A new method of foot orthosis modification that enhances the pronation controlling ability of foot orthoses is presented. The medial heel skive technique involves selectively removing small amounts of the medial portion of the plantar heel of the positive cast of the foot to create a unique varus wedging effect within the heel cup of the foot orthosis. The resulting increase in supination moment across the subtalar joint axis of the foot clinically produces significantly improved pronation control on pediatric flexible flat feet, posterior tibial dysfunction, and other types of excessively pronated feet.
The foot is an engineering marvel that allows the body to perform many physical activities over a wide variety of terrain with remarkable efficiency. The functions of the foot and the lower extremity are biomechanically integrated; thus normal lower-extremity function requires normal foot function and vice versa. Because the subtalar joint is the main pedal joint allowing the triplanar translation of motion between the foot and lower extremity, normal subtalar joint function is critical to normal foot and lower-extremity function. This article provides an overview of the interrelationships between foot and lower-extremity function and mechanically based pathology of the foot and lower extremity, with an emphasis on the subtalar joint.
A review of the rotational forces, or moments, acting across the subtalar joint axis during relaxed bipedal stance is presented. The concept of rotational equilibrium about the subtalar joint axis is used to explain some of the biomechanical differences between feet that stand in the neutral and maximally pronated subtalar joint positions. In addition, the mechanical basis of treatment of sinus tarsi syndrome with foot orthoses using the concepts of subtalar joint axis moments rotational equilibrium of the subtalar joint is presented.