ABSTRACT
PURPOSE OF THE STUDY: 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. MATERIAL AND METHOD: 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. RESULTS: 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. RESULTS: 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.
