The Effect of Force, Posture, and Repetitive Wrist Motion on Intraneural Blood Flow in the Median Nerve

Abstract

Many epidemiological studies have named pinching, deviated wrist postures, and repetitive motion as ergonomic risk factors in the development of carpal tunnel syndrome (CTS). Evidence suggests that hypervascularization of the median nerve and increased intraneural blood flow proximal to the carpal tunnel result in response to ergonomic risk factors (finger pressing and deviated wrist postures). The purposes of this study were to 1) determine the effect of a pinch posture, with and without force exerted by the finger, thumb, or both and 2) determine the effect of repetitive wrist flexion and extension on intraneural blood flow velocity in the median nerve proximal to the carpal tunnel. Eleven healthy and eleven CTS symptomatic individuals participated in this study and completed three components: 15 pinch posture force trials, 3 repetitive wrist motion trials, and 3 static wrist posture trials. Intraneural blood flow was measured using pulse wave Doppler during each trial. Main effects of pinch posture force (F4,80 = 21.397, p < 0.001) and wrist posture (F2,40 = 14.545, p < 0.001) were observed. Trials where force was applied by the finger (2.21 cm/s), thumb (2.22 cm/s) or both (2.34 cm/s) produced higher intraneural blood flow velocities than trials with no force (1.79 cm/s) or relaxed hand (1.89 cm/s). Trials performed in flexion (2.24 cm/s) were greater than neutral (2.06 cm/s) and extension (1.97 cm/s). No interactions or main effects of time were found in response to repetitive wrist motion. These results suggest that at low force levels (6 N) it’s not how the force is applied but rather that the force is being applied that has an effect on the median nerve. Additionally these results suggest that the contribution of repetitive motion to the development of CTS may not be directly to the median nerve.