Adult patients who experience posterior tibial tendon dysfunction may notice a gradual loss of the arch of their foot in a condition known as "flatfoot." The posterior tibial muscle is a deep muscle in the back of the calf and has a long tendon that extends from above the ankle and attaches to several sites around the arch of the foot. The muscle acts like a stirrup on the inside of the foot to help support the arch. The posterior tibial muscle stabilizes the arch and creates a rigid platform for walking and running. If the posterior tibial tendon becomes damaged or tears, the arch loses its stability and as a result, collapses, causing a flatfoot. Surgery may be required to give the patient a more functional and stable foot. Specific procedures for correcting a flatfoot deformity include a tenosynovectomy, osteotomy, tendon transfer, lateral column lengthening, and arthrodesis.