterior side and pairs of articular surfaces at the posterior side.

The arrangement of the disc and articular surfaces ensures auto-limitation of movements both in the plane perpendicular to the vertebral column, during torsion, and in a sagittal plane, during flexions and extensions of the vertebral column.

The shape, the structure and the height of the disc confer on it additional functions of maintaining lordosis, absorbing shocks and distributing stresses. At the rear, the articular surfaces guide the movements and act as hinges.

The ageing process of the subject leads to disturbances in this anterior/posterior equilibrium involving the discs and the surfaces. Generally, the degeneration of the discs precedes that of the surfaces. Collapse and instability of the discs leads to a partial transfer of the stresses to the posterior columns which are formed by the surfaces, which brings about a loss in the surface congruence and a slackening of the ligaments. This results in deterioration of the articular surfaces, which leads to various pathologies having implications of a mechanical and neurological nature.

In order to treat these pathologies, an anterior arthrodesis has been proposed, by insertion of a graft between the plates of the two vertebrae in question. This graft is usually contained in a rigid cage, known as a “fusion cage”.

However, this technique does not prevent rotational instability which can compromise, in the medium term, the anticipated antalgic result, and it has now been established that the anterior arthrodesis must be complemented by a posterior arthrodesis.

An intervention of this type has limits and disadvantages. It is aimed at severe pathologies which are at an advanced stage and is not without risks, given that the patients are often treated at a relatively late stage in the pathological development. Intervention can further have consequences which are detrimental to adjacent articulations in the medium-term and long-term.

For these reasons, techniques known as “non-fusion” techniques have been developed and relate to the early and palliative treatment of degenerative disc/surface phenomena.

With regard to the disc space, there have been developed various shock-absorbent implants, which are intended to replace the nucleus pulposus, in the form of pairs of pads or elliptical or spiral elements.

These implants are introduced either via an anterior access point, which has the disadvantage of damaging the anterior common vertebral ligament, or via a posterior access point, which has the disadvantage of leading to the sacrifice of a large amount of bone, owing to the space requirement of the implants.

Techniques involving percutaneous injection of a colloid which can be polymerised in situ have also been proposed, as have techniques using solid, disc-like prostheses in the form of two metal plates which enclose a shock-absorbent material and which rest on each of the vertebral plates which are adjacent to the disc.

These techniques are not completely satisfactory as regards the treatment of disc degeneration combined with wear of the surfaces and/or ligament distension.

Devices intended to limit the articular play of the surfaces have also been proposed. A device of this type comprises in particular a continuous woven ligament which is positioned between the spinous processes or along the articular surfaces by means of pedicle screws, and/or a shock-absorbent dividing element which is positioned at the lamina/spinous process junction so as to alleviate the surface play while at the same time stretching the posterior capsule/ligament elements.

It has been found that these techniques are also not completely satisfactory with regard to the above-mentioned treatment.

The object of the present invention is to overcome this fundamental disadvantage by providing an assembly for stabilizing two adjacent vertebrae which sustain both disc degeneration with ligament distension, as well as possibly wear of the surfaces, this assembly further having to be relatively simple to implant and, in addition, relatively non-invasive.

In one embodiment, the present invention provides an implant assembly for implantation between upper and lower spinous processes that advantageously restores the anatomical tension to a supra-spinous posterior ligament extending between the spinous processes. The implant assembly comprises an interspinous implant and a removable clip. The interspinous implant comprises an interspinous portion having an upper surface for engagement with the upper spinous process and a lower surface for engagement with the lower spinous process. The interspinous portion has a thickness between the upper surface and the lower surface sufficient to restore anatomical tension to the supra-spinous posterior ligament. The implant also comprises an upper pair of lugs extending from the interspinous portion for interfacing with the upper spinous process and a lower pair of lugs extending from the interspinous portion in a direction substantially opposite from the upper pair of lugs, the lower pair of lugs for interfacing with the lower spinous process. At least one of the upper pair of lugs and at least one of the lower pair of lugs is movable between an insertion configuration and an retention configuration. The insertion configuration is substantially perpendicular to the retention configuration. The removable clip is for engagement with the relevant lugs to selectively retain the same in the insertion configuration. The implant may comprise a flexible, resilient material to allow motion between the spinous processes and to allow the at least one of the upper and lower lugs to resiliently return to the retention configuration from the implantation configuration. The implant may comprise a casing substantially surrounding the flexible, resilient material, which may advantageously be a woven casing. The relevant lugs are advantageously resiliently biased toward their retention configuration.

In another embodiment, the invention provides an implant assembly for implantation between first and second adjacent spinous processes. The assembly comprises an interspinous implant and a clip. The interspinous implant comprises a central body having first and second lateral portions. First and second arms extend from the first lateral portion and third and fourth arms flexibly extend from the second lateral portion. The third arm is moveable relative to the central body between a first position and a second position, and the fourth arm is moveable relative to the central body between a first position and a second position. The third and fourth arms include respective base portions proximate the central body and end portions distal therefrom; wherein the end portions of the third and fourth arms are closer together when the third and fourth arms are in their first positions than in their second positions. The first arm, central body, and third arm form a first saddle for receiving the first spinous process with the third arm in the second position. Likewise, the second arm, central body, and fourth arm form a second saddle for receiving the second spinous process with the fourth arm in the second position. The clip is a retaining clip removably coupled to the implant so as to selectively retain the third and fourth arms in their first positions. The third and fourth arms are advantageously biased toward their second positions. With reference to an axis of the central body, the third and fourth arms, in their first positions, fit within the vertical cross-sectional area of the central body projected onto a plane normal to the axis; but extend outside the vertical cross-sectional area of the central body when in their second positions.

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