Effects of a functional knee brace on the biomechanics of running.

The purpose of the study was to assess the biomechanical effects of a functional knee brace on joint moments of force and joint powers in the lower extremity during the stance phase of running in subjects with a previous ACL injury. Sagittal-plane film records and ground reaction force data were obtained from five previously injured subjects running with and without a functional knee brace and from five healthy subjects running without the brace. Inverse dynamics were performed on these data to obtain the moments of force and joint powers. The angular impulse in the extensor direction was assessed from each moment of force curve, and the work performed during selected portions of the stance phase was assessed from the joint power curves. ANOVA techniques on these variables indicated no significant differences between the brace and no-brace conditions in the previously injured subjects. In comparison with the healthy runners, the previously injured subjects had, on average, 49% and 32% greater extensor angular impulse about the hip and ankle (both P less than 0.05). In contrast, the healthy runners had, on average, 233% greater (P less than 0.05) extensor angular impulse about the knee. The corresponding negative and positive work performed at the knee were 321% and 191% larger (both P less than 0.05) in the healthy runners. The reduction in the extensor moment of force about the knee and the increase in the moments of force about the hip and ankle in the previously injured subjects reduced the stresses on the ACL and tibia while at the same time enabling them to run at the required speed.