Why does an ankle sprain cause lower leg pain?

Rolling or spraining the ankle can cause pain in the entire lower leg. Specifically, there can be pain along the outside portion of the lower leg that can run almost up to the knee. The cause of this is a high ankle sprain or a syndesmotic ankle sprain. There are two bones in the lower leg, the tibia and fibula. In between these two bones is a type of sheath that connects them. When the ankle is sprained, it can cause this sheath to tear, which causes pain in the lower leg. Depending on the length of the tear, the pain can be all the way to the knee. (This answer provided for NATA by the Eastern University Athletic Training Education Program)