Proposed Modified Bone Stress Injury Classification Score

Background: Given that there are 27 bone stress injury (BSI) severity classification and scoring systems described in the literature, most systems are based solely on imaging, while the literature stresses the importance of considering clinical risk factors for return to running. Purpose: To propose a modified BSI classification score incorporating clinical factors, bone location, Fredericson and Nattiv magnetic resonance imaging (MRI) grading systems, and bone type to improve prediction of return-to-running times. Study Design: Cohort study; Level of evidence, 2. Methods: A 7-year prospective study of National Collegiate Athletic Association Division I cross-country and track and field athletes was conducted from 2013 to 2020. Participants completed an annual questionnaire about known risk factors for injury or impaired bone health. Information about BSIs and time to return to running was collected at team physician meetings, in discussions with athletes, from athlete questionnaires, and from medical chart review. A 0 to 7 score was calculated based on the Cumulative Risk Assessment (CRA) category (low, medium, and high risk of female athlete triad), bone location (low-, medium-, and high-risk locations), MRI grade, and type of bone (cortical vs trabecular). Generalized estimating equations accounting for correlated observations assessed the relationship between the score and return-to-running times. Results: In total, 83 athletes, including both men and women, experienced 140 BSIs. The average return-to-running time was 47.8 days for men and 64.8 days for women. Higher modified BSI classification scores were significantly associated with increased return-to-running times: each additional risk point was associated with an 8.5-day longer return-to-running time on average ( P < .0001). When examining the individual components of the score, MRI grade and CRA score were most strongly associated with return-to-running times in men, and bone location and type were most strongly associated in women. However, return-to-running times were highly variable, and the modified BSI classification score explained only a small amount of the total variance in return-to-running times. Conclusion: A higher modified BSI classification score was associated with increased return-to-running times in both men and women; however, the predictive ability was only low to moderate. Adding CRA risk score, bone location, and bone type to MRI grade alone resulted in a moderate improvement in predicting return-to-running times in women, but adding these additional variables to MRI grade alone resulted in no improvement in men. Additional studies will be needed to determine whether this system results in better prediction than MRI grade alone.