Q: I sprained my ankle doing a stupid move on my motorcycle. It never seemed to heal so I finally went in for help. They discovered the tendons along the outside of my leg aren't staying in the groove where they are supposed to be. The doc said it was unusual but I didn't catch what was unusual and why mine aren't staying where they are supposed to. Can you help explain this to me?

A:  Ankle sprain is a common injury in athletes as well as the active adult. Most of the time, the ankle heals with a little care (rest, taping, ice). But one rare complication of lateral ankle sprains is a condition called peroneal tendon instability. It sounds like this may be what you are experiencing.

A lateral ankle sprain means the side of the ankle away from the other leg is sprained. The two peroneal tendons go down the leg and around the back of the ankle bone. The tendons set down inside a tunnel formed by bone and connective tissue called the retromalleolar groove. A fibrous band (the superior peroneal retinaculum) goes across the tendon to hold them in the groove.

When this fibrous retinaculum is ruptured, the tendons can dislocate or pop out of the groove. Traumatic displacement of the peroneal tendons is a rare but painful complication of some lateral ankle sprains. Some people have a naturally shallow groove, which contributes to the likelihood of tendon displacement after ankle sprain.

The result is persistent pain along the outside aspect of the ankle bones. There may be a painful popping or snapping sensation. Swelling may mask the symptoms of tendon displacement at first. It's only weeks to months later when the painful symptoms don't go away that the additional tendon damage is recognized. Early MRIs may not show peroneal tendon instability, especially if the tendon pops in and out of the groove spontaneously. Dynamic ultrasound tests are the best diagnostic tests because they will reveal the movement of the unstable tendon.

Reference: Markus Walther, MD, PhD, et al. Peroneal Tendon Instability: Diagnosis and Authors' Recommended Treatment. In Current Orthopaedic Practice. March/April 2012. Vol. 23. No. 2. Pp. 80-85.