Abstract
Degenerative spondylolisthesis is consistently responsible for narrowing of the spinal canal, but only in a part of the cases it causes lateral or central stenosis. The presence, type and severity of stenosis is related to several factors, such as the constitutional dimensions of the spinal canal, the orientation and severity of degenerative changes of the facet joints, and the amount of vertebral slipping. The type of stenosis, that is whether stenosis is central or lateral, depends on the orientation of the articular processes, and the length of the pedicles. Usually stenosis is lateral initially and central in later stages. Instability, that is hypermobility on flexion-extension adiographs is one of the main characteristics of degenerative spondylolisthesis. However, in many cases there is no appreciable hypermobility of the slipped vertebra. We consider the latter condition as a potential instability, which can become a manifest instability as a result of surgery, or when destabilizing factors unable to destabilize a normal vertebra intervene, such as disc degeneration or severe degenerative changes of the facet joints.
There is no indication for surgery in patients with no significant symptoms. In patients with an unstable motion segment who have only back pain it is usually sufficient to perform a fusion alone if stenosis is mild and asymptomatic. Neural decompression should be performed if stenosis is severe. Bilateral laminotomy, or even total laminectomy, may be carried out with no concomitant fusion in patients with mild olisthesis, no vertebral hypermobility on functional radiographs, mild central stenosis or any degree of isolated lateral stenosis, and mild or no back pain. The indications for monolateral laminotomy with no fusion are: moderate central stenosis in elderly patients with unilateral symptoms; lateral stenosis only on one side; and unilateral additional pathology, such as a synovial cyst. Patients with moderate or severe olisthesis, vertebral hypermobility even of mild degree, and/or severe central stenosis and chronic back pain should undergo decompression and fusion. The association of an arthrodesis allows decompression of the neural structures as widely as necessary.
Posterolateral instrumented fusion, using pedicle screw fixation, is the most common procedure, that can be done at multiple level when olisthesis is present at more than one level. In both cases it requires no, or a short, postoperative immobilization Posterolateral fusion may be replaced by PLIF. This procedure, associated with pedicle screw instrumentation, gives excellent results and a high rate of solid fusion. The devices inserted in the disc space are normally represented by cages filled with bone chips. An alternative are the use of blocks of porous tantalum (hedrocel), the stiffness of which is very similar to that of subchondral bone. We are using blocks of hedrocel since 3 years with excellent results in terms of intersomatic fusion. In 20 cases followed for at least 2 years we never observed mobilization of the implant or loosening of the pedicle screws, and we almost consistently found a tight union between the implant and the adjacent vertebrae.
Theses abstracts were prepared by Professor Roger Lemaire. Correspondence should be addressed to EFORT Central Office, Freihofstrasse 22, CH-8700 Küsnacht, Switzerland.
