Posterior tibial tendon dysfunction (PTTD) causes pain along the inner side of the lower leg, ankle, or foot. 
Tendons are strong bands of connective tissue that attach muscles to bones. The posterior tibial tendon helps point the foot down and in. Tendonitis is inflammation of a tendon.
Posterior tibial tendonitis occurs from overuse of the tendon. This tendon attaches to a bone in the foot called the navicular and helps stabilize your arch. If your arch flattens out more than normal when you walk or run, it is called overpronation. When you overpronate, you strain your tendon and are more likely to get posterior tibial tendonitis.
Symptoms of this condition include:
- Pain or tenderness on the inner side of the shin, ankle, or foot
- Pain when lifting up your foot
- Pain when walking or running