A Portable Insole System to Simultaneously Measure Plantar Pressure and Shear Stress

Objective: This work aims to develop an integrated in-shoe measurement system to fully record plantar loading, including both pressure and shear stresses, across the full contact surface. These data are vital to help understand and prevent the development of complex conditions such as Diabetic Foot Ulcers (DFUs), a worldwide healthcare challenge. Currently no systems exist to reliably record these data. Methods: In this paper we report development of the SLIPS (‘Shear Load Inductive Plantar Sensing’) system which integrates 64 tri-axial force sensors into a flexible insole to measure plantar loading. SLIPS translates our multi-axis inductive load sensing technology into a full sensory array embedded within an insole and complete with communication and power bus. A pilot study evaluates the system in three healthy participants during walking. Results: Testing shows that the SLIPS system is well tolerated by participants and can operate under dynamic gait loading regimes. The pilot study reveals the complex nature of plantar loading. Regions of peak pressure loading align with anatomical landmarks and shear loading forms a significant component of the overall load. Notably, regions of peak shear and pressure are not necessarily collocated or present in unison. Conclusion: This work highlights the need for in-shoe plantar measurement systems like SLIPS capable of mapping both pressure and shear load, and their use to improve understanding of how these factors relate to clinical conditions like DFU. Significance: SLIPS represents the first in-shoe measurement system capable of measuring both pressure and shear across the whole plantar surface in unison.