Stresses in a 3D two arch model of a normal human foot

Abstract

STRESSES IN A 3D TWO ARCH MODEL OF A NORMAL HUMAN FOOT Shanti Jacob, K.M. Patil, L.H. Brank and A. Huson Department of Applied Mechanics, Indian Institute of Technology, Madras, India and Department of Fundamentals of Mechanical Engineering, Eindhoven University of Technology, Eindhoven, The Netherlands (Received 6 July 1995; accepted for print 29 May 1996) Introduction The weakness or paralysis of foot muscles as occurring in leprosy or diabetes is found to alter the pattern of internal stresses in the foot skeleton. Direct measurements of the internal stresses are not possible in vivo. However these stresses can be predicted using an appropriate mathematical or numerical model of the foot skeleton acted upon by the important muscles. It is necessary to model a normal foot to establish the normal stress distribution in the foot before calculating the stresses in a leprotic foot. Available foot models that can be used for stress analysis are two dimensional models [1, 2]. In the first two dimensional model [1], the foot skeleton is simplified as a single bone while considering the shape variation of the bones and forces due to muscles triceps surae and tibialis anterior and ankle joint force are taken into account to find the possible regions of high stresses. In the second model [2], the eadier foot model is modified by introducing cartilages and ligaments between the bones talus and navicular, navicular and cuneiform, cuneiform and metatarsals and metatarsals and toes and the effect of these on stress distribution are studied. Modeling of the foot confronts inherently a three dimensional problem, one to which results from two dimensional analyses cannot necessarily be directly extrapolated. The stresses developed in the foot depend upon the geometry of the foot, and magnitude and insertion points of the muscle forces. Hence it is necessary to model the foot in all the three dimensions of geometry to make a more realistic representation. Therefore, in this study, a three dimensional model of the normal foot skeleton with cartilages and ligaments which enable simulation of articulations (joints) is developed in the mid-stance phase of walking and stress analyses are carried out using finite element technique. Estimation of the regions of high stresses in the normal foot could help in understanding the factors contributing to disintegration of tarsal bones in leprosy or diabetic patients.