Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Implantable prosthesis – Bone
Reexamination Certificate
2000-07-20
2003-05-13
Prebilic, Paul B. (Department: 3738)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Implantable prosthesis
Bone
C623S017160
Reexamination Certificate
active
06562072
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an implant for insertion between the vertebrae of the spinal column, whereby the cover surfaces of the substantially rectangular- or trapezoidal-section implant facing the adjacent vertebrae are porous and/or are provided with a profiled structure.
Implants of this type are used to form supports for vertebral fusions, whereby, after at least a partial removal of an intervertebral disc and preparation of the roof plates of the vertebrae, the implant that is to be inserted between adjacent vertebrae is introduced into the intervertebral interstice, and it is ensured that the intervertebral space is kept clear. By forming the cover surfaces facing the adjacent vertebrae with a porous surface or providing them with a profiled structure, the arrangement will become firmly anchored after the implant has been inserted due to the growth of the bones of the adjacent vertebrae onto the cover surfaces of the implant. In addition, or, as an alternative, at least one break-through or recess in the cover surface of such an implant may be filled with bone mass before being inserted so that the bone mass accommodated in the implant will be urged to knit with the material of the immediately adjacent vertebrae after the implant has been inserted. Moreover, a support system extending over a plurality of vertebrae may be provided externally of the spinal column near the implant for lending additional support, said system being attachable to the individual vertebrae.
Implants of the type mentioned hereinabove can be derived from U.S. Pat. No. 4,834,757, U.S. Pat. No. 5,192,327 or WO 90/00037 for example. In the construction according to U.S. Pat. No. 4,834,757, implants of substantially rectangular cross-section are made use of, whereby two implants are inserted posteriorly between respective pairs of adjacent vertebrae in each of the two side regions of the vertebrae. The disadvantage of this known construction is that, in addition to an at least partial removal of the rear bony and ligamentary elements which is necessary to allow insertion of the implant, it is imperative that two separate implants be used, this thereby not only resulting in increased expenditure for the operation but also requiring that they be mutually correctly positioned, something which it is not easy to achieve.
In the construction according to WO 97/00037, an implant is inserted whose outer dimensions substantially correspond to the total dimensions of two adjacent vertebrae. A particular disadvantage with implants of this type is that in practice they can only be inserted anteriorly, whereby however, in addition to the complicated access via the abdominal cavity with consequent possible injury to the major abdominal vessels and the nerve plexus, the frontal longitudinal ligament has to be cut-through so that the natural supporting function exercised by this longitudinal ligament is no longer available after the implant has been inserted. Moreover, a further operation then has to be effected posteriorly for the insertion of an additional support structure that thereby becomes necessary.
In addition to these embodiments of implants for insertion between vertebrae of the type described above, other implants having substantially cylindrical contours are known, for which reference may be made to EP-A 0 369 603 or DE-C 36 37 314 for example. Such types of cylindrical or tube-shaped implants may be additionally provided with a thread-like outer contour in order to enable them to be screwed between the vertebrae by means of a self-threading action. The particular disadvantage of tube-shaped implants of this type, whereby two implants must again be used between each two adjacent vertebrae in normal circumstances, is that the implants will not have a defined substantially flat support area on the vertebrae thus giving rise to the fear that difficulties will possibly be encountered in regard to the growth of the incorporated bony material. Another disadvantage is that injury to soft bony parts with consequential breakage or subsidence of the bone may be induced by the threading or screwing actions.
Based upon the above-mentioned state of the art, the aim of the present invention is then to provide an implant for insertion between the vertebrae of the spinal column, whereby an adequate and reliable supporting function can be achieved using merely one implant between two vertebrae and wherein the implant in accordance with the invention should be insertable posteriorly, especially laterally, so as, firstly, to simplify the operation and enable the implant to be inserted together with an additional support system if required and secondly, to avoid the necessity of damaging or destroying naturally provided support elements such as the frontal longitudinal ligament for example and/or to avoid having to remove additional ligamentary and bony material, especially in the region of the vertebral or spinous process, in order to allow the implant to be inserted.
SUMMARY OF THE INVENTION
Based upon an implant of the type mentioned hereinabove, the above object is achieved by the implant in accordance with invention, in essence, in that the breadth of the implant is such that it covers at most the rearward half of the vertebra facing the spinous process, and preferably at most the rearward third thereof, and the length of the implant is essentially such that it overlaps the rearward region of the vertebra, and in that the boundary face of the implant facing the interior of the vertebra and extending towards the adjacent vertebrae is curved convexly. Due to the fact that the implant in accordance with the invention basically covers only the rearward portion of the adjacent vertebrae when it is in the installed state, the requisite reach can be found with an appropriately miniature implant, whereby the largest forces and loads are effective in the rear portion of the vertebrae facing the vertebral or spinous process and can thus be reliably accommodated in a corresponding manner by the implant in accordance with the invention, and also the bone strength is at its greatest in said rear portion. In addition to a miniature, one-piece construction of the implant as proposed in accordance with the invention, it is also possible to introduce the implant laterally between and passing-by the protruding nerve roots and the spinal cord into the intervertebral space from behind, especially by virtue of the further matter envisaged in accordance with the invention, namely, the convexly curved boundary face facing the interior of the vertebra when in the installed state, so that, in the case of a posterior operational technique of this type, not only will the frontal longitudinal ligament remain completely undamaged, but one can also dispense with the additional removal of ligamentary and bony material such as was required for implants in accordance with the state of the art. By virtue of the curved boundary face, not only is it possible to ensure a simple sideways introduction of the implant, but exact positioning of the implant can also be achieved so as to cater for the portion of the vertebrae facing the spinous process being covered in the inserted state and thereby providing proper support.
In order to simplify still further the lateral introduction of the implant, provision is preferably made for the boundary face of the implant facing the spinous process to be curved concavely so that overall, when seen from a top view, there will be provided an essentially bow or crescent shaped implant which is correspondingly easily and reliably introducible from the side into the intervertebral space from the rear with the very smallest amount of space being required.
Moreover, for the purposes of adequately supporting adjacent vertebrae by covering an appropriate portion thereof, it is proposed that the radius of curvature of the boundary face of the implant facing the interior of the vertebra amount to 30 to 90%, and especially to 40 to 80%, of the spacing between the frontal edge of the vertebra and
Fuss Franz Konstantin
Sabitzer Ronald J.
Aesculap AG & Co. KG
Lipsitz Barry R.
McAllister Douglas M.
Prebilic Paul B.
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