FIG 5. Interscalene triangle (trunks).

A, Position of the probe to explore the trunks at the interscalene triangle.

B, Sonogram (90° left rotated) in a 28-year-old male volunteer shows the upper, middle, and lower trunks at the interscalene triangle.

C, Sagittal gross anatomic section at the interscalene triangle (lateral part).

In B and/or C, 1 indicates anterior scalene muscle; 2, middle and posterior scalene muscles; 3, subclavian artery; 4, upper trunk; 5, middle trunk; 6, lower trunk; S, skin.