Influence of Pressure in Determining of the Cross Sectional Area and Flattening Ratio of Median Nerve Using Ultrasonography

J Korean Assoc EMG Electrodiagn Med 2007;9(1):51-58.
Published online May 10, 2007.

Abstract

Objective: To evaluate the influence of pressure in determining of the cross sectional area (CSA) and flattening ratio (FR) of median nerve in normal subjects with increasing pressure and to determine the normal value of the CSA of median nerve without pressure. Methods: Forty eight wrists of 24 normal adult subjects were evaluated. Using ultrasonography the CSA and FR of median nerve at the level of the radio-ulnar joint, pisiform and hook of hamate were measured with the pressure of 0 g, 500 g, 1,000 g, and 1,500 g through the probe. The CSAs were calculated by both tracing and indirect method and the FAs were calculated by the anteroposteior/transverse axes of the median nerve in axial view. Results: The normal values of the CSA of median nerve were 8.6±1.4 mm2/8.6±1.3 mm2 (tracing method/indirect method), 8.3±1.3 mm2/7.9±1.3 mm2, 8.7±1.2 mm2/8.4±1.5 mm2 at radio-ulnar joint, pisiform and hook of hamate, respectively. The CSA of median nerve was not influenced by pressure, but the FR of median nerve were significantly increased with increasing pressure (p<0.05). Conclusion: The CSA of median nerve is more reliable parameter than FR when the pressure is not controlled, but it is recommended to control the pressure for the diagnosis of carpal tunnel syndrome using ultrasonography.

Key Words: Median nerve, Carpal tunnel syndrome, Ultrasonography, Pressure