Characterizing In-Situ Metatarsal Fracture Risk During Simulated Workplace Impact Loading.

Metatarsal fractures represent the most common traumatic foot injury; however, metatarsal fracture thresholds remain poorly characterized, which affects performance targets for protective footwear. This experimental study investigated impact energies, forces, and deformations to characterize metatarsal fracture risk for simulated in situ workplace impact loading. A drop tower setup conforming to ASTM specifications for testing impact resistance of metatarsal protective footwear applied a target impact load (22-55 J) to 10 cadaveric feet. Prior to impact, each foot was axially loaded through the tibia with a specimen-specific bodyweight load to replicate a natural weight-bearing stance. Successive iterations of impact tests were performed until a fracture was observed with X-ray imaging. Descriptive statistics were computed for force, deformation, and impact energy. Correlational analysis was conducted on donor age, BMI, deformation, force, and impact energy. A survival analysis was used to generate injury risk curves (IRC) using impact energy and force. All 10 specimens fractured with the second metatarsal being the most common fracture location. The mean peak energy, force, and deformation during fracture were 46.6 J, 4640 N, 28.9 mm, respectively. Survival analyses revealed a 50% fracture probability was associated with 35.8 J and 3562 N of impact. Foot deformation was not significantly correlated (p = 0.47) with impact force, thus deformation is not recommended to predict metatarsal fracture risk. The results from this study can be used to improve test standards for metatarsal protection, provide performance targets for protective footwear developers, and demonstrate a methodological framework for future metatarsal fracture research.