We utilized ultrasonography (1) to obtain normal reference values for radial motor nerve conduction study (NCS); (2) to suggest optimal method about recording electrode placement and stimulation site for radial motor NCS; and (3) to analyze the correlations among NCS parameter, subject’s factor and ultrasonographic findings.
56 volunteer participated this study. Author hypothesized lateral edge of spiral groove (A) was optimal stimulation site and largest CSA portion of extensor indicis proprius muscle (B) was optimal site for recording electrode placement. Using ultrasound, we identified these site. We measured the surface distance between (A) and the lateral epicondyle of humerus, divided this distance by upper arm length and named ‘spiral groove site ratio’ (Figure 1, left). We also measured the surface distance between (B) and ulnar styloid process, divided this distance by forearm arm length and named as ‘EIP muscle site ratio’ (Figure 1, right). Radial motor NCS was conducted according to the result of ultrasonography evaluation.
Total 106 data from both upper extremity of 56 volunteers was collected. The mean age, height, weight, and BMI values were 45.06.8±13.6 years, 164.5±8.9 cm, 65.9±13.3 kg and 24.2±3.6 kg/m2. ‘Spiral groove site ratio’ was 0.34±0.03 and ’EIP muscle site ratio’ was 0.20±0.03 (Table1).
At the spiral groove level, mean latency and amplitude were 5.71±0.51 and 5.71±1.10. Velocity between elbow and spiral groove level was 74.01±7.42. At the forearm level, mean latency and amplitude were 1.99±0.21 and 5.99±1.05. Velocity between forearm and elbow level was 56.88±4.68 (Table2). Latency of CMAP had positive correlation with height, weight, arm length and CSA of EIP muscle. Amplitude of CMAP had positive correlation with subject’s height and CSA of EIP muscle. Velocity of CMAP had negative correlation with forearm length.
Our result of radial motor NCS can be used as reference value regardless of age, sex and left or right side. Optimal radial motor NCS could conducted by placing the recording electrode at the about one-fifth distance of forearm length from styloid process of ulnar bone and stimulating at the about one-third distance of humeral length from lateral epicondyle. By using our standardized method, radial motor NCS can be conducted optimally than conventional technique.
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