When i walk down a flight of stairs my left ankle hurts. pain at the inner side of ankle. what?

Tendonitis?: Sounds like tendonitis and the inner ankle tendons are under a lot of stress when walking down hill or down stairs. Is that left foot arch also "flatter" than the right? If so you need to have that evaluated. Does this happen barefoot or with shoes? Could also be early signs of arthritis or problems from a previous ankle sprain. Needs evaluation of this is more than 6 months old.