Knee The knee changes that result from the primary impairments in children with hyper- tonia are well documented. The knee often flexes in response to abnormal biome- chanics of movement, especially gait, with a resulting flexion contracture (Gage, 1991; Perry, Antonelli, & Ford, 1975; Sutherland & Cooper, 1978). The knee also often ends up with a flexion contracture because of sustained cOcontraction around the knee joint. Occasionally, the knee hyperextends due to hip and ankle pathome- chanics during gait (Gage, 1991; Simon, et al, 1978). In order to successfully treat problems of the knee in movement, the therapist must understand the abnormal mechanics at all trunk and lower extremity joints.