Shape of the Spinal Canal Is Not Associated with Success Rates of Microsurgical Unilateral Laminotomy and Bilateral Decompression for Lumbar Spinal Canal Stenosis.

Abstract

Anatomic shape of the spinal canal (oval, round, trefoil) has been reported to predict outcome of bilateral decompression performed in an undercutting technique via unilateral laminotomy in monosegmental lumbar spinal stenosis, with poorest results observed in a trefoil spinal canal, leading to the proposal of using bilateral instead of unilateral laminotomy. The aim of this study was to assess whether this anatomic classification into oval, round, and trefoil shapes is relevant to surgical treatment of lumbar spinal stenosis. Retrospective chart review of patients undergoing lumbar decompression surgery was performed. Spinal canal configuration was assessed on preoperative computed tomography based on maximal transverse and anteroposterior diameter, and shapes were classified into oval, round, and trefoil. Associations between spinal canal shape and outcome improvement (aggregate of walking distance and leg pain) were tested. Decompression of 236 lumbar levels was performed in 159 patients (mean age, 73 ± 8 years; mean body mass index, 29 ± 6). Average number of operated segments was 1.3 ± 0.6. Oval configurations were detected in 155 (65%) levels, round configurations were detected in 11 (5%) levels, and trefoil configurations were detected in 70 (30%) levels. Postoperative improvement was recorded in 91.7% of patients. Spinal canal shape had no influence on surgical outcome (oval, area under the curve 0.529, P = 0.672; trefoil, area under the curve 0.500, P = 0.997; round, area under the curve 0.471, P = 0.670). Spinal canal configuration varies in frequency with lumbar segment. Our results do not support the idea that this anatomic classification, particularly the nomenclature of oval, round, and trefoil, should influence surgical decision making.