Preoperative multifidus activation during movement and low back pain worsening after lumbar spinal stenosis surgery: a prospective observational study.

PURPOSE: Although lumbar spinal stenosis (LSS) surgery improves pain and function, some patients experience worsening low back pain (LBP). This exploratory study examined whether the preoperative lumbar multifidus (LMF) to lumbar erector spinae (LES, longissimus) activity ratio on surface electromyography (sEMG) is associated with postoperative LBP worsening after LSS surgery. METHODS: This single-center prospective observational study included 70 patients with LSS who underwent surgery and completed 12-month follow-up. Preoperative sEMG signals from the LMF and LES were recorded during a trunk flexion-return task. The main exposure was the LMF/LES activity ratio during movement. The primary and secondary outcomes were change in LBP visual analog scale (VAS) from 6 to 12 months (ΔLBP 6-12 M) and 12-month LBP VAS, respectively. Recurrent LBP, defined as a ≥ 20-mm increase in LBP VAS from 6 to 12 months, was evaluated as an exploratory binary outcome. Multivariable linear regression was adjusted for prespecified covariates. RESULTS: Recurrent LBP occurred in 10 of 70 patients (14.3%). Patients with recurrent LBP had a lower LMF/LES activity ratio than those without recurrent LBP. In the fully adjusted model, a lower LMF/LES activity ratio was associated with greater ΔLBP 6-12 M (B = - 9.59, 95% confidence interval [CI] - 18.92 to - 0.66, P = 0.039) and higher 12-month LBP VAS (B = - 13.16, 95% CI - 24.54 to - 3.42, P = 0.010). CONCLUSION: A lower preoperative LMF/LES activity ratio was associated with postoperative LBP worsening from 6 to 12 months after LSS surgery. This finding suggests that movement-related paraspinal muscle activation may provide complementary information for understanding postoperative LBP worsening.