Simple model of arch support: Relevance to Charcot Neuroarthropathy

Area of Science:

• Biomechanics
• Diabetic Complications
• Medical Device Technology

Background:

• Charcot neuropathy, a diabetic complication, leads to midfoot collapse due to peripheral neuropathy.
• Foot flattening compromises arch support, potentially causing interface slippage between the foot and support surfaces.
• Quantifying this slippage is challenging with standard gait lab equipment, suggesting a need for interface shear stress monitoring.

Purpose of the Study:

• To investigate the relationship between altered arch support and interface shear stresses in the foot.
• To determine if interface shear stress monitoring can assess changes in foot arch support.

Main Methods:

• A sagittal plane foot model was developed using multi-body dynamics software (MSC Adams).
• The model simulated subject swaying to analyze interface stress dependence on arch support variations.
• Plantar spring stiffness was reduced by 10% to simulate decreased arch support.

Main Results:

• Model predictions aligned with existing data for arch lengthening, sway oscillations, and frictional forces.
• A 10% reduction in plantar spring stiffness increased the frictional force difference by approximately 6.5%.
• Arch lengthening of 1-2 mm and frictional force differences of 60 N were observed.

Conclusions:

• While subtle arch changes (<2 mm) are hard to detect in labs, shear sensors offer a repeatable method for assessing foot arch support.
• This approach could aid in evaluating patients with conditions like Charcot neuropathy.
• Interface shear stress monitoring presents a viable clinical tool for assessing foot biomechanics and support.