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Intervertebral implant

Intervertebral implant description/claims

This application is a continuation of U.S. patent application Ser. No. 10/553,495, which is a National Stage application of PCT/CH03/00247, filed Apr. 12, 2003, the entire disclosures of which are incorporated herein by reference.

The invention concerns an intervertebral implant.

An intervertebral disc prosthesis of the generic type is known from U.S. Pat. No. 4,911,718 Lee. This known intervertebral disc prosthesis comprises a central core, that is so formed from a biocompatible elastomer, that it is almost corresponds to that of the nucleus pulposus of a natural intervertebral disc, as well as from a multi-layer laminate from fibres bound in an elastomer, arranged around the core. Each laminate layer has its own yarn system, so that a plurality of fibre groups are present. The fibres of the individual layers have various orientations, whereby the angles of the fibres relative to the central axis of the intervertebral disc are in the range of ±20° and ±50°, preferably 0°, +45° and −45°.

From WO 90/00374 Klaue a hip prosthesis is known, the shaft of which is made from a tubular mesh, i.e. a structure, that comprises at least two series of fibres crossing one another. In this application the interior of the tubular mesh remains empty as the shaft of the femur component.

In the case of the prosthesis disclosed in U.S. Pat. No. 4,911,718 Lee, although the individual fibres are integrated in the laminate that is made from an elastomer or another type of synthetic material, their ends are, however, adhered only to the end plates, so that they do not surround the core and consequently, in the case of a radial expansion of the core, cannot accept any tensile force. When adhering the lateral walls, cut out from the fibrous matrix compound, to the end plate, a fixing of the integrated fibres on the end plate is quite difficult, only the cross-section of the fibre offers a contact surface for the chemical joint. Therefore increased stresses occur especially on these joining places of the fibres on the end plate.

Furthermore, in the case of Lee the length of the individual fibres is only from the bottom cover plate to the top cover plate, what corresponds to the sheathing height or a diagonal of the projected sheathing height. Thus the forces occurring can be reduced only along these lengths due to the transfer of the shearing force of the fibres to the elastomer. Thus positions of increased stresses result at the fixings, i.e. on the ends of the fibres.

The prosthesis disclosed in WO 90/00374 Klaue comprises a system of fibres, the individual fibres of which are not fixed on both ends, as well as there is no deformable core. Therefore in the case of an axial compression of the prosthesis the axial compression forces occurring cannot be transferred as tensile forces to the fibres.

From U.S. Pat. No. 3,867,728 Stubstad et al. an intervertebral disc prosthesis is known, that has an elastomeric sandwich structure with a fibre system. A disadvantage of this known prosthesis is that the fibre system, joined with the cover plates, is either not embedded in the sheathing body or in another embodiment is embedded in a multi-layer laminate of an elastomer.

This is where the invention wants to provide remedy. The object of the invention is to produce an intervertebral implant, that comprises a fibre system joined with the cover plates, by virtue of which a sheathing body, surrounding the central part and made from a homogeneous material, will be reinforced.

The inventions achieve this objective with an intervertebral implant having a central axis including a bottom cover plate and a top cover plate, each with an external surface extending transversely to the central axis, a central part with a sheathing that surrounds a fibre system provided between the cover plates, wherein the fibre system is joined with the cover plates at least partially, characterized in that the fibre system is guided over the external surfaces of both cover plates and surrounds at least partially the central part as well as both cover plates, and the sheathing comprises an elastic sheathing body that surrounds the central part on the periphery and is made from a homogeneous material and is passed through by the fibre system.

The basic advantages, achieved by the invention, are that with the intervertebral implant according to the invention

the fibre system can be first wound around the central part and following this poured into an elastomer forming the elastic sheathing body, so that the sheathing, enveloping the central part, can be easily produced,

by applying the elastic material around the fibre system after its winding, the anchoring of the fibre system is possible by various means, for example also on the opposing inner surfaces of the cover plates,

the central part allows a movement of both adjacent bodies of the vertebra in the case of a compression, flexion or extension, lateral bending and torsion,

the momentary centre of rotation or the momentary axes of rotation are not determined by the intervertebral implant itself, and they can position themselves according to the rule of minimum forces or moments occurring,

by varying the number of fibres in the circumferential direction, the cross-section of the fibres and the choice of material, the behaviour of the intervertebral implant can be so adjusted, that under varying loads the movements occur as in the case of the natural intervertebral disc, and

by varying the arrangement and the execution of the fibre system certain movement limitations can be placed on the intervertebral implant, and from a certain deformation a limit region occurs, where despite the further increasing forces no deformation takes place or in the case of moments occurring the implant will no longer tilt.

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