ankle sprain study

A new study in West Point cadets sheds a bit more light on risk factors for two relatively rare, but severe, types of ankle sprain.

So-called "high" and "inner" ankle sprains account for 10 to 15 percent of all ankle sprains, Dr. Brett D. Owens of Keller Army Hospital in West Point, New York, and his colleagues note in the American Journal of Sports Medicine.

Both types of sprain result in longer time lost due to injury and greater disability than more common sprains.

Ankle sprains usually involve the ligaments linking the lower leg to the heel, and typically occur when the foot twists inward. But high ankle sprains, technically known as syndesmotic sprains, affect the ligament holding together the two long bones of the lower leg, Owens explained in an interview.

Inner, or medial, sprains are even rarer and occur when the foot is twisted outward.

To better understand how common these types of ankle sprains are and what puts people at risk for them, Owens and his team looked at data on all ankle injuries among U.S. Military Academy cadets between 2005 and 2009.

Over the five years, 1,206 cadets sprained an ankle, with seven percent of those injuries being high sprains and five percent inner sprains.

In the entire cadet population during that period, the overall risk of experiencing a high ankle sprain was about half a percent for both men and women. For inner ankle sprains, the annual risk for male and female cadets was also less than one in 100, at 0.39 percent and 0.12 percent, respectively.

Eighty percent of the high sprains that occurred happened during athletics, as did 64 percent of the inner sprains. High-contact, high-impact sports accounted for most injuries, with top offenders for high sprains in men being sprint football, men's team handball, soccer, and basketball; for women, the highest-risk sports for high sprains were intercollegiate volleyball, followed by basketball and soccer. Inner sprains occurred most frequently during men's rugby, gymnastics, and soccer.

Men playing at the intercollegiate level were 3.5 times as likely as women playing intercollegiate sports to have inner ankle sprains, but there was no gender difference in the risk of high sprains. Athletes playing intercollegiate sports had 2.4 times the risk of high sprains compared to athletes playing intramurally.

Bulk also played a role in who was most at risk. The average body mass index (BMI, a measure of weight in relation to height that is used to gauge obesity but can also indicate high muscle mass) was higher for people who sustained either inner or high sprains. The BMI of those who were injured averaged about 26, versus 24 for people who were not hurt. A BMI between 18.5 and 24.9 is considered normal for most of the population.

Time lost to play averaged about two weeks for high sprains, and while data on inner sprains wasn't complete, time lost to sport was higher than seen in previous studies of these injuries. By comparison, a past study by Owens and his colleagues in the same group of cadets found they lost an average of eight days due to lateral sprains, the most common type of ankle sprain.

Inner sprains were probably more common for men because men were more likely to engage in high-impact play, Owens noted.

While efforts to prevent inner and high ankle sprains wouldn't differ much from efforts to prevent more common sprains, such as the use of special braces, Owens said, the findings do help to identify which individuals face the greatest risk, and where these interventions should be targeted. "It's the contact sports that are most problematic, football, rugby...gymnastics, which is not surprising, given the amount of energy that goes into a jump landing," he said.

Bruce Werber DPM, FACFAS

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