I am a sprinter for our high school track team. Whenever I push off from the starting blocks, I get a sharp pain in the back of my ankle. What could be causing this?

You may be experiencing something called posterior ankle impingement. This is the pinching of soft tissue, bone, or scar tissue causing painful and limited ankle motion. Plantar flexion (pointing the toe) is affected most often. It’s the movement you are using to push off from the starting block.

Posterior ankle impingement is caused by traumatic injury or overuse. Dancers, soccer players, runners, and other athletes are affected most often. Sometimes dancing or running on a hard surface contributes to the problem.

In other cases, there is a slight difference in the normal foot and ankle anatomy that eventually leads to posterior ankle impingement. The joint capsule may be thickened causing pain when it gets pinched between two bones in the ankle.

There may be bone fragments inside the joint that have broken off the bone and become free-floating agents that get stuck. Whatever the cause, the end result is the same: chronic ankle pain along the back of the ankle at rest and with palpation, pain with movement, and loss of ankle plantar flexion.

One common cause of posterior impingement syndrome is called the os trigonum. There is an extra piece of bone present (usually at birth) in affected individuals. It is located behind the talus bone (part of the ankle complex). It is connected to the talus by a band of fibrous tissue. When this bony bump gets separated from the main body of the talus, it is referred to as an os trigonum.

For the person who has an os trigonum, pointing the toes downward catches the os trigonum between the ankle and heel. The repetitive force downward on the os trigonum every time the foot is pointed causes the bone fragment to pull loose. As the os trigonum pulls away, the tissue connecting it to the talus is stretched or torn. The area becomes inflamed causing pain and loss of ankle motion.

The best way to find out what’s causing your symptoms is to see an orthopedic surgeon. A clinical exam, X-rays or other imaging studies, and history will result in a diagnosis. An early diagnosis and subsequent treatment may be able to reduce your painful symptoms and restore normal alignment with nonoperative care (e.g., physical therapy, antiinflammatory medications, steroid injection).