Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Implantable prosthesis – Bone
Reexamination Certificate
1997-09-25
2001-02-27
Willse, David H. (Department: 3738)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Implantable prosthesis
Bone
Reexamination Certificate
active
06193755
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a spinal cage assembly.
There are known spinal cord implants that are designed as hollow bodies and driven individually or in pairs into the area of adjacent vertebrae to achieve effective fusion of adjacent vertebrae. Such implants are known, for example, from European Patent 307,741 B1, German Patent 4,416,605 C1, German Patent 4,323,956 C1, European Patent Application 637,440 A1, World Patent Application 95/26164, U.S. Pat. No. 5,015,247 or German Utility Model 29,600,879. The hollow design of the implants serves to accommodate bone material, thus achieving better fusion.
Furthermore, so-called spinal cage assemblies have become known that are inserted after vertebral resection and replace the missing vertebra. Such a spinal cage assembly is disclosed, for example, in German Utility Model 9,107,494, European Patent 188,954 or European Patent 535,215. With the known spinal cage assemblies, the point of action on the vertebrae is relatively centrally located in an area that is relatively soft. Therefore, there is the danger of the spinal cage assembly digging into the vertebra.
There is a similar danger with spinal cage assemblies made of a relatively thin-walled braid.
An object of this invention is a spinal cage assembly that will permit effective support, while at the same time building up new bone substance between the vertebrae.
This and other objects are achieved by the device of the invention.
SUMMARY OF THE INVENTION
According to this invention, a spinal cage assembly has a sleeve-shaped body made of a physiologically compatible material, which has a relatively thick wall that is suitable for transmitting relatively high forces, and which also permits support on the adjacent vertebrae with a relatively low surface pressure. This support is especially effective when the diameter of the sleeve-shaped body is designed so that the wall is supported in the cortical area of the vertebrae because the cortical area is known to be the hardest area of bone.
Also according to the invention, the end faces or leading edges are irregularly designed and the sleeve-shaped body is secured against rotation. The sleeve-shaped body has perforations in its wall through which bone material can be introduced into the interior of the sleeve-shaped body.
According to the invention in another embodiment, the irregular edge of the sleeve-shaped body lies in a plane that forms an angle to the transverse axis of the sleeve-shaped body which is an angle between 3° and 6°. This permits adaptation to the prevailing anatomical conditions.
According to the invention in another embodiment, the leading edge may be shaped with teeth and gaps between the teeth, for example with the teeth having flat surfaces at the tips so that the teeth are prevented from digging deeply into the vertebra. The gaps between the teeth preferably have a rounded contour, with the gaps between the teeth forming relatively sharp edges with the tip surfaces of the teeth.
For inserting a sleeve-shaped body, preferably a tool is used, which has a relatively long shaft and has a threaded stem at the free end. The threaded stem may be engaged with a threaded hole in the sleeve-shaped body to insert the sleeve-shaped body into the space of the resected vertebra in the proper position between two neighboring vertebrae.
The height of the spinal cage assembly depends on the height of the resected vertebra or the remaining distance between neighboring vertebrae and the position of the vertebra in the spinal cord. Therefore, the known spinal cage assemblies are usually adjustable in length. To permit adjustment with the spinal cage assembly according to this invention as well, one embodiment of the invention also provides a second sleeve-shaped body that accommodates the first sleeve-shaped body by telescoping it inward and is shaped like the inner sleeve-shaped body. In addition, both sleeve-shaped bodies have holes that can be aligned with each other and into which threaded screws can be inserted to secure the two sleeve-shaped bodies relative to each other. In this position, the inner sleeve-shaped body projects slightly out of the outer. If a pair of holes is provided according to another embodiment of the invention, two distance steps can be adjusted. Together with the height of the inner body, this thus yields four height levels, which is completely sufficient for most surgical cases encountered. The height is adjusted before inserting the implant, so that difficult manipulations are not necessary for a height adjustment in situ.
According to another embodiment of the invention, it is also conceivable to apply a force element, etc., between the sleeve-shaped telescoping bodies to achieve automatic adjustability in height. For example, a prestressed spring may be provided that moves the two sleeve-shaped bodies apart for elongation purposes when a suitable locking device is released. However, it is also conceivable to provide a different force element.
It is conceivable to provide a square or polygonal cross section for the sleeve-shaped body. However, a circular cross section in adaptation to the contour of the vertebrae is preferable.
As mentioned above, the tool for inserting the sleeve-shaped body has a relatively long shaft. According to one embodiment of the invention, a sleeve may be mounted on the free end of this shaft so it can rotate and is supported on a shoulder of the shaft, and on the free end it has a concave recess that approximately matches the outside contour of the sleeve-shaped body. In this way, the transverse forces that must be applied by the tool when inserting the sleeve body are not applied only through the relatively thin threaded stem but also through the sleeve.
This invention is explained in greater detail below on the basis of figures.
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Metz-Stavenhagen Peter
Robioneck Bernd
Howmedica GmbH
Jackson Suzette J.
Lerner David Littenberg Krumholz & Mentlik LLP
Willse David H.
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