Adjacent Level Canal Area Changes up to 2 years after Lumbar Spinal Stenosis Decompressive Surgery

Study Design. A secondary analysis of data from the NORDSTEN-spinal stenosis trial (SST) Objective. The aim of the present study was to investigate whether the dural sac cross-sectional area (DSCA) on magnetic resonance imaging (MRI) of adjacent segments decreases after decompressive surgery due to lumbar spinal stenosis (LSS) up to 2 years postoperatively, and to investigate possible associations with baseline variables, including preoperative patient and radiological characteristics, and surgical method used. Summary of Background Data. Decompressive surgery for LSS is currently the most common spinal surgery procedure; however, there is limited knowledge on changes in the DSCA over time adjacent to a decompressed segment. Methods. In the NORDSTEN-SST 437 patients were randomized to decompression with one of three minimally invasive surgical methods for LSS. The patients underwent MRI of the lumbar spine (L2-L5) before surgery and at 3 and 24 months postoperatively. Descriptive statistics of adjacent DSCA and changes in adjacent DSCA are presented. Possible prognostic factors (preoperative factors, radiological measures, and surgical method) for changes in the adjacent DSCA were examined using multivariate regression analyses. Results. 322 patients (74%) in the original NORDSTEN-SST had undergone MRI at both 3 and 24 months postoperatively and were included (360 adjacent levels, 263 cranial, and 97 caudal to a decompressed level). Up to 2 years postoperatively, no decrease in adjacent DSCA was observed. No associations were found between the investigated baseline variables, and DSCA change from 0 to 2 years, except for a weak association with baseline adjacent DSCA. Conclusion. Up to 2 years postoperatively, the DSCA did not decrease at adjacent levels after decompressive surgery. None of the investigated baseline variables showed any clinical meaningful prognostic value regarding adjacent DSCA changes 2 years postoperatively. The findings support previous reports that decompression of adjacent levels is not required to prevent subsequent stenosis.