Correlation between three-dimensional medial longitudinal arch joint complex mobility and medial arch angle in stage II posterior tibial tendon dysfunction.

BACKGROUND: The purpose of this study was to evaluate correlation between three-dimensional medial longitudinal arch joint complex mobility and medial arch angle in stage II posterior tibial tendon dysfunction flatfoot under loading. METHODS: CT scans of 15 healthy feet and 15 feet with stage II posterior tibial tendon dysfunction flatfoot were taken both in non- and simulated weight-bearing condition. The CT images of the hindfoot and medial longitudinal arch bones were reconstructed into three-dimensional models with Mimics and Geomagic reverse engineering software. The three-dimensional complex mobility of each joint in the medial longitudinal arch and their correlation with the medial arch angle change were calculated. RESULTS: From non- to simulated weight-bearing condition, the medial arch angle change and the medial longitudinal arch joints mobility were significant larger in stage II posterior tibial tendon dysfunction flatfoot (p<0.05). The eversion of the talocalcaneal joint, the proximal translation of the calcaneus relative to the talus, the dorsiflexion of the talonavicular joint, the dorsiflexion and abduction of the medial cuneonavicular joint, and the lateral translation of the medial cuneiform relative to the navicular, and the dorsiflexion of the first tarsometatarsal joint were all significantly correlated to the medial arch angle change in stage II posterior tibial tendon dysfunction flatfoot (all r>0.5, p<0.05). CONCLUSIONS: There is increased mobility in the medial longitudinal arch joints in stage II posterior tibial tendon dysfunction flatfoot and the medial arch angle change under loading causes displacement not only at hindfoot joints but also involve midfoot and forefoot joint.