Weight-Bearing Ankle Internal Rotation : A Pilot Study In Vivo Kinematics of the Talocrural and Subtalar Joints With Functional Ankle Instability During

Abstract: Functional ankle instabil-ity (FAI) may involve abnormal kine-matics. However, reliable quantitative data for kinematics of FAI have not been reported. The objective of this study was to determine if the abnor-mal kinematics exist in the talocru-ral and subtalar joints in patients with FAI. Five male subjects with unilateral FAI (a mean age of 33.4 ± 13.2 years) were enrolled. All subjects were exam-ined with stress radiography and found to have no mechanical ankle insta-bility (MAI). Lateral radiography at weight-bearing ankle internal rota-tion of 0 ° and 20 ° was taken with the ankle at 30 ° dorsiflexion and 30 ° plan-tar flexion. Patients underwent com-puted tomography scan at 1.0 mm slice pitch spanning distal one third of the lower leg and the distal end of the calcaneus. Three-dimensional (3D) kinematics of the talocrural and sub-talar joints as well as the ankle joint complex (AJC) were determined using a 3D-to-2D regis-tration technique using a 3D-to-2D registration technique with 3D bone models and plain radi-ography. FAI joints in ankle dorsiflexion dem-onstrated significantly greater subtalar internal rotation from 0