BME MS Defense: Cody Hillin

The Effect of Stage II/III PTTD on the Position of the Subtalar Joint Axis and Hindfoot Kinematics during Walking

Supervised by Prof. Jeff Houck

Abstract

Altered position of the subtalar joint axis and abnormal hindfoot movement during gait are hypothesized to occur in subjects with Posterior Tibial Tendon Dysfunction (PTTD), because PTTD is associated with damage to ligaments and muscle weakness hindfoot deformity (Stage II/III). Clinical treatments therefore focus on maintaining hindfoot alignment and function during gait. Key markers of hindfoot function are the position of the subtalar joint axis and hindfoot kinematics during walking. However, the subtalar joint axis has been shown to be highly variable between people, which may be explained by variation in hindfoot deformity. To link this variation in the hindfoot a quantitative position of the subtalar joint axis in subjects with hindfoot deformity is necessary. Therefore, the subject specific position of the subtalar joint axis was determined in ten young controls as well as ten subjects with PTTD by using a device called the Subtalar Axis Locator. The SAL was adapted for subjects with PTTD from previous research on healthy subjects, and the position of the subtalar joint axis was subsequently used to resolve hindfoot motion for a kinematic model of the foot. Subjects with PTTD used a laterally shifted subtalar joint axes compared to controls, yet there were few differences when comparing the position of the subtalar joint axis from the involved to the uninvolved side in either group. The hindfoot kinematics during gait showed greater eversion of the subjects with PTTD compared to the controls. This study suggests an association between hindfoot deformity in subjects with PTTD and the position of the subtalar joint axis. Clinically muscle weakness and breakdown of key ligaments within the foot may be reflected in the altered subtalar joint axis position that results in altered hindfoot kinematics.