[Ultrasound images of the brachial plexus in the axillary region.]

The axillary artery is the anatomical reference, in the surface, for axillary brachial plexus block. Anatomic studies suggest variability in the location of the structures in the brachial plexus in relation to the axillary artery. These variations can hinder blocks by neurostimulation. The ultrasound allows the identification of the structures within the brachial plexus(1). The objective of this report was to describe the position of the nerves in the brachial plexus in relation to the axillary artery.

Thirty volunteers of both genders were studied. They were in the supine position with 90 degrees abduction and external rotation of the shoulder and 90 masculine flexion of the elbow. Using a 5 cm and 5-10 MHz digital transducer, median, ulnar and radial nerves were identified and their position in relation to the artery were recorded in an 8-sector sectional graphic chart, numbered in crescent order starting at the 12-hour position (medial), whose center represented the axillary artery.

The median nerve was located mainly in sectors 8 (55%) and 1 (28%) (medial); the radial nerve was predominantly in sectors 4 (59%) and 5 (34%) (lateral); and the ulnar nerve in sectors 2 and 3 (inferior) in 69% and 24% of the cases, respectively. There was a considerable variation in the location of the nerves in relation to the superior and inferior aspects of the artery.

Real-time ultrasound inspection of the neurovascular structures of the brachial plexus in the axilla demonstrated that the median, ulnar and radial nerves have different relations with the axillary artery.