Muscle strength and bone density in patients with different rheumatic conditions: cross-sectional study

AIM To explore the relationship between muscle strength and bone density in patients with different rheumatic diseases and to examine whether inflammatory arthritis was more harmful for muscle strength and bone loss than degenerative joint diseases. METHODS The study included 361 men and women with a mean±standard deviation age of 60.5±11.4 years and different rheumatic conditions: regional syndromes, osteoarthritis of the hands, shoulders, knees, and hips, and inflammatory arthritis. Maximum voluntary back strength was measured by isometric dynamometry. Bone mineral density (BMD; g/cm2) of the lumbar spine, femoral neck, and distal radius was measured by dual-energy x-ray absorptiometry. Anthropometry and lifestyle characteristics were also assessed. RESULTS Back strength was lowest in patients with hand and shoulder osteoarthritis (20.0±17.9 kg), followed by patients with inflammatory arthritis (24.8±19.2 kg). Patients with inflammatory arthritis had the lowest BMD at the mid-radius (0.650±0.115 g/cm2) and femoral neck (0.873±0.137 g/cm2), while patients with hand and shoulder osteoarthritis had the lowest BMD at the mid-radius (0.660±0.101). In both sexes, muscle strength was significantly lower in patients who had lower BMD (T score<-1.0). Multiple regression analysis identified significant predictors of back strength to be spine BMD (P=0.024) and body mass index (P=0.004) in men and femoral neck BMD in women (P=0.004). CONCLUSION Muscle strength decline may be connected to bone loss in patients with rheumatic conditions, especially those with inflammatory joint diseases.