Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Implantable prosthesis – Bone
Reexamination Certificate
1999-01-07
2001-04-03
Willse, David H. (Department: 3738)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Implantable prosthesis
Bone
Reexamination Certificate
active
06210442
ABSTRACT:
The present invention relates to the subject matter disclosed in international application PCT/EP 97/03730 of Jul. 12, 1997, the entire specification of which is incorporated herein by reference.
The invention relates to an implant for vertebral body fusion having a supporting body, which comprises two opposite-lying support surfaces for application against the opposing end faces of the vertebral bodies to be fused and is insertable into the gap between the two adjacent vertebral bodies.
In the event of damage to intervertebral disks, it is frequently necessary to remove said disks and join the adjacent vertebral bodies permanently to one another. In order to achieve this, it is known to insert a supporting body, which is substantially cuboidal or wedge-shaped, in place of the removed intervertebral disk into the intervertebral space, where it is intended to take over the supporting and spacing function of the intervertebral disk (WO 95/08964).
In order in such a case to achieve a relatively secure fixing of the supporting body in the intervertebral space, the latter has to be highly profiled and this creates problems with the insertion.
On the other hand, it is also known to insert laterally into the intervertebral space a hollow cylindrical bone-screw, which then engages into shell-shaped internal thread regions of the two vertebral bodies and hence mutually fixes the latter. Such a bone-screw is locked against axial displacement but because of the relatively low surface contact high pressure loads arise, which may sometimes lead to the implant in the form of a bone-screw sinking into the vertebral body (EP 0369603 A1).
The object of the invention is to provide an implant which, on the one hand, is easy to insert and, on the other hand, after insertion is locked against displacement.
In the case of an implant of the type described initially, said object is achieved according to the invention in that the supporting body has at least one location channel, which extends between the support surfaces and is open at its top and bottom side, and that there is insertable into the location channel a fixing element provided with an external projection and guided in the location channel so as to be rotatable about its longitudinal axis, which fixing element once inserted into the location channel projects out of the open location channel in that it protrudes at the top and bottom side of the supporting body beyond the support surfaces.
What is proposed, therefore, is a two-part implant substantially comprising a supporting body, which lies with its support surfaces against the end faces of the vertebral bodies and hence provides a mutual supporting of said vertebral bodies over a large area. In addition, a fixing element is provided, which protrudes in an upward and downward direction from said supporting body and hence engages positively into correspondingly shell-shaped recesses of the vertebral bodies.
A substantial portion of the supporting forces is taken over in said construction by the supporting body, with the fixing element also playing a limited role in said regard, but the important point is that the fixing element as a result of the positive engagement with the two vertebral bodies is non-displaceable relative to said vertebral bodies. By virtue of the accommodation of the fixing element in the location channel, the supporting body is also fixed relative to the vertebral bodies.
While it is possible in principle for the fixing element to be guided and hence fixed only in transverse direction in the location channel, in a preferred embodiment means are provided, which fix the fixing element inserted into the location channel in axial direction in said location channel. Said means therefore connect the fixing element and the supporting body also in axial direction, and as a result the supporting body is also fixed in axial direction so as to be non-displaceable relative to the vertebral bodies.
The fixing element is supported rotatably in the location channel, the positive engagement with the vertebral bodies being produced through rotation of the fixing element. In said case, the fixing element might carry for example, in the manner of a key, a bit-shaped projection which, in one angular position of the fixing element, does not protrude beyond the support surfaces so that the supporting body may be inserted into the intervertebral space, whereas by rotating the fixing element said projections are raised above the support surfaces and hence engage positively into the adjacent vertebral bodies. With such a fixing element, a key-like locking is achieved upon rotation of the fixing element.
According to another preferred embodiment, it is provided that the fixing element takes the form of a bone-screw.
Such a bone-screw may be fixed relative to the supporting body in various ways, e.g. a pin penetrating the bone-screw and the supporting bodies might be inserted after the bone-screw has been screwed in.
It is particularly advantageous when, according to a preferred embodiment of the invention, it is provided that the means of fixing the bone-screw in axial direction comprise an internal thread in the location channel, which matches the external thread of the bone-screw. With such a solution, therefore, the bone-screw is screwed into the location channel and at the same time a screwing into the adjacent vertebral bodies is effected, with it being possible to use in the latter a prefabricated internal thread. In principle, it would however also be possible to design the bone-screw in a self-cutting manner so that it itself produces a corresponding thread in the vertebral body.
In a preferred embodiment, it is provided that the location channel separates the parts of the supporting body, which are disposed on either side of the location channel, from one another and that said parts are connected to one another by a bridge.
Said bridge may be, for example, a web which connects the two parts and lies opposite the insertion end of the location channel.
In another embodiment, it may be provided that the bridge is disposed at the insertion end of the location channel and has an insertion opening for the fixing element. It is advantageous when the location channel extends substantially over the entire depth of the supporting body, thereby creating the possibility of inserting a long fixing element, which over a large portion of said length is in engagement with the adjacent vertebral bodies.
In principle, it is possible to provide only a single location channel in the supporting body, preferably in the centre of the latter, although it would in principle also be possible to dispose a plurality of location channels alongside one another in the supporting body, e.g. to dispose symmetrically relative to the centre line two such location channels each receiving a corresponding fixing element.
The support surfaces may be formed parallel to one another, although it is in principle also possible for said support surfaces to be inclined towards one another so that the support surfaces are adapted to the geometry of the end faces of the vertebral bodies, particularly when it is necessary for the vertebral bodies to be inclined in a specific manner towards one another.
In a preferred embodiment, it is provided that the support surfaces are profiled, e.g. the supporting surfaces may carry ribs extending transversely to the longitudinal direction of the location channel. This is of considerable assistance in fixing the supporting bodies in the intervertebral space and ensures a permanent intimate connection between bone tissue and support surface.
In said case, it is particularly advantageous when the supporting surfaces are provided with a bone-friendly surface coating which promotes growing-in of the bone material.
For said purpose, recesses for bone tissue to grow into may also be disposed in the support surfaces.
In a particularly simple refinement, the supporting body is substantially cuboidal in shape.
The bone-screws may in principle be of any desired design although it is particularly advant
Eisen Guntmar
Schultz Robert
Wing Charles
Aesculap AG & Co. KG
Jackson Suzette J.
Lipsitz Barry R.
McAllister Douglas M.
Willse David H.
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