Using a beam theory model to quantify metatarsal bone stress during running

Abstract

Running is a common fitness activity that is associated with a high incidence of overuse injuries, including metatarsal stress fractures. One contributor to stress injury is repetitive loading of the metatarsals without adequate recovery time and experiencing larger volumes and magnitudes of bone loading may increase injury risk. Thus, quantifying metatarsal loads can be beneficial to understanding injury risk. However, it is currently difficult to estimate bone stress in clinical settings and unclear how bone stress changes following a long run. Therefore, the purpose of this thesis was to 1) characterize changes in metatarsal bone stress before and after the completion of a long-distance run, and 2) suggest a clinically feasible method for estimating metatarsal bone stress. Study 1 involved 21 healthy long-distance runners who ran 25% of their average weekly mileage on an instrumented treadmill. Foot kinematics, ground reaction forces, and in-shoe plantar pressures were collected at the beginning and end of the run and a mathematical model was used to estimate bone stresses and bending moments for all five metatarsals. Plantar stress, dorsal stress, and midshaft bending moments in the second and third metatarsals were greater after the completion of the run. This is consequential for injury risk because the second and third metatarsals are the most susceptible to stress fracture development. In study 2, seventeen runners ran barefoot across a force plate overlaid with a plantar pressure mat while foot kinematics were recorded. The same mathematical model of the metatarsals was used to estimate third metatarsal bone stresses and bending moments, and linear regressions determined whether force or pressure beneath the metatarsal predicted bone loads. A model containing head and base pressure differentials and force beneath the metatarsal head was the best predictor of bone loading, indicating that the use of plantar pressure measurements as a surrogate measure of bone stress could be a time and cost-effective method for estimating bone stress in clinical settings. Moving forward, elucidating how metatarsal bone stress changes over the course of a long run and finding more accessible ways to quantify bone stress could help alleviate injury risk.