Ultrasonographic measurement of the mechanical properties of the sole under the metatarsal heads

The sole under the metatarsal heads functions as a shock absorber during wa lking and running. The mechanical properties of the sole provide the primar y defense against the development of metatarsalgia and foot ulceration. How ever, limited information about these properties has been documented. In th is study, we used ultrasonography to evaluate the mechanical properties. in cluding unloaded thickness, compressibility index, elastic modulus, and ene rgy dissipation ratio, of the sole in 20 healthy subjects. The unloaded thi ckness decreased progressively from the first to the fifth metatarsal heads . with values of 1.50, 1.36, 1.25, 1.14, and 1.04 cm. The sole under the fi rst metatarsal head had the greatest values for the compressibility index a nd elastic modulus (55.9% and 1.39 kg/cm(2)), and the sole under the third metatarsal head had the smallest values (50.8% and 1.23 kg/cm(2)). The sole under the fifth metatarsal head had the greatest energy dissipation ratio (33.7%), followed by that under the third, second, first, and fourth metata rsal heads. Multivariate adjusted linear regression showed that the unloade d thickness, compressibility index, and elastic modulus values increased si gnificantly with age and body weight (p < 0.05) and that the energy dissipa tion ratio increased significantly with body weight (p < 0.05).