Ultrasound of the Carpal Tunnel and Median Nerve

The authors describe a protocol for measuring the carpal tunnel and median nerve in a reproducible manner using ultrasound, as well as the variability of ultrasound measurements of the median nerve in the carpal tunnel on repeated testing. Measurements of the median nerve in the wrist and carpal tunnel and measurements of the carpal tunnel were taken on 23 wrists using high-resolution ultrasound following a specified protocol. These measurements were repeated a short time later to enable the initial measurements to be tested for reproducibility and stability. The same person obtained all measurements for the purposes of this study; thus, the results represent findings in an intraobserver variability study. Good correlation between the test and retest measurements was demonstrated, with r 2 values between 0.72 and 0.98. Paired t test demonstrated no significant difference between the test and retest measurements. The study shows that repeated ultrasound measurements of the cross-sectional areas of the carpal tunnel, median nerve at the proximal edge of the carpal tunnel, distal to the carpal tunnel and at the level of the proximal wrist crease can all be satisfactorily reproduced when a strict ultrasound protocol is adhered to.