We report a case of tibialis posterior tendon dislocation into the disrupted ankle mortise between the tibia and fibula that was overlooked in the initial operative treatment of a fracture dislocation of the ankle with syndesmosis disruption. Recurrent widening of the ankle mortise prompted revision surgery where the posterior tibialis tendon dislocation was discovered to be the cause of secondary joint subluxation. The course of the tendon was corrected and the anatomy of the joint restored. One year after revision there is a good clinical result, however early posttraumatic osteoarthritis of the tibiotalar joint is seen radiologically.