Method
A cross-sectional area and a flattening ratio of the median nerve, and a cross-sectional area of the carpal tunnel were measured in neutral, maximally flexed (Phalen's test), and maximally extended (reverse Phalen's test) positions in 59 wrists of 30 normal subjects.

Results
The cross-sectional area of median nerve was significantly decreased in maximal flexion (p＜0.01), and in maximal extension (p＜0.01). The mean flattening ratio of median nerve was revealed significant change in maximal flexion (p＜0.01), and in maximal extension (p＜0.01). The mean cross-sectional area of the carpal tunnel was significantly decreased in maximal flexion (p＜0.01), and in maximal extension (p＜0.01), with comparing to neutral position, respectively.

Conclusion
Phalen's test reveals higher degree of irritation to median nerve. The high-resolution ultrasonography is suggested as an available tool for the screening and follow up aid-test for the CTS. (J Korean Acad Rehab Med 2003; 27: 228-231)