We report a case of 20 year-old man who had unusual equinus and checkrein deformity following dislocation of his right ankle joint. He had been treated with distal tibiofibular screw fixation and external fixation. After removal of external fixator, he had suffered from progressive deformity of foot and ankle. Widening of distal tibiofibular joint and medial clear space was found on radiograph and it was revealed that posterior tibial tendon had been dislocated and incarcerated into the distal tibiofibular joint on MRI. We corrected the deformity with excision of incarcerated posterior tibial tendon, adhesiolysis and lengthening of flexor hallucis longus tendon, reconstruction of deltoid ligament and flexor digitorum longus tendon transfer.