Spinal canal morphology and clinical outcomes of microsurgical bilateral decompression via a unilateral approach for lumbar spinal canal stenosis

Purpose: Microsurgical bilateral decompression via a unilateral approach for lumbar spinal stenosis is a less invasive technique compared to conventional laminectomy. Although many technical reports have demonstrated acceptable overall surgical outcomes for this approach, no studies have attempted to clarify the clinical outcomes thereof in regard to anatomical variance of the spinal canal. This study was conducted to analyze the clinical outcomes of microsurgical bilateral decompression via a unilateral approach according to spinal canal morphology in degenerative lumbar spinal stenosis. Methods: Between January 2008 and December 2009, 144 patients with single-level spinal lumbar stenosis underwent microsurgical bilateral decompression via a unilateral approach by a single surgeon. Patients were categorized into three groups according to spinal canal shape: round (n = 42), oval (n = 36), and trefoil (n = 66), and clinical parameters were assessed both before and after surgery with 2-3 years of follow-up. Results: Mean visual analog scale (VAS) and Oswestry disability index (ODI) decreased after surgery, respectively, from 8.1 and 59.8 % to 2.1 and 19.1 % in the round shaped spinal canal group, from 7.2 and 47.1 % to 2.2 and 15.1 % in the oval shaped spinal canal group, and from 6.8 and 53.6 % to 3.6 and 33.3 % in the trefoil shaped spinal canal group. In all groups, VAS and ODI scores significantly improved postoperatively (p < 0.01), although less improved VAS and ODI scores were observed in the trefoil shaped spinal canal group (p < 0.01). The overall patient satisfaction rate was 66.7 %; however, statistically significant lower satisfaction rates were reported in the trefoil shaped spinal canal group (p < 0.01). Conclusions: Microsurgical bilateral decompression via a unilateral approach may be a good modality for treating round or oval shape spinal canal stenosis, but is not recommended for trefoil-shaped-stenosis. The current authors recommend performing the bilateral decompression technique in cases of trefoil-shaped-spinal canal stenosis.