Ultrasonic measurement of the human achilles tendon stress during loading: preliminary experimental and theoretical results

Our purpose is to present a non-invasive quantitative ultrasound (US) method to measure the level of stress in the human Achilles tendon during effort. This technique, first developed for the equine forelimb tendon by the UMR INRAENVA BPLC (Maisons-Alfort, France) and the LUSSI, consists in the measurement of the US velocity using an axialtransmission method along the tendon fibers axis, during effort. The tendon celerity is estimated by the analysis of a particular longitudinal wave called Lateral Wave (LW). A dedicated electronic and probe modules have been developed in order to acquire simultaneously the ultrasonic and the force data in the Achilles tendon during a specific effort. Several types of muscular exercises have been tested, and particularly cycles of isometric contraction of the triceps surae muscle/Achilles tendon complex. As expected, the tendon velocity is highly correlated with the effort. At the same time, we have been developing a 2D simulation of the tendon waves propagation to better understand the propagation and to correctly estimate the US tendon velocity in the complex RF signals. This model uses partial differential wave propagation equations solved by pseudospectral and finite difference methods, including Perfectly Matched Layers (PML). Keywords-lateral wave; tendon stress; tendon celerity; wave propagation model