The Ultrasound Anatomy of Nerves in the Interscalene Groove: Can We Reliably Distinguish the Nerve Structures for Needle Placement During Nerve Blocks?

In the interscalene groove, nerve structures are in close proximity and may not be visible as separate structures, increasing the risk of insertion of the needle tip within the epineurium. We evaluated whether experienced regional anesthesiologists can distinguish between nerve elements lying in close proximity on ultrasound images.Brachial plexus elements from 4 nonpreserved cadavers were arranged in a water bath. Ultrasound images of the nerve roots and trunks were taken. Regional anesthesiologists and residents were asked whether they could distinguish the nerves as 2 separate structures and if they could identify a pair of nerve roots versus a single trunk.Attending anesthesiologists reported the ability to discriminate 2 nerve structures when a 2-mm space was arranged between them in 54% of images; however, when in direct contact, this recognition was significantly lower. The residents reported a higher ability to discriminate the 2 nerves in all scenarios. In addition, the attending anesthesiologists successfully identified paired nerve roots versus nerve trunks in 70% of the images, significantly higher than chance (P = 0.01), whereas the fraction of correct resident responses was not significantly different from guessing.When nerves were placed in close proximity, experienced regional anesthesiologists had difficulty identifying them as separate structures and were incorrect nearly one-third of the time in discriminating 2 closely positioned roots versus a nerve trunk. This underscores the importance of cautious needle insertion into the interscalene groove, where nerve elements are often juxtaposed one to another.