Persistent redundant nerve roots two years after decompression for lumbar spinal stenosis: clinical outcomes and radiologic findings—a secondary analysis of the NORDSTEN spinal stenosis trial

Nearly 40% of patients with symptomatic lumbar spinal stenosis (LSS) scheduled for surgery have redundant nerve roots (RNR) on preoperative MRI. The evolution of RNR after decompression remains uncertain; we aimed to determine whether disappearance reflects adequate decompression and better outcome, while persistence of RNR indicates insufficient decompression and potential need for reoperation. This secondary analysis of the NORDSTEN Spinal Stenosis Trial included patients with preoperative RNR, categorized according to resolution (RNR0) or persistence (RNR+) of RNR on MRI 2 years after decompression. Baseline characteristics and changes in pain and function were compared between groups. Dural sac cross‑sectional area (DSCA) and Schizas grade were recorded at L2/3, L3/4, and L4/5 at baseline and 2 years. The primary outcome was change in Oswestry Disability Index (ODI); secondary outcomes were changes in Zurich Claudication Questionnaire (ZCQ) scores and numerical rating scales (NRS) for leg and back pain. Of 125 patients with RNR at baseline, 58 (46%) had persistent RNR at 2‑year follow‑up. Groups did not differ preoperatively in demographics, ODI, ZCQ, NRS, or symptom duration, but the RNR+ group had smaller DSCA and more multilevel stenosis. At 2 years, both groups showed substantial improvement in ODI, ZCQ, and NRS with no significant between‑group differences; mean ODI change was − 23.0 in RNR0 versus − 22.5 in RNR+ (p = 0.86). Persistent RNR was associated with less decompression and more residual stenosis. Despite indicating less extensive decompression radiologically, persistent RNR was not associated with worse 2‑year clinical outcomes compared with resolved RNR. Among patients with LSS and RNR before decompression surgery, persistent RNR were observed in nearly half of cases two years postoperatively. Persistent RNR were associated with more severe spinal stenosis at baseline and greater residual stenosis at two-year follow-up. Patients with persistent RNR at two years reported clinically important improvements comparable to those without that sign. Persistent RNR on postoperative MRI at two years was not a negative predictor of clinical outcomes.