Impact of appendicular and trunk skeletal muscle mass and back extensor strength on sagittal spinal alignment in Japanese women without vertebral fracture

OBJECTIVES: Progressive and generalized loss of skeletal muscle mass (SMM) and strength are characteristics of sarcopenia. However, the impact of appendicular and trunk SMM and back extensor strength (BES) on spinal sagittal alignment remains unclear. Herein, we investigate the relationship between these factors and spinal sagittal alignment. METHODS: In total, 202 women without vertebral fractures (median age, 66.9 years; interquartile range, 61.4–71.9 years) were analyzed at an orthopedic outpatient clinic. Pelvic incidence (PI), lumbar lordosis (LL), sagittal vertical axis (SVA), and pelvic tilt (PT) were measured on whole spine radiographs. Body mass index (BMI), appendicular and trunk relative SMM index, and BES were also evaluated. These measurements were compared between spinal sagittal alignment groups using the Mann–Whitney U test. Finally, the factors contributing to abnormal alignment were analyzed using multiple logistic regression analysis. RESULTS: BES was significantly lower in all abnormal sagittal alignment groups, as defined by PI-LL (≥ 10°), SVA (≥4 cm), and PT (≥20°) (all P < 0.001). On multivariate analysis, BES was a contributing factor for abnormal PI-LL (P < 0.001), SVA (P = 0.001), and PT (P < 0.001). Conversely, a decrease in appendicular and trunk relative SMM index did not statistically affect abnormal spinal sagittal alignment. CONCLUSIONS: BES was associated with changes in spinal sagittal alignment; however, SMM, which is often used for diagnosing sarcopenia, did not affect spinal sagittal alignment.