Subtalar stress radiography using forced dorsiflexion and supination.

We investigated a new method of stress radiography of the subtalar joints using forced maximum dorsiflexion of the ankle in a supinated position. We measured transposition of the lateral process of the talus at the posterior subtalar joint in lateral views of normal amputated ankles, normal control subjects and patients with recurrent ankle sprains. The mean displacement in the control groups (n = 36) was 29.9%, significantly different from the 43.0% in patients with recurrent ankle sprains (n = 24). In the amputated specimens with intact ligaments movement was similar to that in normal subjects. Section of the calcaneofibular and the interosseous ligaments allowed much the same movement as in patients with recurrent ankle sprains. The new method is simple and useful for detecting subtalar instability.