Figure 2 : (a) Schema of the superior, medial and inferior trunks.

(*) of the brachial plexus lying between the anterior (AS) and medial (MS) scalene muscles, covered by the sternocleidomastoid muscle (SCM). The needle should be placed near but not through the nerves. (b) In the sonographic view, the trunks appear as hypoechoic round structures within the interscalene groove. During the injection the spread of LA around the nerves may be visualized (figure below).

Schoell et al.Emergency Medicine and Health Care  2017 5:1DOI : 10.7243/2052-6229-5-1