A case of an 18-year-old male with extensive posterior and lateral soft-tissue loss of the lower leg is reported. There was a segmental defect of 20 cm in the tibialis posterior neurovascular bundle, and the injury was not considered reconstructable. There was extensive soft-tissue trauma to the posterior compartments of the leg, with an intact and well-perfused foot. A primary amputation was indicated. The foot was used as a fillet flap for tibial length preservation and optimal stump coverage. The foot fillet flap was pedicled on the tibialis anterior vessels, preserving the deep plantar, first dorsal metatarsal, and anterior communicating vessels. The postoperative evolution was uneventful, with successful prosthetic adaptation.