Technique to study the biomechanical properties of the human calcaneal heel pad

Abstract Background : The biomechanical properties of the human foot may depend on the health of the individual. Patients diagnosed with diabetes mellitus, for example, may suffer from observable change in biomechanical properties and subsequently result in foot ulceration. To date, only limited published studies have been carried out to show differences in heel pad mechanical properties of diabetic individuals and healthy individuals. It has been hypothesised that collagen septa of a diabetic's heel fat pads are thicker and fat cells smaller, and that these occurrences could reduce their resilience, making the heel more vulnerable to ulceration. Furthermore, there is still not a clinical yet quantitative biomechanical tool that could provide an easy assessment on the heel pad stiffness in vivo. This paper reports the preliminary development of a test rig and subsequent protocol for its use to acquire the biomechanical properties of the human heel pad. The paper reports and discusses the results obtained from the test rig developed. Objectives : The first objective of this work was to develop a suitable technique and protocol to acquire the biomechanical properties of the human heel pad. The second objective was to investigate the heel pad properties of healthy individuals and compare these with patients diagnosed with plantar heel pain (PHP) and diabetes mellitus. Method : A test rig was designed and built by the authors for the purpose of acquiring the biomechanical properties of the human heel pad. A total of 17 heels (from 9 patients with diabetes), 17 heels (from 12 patients with PHP) and 21 heels (from 14 healthy subjects) were measured. All patients were of Asian descent. A convenience sample was recruited from both Type 1 and Type 2 diabetic patients, and patients diagnosed with PHP. The heel pad thickness (loaded and unloaded), compressibility index, strain and ultrasound images were acquired. Results : The results revealed significantly lower loaded thickness and compressibility index, and significantly higher strain in the control group when compared with the two patient groups. The load deformation curve for the human heel pad showed non-linear characteristics indicating low initial stiffness and high final stiffness with an increasing deformation. Conclusions : The dynamic characteristic of the human heel pad may depend on underlying pathology. The heel pad properties reveal that patients with plantar heel pain and diabetic patients were less compressible compared with those of healthy individuals.

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