Surgery – Instruments – Orthopedic instrumentation
Patent
1995-05-10
1998-09-29
Buiz, Michael
Surgery
Instruments
Orthopedic instrumentation
606 72, 606 73, 81443, A61B 1756
Patent
active
058140468
DESCRIPTION:
BRIEF SUMMARY
The invention relates to lumbar osteosynthesis instrumentation for the correction of spondylolisthesis.
It is known that, substantially, spondylolisthesis is the forward displacement of a vertebra relative to its lower neighbour. In theory, any vertebra may be affected, but the fifth and the fourth lumbar vertebrae are the most commonly concerned.
Affecting more frequently women or young girls than men, spondylolisthesis is usually classified into five types: dysplastic, isthmian, traumatic, degenerative and pathological.
Its degree of seriousness is measured by the distance travelled through by the displaced vertebra with respect to its lower neighbour.
There are four stages:
The first stage is a displacement of a quarter of the antero-posterior diameter of the vertebral body.
The fourth stage corresponds to a complete displacement of the vertebral body.
The second and third stages are the intermediate stages.
Heretofore, although there are certain surgical techniques for the treatment of spondylolisthesis, either by the direct traction on the slipped vertebra, or by the screwing of the pedicles of this slipped vertebra, the reduction of the spondylolisthesis is not always satisfactory, above all in the cases of serious spondylolisthesis.
Surgery is indeed indicated for those who have a long past of lumbalgia or sciatica, in the case of evidence of a vertebral canal stenosis, a compression of the cauda equina or a subjacent motor lesion, or those whose spondylolisthesis rapidly evolves toward stage 3 or stage 4.
Generally, in surgery, an anterior or posterior vertebral fusion, laminectomy with decompression of the posterior structures and an excision of the hypertrophied mass of the fibrous tissue in the region of the lysis may be indicated.
In isthmian spondylolisthesis, the bilateral isthmian lyses are liable to be associated with a considerable pseudoarthrosis in relation with an emerging nerve root. The discal state in the region of the spondylolisthesis sometimes requires a radiculographic or discographic assessment. In vertebral canal stenoses, the decompression without fusion may be a surgical operation.
In actual fact, an effective orthopedic surgery consists in returning the vertebra not only onto the axis of the spine but also to a position which is as correct as possible relative to the neighbouring vertebrae. Over a period of time, or in the course of its displacement, this vertebra in fact might have been subjected to lateral thrusts which have caused it to pivot horizontally to a more or less large extent so that a correct repositioning of the vertebra of course implies its rearward return but also a derotation.
Attempts have already been made to correct spondylolisthesis, for example by means of devices consisting of two pedicular screws interconnected by a transverse plate which, by screwing a nut bearing against the plate, act solely by translation of the concerned vertebra for putting it into alignment with the neighbouring vertebrae.
Thus, the device disclosed in French patent 2 615 095 (87 06 864) employs two rods which are longitudinally fixed in the vertebral column with the aid of pedicular screws and each serve as support means for two screws having a double screw thread connected to the vertebra to be corrected. These two double thread screws are transversely connected by a rigid plate constituting a bipedicular base. It is this transverse plate which permits acting on the vertebra to be corrected owing to the provision of a median opening for receiving traction forceps.
In fact, such a device does not permit acting in a sufficiently satisfactory manner, and experience has shown that a traction on the median part of the plate has for effect to rearwardly return the vertebra to be corrected too rapidly. Further, if this vertebra must be derotated, it has been found that the presence of the plate is liable to prevent the required derotation action owing to the fact that this induces at the same time a certain return of the vertebra.
Now, surgical experience has revealed that it is d
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Buiz Michael
Sofamor S.N.C.
Woo Julian W.
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