Abstract:
"Investigating the Internal Stress/Strain State of the Foot Using Magnetic Resonance Imaging and Finite Element Analysis"
This dissertation investigates the internal stress and strain states of the human foot, focusing on their role in the formation of neuropathic ulcers, which are a major complication of diabetes. The study addresses the limitations of clinical practice, which relies on surface measurements of plantar pressure that may not accurately reflect the damaging internal mechanical forces within the soft tissues. A novel MRI-compatible foot-loading device was developed to apply gait-like loads to the forefoot during magnetic resonance imaging, allowing for the in vivo visualization of 3-dimensional internal strains. This experimental data was used in conjunction with a novel, layered, multi-tissue finite element model of the forefoot. An inverse finite element technique was employed to determine subject-specific, nonlinear material properties for the skin, plantar fat pad, and muscle tissues. The biomechanical analysis revealed that the location of peak internal stresses (under the 3rd metatarsal) did not align with the location of peak plantar pressure (under the 2nd metatarsal). Furthermore, the study demonstrated that a cushioning foam mat, which reduced peak plantar pressure by 66%, had only a minimal effect on reducing the magnitude of peak internal stresses (around 2%). This finding suggests that strategies aimed solely at reducing surface pressure may not be sufficient to mitigate potentially damaging internal tissue stresses. The research provides significant original contributions in the areas of in vivo mechanical testing, nonlinear material parameter determination, and 3D finite element modeling of the foot, offering new insights into the biomechanical mechanisms underlying ulceration.
