Radiographic Measurement of Psoas Muscle Width: A Simple and Reliable Screening Tool for Sarcopenia

BACKGROUND: Sarcopenia, characterized by the progressive loss of skeletal muscle mass and strength, is associated with adverse outcomes, including increased postoperative complications in patients with orthopaedic conditions. Although computed tomography (CT) and magnetic resonance imaging (MRI) remain the gold-standard modalities for assessing sarcopenia, their cost, radiation exposure, and limited availability restrict widespread screening. This study investigated the potential of lumbar spine radiographs as a practical alternative for sarcopenia screening. METHODS: We retrospectively reviewed data of patients who underwent surgery for degenerative lumbar spine diseases at our hospital's Department of Orthopedic Surgery between June 2013 and April 2024 and had both preoperative standing lumbar spine radiographs and supine CT scans. Demographic variables (age and sex) were collected. The psoas muscle width at the caudal end plate of L3 was measured on anteroposterior lumbar spine radiographs and was compared with CT-based cross-sectional psoas muscle area. Sarcopenia was defined on the basis of previously established psoas muscle index thresholds. Interobserver reliability was assessed with the intraclass correlation coefficient (ICC), and correlation analyses, multivariable regression, and receiver operating characteristic (ROC) curve analyses were performed. RESULTS: There were 305 patients (177 male patients [58.0%], with a median age of 71.7 years; and 128 female patients [42.0%], with a median age of 69.8 years; all ethnic Japanese) included in the analysis. Of these 305 patients, 114 (37.4%) were classified as having sarcopenia (78 male patients and 36 female patients). Radiographic psoas muscle width demonstrated excellent interobserver reliability (ICC, 0.94) and strongly correlated with the CT-measured psoas muscle area (male patients, r = 0.71; female patients, r = 0.64; both p < 0.001). Multivariable analysis identified the psoas width as a significant predictor of the psoas muscle area. ROC curve analysis revealed that optimal cutoff values for sarcopenia screening were 118.8 mm (area under the curve [AUC], 0.847) for male patients and 99.9 mm (AUC, 0.777) for female patients. CONCLUSIONS: Radiographic psoas muscle width measurement is a simple and reliable method for sarcopenia screening that may facilitate early sarcopenia identification, enabling timely interventions and improving surgical outcome predictions. Lumbar spine radiographs hold potential as a novel screening tool for sarcopenia beyond their conventional diagnostic role. LEVEL OF EVIDENCE: Prognostic Level III. See Instructions for Authors for a complete description of levels of evidence.