Changes in the position of skeletal elements of the ankle and foot during late embryonic and fetal periods.

The morphology of the ankle joint and foot during early development exhibits distinct differences from that observed in adults, with physiological clubfoot being a well-documented phenomenon. To better understand this posture and its transformation, the skeletal elements in this region were three-dimensionally reconstructed using high-resolution phase-contrast x-ray computed tomography and magnetic resonance imaging of specimens (n = 23) during the late embryonic and early fetal periods, before joint cavity formation. Sequential changes were analyzed both morphologically and morphometrically from anterior, lateral, posterior, and plantar views. The reduction in plantar flexion of the ankle joint rendered the positional change of the hindfoot substantially more complex, and three-dimensional reconstruction facilitated its comprehension. Continuous supination of the hindfoot, pronation of the forefoot along the foot axis, and reduced plantar flexion of the ankle joint were identified as key postural changes that contributed to the development of temporal physiological clubfoot, initiated as early as the late embryonic period. Twisting between the forefoot and hindfoot and the abduction of the ankle joint, resulting from the obliquity of the tibia-talus joint, were substantial. The offset effect of the two angle changes conceals such changes in most previous studies. Changes in the shape of the tarsal bones, especially the calcaneus and talus, affected the relative bone positions, indicating that the concept of "differential growth" may apply to ankle-joint and foot morphogenesis. Findings of the present study are expected to enhance understanding of the pathogenesis and mechanisms underlying clubfoot and facilitate fetal diagnosis via morphological assessments.