Early embryonic development of long tendons in the human foot.

To examine a common plantar tendinous plate for long flexors of the toe and fingers in human embryos, we observed sections of 10 embryos at 5-6 weeks (crown-rump length or CRL 15-21 mm). The heel or tuber of the calcaneus was underdeveloped in 3 embryos with CRL 15 mm and the talus appeared not to be piled up on the calcaneus but these two bones were arranged along the lateromedial axis. As reported in the hand, we demonstrated, in the deep side of tarsal bones, a common tendinous plate formed by a joining of the flexor halluces longus and flexor digitorum longus tendons. In the tendinous plate, much or less, some connections between tendons seemed to remain even after birth to provide much greater types of tendon anomalies than in the hand. In addition, we postulated a hypothetical change in course of the peroneus longus tendon. In the initial phase, because of the underdeveloped calcaneus, the peroneus tendon might take an almost straight course similar to long flexor tendons. However, at 6 weeks and later, the inferomedially expanding calcaneus beneath the talus was likely to push the tendon to the cuboid bone.