Risk factors for stress fractures in adolescent runners

Stress fractures are a relatively common problem in runners, and I would speculate they have become more common recently. A new study attempted to identify the risk factors for stress fractures in adolescent runners:

Identifying Sex-Specific Risk Factors for Stress Fractures in Adolescent Runners
Tenforde, Adam S.; Sayres, Lauren C.; Liz McCurdy, Mary; Sainani, Kristin L.; Fredericson, Michael
Medicine & Science in Sports & Exercise: 11 April 2013
Purpose: Adolescent females and males participating in running represent a population at high risk of stress fracture. Few investigators have evaluated risk factors for prospective stress fracture in this population.
Methods: To better characterize risk factors for and incidence of stress fractures in this population, we collected baseline risk factor data on 748 competitive high school runners (442 girls and 306 boys) using an online survey. We then followed them prospectively for the development of stress fractures for an average of 2.3+/-1.2 total seasons of cross-country and track and field; follow-up data were available for 428 girls and 273 boys.
Results: We identified prospective stress fractures in 5.4% of girls (N=23) and 4.0% of boys (N=11). Tibial stress fractures were most common in girls, and the metatarsus was most frequently fractured in boys. Multivariate regression identified four independent risk factors for stress fractures in girls: prior fracture, BMI <19, late menarche (age menarche >=15 years), and previous participation in gymnastics or dance. For boys, prior fracture and increased number of seasons were associated with an increased rate of stress fractures, whereas prior participation in basketball was associated with a decreased risk of stress fractures.
Conclusion: Prior fracture represents the most robust predictor of stress fractures in both sexes. Low BMI, late menarche, and prior participation in gymnastics and dance are identifiable risk factors for stress fractures in girls. Participation in basketball appears protective in boys and may represent a modifiable risk factor for stress fractures. These findings may help guide future translational research and clinical care in the management and prevention of stress fractures in young runners.

This was a prospective study of boys and girls participating in cross country or track and investigated a number of anthropometric, previous history, dietary, and menstrual factors. Just over 5% of the girls and 4% of the boys developed a stress fracture in the mean of almost 12 months of follow-up. They identified that the main risk factor for a stress fracture was a previous stress fracture, which would make sense if they have the risk factors for a stress fracture and if they were still present, then they are obviously at risk for another.

In the girls the main factors identified were related to a delayed menarche and a lower BMI. This is consistent with the issues surrounding the female athlete triad and the impact that this has on bone health and decreases the ability of the bone to take the cumulative load.

Prior participation in other sports was interesting. For girls previous participation in dance and gymnastics was a risk factor and may have been related to the lower mean body weight and body image issues in those activities and related bone health issues associated with that. For boys, prior participation in basketball lowered the risk for a stress fracture and may be related to the jumping activities better conditioning the bones to take the cumulative loads of running.

This was a sound study and the results are consistent with prior research and strengthens the understanding of the risk factors.

The major shortcoming of the study is that there were no biomechanical factors included and the risk of those factors for specific stress fractures. Obviously, in studies of this nature it is not feasible to include them as this is a significantly more major undertaking. For example, tibial stress fractures have previously been linked to the magnitude of heel impact and metatarsal stress fractures are assumed to be linked to the magnitude of forefoot dorsiflexion moments. It is not known how much these biomechanical factors can add to the above risk factors or if they can mitigate them. For example, a girl may have all the above risk factors identified by the study, but may have low heel impact and low forefoot dorsiflexion moments, so then may not really be at risk for a stress fracture. Similarly, for example, a boy may have none of the risk factors identified in the study, but have high forefoot dorsiflexion moments and as such, may be at increased risk for a metatarsal stress fracture.

Generally, an overuse injury is due to the cumulative loads in a tissue beyond what the tissue can tolerate. The study has identified factors that contribute to that equation related to what the tissues can tolerate (eg bone health issues in girls and higher tissue tolerance from basketball participation in boys). More work is needed on the mechanical factors contributing to the cumulative load side of the equation.

Tenforde, A., Sayres, L., Liz McCurdy, M., Sainani, K., & Fredericson, M. (2013). Identifying Sex-Specific Risk Factors for Stress Fractures in Adolescent Runners Medicine & Science in Sports & Exercise DOI: 10.1249/MSS.0b013e3182963d75

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