Association between phase angle and clinical outcomes in patients with lumbar spinal stenosis from the preoperative to 12-month postoperative period: A prospective observational study.

No reports of longitudinal studies on phase angle (PhA) in lumbar spinal stenosis (LSS) exist, and its association with postoperative clinical outcomes is unclear. We longitudinally investigated PhA in patients with LSS preoperatively to 12 months postoperatively and determined the association between PhA and the Japanese Orthopedic Association (JOA) score. This prospective observational study included patients who underwent consecutive surgical treatments for clinically and radiologically defined LSS. Outcome measures including walking speed, Timed Up and Go test (TUG), JOA score, and PhA based on bioelectrical impedance analysis were measured preoperatively and at 3, 6, and 12 months postoperatively. Correlations between PhA and the JOA score and motor function were analyzed. The effect of PhA on JOA scores was evaluated using mixed-effect models for repeated measurements (MMRM). Eighty-nine patients were included at baseline, and 85, 85, and 78 patients were analyzed at 3, 6, and 12 months postoperatively, respectively. PhA was 3.9 ± 0.8 (p = 0.086), 4.0 ± 0.8 (p = 0.644), and 4.1 ± 0.9 (p = 0.791) at 3, 6, and 12 months postoperatively and 4.2 ± 0.8 at baseline. PhA was significantly correlated with the JOA score (p < 0.01) and walking speed and TUG results (p < 0.01) at all assessment points. In the MMRM, PhA was associated with the JOA score at all assessment points. Changes in postoperative JOA scores after lumbar spine surgery are associated with PhA at each assessment time point. PhA may be a useful postoperative clinical indicator after surgery for LSS.