THE EFFECT OF POSTLAMINECTOMY SPINAL INSTABILITY ON THE OUTCOME OF LUMBAR SPINAL STENOSIS PATIENTS

Between 1986 and 1990, 37 of 72 patients undergoing decompressive lumb ar laminectomy with medial facetectomy for lumbar stenosis at The Ohio State University were seen in follow-up at a mean of 31 months (range , 14-63 months) after their laminectomy and were evaluated by question naire, detailed neurologic examination, and static and dynamic lumbar radiographs. Thirteen patients who had undergone fusion or who had ext enuating medical circumstances were excluded, leaving 24 patients for whom laminectomy was the sole treatment for lumbar stenosis. Postopera tively, normal walking improved from 4 to 45% of patients, sensory def icits decreased from 63 to 25%, and ability to perform most or all des ired activities increased from 25 to 70%. Urinary function was unchang ed. Thirteen patients (54%) showed radiographic signs of instability. All patients who were declared radiographically stable could walk with out a prosthetic aid or normally; 62% of the unstable patients require d aid for walking. All of the patients with a poor ambulatory outcome were radiographically unstable. Compared with stable patients, unstabl e patients had a significant (p < 0.01) decrease in their ambulatory a bility. There was a clear correlation between the degree of listhesis and postoperative ambulatory status (p < 0.01). The unstable patients with a poor ambulatory outcome followed one of three clinical courses: improvement with later deterioration, improvement with a plateau at a poor functional level, or failure to improve from a poor functional l evel. In conclusion, (a) although instability did not necessarily prec lude a good outcome, a poor ambulatory outcome was always associated w ith instability; (b) laminectomy can effectively ameliorate the sympto ms of lumbar stenosis; however, there is a subset of patients in whom laminectomy is associated with instability and a poor clinical course.