Objectives: To quantify the dynamic behavior of the heel pad in type 2 diabetic patients and age-matched healthy individuals using mathematical modeling.
Background: No single parameter can fully describe the heel-pad biomechanical properties during the loading–unloading process.
Design: A descriptive study using pseudoelastic modeling was conducted to simulate the heel-pad stress–strain relationship in the loaded and unloaded states. Transmission electron microscope was used to examine six heel specimens taken from amputated legs in diabetic and non-diabetic patients.
Methods: Energy dissipation ratio, loading curvature, and unloading curvature were calculated from the stress–strain curve-fits. Differences in ultrastructure between the heel pad of healthy subjects and those with diabetes were described.
Results: The diabetic patients had a significantly higher mean energy dissipation ratio (mean 36.1% (SD, 8.7%) vs mean 27.9% (SD, 6.1%); P<0.001) and mean unloaded curvatures (mean 11.8 (SD, 5.1) vs mean 8.46 (SD, 2.6); P<0.001) than those of the control group. The collagen fibrils in diabetic heel samples were ruptured with unclear striation and uneven distribution.
Conclusions: The curvature parameters may explain the poor rebound phenomenon resulting in the high impact energy in diabetic heel pads. Breakdown in collagen fibrils may be responsible for this observation.
Relevance: These findings can be integrated into the fabrication of orthotics that dissipate excessive heel impact energy and protect against injury.