In vivo three-dimensional analysis of hindfoot kinematics in stage II PTTD flatfoot.

BACKGROUND This study aims to evaluate the rotation and translation of each joint in the hindfoot and compare the differences in healthy foot with that in stage II PTTD flatfoot by analyzing the reconstructive three-dimensional (3D) computed tomography (CT) image data during several extreme positions. METHODS CT scans of 20 healthy feet and 20 feet with stage II PTTD flatfoot were taken in maximal positions of plantarflexion, dorsiflexion, inversion, eversion, external rotation and internal rotation conditions. The images of the hindfoot bones were reconstructed into 3D models. The "twice registration" method was used to calculate the spatial changes of the talus relative to the calcaneus in the talocalcaneal joint, the navicular relative to the talus in talonavicular joint, and the cuboid relative to the calcaneus in the calcaneocuboid joint. RESULTS Compared with normal participants, with the calcaneus relative to the talus, participants with stage II PTTD flatfoot presented more dorsiflexion (p < 0.05), adduction (p < 0.05), and eversion (p < 0.05) in rotation, and more anterior (p < 0.05) and distal translation (p < 0.05) from maximal plantarflexion to maximal dorsiflexion; more dorsiflexion (p < 0.05), eversion (p < 0.05), and abduction (p < 0.05) in rotation and more lateral translation (p < 0.05) from maximal inversion to maximal eversion; and a greater degree of adduction (p < 0.05) in rotation, and more lateral (p < 0.05) and posterior translation (p < 0.05) from maximal internal rotation to maximal external rotation condition. For navicular relative to the talus, they demonstrated more eversion (p < 0.05) and adduction (p < 0.05) in rotation, and more lateral (p < 0.05), anterior (p < 0.05), and distal translation (p < 0.05) from maximal plantarflexion to maximal dorsiflexion; more eversion (p < 0.05) and adduction (p < 0.05) in rotation, and more lateral (p < 0.05) and proximal (p < 0.05) translation from maximal inversion to maximal eversion; more eversion (p < 0.05) and abduction (p < 0.05) in rotation and more lateral (p < 0.05) translation from maximal internal to maximal external rotation condition. The cuboid position relative to the calcaneus in the calcaneocuboid joint did not change significantly in rotation and translation in different positions (p > 0.05). CONCLUSIONS As previous studies shown, regarding both of the cadaveric foot and the live foot, hindfoot joint instability occurred in patients with stage II PTTD flatfoot.