Comparison of the mechanical properties of the heel pad between young and elderly adults

Objective: To compare the mechanical properties of the human heel pad between young and aged adults. Design: A 7.5-MHz linear-array ultrasound transducer was incorporated into a specially designed device to measure the thickness of the heel pad under different loads. The heel pad was compressed with serial increments of 0.5kg to a maximum of 3kg and then relaxed sequentially. Then the load-displacement curve of the heel pad during a loading-unloading cycle was plotted. Participants: Convenience sample of 33 volunteers without heel problems, aged 18 to 78 years, were divided into young (less than 40 years) and elderly (older than 60 years) groups. Main Outcome Measures: Unloaded heel-pad thickness, compressibility index, stiffness, and energy dissipation ratio were calculated from the load-displacement curves. Student's t-test was used to compare the mechanical properties of the heel between these two groups. Results: The average unloaded heel-pad thickness was 1.76 ± .20cm in the young group and 2.01 ± .24cm in the elderly group ( p < .001). The average compressibility index was 53.3% ±7.7% in the young group and 61.3% ± 5.5% in the elderly group ( p < .001). Energy dissipation ratio representing shock absorbency of the heel pad, was 23.7% ± 6.9% in the young group and 35.3% ± 10% in the elderly group ( p < .001). Conclusion: Unloaded heel-pad thickness, compressibility index, and energy dissipation ratio of the heel pad were significantly increased in the elderly group, indicating loss of the elasticity of the heel pad. The loss of elasticity may be responsible for the higher incidence of heel injury in elderly individuals.