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Effects of Simulated Genu Valgum and Genu Varum on Ground Reaction Forces and Subtalar Joint Function During Gait

Bart Van Gheluwe, DrSc ^*, Kevin A. Kirby, DPM  and Friso Hagman, DrSc ^*

^* Laboratory of Biomechanics, Vrije Universiteit Brussel, Brussels, Belgium.
Department of Applied Biomechanics, California School of Podiatric Medicine at Samuel Merritt College, Oakland; private practice, Sacramento, CA.

Corresponding author: Bart Van Gheluwe, DrSc, Laboratory of Biomechanics, Vrije Universiteit Brussel, Fac LK, Pleinlaan 2, 1050 Brussels, Belgium.

Abstract

The mechanical effects of genu valgum and varum deformities on the subtalar joint were investigated. First, a theoretical model of the forces within the foot and lower extremity during relaxed bipedal stance was developed predicting the rotational effect on the subtalar joint due to genu valgum and varum deformities. Second, a kinetic gait study was performed involving 15 subjects who walked with simulated genu valgum and genu varum over a force plate and a plantar pressure mat to determine the changes in the ground reaction force vector within the frontal plane and the changes in the center-of-pressure location on the plantar foot. These results predicted that a genu varum deformity would tend to cause a subtalar pronation moment to increase or a supination moment to decrease during the contact and propulsion phases of walking. With genu valgum, it was determined that during the contact phase a subtalar pronation moment would increase, whereas in the early propulsive phase, a subtalar supination moment would increase or a pronation moment would decrease. However, the current inability to track the spatial position of the subtalar joint axis makes it difficult to determine the absolute direction and magnitudes of the subtalar joint moments. (J Am Podiatr Med Assoc 95(6): 531–541, 2005)