Tendon and nerve excursion in the carpal tunnel in healthy and CTD wrists

BACKGROUND: During hand and finger motions, friction between flexor digitorum superficialis tendon and the median nerve is thought to play a role in the development of cumulative trauma disorders. This study investigated three methods to determine excursions of the flexor digitorum superficialis tendon and median nerve using several motions. METHODS: Twenty-five participants (mean age 37.2 years SD 13.4) were classified as healthy (n=16), self-reported distal upper extremity cumulative trauma disorders (6), or wheelchair users (3). Static carpal tunnel measurements were taken and displacements of the index flexor digitorum superficialis tendon and median nerve were determined via the velocity time integral and post hoc integration of the Doppler ultrasound waveform using a 12-5 MHz linear array transducer, as well as using predictive equations. FINDINGS: Median nerves in symptomatic wrists were larger than healthy wrists by 4.2 mm(2) (left) and 4.1 mm(2) (right) proximally to less than 1.4 mm(2) distally. In healthy wrists, left-right tendon excursion differences ranged from 0.7 mm to 4.3 mm depending on the motion while left to right differences in symptomatic wrists ranged over 22.2 mm. Ultrasound measures of tendon excursion overestimated those determined using predictive equations and were poorly correlated. The ratio of median nerve excursion to tendon excursion was lower in finger only motions compared to wrist motions with or without finger motion. INTERPRETATION: Spectral Doppler ultrasound imaging provided insights into tendon excursion that was not apparent with mathematical modeling. The difference in excursion between finger motions and wrist motions could be beneficial in therapeutic techniques.