Calibration of the Shear Wave Speed-Stress Relationship in In Situ Achilles Tendons using Cadaveric Simulations of Gait and Isometric Contraction

Abstract It has been shown that shear wave speed is directly dependent on axial stress in ex vivo tendons. Hence, a wave speed sensor could be used to track tendon loading during movement. However, adjacent soft tissues and varying joint postures may affect the wave speed-load relationship for intact tendons. The purpose of this study was to determine whether the proportional relationship between squared wave speed and stress holds for in situ cadaveric Achilles tendons, to evaluate whether this relationship is affected by joint angle, and to assess potential calibration techniques. Achilles tendon wave speeds and loading were simultaneously measured during cadaveric simulations of gait and isometric contractions performed in a robotic gait simulator. Squared wave speed and axial stress were highly correlated during isometric contraction at all ankle postures (R2avg = 0.98) and during simulations of gait (R2avg = 0.92). Ankle plantarflexion angle did not have a consistent effect on the constant of proportionality (p = 0.217), but there was a significant specimen-angle interaction effect (p