Purpose To investigate differences in metatarsal bone structure and training habits in runners with and without a recent metatarsal bone stress injury (BSI).

Methods Fifty-four runners (14 male/40 female, age 25.8±7.3 yrs) who ran 47±32 kilometers weekly participated in this study. Training and injury history data were collected, along with CT images from metatarsals 2-4 of the non-injured foot of recently injured runners (n=11, 5 male), and the left foot from the healthy runners (n=43, 9 male). Quantitative CT analysis was performed and subject-specific finite element (FE) models simulated a “virtual mechanical test” on each bone at a range of biomechanically relevant angles. Key FE outcomes included principal strains and a measure of total damaged volume, which is related to fatigue life.

Results Injured runners reported significantly higher training volume (78.9±33.9 km/week) than healthy runners (39.2±20.2 km/week) and had lower BMI (21.3±1.7 vs. 22.7±2.6 kg/m2) but the groups were otherwise similar. In the female group, injured runners had significantly larger bone volume and BMC, similar bone strains, and significantly higher damaged volume metrics than healthy females. The FE simulations showed that decreasing the loading angle of the metatarsals by 10 degrees was associated with a 22% decrease in strain and damaged volume.

Conclusion The metatarsals of injured and healthy runners are only slightly different from each other, and there are no obvious structural deficits in the injured runners. Other factors including training volume, footstrike biomechanics, and sex differences may explain BSI in this cohort. Interventions that decrease metatarsal loading angle or magnitude may reduce BSI risk by reducing bone microdamage.

The authors have declared no competing interest.

This research was supported by a Midcareer grant from the Foundation for Physical Medicine and Rehabilitation (to AST) and by NICHD of the National Institutes of Health under award number R15HD104169 (to KLT, with supplement to BAY). The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health. The results of this study are presented clearly, honestly, and without fabrication, falsification, or inappropriate data manipulation.

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The Ethics committee/IRB of Worcester Polytechnic Institute gave ethical approval for this work.

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