A DYNAMIC BIOMECHANICAL ANALYSIS OF THE ETIOLOGY OF ADOLESCENT TIBIA VARA

Biomechanical overload of the proximal tibial physis due to static var us alignment and excessive body weight has been implicated in the etio logy of infantile tibia vara. Whether a similar pathophysiologic proce ss applies to adolescent tibia vara is controversial, with poor consen sus concerning the nature and significance of static knee alignment ea rly in the course of the disease. This study examines the hypothesis t hat dynamic gait deviations to compensate for increased thigh girth as sociated with obesity (fat-thigh gait) could result in increased loadi ng of the medial compartment of the knee during the gait cycle. Three- dimensional motion analysis was used to identify the kinematic/kinetic profile associated with fat-thigh gait. Gait deviations identified we re dynamic stance-limb knee varus, increased stance-limb knee rotation , and swing-limb circumduction. Pathologic compressive forces were gen erated in an anthropometric model by using recorded fat-thigh gait dev iations and clinically appropriate excessive body weight. This analysi s supports the clinical observation that underlying static varus malal ignment of the knee is not a prerequisite for the development of adole scent tibia vara and illustrates the significance of dynamic gait devi ations when considering knee-joint loading.