Median nerve conduction study through the carpal tunnel using segmental nerve length measured by ultrasonographic and conventional tape methods.

Abstract

OBJECTIVE: (1) To determine whether a 5-cm segment includes the entire anatomic carpal tunnel in live subjects, and to compare surface, ultrasonographic, and direct measures of the median nerve length in human cadavers. (2) To investigate the actual difference of sensory conduction velocities between the conventional tape method and the ultrasonographic method.

DESIGN: Cross-sectional study.

SETTING: University rehabilitation hospital.

PARTICIPANTS: Healthy volunteers (N=40; 20 men, 20 women).

INTERVENTIONS: Not applicable.

MAIN OUTCOME MEASURES: Onset latencies at the palm and wrist, nerve conduction velocity (NCV) in nerve conduction study (NCS), median nerve length measured by ultrasound and tape method.

RESULTS: A real-time ultrasonographic study revealed that a 5-cm segment included the entire carpal tunnel. In the cadaveric study, the median nerve length measured by ultrasound was closer to the actual nerve length than the conventional surface length. The median nerve length in the wrist-to-palm segment measured by ultrasound was shorter than the surface distance. The sensory NCV using the nerve length measured by ultrasound was slower than that using the surface distance (P<.05).

CONCLUSIONS: The 5-cm segment test included the entire carpal tunnel and might be advantageous in the diagnosis of carpal tunnel syndrome (CTS), especially for early lesions. We expect that ultrasonographic measurement of nerve length might raise the sensitivity of NCSs for the diagnosis of CTS.