The purpose of this study is twofold: first, to measure the joint contact pressure across the calcaneocuboid joint in a planovalgus deformity and compare the results to pressures measured in a normal foot; and second, to determine the change in pressure across the calcaneocuboid joint after an Evan's-type calcaneal lengthening osteotomy. The effect of this procedure on the calcaneocuboid joint was evaluated using seven cadaver feet to measure peak pressure across the calcaneocuboid joint under a constant load. Each foot was sectioned medially to reproduce a deformity consistent with an adult, acquired flatfoot. Each flatfoot deformity was then corrected using a ten-millimeter lateral column lengthening osteotomy. Joint pressures were measured in the normal foot, the created flatfoot and then in the corrected flatfoot. Peak pressures across the joint increased significantly from baseline in the flatfoot (p <0.05). However, the change in pressure from the flatfoot to the corrected foot was not significant, and in some cases peak pressures in the corrected foot were actually lower than in the flatfoot. These findings indicate that calcaneal lengthening through an Evan's osteotomy does not increase pressure across the calcaneocuboid joint beyond physiologic loads in the flatfoot.