Preoperative and postoperative instability in lumbar spinal stenosis.

Sixty-one patients operated on for spinal stenosis, without a fusion, were studied retrospectively. Preoperative instability, as revealed by functional myelography, was found to predict a poor prognosis (P less than 0.01). Women had less favorable results (P less than 0.05). The "slipping" group was significantly more often radically decompressed than the "nonslipping" group (P less than 0.01). Postoperative slipping was found in 26 patients, significantly more often in those with unsatisfactory results (P less than 0.001).