Development of a foot scanner for assessing the mechanical properties of plantar soft tissues under different bodyweight loading in standing

Mechanical properties of plantar soft tissues are important characteristics of the foot and are prone to being affected by foot pathologies such as diabetes. Therefore, it is of great importance to measure the mechanical properties of plantar soft tissues in vivo. However, such measurement in previous studies is mostly conducted in foot without loading and there is a paucity of instrument available which can assess the foot mechanical properties under a weight-loading status. In this study, a foot scanner incorporating a tissue ultrasound palpation (indentation) system (TUPS) which could assess the mechanical properties of plantar soft tissues under different body-weight loading was developed. The movement of the foot could also be monitored in real time during the indentation test to improve the test reliability. Preliminary tests were conducted on ten normal subjects at the heel region under various loading of the bodyweight. The results showed that the thickness decreased by 12.0% (from 13.83 ± 2.52 mm to 12.10 ± 1.95 mm) while the stiffness increased by 83.4% (from 40.0 ± 20.7 kPa to 69.0 ± 26.0 kPa) when the loading increased from 0% to 80% of the bodyweight (both p < 0.001, repeated measure one-way ANOVA). Therefore, our system has been demonstrated to be useful in studying the loading dependence of mechanical properties of plantar soft tissues. Potential applications of the system in clinical studies for characterization and monitoring of foot pathologies such as ageing and diabetes are discussed at the end of this note.