Stage IV posterior tibial tendon rupture.

Adult acquired flatfoot deformity progresses through well defined stages as set out by Johnson and Strom. Myerson modified this classification system with the addition of a fourth, more advanced stage of the disease. This stage describes the involvement of the tibiotalar joint in addition to the hindfoot malalignment seen in stages II and III. This most advanced stage is comprised of a hindfoot valgus deformity, resulting from degeneration of the posterior tibial tendon, with associated valgus tilting of the talus within the mortise. The deformity at the tibiotalar joint may or may not be rigid. Although rigid deformities are still best treated with fusions of the ankle and hindfoot, supple tibiotalar deformity may be treated with joint sparing procedures involving reconstructive procedures of the foot and deltoid ligaments.