Investigation of Plantar Barefoot Pressure and Soft-tissue Internal Stress: A Three-Dimensional Finite Element Analysis

Abstract

Mechanical loading acting on the foot plantar soft-tissue in the form of focal stress plays a central pathogenic role in the onset of diabetic neuropathic ulcers. Current instruments which merely allow superficial estimate of plantar loading acting on the foot, severely limit the scope of many biomechanical/clinical studies on this issue. Recent studies have suggested that peak plantar pressure may be only 65% specific for the development of ulceration. These limitations are at least partially due to surface pressures not being representative of the complex mechanical stress developed inside the subcutaneous plantar soft-tissue, which are potentially more relevant for tissue breakdown. This study established a threedimensional and nonlinear finite element model of a human foot complex with comprehensive skeletal and soft-tissue components capable of predicting both the external and internal stresses and deformations of the foot. The model was validated by experimental data of subject-specific plantar foot pressure measures. The stress analysis indicated the internal stresses doses were site-dependent and the observation found a change between 1.5 to 4.5 times the external stresses on the foot plantar surface. In the forefoot, peak external stress was found in the medial region (the first metatarsal heads). Peak internal stress, however, was shifted to the lateral forefoot region (the fourth and fifth metatarsal heads). It suggested that the normal protective plantar soft-tissue has the potential to redistribute the plantar load such that the internal peak stress can have a significantly different location than the external. The results yielded insights into the internal loading conditions of the plantar soft-tissue, which is important in enhancing our knowledge on the causes of foot ulceration and related stressinduced tissue breakdown in diabetic foot.