The posterior tibial tendon runs along the inner aspect of the foot and ankle. It helps support the arch of the foot. Posterior tibial tendonitis occurs when this tendon becomes inflamed or torn. This causes pain and lack of support in the inner arch. resulting in a flat foot and with time severe arthritis of the foot and ankle. Nonoperative treatment can include rest, immobilization, walking boots, orthotics, anti-inflammatories and physical therapy. In some cases posterior tendonitis can require surgical intervention.