Validation of an ultrasound-embedded shoe for calculating stiffness of the plantar soft tissue

Abstract

In the United States, diabetes affects approximately 38.4 million people, or 11.6% of the population, including nearly 29% of adults aged 65, and older and can lead to foot complications such as peripheral neuropathy and ulceration. Quantifying tissue-level structural changes due to diabetes may improve our understanding of ulcer formation. This work focused on the Ultrashoe, a device that integrates an ultrasound sensor and load cells to assess plantar soft tissue mechanics. To calculate stiffness, the Ultrashoe must accurately measure both force and displacement. The most accurate speeds of sound for the plantar tissue were identified as 1600 m/s for the heel and 1660 m/s for the second metatarsal head. Load cell error was found to be acceptable. In cadaver testing, stiffness increased with loading frequency and decreased with higher assumed sound speed. This work represents an important validation step toward using the Ultrashoe to study diabetes-related structural changes in the foot and to explore its potential integration with plantar pressure measurements to investigate the effect of diabetes in the foot.