Inter- and Intraobserver Reliability of Predefined Diagnostic Levels in High-Resolution Sonography of the Carpal Tunnel Syndrome - a Validation Study on Healthy Volunteers

Purpose: High-resolution ultrasound is becoming increasingly important in the diagnosis of carpal tunnel syndrome (CTS). Most studies define cut-off values of the cross-sectional area (CSA) of the median nerve in different locations. The individual range of nerve swelling, the size of the nerve, and its CSA are not addressed. The aim of the study is to define the intra-and interobserver reliability of diagnostic ultrasound using two different cross-sectional areas of the median nerve at the carpal tunnel in predefined locations. Materials and Methods: Two observers using high-resolution ultrasound examined 50 wrists of healthy volunteers independently. The CSA of the median nerve was measured at the entrance of the carpal tunnel and 2 cm proximal to the palmar wrist crease. The height and width of the carpal tunnel were determined using anatomical landmarks. The intra-and interobserver reliability was determined using Cronbach's alpha. Results: Depending on the observer, the mean width of the carpal tunnel ranged from 3.37 to 3.43cm with the height ranging from 1.18 and 1.19 cm. The CSA of the nerve was measured with values of 8.43 and 9.05mm(2) on the pisiform level and 9.37 and 9.68mm(2) on the proximal level. Cronbach's alpha ranged from 0.754 to 0.940 for the interobserver reliability and from 0.924 to 0.996 for the intraobserver reliability. Conclusion: To use high-resolution ultrasound for the diagnosis of carpal tunnel syndrome, the reproducibility of this method has to be evaluated. Our study confirms examiner-independent reproducibility of two predefined diagnostic cross-sectional areas resulting in good alpha values.