Tibialis Posterior Tendinopathy affects the tibialis posterior tendon, which is a muscle deep in your leg that moves your ankle inward and also supports your arches. Dysfunction of this muscle is the most common cause of flat feet in adults. This muscle may develop into Tibialis Posterior Tendinopathy due to repetition or trauma. You may also have pain and swelling along the medial aspect of the foot that gets worse with activity. Your therapist will help to reduce symptoms, restore foot posture and arch, and provide education about activity modification if needed. Orthotics may be a suitable option for this condition as well.