Quadriceps strength in women with a previous hip fracture: relationships to physical ability and bone mass

Associations between physical ability, level of current physical activity and bone mass were examined in 47 elderly women (mean age 80 years) who had suffered from a hip fracture 3-36 months (mean 17 months) previously. Measures of physical ability included isokinetic quadriceps strength of both the non-fractured and fractured leg, and walking and stair climbing speed. An estimate of current physical activity was made using the Northwick Park activity index questionnaire specifically designed for hip fracture patients. Bone mineral density of the spine and hip (Ward's triangle, femoral neck and trochanter) was assessed by dual energy X-ray absorptiometry. Relationships between the measured parameters were analysed using multiple regression analyses, taking into account the confounding effects of age, height, weight and months since fracture. Quadriceps strength of the fractured leg was on average 18% lower than that of the contralateral leg (p < 0.001). Quadriceps strength of the fractured leg proved to be the most robust predictor of walking speed (Rpartial = 0.69, p < 0.0001), stair climbing speed (Rpartial = 0.46, p < 0.001) and the activity index (Rpartial = 0.56, p < 0.0001). Bone mineral density was independently predicted only by body weight (Rpartial range: 0.45-0.72, p < 0.001), not by any of the parameters of physical ability or by the Northwick Park activity index. In conclusion, quadriceps strength is markedly affected in women with a previous hip fracture and is associated with walking ability and level of physical activity. This study showed that bone mass is linked to body weight, not to physical ability and activity. Thus, the main benefit of muscle strengthening exercises in these women may be to promote mobility.