In-Situ Fracture Tolerance of the Metatarsals During Quasi-Static Compressive Loading of the Human Foot

Accidental foot injuries including metatarsal fractures commonly result from compressive loading. The ability of personal protective equipment to prevent these traumatic injuries depends on the understanding of metatarsal fracture tolerance. However, the in-situ fracture tolerance of the metatarsals under direct compressive loading to the foot's dorsal surface remains unexplored, even though the metatarsals are the most commonly fractured bones in the foot. The goal of this study was to quantify the in-situ fracture tolerance of the metatarsals under simulated quasi-static compressive loading. Fresh-frozen cadaveric feet (n=10) were mounted into a testing apparatus to replicate a natural stance and loaded at the mid-metatarsals with a cylindrical bar to simulate a crushing-type injury. A 900N compressive force was initially applied, followed by 225N successive load increments. Specimens were examined using X-ray imaging between load increments to assess for the presence of metatarsal fractures. Descriptive statistics were conducted for metatarsal fracture force and deformation. Pearson correlation tests were used to quantify the correlation between fracture force with age and BMI. The force and deformation at fracture were 1861 ± 642 N (mean ± SD) and 22.6 ± 3.4 mm, respectively. Fracture force was correlated with donor BMI (r=0.90). Every fractured specimen experienced a transverse fracture in the second metatarsal. New biomechanical data from this study further quantifies the metatarsal fracture risk under compressive loading and will help to improve the development and testing of improved personal protective equipment for the foot.