Stress analysis in three-dimensional foot models of normal and diabetic neuropathy

In this paper, a three-dimensional two-arch model of the foot is developed, taking foot geometry from X-rays of normal and diabetic subjects, which considered bones, cartilages, ligaments, important muscle forces and foot-sole soft-tissue. The stress analysis is carried out by a finite element technique using NISA software for the foot models simulating quasi-static walking phases of heel-strike, mid-stance and push-off. The analysis shows that the highest stresses occur during the push-off phase in the dorsal central part of the lateral and medial metatarsals and the dorsal junction of the calcaneus and cuboid. The vertical stresses, in the foot-sole soft-tissue at the foot-ground interface, for normal and diabetic neuropathic subjects, are the highest in the push-off phase and were in good agreement with the experimentally measured foot pressures. It is found that the foot-sole vertical stresses (at the foot-ground interface), in diabetic neuropathy, increase considerably in the heel region in the heel-strike phase and in the fore-foot regions in the push-off phase. The high stress concentration areas, in the plantar surfaces indicated above, are of great importance since it is found from clinical reports that in diabetic neuropathic patients these areas of the foot-sole are prone to ulcers. Thus, this investigation could possibly provide information on the areas of high stress concentration of the foot bones in the normal foot giving rise to arthritis when the mechanical strength decreases and possible high stress regions of foot bone giving rise to disintegration of tarsal bones in leprosy, as well as an insight into the factors contributing to plantar ulcers in diabetic neuropathy.