A dynamic biomechanical analysis of the etiology of adolescent tibia vara.

Biomechanical overload of the proximal tibial physis due to static varus alignment and excessive body weight has been implicated in the etiology of infantile tibia vara. Whether a similar pathophysiologic process applies to adolescent tibia vara is controversial, with poor consensus concerning the nature and significance of static knee alignment early in the course of the disease. This study examines the hypothesis that dynamic gait deviations to compensate for increased thigh girth associated with obesity (fat-thigh gait) could result in increased loading 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 were dynamic stance-limb knee varus, increased stance-limb knee rotation, and swing-limb circumduction. Pathologic compressive forces were generated in an anthropometric model by using recorded fat-thigh gait deviations and clinically appropriate excessive body weight. This analysis supports the clinical observation that underlying static varus malalignment of the knee is not a prerequisite for the development of adolescent tibia vara and illustrates the significance of dynamic gait deviations when considering knee-joint loading.