Ultrasound-Tensiometry: A New Method for Measuring Differential Loading within a Tendon During Movement

BackgroundTendons enable human movement by transferring load from muscle to bone. Tension within tendon can be variable, especially if it contains distinct subtendons originating from different muscles. However, there are no direct, non-invasive tools that can achieve sufficiently high acquisition rates for measuring differential loading within a tendon during human movement. Research questionCan our new method, ultrasound-tensiometry, measure differential tendon tension in vivo?MethodsOur new method, ultrasound-tensiometry, measures differential tendon tension during locomotor tasks, using the surrogate measure of shear wave speed. Ultrasound-tensiometry has the spatial resolution of conventional shear wave elastography while achieving the framerates required to measure active physiological loads.Ultrasound-tensiometry is composed of an electrodynamic tapping device and an ultrasound probe. An electrodynamic tapper induces a shear wave into a superficial tendon. The shear wave’s propagation is synchronously visualized with plane wave ultrasound imaging at an ultra-high framerate (20 kHz). Each pixel’s displacement is temporally and spatially filtered to remove high-frequency noise and reflected waves. A radon transform computes the shear wave speed through the tendon depth.We test our hypothesis that we can measure differential loading in silico using a finite element model of two adjacent subtendons, ex vivo with an experiment designed to induce differential loading in porcine flexor subtendons, and in vivo in the Achilles tendon, which contains three subtendons. In vivo, our participants performed specific calf stretches to load different subtendons (n=1) and walked on a treadmill at 1.5 m/s (n=1).ResultsOur experiments show that we can measure differential tendon loading in a finite element model, ex vivo in porcine flexor subtendons, and in vivo in the Achilles subtendons.SignificanceThis method captures changes in subtendon load, which will lead to an improved understanding of muscular contributions to human movement.