Preseason Vertical Center of Mass Displacement During Running and Bone Mineral Density Z-Score Are Risk Factors for Bone Stress Injury Risk in Collegiate Cross-country Runners

OBJECTIVES: To (1) assess relationships between running biomechanics, bone health, and bone stress injuries (BSIs), and (2) determine which variables constitute the most parsimonious BSI risk model among collegiate cross-country runners. DESIGN: Prospective, observational cohort study. METHODS: Running gait and bone mineral density (BMD) data from healthy collegiate cross-country runners were collected at preseason over 6 seasons. A generalized estimating equation model with backward selection was used to develop the most parsimonious model for estimating BSI risk, controlling for sex, running speed, and prior BSI. The variables assessed were spatiotemporal, ground reaction force, and joint kinematics, based on previous literature. Quasi-likelihood under the independence model criterion values and R2 values were used to select the best-fitting model. RESULTS: Data from 103 runners were included in the analysis. The best-fitting model included vertical center of mass (COM) displacement and BMD z-score. Injury risk increased with greater vertical COM displacement (unit = 0.5 cm; relative risk [RR] = 1.14; 95% confidence interval [CI]: 1.01, 1.29; P = .04) and decreased with greater BMD z-score (unit = 0.5; RR = 0.83; 95% CI: 0.72, 0.95; P = .007). The model performed similarly when step rate was included instead of vertical COM displacement. CONCLUSION: Vertical COM displacement and BMD z-score contributed to the best model for estimating risk the risk of bone stress injury in cross-country runners. Step rate was also an important variable for assessing injury risk. J Orthop Sports Phys Ther 2023;53(12):761-768. Epub 20 October 2023. doi:10.2519/jospt.2023.11860