The foot is the primary physical means of interaction between the body and the ground during locomotion. The shape or structure of the foot combined with the intrinsic tissue characteristics dictates the forces between various tissue layers (i.e., internal stresses). Aberrant internal stresses are thought to cause diabetic, neuropathic ulceration. The successful completion of this proposal will provide a better understanding of how foot deformity and changes in tissue characteristics due to diabetes alter these stresses. For diabetic patients who have lost protective sensation and who may have misshapen feet, high stresses can lead to ulcer development and potentially amputation. Interventions that might reduce these stresses are widely desired. However, it is technically very challenging to measure internal tissue deformation to compare how various treatment strategies lower internal stresses. Therefore, the purpose of this study is to develop a patient- specific computational model to explore how foot deformity and stiffer diabetic tissues can lead to increased internal stresses, and to quantify how conservative and surgical treatment options can modulate these stresses.
Our specific aims are: [1] To develop patient-specific computational foot models of subjects with a range of foot conditions, including: i) healthy, ii) diabetic neuropathic, iii) diabetic neuropathic with claw toes, and iv) diabetic neuropathic with a history of ulceration; where appropriate, both pre- and post-surgical and/or conservative treatment options will also be modeled. [2] To explore how these conditions and treatments increase or decrease the internal stress in the foot. [3] To reduce the time required to generate a patient- specific computational foot model. Patient-specific computational foot models will be generated from highly detailed CT scans, and specialized loading devices will be used to quantify soft tissue anatomical and mechanical properties from MRI scans. Both conservative (i.e., shoe inserts) and surgical (i.e., correction of clawed toes) treatment options will also be modeled to determined if these techniques due in fact lower internal stresses. A long-term goal of this research is to increase the clinical usability of computational foot models. As such, advanced mathematical techniques will be used to reduce the time needed to create the patient-specific models. This research is relevant to the VA mission and the veteran population, which is in general older and has higher incidences of diabetes and foot complications than the population as a whole.
The veteran population is likely to have a prevalence of foot problems at least equal to that in the general population. In 2000 (www.census.gov), there were 281 million Americans with a mean age of 35.3 years, and 26.4 million veterans with a mean age of 57.4. Demographically, most foot problems are more prevalent in older populations. Foot deformities linked to increased plantar pressures (i.e., bunions, hammer toes, metatarsal calluses, high arched feet, low arched feet) were prevalent among subjects who were 60 years or older. The prevalence of diabetes is also higher in older populations. According to NIH, 20.9% of all people older than 65 years of age have diabetes as compared to 9.6% of all people older than 20 years of age. The morbidity due to plantar ulceration and subsequent infection and/or amputation is a risk to diabetic subjects. Furthermore, in 2002, the national prevalence of diabetes among all Americans was about 6.3%, and it increased to 7.0% in 2005 while among veterans it was over 15% in 1999 and increased to 22% in 2003. These diabetic veterans are an average age of 68 years of age and typically suffer multiple chronic conditions. Although traumatic amputation among veterans is increasing due to the conflicts in Iraq and Afghanistan, the majority of amputations at VHA facilities are still due to vascular disease, neuropathy and/or foot deformity arising as complications of diabetes, with between 5,081 and 5,613 lower extremity amputations each year between 1997 and 2003.
