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Effect of metatarsal phalangeal joint extension on plantar soft tissue stiffness and thickness
Christopher A Garcia1, Shannon L Hoffman, Mary K Hastings
1Program in Physical Therapy, Washington University School of Medicine, Campus Box 8502, 4444 Forest Park Boulevard, St. Louis, MO 63108-2212, USA.
Background:
Plantar soft tissue stiffness and thickness are important biomechanical variables to understand stress concentrations that may contribute to tissue injury.
Objective:
The purpose of this study was to determine the effects of passive metatarsal phalangeal joint (MPJ) extension on plantar soft tissue stiffness and thickness.
Methods:
Seventeen healthy participants (7 male, 10 female, mean age 25.3 years, S.D. 4.4 years, mean BMI 24.7 kg/m(2), S.D. 3.2 kg/m(2)) 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.
Results:
Indicators 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 13.5mm and decreased, on average, by 8.8% (S.D. 2.9%) with MPJ extension.
Conclusions:
MPJ 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.