OBJECTIVETo explore the characteristics of the talonavicular joint movement in vivo and its effects on changes of the medial longitudinal arch.

METHODSFoot CT images in the initial position (neutral position) and terminal position (maximum varus-adduction-dorsiflexion position) were acquired from 9 cases (5 healthy volunteers, including 4 males and 1 female) during foot varus-adduction-dorsiflexion motion. Based on the principle of rigid body kinematics, the CT data were reconstructed and analyzed with Mimics and Geomagic reverse engineering software. The changes of the talonavicular joint in three-dimensional in 6 degrees of freedom were calculated to determine its correlation to the medial longitudinal arch angle.

RESULTSDuring foot varus-adduction-dorsiflexion motion, the talonavicular joint underwent varus-adduction-plantarflexion motion, with the motion range of 38.82∓5.98° in varus, 19.71∓6.33° in adduction, and -5.09∓6.89° in plantarflexion. During talonavicular joint motion, the medial shift of the navicular was significantly correlated to the changes of foot medial longitudinal arch (P<0.05).

CONCLUSIONDigital technology can solve the problem of measurement of talonavicular joint three-dimensional motion in vivo. Though as a ball-and-socket joint, the talonavicular joint mainly rotates around the sagittal axis, and its movement is a major factor to cause changes of foot medial longitudinal arch.