Effect of loading history on material properties of human heel pad: an in-vivo pilot investigation during gait

Abstract

Background This study was aimed to develop a novel dynamic measurement technique for testing the material properties and investigating the effect of continuous compression load on the structural and mechanical properties of human heel pad during actual gait. Methods The dual fluoroscopic imaging system (DFIS) and dynamic foot-ground contact pressure-test plate were used for measuring the material properties, including primary thickness, peak strain, peak stress, elastic modulus, viscous modulus and energy dissipation rate (EDR), both at time zero and following continuous loading. Ten healthy pilot subjects, aged from 23 to 72 (average: 46.5 ± 17.6), were enrolled. A “three-step gait cycle” is performed for all subjects, with the second step striking at a marked position on the force plate with the heel to maintain the location of the tested foot to be in the view of fluoroscopes. The subjects were measured at both relaxed (time-zero group) and fatigue (continuous-loading group) statuses, and the left and right heels were measured using the identical procedures. Results The peak strain, peak stress, elastic modulus, and EDR are similar before and after continuous load, while the viscous modulus was significantly decreased (median: 43.9 vs. 20.37 kPa•s; p < 0.001) as well as primary thicknesses (median: 15.99 vs. 15.72 mm; p < 0.001). Age is demonstrated to be moderately correlated with the primary thicknesses both at time zero (R = -0.507) and following continuous load (R = -0.607). The peak stress was significantly correlated with the elastic modulus before (R = 0.741) and after continuous load (R = 0.802). The peak strain was correlated with the elastic modulus before (R = -0.765) and after continuous load (R = -0.801). The correlations between the viscous modulus and peak stress/ peak strain are similar to above(R = 0.643, 0.577, − 0.586 and − 0.717 respectively). The viscous modulus is positively correlated with the elastic modulus before (R = 0.821) and after continuous load (R = 0.784). Conclusions By using dynamic fluoroscopy combined with the plantar pressure plate, the in vivo viscoelastic properties and other data of the heel pad in the actual gait can be obtained. Age was negatively correlated with the primary thickness of heel pad and peak strain, and was positively correlated with viscous modulus. Repetitive loading could decrease the primary thickness of heel pad and viscous modulus.

Prediction of Foot Soft Tissue Stiffness Based on Plantar Pressure During Walking

“…Due to its viscoelasticity, the plantar soft tissue can coordinate the rigid structures of the foot to adapt to different modes of movement. In the plantar soft tissue, the fat pad in the heel can provide cushioning and protect the bones and joints during movement 1,3 ; the muscles in the sole can increase the rigidity of the foot to provide power for improved locomotion e ciency 4 ; the plantar fascia can store energy during weight bearing, improving locomotion economy through its viscoelasticity 5,6 . Studies show that the stiffness of the proximal plantar fascia increases with greater dorsi exion angles and tension in the Achilles tendon 7,8 , and the stiffness of the Achilles tendon and plantar fascia are important indicators for assessing plantar fasciitis 9,10 .…”

Comparison of material properties of heel pad between adults with and without type 2 diabetes history: An in-vivo investigation during gait

“…Instead, the dual fluoroscopic imaging system (DFIS) could capture two perpendicularly intersected images for reconstructing a three-dimensional structure, and has been recently applied in many situations to help investigate the structural and locational indexes. In a previous preliminary study, we have established a novel system for testing the material properties of heel pad, and performed pilot investigation within several healthy adults ( 38 ).…”