POSTOPERATIVE INSTABILITY AFTER LAMINOARTHRECTOMY FOR DEGENERATIVE LUMBAR STENOSIS

Purpose of the study The purpose of this paper was to investigate the post-operative instability after laminoarthrectomy for degenerative lu mbar stenosis, and to evaluate the functional results when instability was present. Material and method Thirty-eight patients presenting wit h degenerative lumbar stenosis were operated on at a mean age of 64 ye ars, and were reviewed after a 6 years average follow-up (range 4-8). A laminectomy with partial arthrectomy removing the medial aspect of t he 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 i n 2 cases. Functional results were evaluated according to Lassale crit eria. Radiographic evaluation included measurement of static instabili ty by comparing pre operative and last available X-Rays according to J ohnsson and Lassale, and measurement of dynamic instability according to Dupuis. Results Mean relative gain was 57 per cent; result was rate d 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 aggravat ed or induced by surgery in 14 cases, with 8 antelisthesis (mean slip 6 mms), 2 retrolisthesis, and 4 scoliosis with rotatory dislocation: m ean 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-poste rior instability, relative gain was 40 per cent in patients with rotat ory instability and scoliosis. No correlation was observed between fun ctional results and static or dynamic instability. Results These resul ts suggest that post-operative dynamic instability is uncommon after l amino-arthrectomy in elderly. On the other hand, a static instability is observed in half of patients at follow-up. Increase of a pre-existi ng slip is frequently observed but is moderate and does not impair the functional result. Increase of a pre-existing scoliosis is more worry ing and is associated with less satisfactory functional results. Inter nal fixation should be recommended particularly when a scoliosis is pr esent.