Patients with rheumatoid arthritis (RA) have a higher risk of falls and fractures due to muscle weakness and painful joints of the lower extremities. Evaluation of muscle functions is important to predict falls and fractures. The aim was to investigate the relationships of muscle functions with falls and fractures in RA patients.
Stand-up muscle power, speed, and stabilizing time were evaluated by a muscle function analyzer in 90 RA patients in the CHIKARA study (UMIN000023744). The relationships of the muscle functions with falls, fractures, body composition, Disease Activity Score of 28 joints - erythrocyte sedimentation rate (DAS28-ESR), modified Health Assessment Questionnaire (mHAQ) scores, Steinbrocker class, stage, sarcopenia, and frailty were investigated in a cross-sectional study.
Each parameter of muscle function was related to age, falls, frailty, and the leg muscle score. However, only stabilizing time was related with fractures (r = .217, P = .04). When stabilizing time was ≥ 1.13 and ≥1.36 seconds, the odds ratios for falls and fractures were increased 6.2-fold compared to < 1.13 seconds (95% CI: 1.2-20.1, P = .002) and 11.4-fold compared to <1.36 seconds (95% CI: 1.7-92.5, P = .071), respectively. Sarcopenia and skeletal muscle mass were not significantly related to each muscle function. There was a negative correlation between DAS28-ESR and power. Steinbrocker class and mHAQ had negative correlations with power and speed.
Sarcopenia and skeletal muscle mass were not adequate indicators of muscle functions in RA patients. Analyzing muscle functions is helpful to predict falls and fractures. Patients with extended stabilizing times should recognize the increased risk of falls and fractures.