[Post-operative instability after lamino-arthrectomy for degenerative lumbar stenosis]

The purpose of this paper was to investigate the post-operative instability after laminoarthrectomy for degenerative lumbar stenosis, and to evaluate the functional results when instability was present.

Thirty-eight patients presenting with degenerative lumbar stenosis were operated on at a mean age of 64 years, and were reviewed after a 6 years average follow-up (range 4-8). A laminectomy with partial arthrectomy removing the medial aspect of the articular facets was performed in all cases, extended on one level in 16 cases, 2 levels in 16 cases, 3 levels in 4 cases, and 4 levels in 2 cases. Functional results were evaluated according to Lassale criteria. Radiographic evaluation included measurement of static instability by comparing pre operative and last available X-Rays according to Johnsson and Lassale, and measurement of dynamic instability according to Dupuis.

Mean relative gain was 57 per cent; result was rated as excellent in 11 cases, good in 17 cases, and poor in 10 cases. No instability was observed in 14 cases. A pre-existing instability was not modified at follow-up in 10 cases; spinal instability was aggravated or induced by surgery in 14 cases, with 8 antelisthesis (mean slip 6 mms), 2 retrolisthesis, and 4 scoliosis with rotatory dislocation: mean pre-operative angulation was 7 degrees; mean angulation at follow-up was 17 degrees. A dynamic instability was observed in 4 cases. Mean relative gain of the 14 patients with instability at follow-up was 58 per cent; relative gain was 62 per cent in patients with antero-posterior instability, relative gain was 40 per cent in patients with rotatory instability and scoliosis. No correlation was observed between functional results and static or dynamic instability.

These results suggest that post-operative dynamic instability is uncommon after lamino-arthrectomy in elderly. On the other hand, a static instability is observed in half of patients at follow-up. Increase of a pre-existing slip is frequently observed but is moderate and does not impair the functional result. Increase of a pre-existing scoliosis is more worrying and is associated with less satisfactory functional results. Internal fixation should be recommended particularly when a scoliosis is present.