Difference in Effect of Muscle Weakness versus Obesity on Stability of Knee Joint.

This research examines a question about which is worse to the knee joint: increasing body weight or decreasing muscle force. We simulated unilateral weight bearing and analyzed the extent to which each had a deleterious effect on the knee joint. We used a rigid body model in which body weight was increased and quadriceps muscle force decreased. Also, to account for differences between men and women, the model reflected difference in pelvic width. In this simulation, decreasing muscle strength by 30% of its initial normal value had a stronger unfavorable effect than that of increasing body weight to the same relative degree. The effect of differences in body proportion between men and women did not appreciably influence the results, as long as masses and linear dimensions were average values of the respective sexes. Our results suggest that a patient with osteoarthritis in the knee should pay particular attention to problems of muscle weakness.