Lower-limb pain, disease, and injury burden as determinants of muscle strength deficit after hip fracture.

BACKGROUND Hip fracture may result in an asymmetrical lower-limb strength deficit. The deficit may be related to the trauma, surgical treatment, pain, or disuse of the fractured limb. However, disease and injury burden or musculoskeletal pain in the other limb may reduce muscle strength on that side, reducing the asymmetrical deficit. The aim of our study was to explore the asymmetrical strength deficit and to determine the potential underlying factors in patients from six months to seven years after a hip fracture. METHODS The asymmetrical deficit was calculated ([fractured limb/sum of both lower limbs] x 100%) for isometric knee extension torque, rate of force development during isometric testing, and leg extension power. The asymmetrical measures for lower-limb muscle mass (fractured limb--nonfractured limb), and that of lower-limb pain and disease and injury burden (nonfractured limb--fractured limb), were calculated. RESULTS Half of the participants had no consistent asymmetrical deficit on the fractured side. Regression analyses showed that asymmetrical measures of lower-limb pain, muscle mass, and disease and injury burden predicted asymmetrical deficit in knee extension torque (R(2) = 0.43) and in the rate of force development (R(2) = 0.36). More intense pain and disease and injury burden affecting the nonfractured limb and smaller muscle mass relative to the fractured limb were associated with a smaller asymmetrical deficit. CONCLUSIONS Following a hip fracture, the prevention of decreases in muscle strength and power as well as a large asymmetrical deficit by the use of targeted pain management and rehabilitation may help to reduce the risk of subsequent mobility limitations and falls.