Muscle contributions to knee extension in the early stance phase in patients with knee osteoarthritis.

The aim of this study was to analyze individual muscle contributions to knee angular acceleration using a musculoskeletal simulation analysis and evaluate knee extension mechanics in the early stance phase in patients with knee osteoarthritis (OA). The subjects comprised 15 patients with medial knee OA and 14 healthy elderly individuals. All participants underwent gait performance test using 8 infrared cameras and two force plates to measure the kinetic and kinematic data. The simulation was driven by 92 Hill-type muscle-tendon units of the lower extremities and a trunk with 23° of freedom. We analyzed each muscle contribution to knee angular acceleration in the 5%-15% and 15%-25% periods of the stance phase (% SP) using an induced acceleration analysis. We compared accelerations by individual muscles between the two groups using an analysis of covariance for controlling gait speed. Patients with knee OA had a significantly lesser knee extension acceleration by the vasti muscles and higher knee acceleration by hip adductors than those in controls in 5-15% SP. In addition, knee OA resulted in significantly lesser knee extension acceleration by the vasti muscles in 15-25% SP. These results indicate that patients with knee OA have decreased dependency on the vasti muscles to control knee movements during early stance phase. Hip adductor muscles, which mainly control mediolateral motion, partly compensate for the weak knee extension by the vasti muscles in patients with knee OA.