Talo-calcaneal relationship in clubfoot.

Talo-calcaneal angles were measured on anteroposterior, stress dorsiflexion, and plantarflexion lateral radiographs of 75 normal feet and 145 clubfeet. The talus and calcaneum from 15 normal fetal limbs were dissected without disturbing the subtalar capsule. Anteroposterior and lateral radiographs of these specimens were also obtained. The long axes of the ossific nuclei and the long axes of the cartilaginous anlagen of the bones were marked, and the talo-calcaneal angles were measured. The talo-calcaneal angles were lower in clubfeet than in normal feet, but there was considerable overlap in the ranges of normal and clubfeet for all the angles measured. The lateral talo-calcaneal angles in normal feet were higher in dorsiflexion than in plantarflexion, whereas the converse was true in clubfeet. The talo-calcaneal angles measured from the axes of the ossific nuclei of the fetal specimens were higher than those measured from the axes of the cartilaginous anlagen. Using logistic regression analysis, a mathematical model was made to predict the probability of correction of clubfeet. A lateral talo-calcaneal angle difference (between the stress dorsiflexion and plantarflexion angles) of 20 degrees suggests that there is a 93% probability that the hindfoot deformity of clubfoot has been adequately corrected. A talo-calcaneal angle of 30 degrees or a talo-calcaneal index of 40 degrees does not ensure correction of clubfoot. A decrease of the talo-calcaneal angle by up to 10 degrees occurs as the child grows because of the alteration of the shape of the ossific nucleus of the talus that occurs normally with growth.