Central Canal Stenosis Severity Does Not Predict Residual Leg Pain After Percutaneous Transforaminal Endoscopic Decompression in Frail Elderly Patients: A Propensity Score-Weighted Cohort Study

Purpose: Severe central canal stenosis is often considered a relative contraindication for minimally invasive decompression in frail elderly patients with lumbar spinal stenosis, yet evidence supporting this practice is limited. This study evaluated whether stenosis severity predicts persistent leg pain after percutaneous transforaminal endoscopic decompression (PTED). Methods: This retrospective cohort study included 152 frail elderly patients (age ≥ 75 years, FRAIL score ≥ 3) who underwent single-level PTED for unilateral symptomatic lumbar spinal stenosis (2022– 2024). The primary outcome was persistent residual leg pain, defined as visual analogue scale (VAS) score ≥ 4 or regular analgesic use (≥ 3 days/week for > 1 month) at all 3-, 6-, and 12-month follow-ups. Inverse probability of treatment weighting (IPTW) balanced 16 baseline covariates between severe (Schizas grade C–D) and non-severe (grade A–B) stenosis groups. Propensity score matching and multivariable regression were sensitivity analyses. Linear mixed models assessed recovery trajectories. Results: Severe stenosis was present in 59 patients (38.8%). After IPTW, all covariates were well balanced (all SMD< 0.1). Persistent leg pain occurred in 33 patients (21.7%), with similar rates between groups (non-severe: 21.5% vs severe: 22.0%). Severe stenosis was not associated with increased pain risk in any analysis: IPTW-adjusted OR=0.63 (95% CI: 0.26– 1.52, P=0.306); PSM OR=0.38 (95% CI: 0.13– 1.07, P=0.066); multivariable OR=0.56 (95% CI: 0.21– 1.51, P=0.250). The strongest independent predictor was FRAIL score ≥ 4 (OR=15.57, 95% CI: 3.32– 73.11, P=0.001). Recovery trajectories were similar between groups (group×time interaction: VAS P=0.535, ODI P=0.975). Recurrent pain occurred in only 3 patients (2.0%), none requiring reoperation. Conclusion: Preoperative central canal stenosis severity does not predict persistent leg pain or recovery trajectory after PTED in frail elderly patients. These findings support a symptom-guided rather than image-guided surgical strategy. Patient frailty, rather than the degree of central canal narrowing, is a more important determinant of postoperative pain outcomes. Keywords: lumbar spinal stenosis, central canal stenosis, percutaneous transforaminal endoscopic decompression, frail elderly, inverse probability of treatment weighting, propensity score, residual pain