Up to sixty percent of recreational runners may get injured over the course of a year. Most of these injuries come from overuse. Ten to 15 percent of them are thought to be tibial stress syndrome.

Formerly lumped under "shin splints," tibial stress syndrome happens when muscles tear away from the shinbone, causing inflammation. When the syndrome strikes along the inside edge of the lower shin, it's called "medial tibial stress syndrome," or MTSS. Symptoms of MTSS may be anything from a dull ache to intense pain with touch. The pain usually gets worse with repetitive weight-bearing activities like running.

Researchers think that runners who wind up with MTSS may be compensating for structural problems in their feet. If the feet are not properly aligned, runners may pronate--or put excessive downward pressure on the big-toe sides of the feet. This motion can tug at the muscles in the shins, leading to MTSS.

These authors studied the foot structure of 125 runners from three high school cross-country teams. The runners were roughly half male, half female. They were an average of 16 years old and had been running for about two years.

During the first three weeks of the cross-country season, the authors took a series of measurements of the runners' feet. These measures included heel position, leg angle, and the ability to flex the foot up.

Pronation was measured for this group with a navicular drop test. The navicular bone is on the big-toe side of the foot. The test measures how far the navicular bone "drops" when the foot goes from a corrected alignment to a pronated one. The test was also done on 15 noninjured runners, to act as a comparison group.

The study showed that a pronated foot posture was related to symptoms of MTSS. Injured runners showed much greater pronation as measured by the navicular drop test. Their measurements were almost twice those of noninjured runners. And of the 25 legs with MTSS, almost a third showed nearly three times the "drop" of noninjured legs. Other measures of foot structure, including heel position and leg angle, were not related to injury, however.

Fifteen runners (12 percent) developed symptoms of MTSS within eight weeks. Yet there were no differences between injured and noninjured runners in age, years running, or years in school. Notably, girls were a lot more likely than boys to develop MTSS. Thirteen of the injured runners were girls. That means 19 percent of female runners developed MTSS. Meanwhile, only two boys showed symptoms. It could be that girls are more likely to report symptoms than boys.

The authors conclude that sex and pronation are the best predictors of MTSS. Sex correctly predicted MTSS 74 percent of the time. And pronation predicted MTSS 68 percent of the time. Together, these two characteristics accurately gauged who developed MTSS 76 percent of the time.

The authors intend to test their model over a longer period of time. If runners susceptible to MTSS can be identified early, symptoms might be successfully prevented by using orthotics.