The aim of this cross-sectional study was to determine the extent of deficits in knee extensor and flexor muscle torque and power (ability to perform work over time) and in the extensor muscle cross-sectional area (CSA) after knee joint replacement. In addition, the association of lower-leg muscle deficits with mobility limitations was investigated.Â Participants were 29 women and 19 men who were 55 to 75 years old and had undergone unilateral knee replacement surgery an average of 10 months earlier. The maximal torque and power of the knee extensor and flexor muscles were measured with an isokinetic dynamometer. The knee extensor muscle CSA was measured with computed tomography. The symmetry deficit between the knee that underwent replacement surgery (“operated knee”) and the knee that did not undergo replacement surgery (“nonoperated knee”) was calculated. Maximal walking speed and stair-ascending and stair-descending times were assessed.Â The mean deficits in knee extensor and flexor muscle torque and power were between 13% and 27%, and the mean deficit in the extensor muscle CSA was 14%. A larger deficit in knee extension power predicted slower stair-ascending and stair-descending times. This relationship remained unchanged when the power of the nonoperated side and the potential confounding factors were taken into account.
Deficits in muscle torque and power and in the extensor muscle CSA were present 10 months after knee replacement, potentially causing limitations in negotiating stairs. To prevent mobility limitations and disability, deficits in lower-limb power should be considered during rehabilitation after knee replacement.