Biomechanical factors affecting metatarsal fatigue and bone stress injury risk

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Project Summary Nearly 50% of all bone stress injury (BSI) diagnoses occur in individuals under age 20 and the prevalence of adolescent BSI has tripled over the past decade. A BSI is the result of repetitive overload of the skeleton that exceeds bone remodeling, resulting in accumulation of microdamage. Foot anatomy, biomechanics, muscle function, and external factors dictate forces transmitted onto the metatarsals during walking or running. In turn, resulting forces create mechanical strain that varies by metatarsal structure and regional bone density. Here, we propose a novel combination of mechanical testing, computational modeling, and quantitative image analysis to characterize the interactions between foot muscle forces, metatarsal bone structure, and metatarsal damage accumulation. We hypothesize that muscles supporting the arch reduce dorsal bending and increase compression of the metatarsals (Aim 1). We believe this may reduce damage accumulation during fatigue loading, due to the anistropic material properties of bone (Aim 2). We also expect that impaired muscle function and bone structure will be associated with BSI (Aim 3) through mechanisms of increased bone strain. These hypotheses are based on clinical reports of foot muscle weakness, variations in foot anatomy, and observations of low bone density in runners with a BSI. To better understand the interactions between metatarsal damage and muscle activation during running, we propose three aims. Aim 1: Determine how muscle activation can influence metatarsal loading during running, by using simulation to analyze the biomechanical contribution of intrinsic and extrinsic foot muscles. Aim 2: Compare the effect of bending vs. axial loading on whole metatarsal fatigue failure/damage accumulation using experimental testing. Aim 3: Compare foot muscle strength and metatarsal bone structure between female runners with recent (within 4 weeks of testing) versus no metatarsal BSI. If our hypotheses are supported, it suggests that the risk of metatarsal BSI may be reduced via strengthening and activation of foot muscles, through mechanisms of altered metatarsal loading direction and reduced strain. This may directly inform clinical interventions such as gait retraining, foot strengthening, or changes in footwear. This research will provide evidence for the mechanisms contributing to metatarsal fatigue failure and the identification of individuals at risk for metatarsal BSI. Our research team includes experts in orthopaedic biomechanics (Troy), running injury biomechanics (Davis), and bone health and sports injury (Tenforde), making us uniquely qualified to pursue this multidisciplinary project. Additionally, our plan demonstrates our ongoing commitment to student training through integration of both undergraduate and graduate student involvement in all aspects of the project.