Preoperative Multifidus Activation During Movement and Recurrent Low Back Pain at 6 to 12 Months After Lumbar Spinal Stenosis Surgery: A Prospective Observational Study

Purpose Although lumbar spinal stenosis (LSS) surgery improves pain and function, some patients experience recurrent low back pain (LBP). This exploratory study examined whether the preoperative lumbar multifidus (LMF) to lumbar erector spinae (LES, specifically the longissimus muscle) activity ratio on surface electromyography (sEMG) is associated with recurrent LBP and pain outcomes 6–12 months after LSS surgery. Methods Seventy patients with LSS undergoing surgery were enrolled and followed for 12 months. Preoperative sEMG of back extensor muscles was recorded during a trunk flexion–return task. The primary outcome was the postoperative change in LBP visual analog scale (VAS) from 6 to 12 months (ΔLBP 6–12M). The secondary outcome was LBP VAS at 12 months. Recurrent LBP was defined as a ≥ 20-mm VAS increase between 6 and 12 months. The main exposure was the LMF/LES activity ratio; multivariable linear regression adjusted for prespecified covariates. Results Recurrent LBP occurred in 9 of 70 patients (12.9%). These patients had a lower LMF/LES ratio than those without recurrence. This ratio was significantly associated with ΔLBP 6–12M (β=−22.9, 95% CI − 44.6 to − 1.3, p = 0.038) and 12-month LBP VAS (β=−20.6, 95% CI − 40.2 to − 0.9, p = 0.041). However, the latter association was attenuated after body mass index adjustment (β=−18.8, 95% CI − 38.7 to 1.1, p = 0.064). Conclusion Lower preoperative LMF activation during movement is associated with mid-term postoperative LBP worsening after LSS surgery. Therefore, preoperative assessment of LMF activation patterns may identify patients at risk for postoperative LBP recurrence.