A magnetic resonance imaging study of modifications to the infraclavicular brachial plexus block

A previously described infraclavicular brachial plexus block may be modified by using a more lateral needle insertion point, while the patient abducts the arm 45 degrees or 90 degrees. In performing the modified block on patients abducting 45 degrees, we often had problems finding the cords of the brachial plexus. Therefore, we designed an anatomic study to describe the ability of the recommended needle direction to consistently reach the cords. Additionally, we assessed the risk of penetrating the pleura by the needle. Magnetic resonance images were obtained in 10 volunteers. From these images, a virtual reality model of each volunteer was created, allowing precise positioning of a simulated needle according to the modified block, without exposing the volunteers to actual needle placement. In both arm positions, the recommended needle angle of 45 degrees to the skin was too shallow to reach a defined target on the cords. Comparing the two arm positions, target precision and risk of contacting the pleura were more favorable with the greater arm abduction. We conclude that when the arm is abducted to 90 degrees, a 65 degrees-needle angle to the skin appears optimal for contacting the cords, still with a minimal risk of penetrating the pleura. However, this needs to be confirmed by a clinical study.