Skeletal relationships in the human embryonic foot based on three-dimensional reconstructions

Several investigators have reported that the relationships of the embryonic skeletal elements are strikingly different from the adult condition.The present study examined these relationships during the final four stages of the embryonic period (i.e., stages 20-23). Six serially sectioned human embryos, ranging from 21.7 to 34.0 mm crown-rump length, approximately 51-57 postovulatory days, were studied. Three-dimensional reconstruction, involving wax plate and transparency models, was used to recreate the skeletal elements of the embryonic foot, representing each of the four developmental stages by a separate reconstruction. These models provided three different views of the embryonic foot because they were developed from specimens that were sectioned in three different sectional planes. The serial sections of the other two embryos were subsequently studied by microscopic examination. For each of the six embryos, the skeletal relationships were determined, paying particular attention to the arrangement in the hind-foot. These observations were compared with skeletal material of the adult foot which represented the end point of the developmental continuum. In contrast with much of the previous literature, the skeletal relationships of the embryonic hindfoot were found to be similar to the adult condition: The fibula projected further distally than the tibia; there was no evidence that the tip of the fibular malleolus was in contact with the calcaneus; and most importantly, the calcaneus was situated below the talus, not beside it as reported by other investigators.