FEA Optimization of Pedorthic Treatment for Podalgia

Abstract

Foot problems are quite common. Epidemiological studies have shown as many as 86% of elderly individuals report having problems with their feet, ranging from calluses, cracking and ingrown nails to inflammation, swelling, ischemia, ulceration, and gangrenous necrosis [1]. Persons suffering chronic Diabetes Mellitus are at particular risk of trauma to their feet because of peripheral neuropathy, plantar fat pad and muscle atrophy, and vascular insufficiency. Half of all lower limb amputations each year in the United States are performed on diabetics because of foot and ankle injuries that fail to heal [2]. At the very least, podalgia and pedal trauma restrict person’s mobility and limit their independence, impacting their fiscal as well as their physical well-being. With the exception of memorable catastrophic events, the etiopathogenesis of podalgia and other problems contributing to pedal trauma are generally not well understood. In work with Hansen’s disease and diabetic patients, Brand et al. [3] showed that stresses as small as 1/2 psi could produce trauma in the foot fat pads of even healthy animals, if chronically and repetitively applied without adequate time for tissues to recover and rest, Pedorthic insoles (often with orthopedic shoes) are prescribed for curative as well as prophylactic treatment of podalgia and pedal trauma, especially for diabetic patients with peripheral vascular disease, and arthritic patients with osseous deformity. There are hundreds of such devices commercially available, that range in composition and mechanical characteristics from extremely soft silicone elastomers to stiff plastic and metal plates. They maybe thin or thick, flat or custom milled with precision CAD/CAM systems using 3D laser scans of the individual’s feet to match their pedal contours. Although numerous studies [4, 5, 6] have been conducted, measuring pedal plantar interface stresses, no general quantitative principles for design, performance assessment, or prescription have been developed. These procedures remain highly subjective, and quite variable, depending upon the training, experience, and skill of the patient’s pedorthotist, podiatrist, and/or physcian. The objective of this study was to investigate the stresses and strains incurred in the soft plantar tissues of the foot as a function of insole material and design geometry to enhance understanding of footwear biomechanics and contribute to development of quantitative criteria for prescription, design, and performance assessment of pedorthic footwear.