Risk Factors Associated with Osteonecrosis of the Femoral Head after Undergoing Lumbar Decompression and Fusion.

INTRODUCTION: Osteonecrosis of the femoral head (ONFH) after spinal fusion is poorly characterized. This study sought to identify factors associated with ONFH following lumbar, lumbo-sacral, or lumbo-pelvic fusion. We hypothesized that abnormal postoperative spino-pelvic alignment and modifiable intraoperative factors may increase ONFH risk. Furthermore, we felt these factors may reduce survivorship free from total hip arthroplasty (THA) after lumbar fusion. METHODS: We retrospectively reviewed 9,380 lumbar fusion patients from 2013 to 2021 at a single institution. There were 50 patients who had concern for ONFH who were identified and matched by age and sex to 100 fusion patients who did not have ONFH. Exclusion criteria included preoperative ONFH and lack of standing radiographs. Of the 50 ONFH patients, 21 met inclusion criteria, and of the 100 matched controls, 69 met criteria. Variables assessed included spino-pelvic parameters, corticosteroid use, smoking, surgical approach, pelvic fixation, American Society of Anesthesiologists classification, intraoperative hypotension, and postoperative Pelvic Incidence-Lumbar Lordosis alignment (PI-LL). Statistical analyses included t-tests, Chi-square tests, logistic regressions, and survival analyses. RESULTS: Postoperative overcorrection (PI-LL less than -10°) significantly increased the odds of ONFH (odds ratio (OR): 17.05 (1.85 to 156.97); P = 0.01). Intraoperative hypotension (P = 0.22), anterior approaches (P = 0.52), and pelvic fixation (P = 0.35) were not associated with increased ONFH risk. Overcorrected patients also demonstrated worse THA-free survival at one year (hazard ratio (HR): 24.71 (1.55 to 395.30); P = 0.02) and five years (HR: 9.67 (2.46 to 38.06); P = 0.001) compared with matched and undercorrected groups. CONCLUSION: Postoperative spino-pelvic overcorrection is strongly associated with femoral head ONFH and inferior THA-free survivorship after lumbar fusion. In contrast, hypotension, anterior approaches, and pelvic fixation were not significant contributors. Careful restoration of sagittal alignment may reduce ONFH risk and improve long-term hip outcomes following spinal fusion.