Assessment of hindfoot deformity by three-dimensional MRI in infant club foot.

In 12 infants aged under 16 months with unilateral club foot we used MRI in association with multiplanar reconstruction to calculate the volume and principal axes of inertia of the bone and cartilaginous structures of the hindfoot. The volume of these structures in the club foot is about 20% smaller than that in the normal foot. The reduction in volume of the ossification centre of the talus (40%) is greater than that of the calcaneus (20%). The long axes of both the ossification centre and the cartilaginous anlage of the calcaneus are identical in normal and club feet. The long axis of the osseous nucleus of the talus of normal and club feet is medially rotated relative to the cartilaginous anlage, but the angle is greater in club feet (10 degrees v 14 degrees). The cartilaginous structure of the calcaneus is significantly medially rotated in club feet (15 degrees) relative to the bimalleolar axis. The cartilaginous anlage of the talus is medially rotated in both normal and club feet, but with a smaller angle for club feet (28 degrees v 38 degrees). This objective technique of measurement of the deformity may be of value preoperatively.