Morphologic Evaluation of the Flexor Carpi Radialis Muscle Using Ultrasonography for Accurate and Safe Needle Electromyography

Abstract

This study aimed to determine the proper and safe needle insertion point in the flexor carpi radialis (FCR) muscle under ultrasonography guidance. Methods: We identified the center point (CP) of the FCR as the optimal needle insertion point using ultrasonography. The location of the CP was analyzed using ratios and distances from other landmarks. The vertical distance (CP-VD) was measured by drawing an imaginary vertical line from the CP to the elbow crease. We measured the horizontal distance from the point where the imaginary vertical line from the CP meets the elbow crease to the biceps tendon at the elbow crease level (CP-HD). We presented the ratio of CP-HD to forearm circumference (HD ratio) and the ratio of CP-VD to forearm length (VD ratio) as percentages. Results: The mean values of CP-HD and CP-VD were 2.0 ± 1.0 cm and 8.2 ± 1.1 cm, respectively. The mean HD and VD ratios were 8.4% ± 4.2% and 32.0% ± 3.1%, respectively. Conclusion: When performing electromyography (EMG) of the FCR muscle, it is recommended to perform EMG at the point about 2 cm medial from the biceps tendon at the elbow crease level, to nearly the proximal one-third of forearm length.