A supraomohyoidal plexus block designed to avoid complications

Interscalene blocks of the brachial plexus are used for surgery of the shoulder and are frequently associated with complications such as temporary phrenic block, Horner syndrome or hematoma. To minimize the risk of these complications, we developed an approach that avoids medially directed needle advancement and favors spread to lateral regions only: the supraomohyoidal block. We tested this procedure in 11 cadavers fixed by Thiel's method. The insertion site is at the lateral margin of the sternocleidomastoid muscle at the level of the cricoid cartilage. The needle is inserted in the axis of the plexus with an angle of approximately 35 degrees to the skin, and advanced in lateral and caudal direction. Distribution of solution was determined in ten cadavers after bilateral injection of colored solution (20 and 30 ml) and followed by dissection. In an eleventh cadaver, computerized tomography and 3D reconstruction after radio contrast injection was performed. In additional five cadavers we performed Winnie's technique with bilateral injection (20 and 30 ml). Concerning the supraomohyoidal block the injection mass reached the infraclavicular region surrounded all trunks of the brachial plexus in the supraclavicular region and the suprascapular nerve in all cases. The solution did not spread medially beyond the lateral margin of the anterior scalene muscle into the scalenovertebral triangle. Therefore, phrenic nerve, stellate ganglion, laryngeal nerve nor the vertebral artery were exposed to the injected solution. Distribution was comparable with the use of 20 and 30 ml of solution. Injections on five cadavers performing the interscalene block of Winnie resulted in an extended spread medially to the anterior scalene muscle. We conclude that our method may be a preferred approach due to its safety, because no structures out of interest were reached. Solution of 20 ml is suggested to be enough for a successful block.