Relative displacement of the tendon and subsynovial connective tissue using ultrasound captures different phenomena than mechanical tendon shear

The most common finding in carpal tunnel syndrome is fibrosis and thickening of the subsynovial connective tissue (SSCT). While the SSCT mediates tendon gliding in the carpal tunnel, this histopathology suggests excessive shear forces are involved in injury development. Ultrasound is often used to quantify relative motion between the finger flexor tendons and SSCT as an indirect measure of "shear-strain"; however, the underlying mechanical …