Clinical outcomes after fully visualized transforaminal endoscopic spine surgery in patients with lumbar disc herniation stratified by paraspinal muscle degeneration: A retrospective cohort study

Objective To evaluate pain and functional outcomes after fully visualized transforaminal endoscopic spine surgery in patients with lumbar disc herniation (LDH) stratified by preoperative paraspinal muscle degeneration, and to examine whether degeneration grade was associated with 2-year outcomes. Methods This retrospective cohort study included 129 patients with single-level LDH who underwent surgery between December 2021 and December 2023 and had complete preoperative, 1-month, 6-month, and 2-year follow-up data. Two blinded spine surgeons independently graded bilateral multifidus fatty infiltration from 0 to 4 on axial T2-weighted MRI at the mid-disc level; linearly weighted kappa was 0.967(95% CI, 0.937 to 0.989). Longitudinal outcomes were analyzed using covariate-adjusted patient-level random-intercept mixed-effects models with degeneration grade treated as a categorical factor, followed by adjusted 2-year regression and post hoc sensitivity analyses. Results Of 136 screened patients, 129 were included after excluding 2 with incomplete records and 5 lost to follow-up. The cohort included 64 men and 65 women, with a mean age of 57.36 ± 11.63 years; grades 0–4 included 13, 25, 33, 32 and 26 patients, respectively. All grades improved substantially. In covariate-adjusted mixed models treating grade as a factor, the grade effect was significant for back pain VAS (P < 0.001), leg pain VAS (P = 0.010), and ODI (P < 0.001). The time-by-grade interaction was nominally significant for leg pain VAS (P = 0.036) but not after false-discovery-rate adjustment (q = 0.053), and not significant for back VAS and ODI. Each one-grade increase was associated with higher 2-year back pain VAS (β = 0.114, 95% CI, 0.001 to 0.227, P = 0.048) and ODI (β = 1.001, 95% CI, 0.168 to 1.833, P = 0.019), but not leg pain VAS. Conclusions Fully visualized transforaminal endoscopic spine surgery was associated with substantial pain relief and functional improvement across all multifidus degeneration grades. More severe degeneration showed modest prognostic associations with residual back pain and disability, but the estimated effects were smaller than published minimal clinically important differences. These findings should inform cautious counseling and hypothesis generation rather than be used as a standalone surgical decision rule.