The posterior tibial tendon runs down the calf, behind the inside of the ankle, and attaches to the middle of the foot. It helps maintain your arch and aids in walking. Inflammation of this tendon can lead to ankle pain and flatfoot. Tendon dysfunction is most common in women over 50 and often has no clear cause. Other risk factors include being overweight, diabetes, high blood pressure, previous surgery or steroid injections, previous injury, and inflammatory disorders.