title: The importance of swing-phase initial conditions in stiff-knee gait.
abstract: The diminished knee flexion associated with stiff-knee gait, a movement abnormality commonly observed in persons with cerebral palsy, is thought to be caused by an over-active rectus femoris muscle producing an excessive knee extension moment during the swing phase of gait. As a result, treatment for stiff-knee gait is aimed at altering swing-phase muscle function. Unfortunately, this treatment strategy does not consistently result in improved knee flexion. We believe this is because multiple factors contribute to stiff-knee gait. Specifically, we hypothesize that many individuals with stiff-knee gait exhibit diminished knee flexion not because they have an excessive knee extension moment during swing, but because they walk with insufficient knee flexion velocity at toe-off. We measured the knee flexion velocity at toe-off and computed the average knee extension moment from toe-off to peak flexion in 17 subjects (18 limbs) with stiff-knee gait and 15 subjects (15 limbs) without movement abnormalities. We used forward dynamic simulation to determine how adjusting each stiff-knee subject's knee flexion velocity at toe-off to normal levels would affect knee flexion during swing. We found that only one of the 18 stiff-knee limbs exhibited an average knee extension moment from toe-off to peak flexion that was larger than normal. However, 15 of the 18 limbs exhibited a knee flexion velocity at toe-off that was below normal. Simulating an increase in the knee flexion velocity at toe-off to normal levels resulted in a normal or greater than normal range of knee flexion for each of these limbs. These results suggest that the diminished knee flexion of many persons with stiff-knee gait may be caused by abnormally low knee flexion velocity at toe-off as opposed to excessive knee extension moments during swing.
authors.affiliation: Mechanical Engineering Department, Biomechanical Engineering Division, Stanford University, Stanford, CA 94305-3030, USA.
authors.forename: Saryn R
authors.initials: SR
authors.lastname: Goldberg
authors.forename: Sylvia
authors.initials: S
authors.lastname: Ounpuu
authors.forename: Scott L
authors.initials: SL
authors.lastname: Delp
mesh_terms: D000293:Adolescent; D002547:Cerebral Palsy / Q000150:complications / Q000503:physiopathology*; D002648:Child; D003198:Computer Simulation; D005260:Female; D005684:Gait; D020233:Gait Disorders, Neurologic / Q000209:etiology / Q000503:physiopathology*; D006801:Humans; D007719:Knee Joint / Q000503:physiopathology*; D008297:Male; D008954:Models, Biological; D016059:Range of Motion, Articular; D012016:Reference Values; D014034:Toes / Q000503:physiopathology*