Appositional ossification following lumbar laminectomy

Question: Post-laminectomy segmental hypermobility as well as appositional ossification were suggested by many authors to contribute to the unsatisfac tory long-term results of laminectomy. The aim of this study was to find ou t whether segmental instability, among other factors, influences the degree of appositional ossification following laminectomy. Methods: 55 out of 72 patients operated upon by laminectomy or hemilaminect omy for degenerative lumbar spinal stenosis were examined by radiography af ter an average follow-hip period of 5.2 years. Appositional ossification at the site of surgery was evaluated in relation to lumbar instability, the n umber of segments undergoing laminectomy, and whether simultaneous fusion w as done. Instability was determined by measuring angulation and translation using lateral flexion and extension views of the lumbar spine, whereas new -bone formation was best evaluated on antero-posterior radiographs. Results: 94 % of the patients had appositional ossification at the site of laminectomy. Patients undergoing simultaneous fusion with laminectomy had a significantly lower amount of appositional ossification compared to patien ts undergoing laminectomy without segmental fusion. Radiographically measur ed segmental instability, the number of segments undergoing laminectomy, ag e, and sex of the patients did not influence the extent of ossification. Conclusions: Postoperative appositional ossification at the posterior site of resection are seen regularly following laminectomy. The extent of apposi tional ossification does correlate with lumbar fusions, but does not correl ate with the extent of radiographically measured lumbar instability, the nu mber of segments undergoing laminectomy, or the age and sex of the patients . Clinical relevance: Simultaneous lumbar fusion with laminectomy is proved t o be associated with less appositional ossification. Therefore lumbar fusio n should be considered when planning surgery for spinal stenosis.