Abstract
Stress fracture of the second metatarsal is a common and problematic injury for runners. The choice of foot strike pattern is known to affect external kinetics and kinematics but its effect on internal loading of the metatarsals is not well understood. Models of various complexities can be used to investigate the effects of running characteristics on metatarsal stresses. This study aimed to compare second metatarsal stress between habitual rearfoot and non-rearfoot strikers during barefoot running, using a novel participant-specific finite element model, including accurate metatarsal and soft tissue geometry. Synchronised force and kinematic data were collected during barefoot overground running from 20 participants (12 rearfoot strikers). Stresses were calculated using a previously evaluated and published 3D finite element model. Non-rearfoot strikers demonstrated greater external loading and joint contact forces than rearfoot runners, but there were no differences in stresses between groups. Additionally, the study allowed for a qualitative assessment of bone geometries and stresses. No correlation was found between bone volume and stresses, however, there was found to be a large variation in metatarsal shapes, possibly accounting for the lack of difference in stresses. This emphasises the importance of bone geometry when estimating bone stress and supports the suggestion that external forces should not be assumed to be representative of internal loading.
Highlights
Stress fracture to the second metatarsal is a common and problematic injury amongst runners (Bennell et al, 1996; Iwamoto and Takeda, 2003; Milgrom et al, 1985; Chuckpaiwong et al, 2007)
This study aimed to use a participant-specific finite element model (Ellison et al, 2020a) to investigate second metatarsal stresses between different habitual foot-strike groups and to investigate whether there is any correlation between bone volume and peak stress
Vertical ground reaction forces were significantly greater in the non-rearfoot runners than the rearfoot runners at all three time points
Summary
Stress fracture to the second metatarsal is a common and problematic injury amongst runners (Bennell et al, 1996; Iwamoto and Takeda, 2003; Milgrom et al, 1985; Chuckpaiwong et al, 2007). Mathematical modelling has been shown to be a valuable alternative to direct measurement of bone stresses on the metatarsal bones in the past (Gross and Bunch, 1989; Fung et al, 2017; Nunns et al, 2017) and these have ranged from beam theory models with limited participant-specific geometry (Gross and Bunch, 1989) to models incorporating complete participant-specific geometry and using finite element methods to estimate highly realistic bone deformations (Firminger et al, 2017; Li et al, 2017). Evaluation of a three-dimensional finite element model of the second metatarsal, incorporating participant-specific bone geometry, was recently evaluated and deemed appropriate for the estimation of peak second metatarsal stresses on the dorsal and plantar surfaces of the bone during running (Ellison et al, 2020a)
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