Surgery – Instruments – Orthopedic instrumentation
Reexamination Certificate
2000-03-29
2001-10-09
Hirsch, Paul J. (Department: 3732)
Surgery
Instruments
Orthopedic instrumentation
C606S060000
Reexamination Certificate
active
06299614
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a device for stabilizing vertebra bodies of the spinal column.
2. Description of the Related Art
Such stablizing devises have screws that can be threaded with thier threaded portion through the vertebra pedicles of adjacent vertebra bodies and have a stabilizing rod connecting the screws wherein a clamp is positioned between each screw and the rod.
It is easily understood that the spinal column is subjected to extremly high forces. The stabilizing device must be suitable to recieve these forces and to transmit them.
SUMMARY OF THE INVENTION
It is an object of the present invention to improve the device of the aforementioned kind in a simple and effective manner such that a connection is provided between the screws and the stabilizing rod connecting them that provides angular stability despite the great force loading acting thereon.
In accordance with the present invention, this is achieved in that the screws have a screw head, at a side facing away from the threaded vertebra-engaging portion, and a threaded clamping portion projecting past the screw head. The threaded clamping portion can penetrate the transverse bores in the two legs of the clamp which is slidably positioned on the stabilizing rod but can be fastened thereto. The threaded clamping portion can be loaded by a clamping nut such that the two legs of the clamp are brought closer to one another. At least one of the two transverse bores has coordinated therewith a bore insert member which is supported on the leg and has an eccentric insert bore. Its position relative to the transverse bore determines a more or less slanted position of the clamp and thus of the stabilizing rod relative to the screw.
The device elements which are clamped to one another and thus form the device according to the invention allow, because of their configuration, in an advantageous manner a plurality of different fixed positions of the screws relative to one another. It was found to be very beneficial with regard to the desired stability of the device for its use to provide the insert-receiving transverse bore of the leg of the clamp with a diameter which, in comparison to the transverse bore of the other leg, is greater and tapers in the direction toward the other leg. Furthermore, the outer diameter and the shape of the bore insert member are matched to those of the transverse bore.
Expediently, the eccentric insert bore of the bore insert member is positioned at an acute angle relative to the central axis of the insert and the acute angle has a magnitude of up to 20°. In this way, it is possible to provide a large number of relative positions of the screws to one another with very fine adjustment.
In order to ensure an especially safe clamping of the bore insert member relative to the clamp, it is very advantageous when the insert member is provided with a radial slot extending from the eccentric insert bore to the outer mantle surface of the bore insert member. The radial slot expediently extends in the area of the bore insert member which has the greatest spacing between the eccentric insert bore and the outer mantle surface. This provides an optimal adaptability of the position of the bore insert member to the respective requirements because the area with the smallest wall thickness of the bore insert member is positioned opposite the radial slot, and this configuration provides a sufficient flexibility of the bore insert member.
A close fit and contact of the cooperating surfaces of the clamping leg and the screw will advantageously result when the other leg of the clamp has a recess which is matched to the diameter of the transverse bore, diminishes in the direction toward the edge of the transverse bore, and whose wall is configured to be the contact surface for the screw head. Expediently, in a further advantageous embodiment, the screw head is spherically convex and the wall of the recess providing the contact surface for the screw head is correspondingly spherically concave.
An advantageously defined positioning of the bore insert member relative to the corresponding clamp leg can be achieved when the bore insert member is provided with a radially projecting rim portion at its side facing away from the other leg of the clamp which is supported in a matching partially recessed support surface in the leg of the clamp.
Usually, the outer leg surfaces of the clamp which face one another extend in parallel planes and are positioned at a right angle relative to the central axis of the receiving bore for the stabilizing rod and thus to the axis of the stabilizing rod.
However, a greater range of angular positions can be achieved according to a further embodiment of the invention by positioning the parallel outer leg surfaces of the clamp facing one another such that they are positioned at an angle which differs from a right angle by up to ±10° relative to the central axis of the receiving bore and the axis of the stabilizing rod. In this manner, the slanted positioning range of the screws in relation to the axial plane of the stabilizing rod can be increased by 10° beyond the maximum achievable slanted position resulting from the eccentric arrangement of the eccentric insert bore of the bore insert member. Accordingly, the adjusting range can be increased without compromising the stability of the respectively selected and fixed adjustment position.
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Kretschmer Peter
Siedler Uwe
Hirsch Paul J.
Kueffner Friedrich
Priddy Michael B.
Signus Medizintechnik GmbH
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