The posterior tibial tendon helps point the foot down and in. Tendonitis can occur when the posterior tibial tendon becomes inflamed or torn. As a result, the tendon may not be able to provide stability and support for the arch of the foot, resulting in flatfoot.
Posterior Tibial Tendonitis Exercise Instructions
More Information:
More on Posterior Tibial Tendonitis from the American Academy of Orthopedic Surgeons (AAOS).