Children are urged to participate in sports at younger and younger ages and at greater levels of intensity. While weight-bearing activity is generally thought to increase bone density, a study from Children's Hospital Boston finds that for preadolescent and adolescent girls, too much high-impact activity can lead to stress fractures.
If these are detected too late in children and adolescent athletes, they pose a risk of true fracture, deformity or growth disturbance requiring surgical treatment, say the researchers, led by Alison Field, ScD, of Children's Division of Adolescent Medicine, and Mininder S. Kocher, MD, MPH, associate director of Sports Medicine at Children's.
The study, published online April 4 by the Archives of Pediatric and Adolescent Medicine, followed 6831 girls aged 9 to 15 participating in the large national Growing Up Today Study, co-founded by Field. During the 7 years after enrollment, 4 percent of the girls developed a stress fracture. The most significant predictors were high-impact activities, particularly running, basketball, cheerleading and gymnastics.
"This is the first study to look prospectively at causes of stress fracture among a general sample of adolescent girls," says Field, who is also affiliated with Brigham and Women's Hospital. "Most research has been on specialized groups, such as army recruits or college athletes, making it difficult to figure out if the results apply to average adolescents. Our study was large enough to look at risk associated not only with hours per week of activity, but also hours per week in a variety of different activities."
When the researchers adjusted for other risk factors (age, later onset of menstruation and family history of osteoporosis and low bone density), the association between high-impact sports and fractures only strengthened. Girls engaging in 8 or more hours of high-impact activity per week were twice as likely to have a stress fracture as those engaged in such activity for 4 hours or fewer.
"We are seeing stress fractures more frequently in our pediatric and adolescent athletes," says Kocher, senior author on the report. "This likely reflects increased intensity and volume of youth sports. Kids are often playing on multiple teams, including town and travel teams, and participating in high intensity showcases and tournaments. It's not uncommon to see young athletes participating in more than 20 hours of sports per week."
Each hour of high-impact activity per week increased fracture risk by about 8 percent. Basketball, cheerleading/gymnastics and running were independent predictors.
"The youth athlete is specializing in a single sport at a younger age," says Kocher. "This does not allow for cross-training or relative rest, as the athlete is constantly doing the same pattern of movement and impact. Small injuries are being made in the bone with greater cumulative frequency than the body can handle."
The key to the treatment of stress fractures is early recognition, Kocher adds. If recognized early, most stress fractures will heal fully with activity restriction.
"Kids should not play through pain," he says. "'No pain-No gain' is not an appropriate adage for the young athlete."
The study was supported by the Department of Orthopedics at Children's Hospital Boston and the National Institutes of Health.
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