Incidence and preoperative risk factors for failed back surgery syndrome: a nationwide population-based cohort study.

Failed back surgery syndrome (FBSS), recently redesignated as persistent spinal pain syndrome type 2, is a common complication after lumbar spine surgery, yet population-level data on its incidence and preoperative determinants remain limited. This study aimed to quantify the incidence of FBSS under multiple definitions and to identify preoperative risk factors for its development. This retrospective cohort study analyzed claims data from the Korean National Health Insurance Service (2009-2023), including 1,029,500 adults who underwent lumbar spine surgery. FBSS was operationalized using two mutually exclusive criteria assigned hierarchically: patients who underwent any subsequent lumbar spine procedure were first classified as the Reoperation group, and the remaining patients who received an International Classification of Diseases-10 M96.1 (post-laminectomy syndrome) diagnosis after the index surgery were classified as the Disease-code group. Cox proportional hazards models adjusted for demographic, clinical, and lifestyle covariates were used to identify preoperative risk factors. The overall FBSS incidence was 26.7% (n = 274,955) based on the combined Disease-code and Reoperation definitions. In multivariable analysis, advancing age, peripheral polyneuropathy, obesity, diabetes mellitus, hypertension, and current smoking were independently associated with increased FBSS risk. Decompression surgery and spinal canal stenosis also conferred elevated risk. Higher income, employment-based insurance, and moderate physical activity (500-1499 MET-minutes/week) were protective. FBSS affects approximately one-quarter of lumbar surgery patients. Multiple modifiable and non-modifiable preoperative factors were identified. These findings support individualized preoperative risk assessment to optimize surgical decision-making and patient counseling.