The Reliability of Ultrasound Measurements of the Median Nerve at the Carpal Tunnel Inlet

Purpose: To determine the interrater and intra-rater reliability of ultrasound (US) measurement of the cross-sectional area (CSA) of the median nerve at the carpal tunnel inlet.

Methods: Three examiners of varying levels of experience performed US measurements of the CSA of the median nerve at the carpal tunnel inlet of both wrists of 11 healthy volunteers. Each examiner was blinded to the measurements of the other examiners. The measurements were repeated 2 weeks later in random order to test intra-rater reliability. The Lin concordance correlation coefficient (LCCC) for interrater and intra-rater reliability was calculated.

Results: The overall inter-rater LCCC was 0.59 (95% confidence interval [CI], 0.41-0.73). Intra-rater LCCC varied based on examiner experience. The senior author had an intra-rater LCCC of 0.91 (95% CI, 0.80-0.96), the hand fellow had an intra-rater LCCC of 0.45 (95% CI, 0.17-0.66), and the first-year resident had an intra-rater LCCC of 0.78 (95% CI, 0.55-0.90).

Conclusions: There is moderate agreement among examiners of varying levels of experience when measuring the CSA of the median nerve at the carpal tunnel inlet. Examiner experience affected intra-rater reliability of measurements; an experienced examiner had nearly perfect agreement compared with moderate agreement for less experienced examiners.