The superior articular surface of the talus is wider anteriorly than posteriorly, the difference in widths being as much as 6 mm. The articular surfaces of the tibial and fibular malleoli maintain a close fit against the medial and lateral articular surfaces of the talus in all positions of plantar flexion and dorsiflexion. As the foot moves from full plantar flexion into full dorsiflexion the talus rolls backward in the mortise. It would seem, then, that with ankle dorsiflexion the malleoli must separate to accommodate the greater anterior width of the talus. This separation could occur as a result of a lateral shift of the fibula, a lateral bending of the fibula, or both. However, it is found that the amount of separation that occurs between the malleoli during ankle dorsiflexion varies from none to only 2 mm, which is much less than would be expected, considering the amount of wedging of the superior articular surface of the talus. There appears to be a significant discrepancy between the difference in anterior and posterior widths of the trochlea of the talus and the amount of separation that occursbetween the tibial and fibular malleoli with ankle dorsiflexion.