Congenital tibial aplasia with preaxial polydactyly: soft tissue anatomy as a clue to teratogenesis.

We performed preoperative arteriography and postamputation dissection on a human limb having complete tibial aplasia and preaxial polydactyly. The tibia was replaced by a tendinous band with an attached connective tissue mass. In the leg, the muscles were normal. Muscles usually arising from the tibia arose from the tendinous band, Intrinsic muscles of the foot were absent where skeletal elements were absent and there were supernumerary muscles where there were supernumerary skeletal elements. The tendinous insertions of the muscles that originated in the leg followed the skeletal pattern of the foot. The nerves were normally distributed with the exception that extra branches innervated the supernumerary toes. Both the anterior tibial and peroneal arteries were smaller than normal and progressively reduced in size as they coursed distally and could not be identified below the ankle. The dorsalis pedis artery was absent. The other arteries of the leg and foot were normal with the exception of extra branches supplying the supernumerary toes. The anatomy indicates that the foot is probably a double posterior duplication. Such a defect implies abnormal specification of the foot pattern due to a prespecification event. The tibial remnant with normal leg soft tissues indicates normal specification of the leg pattern and subsequent interruption of tibial morphogenesis due to a postspecification event. The presence of these different types of malformations in the same limb may seem to be contradictory. We suggest, however, that a single teratogenic event occurring at one moment in time could cause combined pre- and postspecification malformations. We further suggest that a diminished anterior tibial artery reduced the number of vessels available for collateral circulation and thus put the limb at risk for subsequent malformation.