Tendons connect muscles to bones and stretch across joints, enabling you to bend those joints. One of the most important tendons in the lower leg is the posterior tibial tendon. This tendon starts in the calf, stretches down behind the inside of the ankle, and attaches to bones in the middle of the foot.
The posterior tibial tendon helps hold up your arch and provides support as you step off on your toes when walking. If this tendon becomes inflamed, overstretched, or torn, you may experience pain on the inner ankle and gradually lose the inner arch on the bottom of your foot, leading to flatfoot.