The Neuropathic Foot: Effect of peak pressure and pressure gradient on subsurfac

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J Biomech. 2006 May 3

Effect of peak pressure and pressure gradient on subsurface shear

stresses in the neuropathic foot.

Zou D, Mueller MJ, Lott DJ.

Program in Physical Therapy, Washington University School of

Medicine, 4444 Forest Park Blvd., Campus Box 8502, St. Louis, MO

63108, USA.

The pressure distribution on the plantar surface of the foot may

provide insights into the stresses within the subsurface tissues of

patients with diabetes mellitus and peripheral neuropathy (PN) who

are at risk for skin breakdown.

The purposes of this study were to (1) estimate the stress

distribution in the subsurface soft tissue from a measured surface

pressure distribution and determine any differences between values in

the forefoot and rearfoot, and (2) determine the relationship between

maximum shear stress (MSS) (magnitude and depth) and characteristics

of the pressure distribution. The measured in-shoe pressure

distributions during walking characterized by the peak plantar

pressure and maximum pressure gradient on the plantar surface of the

feet for 20 subjects with diabetes, PN and history of a mid foot or

forefoot plantar ulcer were analyzed.

The effects of peak pressure and maximum pressure gradient at the

peak pressure location on the stress components in the subsurface

soft tissue were studied using a potential function method to

estimate the subsurface tissue stress. The calculated MSSs are larger

in magnitude and located closer to the surface in the forefoot, where

most skin breakdown occurs, compared to the rearfoot. In addition,

the MSS (magnitude and depth) is highly correlated with the pressure

gradient (r=-0.77 & 0.61) and the peak pressure (r=-0.61 & 0.91). The

peak pressure and the maximum pressure gradient obtained from the

surface pressure distribution appear to be important variables to

identify where MSSs are located in the subsurface tissues on the

plantar foot that may lead to skin break down.