Effect of metatarsal phalangeal joint extension on plantar soft tissue stiffness and thickness

BackgroundPlantar soft tissue stiffness and thickness are important biomechanical variables to understand stress concentrations that may contribute to tissue injury.ObjectiveThe purpose of this study was to determine the effects of passive metatarsal phalangeal joint (MPJ) extension on plantar soft tissue stiffness and thickness.MethodsSeventeen healthy participants (7 male, 10 female, mean age 25.3 years, S.D. 4.4 years, mean BMI 24.7 kg/m2, S.D. 3.2 kg/m2) were tested. Plantar soft tissue stiffness and thickness were measured at the metatarsal heads, midfoot and heel using a custom-built indentor device and an ultrasound machine.ResultsIndicators of soft tissue stiffness (K1 values) at the metatarsal heads and midfoot showed increases in stiffness of 81–88% (S.D. 20–33%) in the MPJ extension position compared with the MPJ neutral position. Soft tissue thickness measures at the metatarsal heads with the MPJ in neutral ranged from a mean of 8.9 to 13.5 mm and decreased, on average, by 8.8% (S.D. 2.9%) with MPJ extension.ConclusionsMPJ extension has a profound effect on increasing forefoot plantar soft tissue stiffness and a consistent but minimal effect on reducing soft tissue thickness. These changes may help transform the foot into a rigid lever at push-off consistent with the theory of the windlass mechanism.