Associations of BMI-Waist Circumference Phenotypes With Sagittal Alignment and 6-Month Residual Low Back Pain After Single-Level L4-5 PLIF/TLIF.

BACKGROUND: Body mass index (BMI) does not fully capture fat distribution. We evaluated associations of BMI-waist circumference phenotypes with perioperative outcomes, preoperative sagittal alignment, and postoperative recovery after single-level L4-5 PLIF/TLIF. METHODS: This retrospective cohort study included 315 patients undergoing conventional open L4-5 PLIF/TLIF between June 2022 and June 2024. Patients were classified as having normal BMI without central obesity (Group A, n = 105), normal-BMI central obesity (Group B, n = 55), or high-BMI central obesity (Group C, n = 155). Perioperative variables, preoperative sagittal parameters, pain, disability, and residual low back pain at 6 months (VAS-back ≥3) were compared among groups. BMI, WC, and abdominal circumference were evaluated in separate adjusted models. RESULTS: Perioperative outcomes and several preoperative sagittal parameters differed among the phenotypes. Groups B and C generally had higher pain and disability scores than Group A at 3 and 6 months, and residual low back pain occurred in 11%, 24%, and 28% of Groups A, B, and C, respectively (P = 0.005). No significant between-group differences in pain or disability remained at 12 months. In separate adjusted models, BMI, WC, and abdominal circumference were associated with several sagittal parameters and 6-month clinical outcomes. CONCLUSIONS: BMI-WC phenotypes were associated with perioperative outcomes, preoperative sagittal alignment, and early-to-intermediate postoperative outcomes. The observed pattern was more consistent with slower early recovery than with persistent 12-month impairment. WC and abdominal circumference may complement BMI in anthropometric assessment, but their incremental prognostic value requires further investigation.