Lowering Bone Stress Injury Risk by Understanding Loading Angle, Bone Strength, and Training Load

Young, Bryhannah

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Lowering Bone Stress Injury Risk by Understanding Loading Angle, Bone Strength, and Training Load

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Background Bone Stress Injuries (BSI) leads to structural fatigue, localized bone pain, and in severe cases loss of bone function. Currently there is minimal research in understanding how foot loading and biomechanics contribute to high metatarsal strain and damage accumulation within the metatarsals of runners. Methods Utilizing computed tomographic images of the feet of 28 long distance runners (7 injured and 21 healthy) three-dimensional orthotropic models of the second, third, and fourth metatarsals at various loading angles relative to running. Maximum principal strain, minimum principal strain, von Mises stress, maximum principal stress, minimum principal stress, and strained volume of the midshaft and whole metatarsal was collected using the 90th percentile values collected from each element. We compared the effect of loading angle and injury status from this analysis to understand how different associated risk factors affect the mechanical behavior of the metatarsals. These calculations made using the feet of injured and healthy runners along with an in-depth analysis of the self-identified training data was used to understand the correlation between strain magnitude and strained volume in the metatarsals in competitive athletic runners. Results Our evaluation of the effect of metatarsal loading angle concluded by loading metatarsals to a more axially, would significantly decrease in strain in metatarsals (p<0.001).Our comparison of the healthy foot of the injured versus healthy runners found that there was an excess amount of strained volume within the cortical bone region of healthy feet of the injured runners (>17%). This translated to a large amount of damage accumulation within the metatarsal. This damage accumulation leaded to the imbalance within the bone remodeling process causes bones to weaken rapidly when loaded in excess. Our injured runners surpassed the theoretical loading capacities of their bone by running more than 60 km a week (BCLR of >1.0), and we found biomechanical and demographics are important factors used to understand the risk factors associated with BSI. Conclusions This study uses an integrated approach in understanding BSI by understanding biomechanics of metatarsal loading through changes in loading angle, the structural mechanics of bone in injured and healthy runners and created bone cumulative loading ratio (BCLR) to understand the possible modifications plausible in lower the risk of BSI. The BCLR represents a promising concept to assess BSI risk, relative to the training load and individual bone structure. In the future, predictive models such as the ones developed here could help reduce the risk of BSI through managing biomechanics, training load, and personal risk factors.

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