Sinus tarsi syndrome is a common problem that can affect the outside of the ankle joint. The problem is due to some damage within the subtalar joint and the sinus tarsi which passes between the two bones involved in that joint.

Resources:

http://www.podiatry-arena.com/podiatry-forum/tags/index.php?tag=/sinus-tarsi-syndrome/

http://www.podiatry-arena.com/podiatry-forum/showthread.php?t=7534