The effect of a standard activity on the size of the median nerve as determined by ultrasound visualization.

The purpose of this study was to determine whether a standardized hand activity would produce changes in the cross-sectional diameter of the median nerve. Ultrasound measures of proven reliability of the cross-sectional diameter of the median nerve in the wrist were taken. These measures were taken before activity and immediately after the activity, after 5 minutes, and after 10 minutes. The median nerves of 40 normal subjects showed an increase in cross-sectional diameter immediately after hand activity then returned to a size close to the preactivity size within 10 minutes. The cross-sectional area of the carpal canal did not change significantly after the hand activity was performed. Female gender and body mass index over 25 were associated with significantly larger size increases in the median nerve. This preliminary study suggests that ultrasound is sensitive to the effects of activity upon the hand.