Association between preoperative low muscle mass and psychological factors after surgery among patients with lumbar spinal stenosis: A longitudinal study.

It remains controversial whether preoperative low muscle mass affects clinical outcomes after lumbar surgery. Previous studies evaluated outcomes such as pain, quality of life, and disability, but none investigated preoperative low muscle mass and psychological factors. The purpose of this study was to clarify the association between preoperative low muscle mass and postoperative psychological factors in lumbar spinal stenosis (LSS). A longitudinal analysis was performed in 85 consecutive preoperative patients with LSS. Demographic data, leg pain, low back pain, Japanese Orthopaedic Association score, Pain Catastrophizing Scale (PCS) score, Fear-Avoidance Beliefs Questionnaire on Physical Activity (FABQ-PA) score, Hospital Anxiety and Depression Scale (HADS) score, walking velocity, grip strength, and appendicular lean mass were assessed. Muscle mass was measured using bioelectrical impedance analysis. Patients were divided into two groups based on skeletal muscle mass index. These clinical outcomes were evaluated preoperatively and 1 year after surgery. In the 73 patients who were analyzed 1 year after surgery, the prevalence of preoperative low muscle mass was 21.9%. The normal muscle mass group showed significantly improved PCS, FABQ-PA, HADS-anxiety, and HADS-depression scores 1 year after surgery. The low muscle mass group did not demonstrate significantly improved PCS, FABQ-PA, or HADS-depression scores, and had a significantly smaller increase in the FABQ-PA score than the normal muscle mass group. Multivariate analysis showed that low muscle mass was significantly related to change in FABQ-PA score. Our results suggest that preoperative low muscle mass hinders improvement in fear-avoidance beliefs 1 year after surgery.