Investigating the effects of altered blood flow, force, wrist posture, finger movement speed, and population on motion and blood flow in the carpal tunnel

Abstract

Data from the McMaster Occupational Biomechanics Laboratory were consolidated to evaluate overall trends relating to tissue motion and blood flow in the carpal tunnel. Regarding tissue motion, displacements of the flexor digitorum superficialis (FDS) tendon and its subsynovial connective tissue (SSCT) were found to decrease with greater movement speed and a flexed wrist posture. Notably, changes to shear outcomes including relative tendon-SSCT displacement, the shear strain index (SSI), and maximum velocity ratio (MVR) demonstrate that greater movement speed contributes to SSCT damage according to the shear strain mechanism of injury theorised to promote carpal tunnel syndrome (CTS). Median nerve blood flow was also found to be implicated by wrist flexion, and appeared to decrease with greater CTS severity status. Finally, induced blood flow alteration of the carpal tunnel was found to elicit a median nerve blood flow response similar to the level found in CTS subjects, confirming its effectiveness as an intervention to study tissue motion in a CTS-like state. The influence of altered blood flow on tissue motion was differential, where the higher supradiastolic condition altered FDS displacement, and the lower subdiastolic condition affected SSCT displacement and SSI. These findings provide valuable evidence for changes in median nerve blood flow—and by extension, the local fluid environment within the carpal tunnel—not only being a consequence of SSCT fibrosis characteristic of CTS, but potentially also acting as a cause for said changes in carpal tunnel tissue motion.