Shear-wave elastography of healthy individual thenar muscles

The purpose of this study was to assess the variations in shear-wave speed (SWS) in individual thenar muscles under varied pinch forces in healthy adults. It was hypothesized that (1) SWS would vary among the individual thenar muscles, and (2) there would be an increase in SWS with increased pinch force.

Thirteen healthy participants' dominant hands were imaged using an ultrasound probe aligned longitudinally along the muscle fibers of the abductor pollicis brevis (APB), opponens pollicis (OPP), and flexor pollicis brevis (FPB). The SWS of each muscle was derived. Each participant completed trials consisting of randomly ordered pinch forces at 0, 10, and 20 N, 10% of maximum pinch force (MPF), and 20% MPF.

The SWSs varied significantly among individual thenar muscles ( $p<0.01$ ) under absolute ( $p<0.01$ ) and relative forces ( $p<0.05$ ). There was a significant increase in SWS as the force increased from 0 to 20 N in the APB ( $p<0.001$ ) and OPP ( $p<0.001$ ), and not in the FPB ( $p=0.873$ ). There was a significant increase in SWS as the force increased from 0 to 20% MPF in the APB ( $p=0.005$ ), and not in the OPP ( $p=0.586$ ) or the FPB ( $p=0.984$ ).

The SWS of the APB and OPP increased as force increased and was different among the thenar muscles. This suggests SWS evaluations may be an appropriate method for evaluating muscles under tension, or different voluntary force conditions, specifically for the APB and OPP muscles.