Background: In the diagnosis of lumbar spinal stenosis (LSS), finding stenosis with magnetic resonance imaging (MRI) does not always correlate with symptoms such as sciatica or intermittent claudication. We perform decompression surgery only for cases where the levels diagnosed from neurological findings are symptomatic, even if multiple stenoses are observed on MRI. The objective of this study was to examine the time course of asymptomatic stenosis in patients with LSS after they underwent decompression surgery for symptomatic stenosis. Materials and Methods: The participants in this study comprised 137 LSS patients who underwent single-level L4-5 decompression surgery from 2003 to 2013. The dural sac cross-sectional area at the L3-4 disc level was calculated based on preoperative MRI. A cross-sectional area less than 50 mm2 was defined as stenosis. The patients were grouped, according to additional spinal stenosis at the L3-4 level, into a double group (16 cases) with L3-4 stenosis, and a single group (121 cases) without L3-4 stenosis. Incidences of new-onset symptoms originating from L3-4 and additional L3-4-level surgery were examined. Results: Five years after surgery, 98 cases (72%) completed follow-up. During follow-up, 2 of 12 patients in the double group (16.7%) and 9 of 86 patients in the single group (10.5%) presented with new-onset symptoms originating from L3-4, showing no significant difference between groups. Additional L3-4 surgery was performed for one patient (8.3%) in the double group and three patients (3.5%) in the single group; again, no significant difference was shown. Conclusion: Patients with asymptomatic L3-4 stenosis on preoperative MRI were not prone to develop new symptoms or need additional L3-4-level surgery within 5 years after surgery when compared to patients without preoperative L3-4 stenosis. These results indicate that prophylactic decompression for asymptomatic levels is unnecessary.
Keywords: asymptomatic stenosis; decompression; dural sac cross-sectional area; gait-loading test; lumbar extension-loading test; lumbar spinal stenosis; natural course; neurological finding; prophylactic decompression; surgical outcome.