Effect of sock on biomechanical responses of foot during walking.

BACKGROUND Except the plantar pressure and gross joint motion, we know little about the mechanical state of a foot during walking. This study aimed at investigating the effect of wearing socks with different frictional properties on plantar shear, which is a possible mechanical risk factor of foot lesion development. METHOD A 3-D finite element model for simulating the foot-sock-insole contact was developed to investigate the biomechanical effects of wearing socks with different combinations of frictional properties on the plantar foot contact. The dynamic plantar pressure and shear stress during the stance phases of gait were studied through finite element computations. Three cases were simulated, a barefoot with a high frictional coefficient against the insole (0.54) and two socks, one with a high frictional coefficient against the skin (0.54) and a low frictional coefficient against the insole (0.04) and another with an opposite frictional properties assignment. FINDINGS Wearing sock of low friction against the insole to allow more relative sliding between the plantar foot and footwear was found to reduce the shear force significantly: at the rearfoot from 3.1 to 0.88 N, and at the forefoot from 10.61 to 1.61 N. The shear force can be further reduced to 0.43 N at the rearfoot, and 1.18 N at the forefoot, when wearing the sock with low friction against the foot skin and high friction set against the insole. INTERPRETATION Wearing sock with low friction against the foot skin was found to be more effective in reducing plantar shear force on the skin than the sock with low friction against the insole. The risk of barefoot walking in developing plantar shear related blisters and ulcers might be reduced by socks wearing especially those with low friction against the foot skin.