Body composition and muscle strength in women scheduled for a knee or hip replacement. A comparative study of two groups of osteoarthritic women.

It is unclear whether patients with knee osteoarthritis (OA) and hip OA differ regarding soft tissue composition and bone mineral density (BMD). A total of 42 women waiting for a replacement of the hip (n=20) or the knee (n=22) due to OA were examined. Fat mass (FM), percent body fat (%fat), lean mass (LM) and BMD were measured by dual energy X-ray absorptiometry (DEXA). Knee extensor and flexor strength was measured by an isokinetic dynamometer. No significant differences in age, height, disease duration: Lequesne score or pain scores were found between the groups. Comparing the radiographic changes of the knees with those of the hips, changes were most severe in the joints which were to be replaced. Body weight, body mass index, total and regional FM, and %fat were more than 15% higher in patients waiting for a knee replacement (p <0.001). Also lean mass tended to be higher in the knee patients. Differences in BMD did not remain statistically significant after correction for body weight. Muscle strength was similar in the two groups but was reduced by 20% in the legs in which the joint was to be replaced compared to the contralateral legs. However, the mean difference in lean mass between the two legs was only 3% (p <0.05). The scores for pain felt during strength testing were significantly higher for the involved legs than for the contralateral legs. In conclusion, fat mass values were considerably higher in patients scheduled for a knee replacement. Impaired strength performance in OA may be more strongly associated with pain than with reduced muscle mass.