The effect of posterior tibialis tendon dysfunction on the plantar pressure characteristics and the kinematics of the arch and the hindfoot.

OBJECTIVE To study posterior tibialis tendon dysfunction using an in vitro model of the foot and ankle during the heel-off instant of gait. BACKGROUND Previous studies have concentrated primarily on the effect of posterior tibialis tendon dysfunction on the kinematics of the hindfoot and the arch. METHODS The specimens were loaded using a custom designed axial and tendon loading system and the location of the center of pressure was used to validate heel-off. Arch position, hindfoot position and plantar pressure data were recorded before and after the posterior tibialis tendon was unloaded. These data were recorded with the ligaments intact and after creating a flatfoot deformity. RESULTS Unloading the posterior tibialis tendon caused significant posterior movement in the center of pressure for the intact and flatfoot conditions. This also resulted in a medial shift in the force acting on the forefoot. The forefoot loads shifted medially after a flatfoot was created even when the posterior tibialis tendon remained loaded. The spatial relationships of the bones of the arch and the bones of the hindfoot also changed significantly for the intact specimen, and to a lesser extent after a flatfoot. CONCLUSIONS The posterior tibialis tendon plays a fundamental role in shifting the center of pressure anteriorly at heel-off. Posterior tibialis tendon dysfunction causes posterior shift in the center of pressure and abnormal loading of the foot's medial structures. This may be the reason that posterior tibialis tendon dysfunction leads to an acquired flatfoot deformity. Conversely, flatfoot deformity may be a predisposing factor in the onset of posterior tibialis tendon dysfunction. This tendon also acts to lock the bones of the arch and the hindfoot in a stable configuration at heel-off, but a flatfoot deformity compromises this ability.