The SPA arrangement of the branches of the upper trunk of the brachial plexus: a correction of a longstanding misconception and a new diagram of the brachial plexus.

OBJECT Brachial plexus (BP) diagrams in most textbooks and papers represent the branches and divisions of the upper trunk (UT) in the following sequence from cranial to caudal: suprascapular nerve, anterior division, and then posterior division. This concept contradicts what is seen in the operating room and is noticed by most peripheral nerve surgeons. This cadaveric study was conducted to look specifically at the exact pattern of branching of the upper trunk of the BP. METHODS Ten cadavers (20 BPs) were dissected. Both supra- and infraclavicular exposures were performed. The clavicle was retracted or resected to identify the divisions of the BP. A posterior approach was used in 2 cases. RESULTS In all dissections the origin of the posterior division was in a more cranial and dorsal plane in relation to the anterior division. In most dissections the supra scapular nerve branched off distally from the UT, giving it the appearance of a trifurcation, taking off just cranial and dorsal to the posterior division. The branching pattern of the UT consistently had the following sequential arrangement from cranial and posterior to caudal and anterior: suprascapular nerve (S), posterior division (P), and anterior division (A), hence the acronym SPA. CONCLUSIONS Supraclavicular exposure of the BP exposes only the trunks and divisions. Recognizing the "SPA" arrangement of the branches helps in identifying the correct targets for neurotization, especially given that these 3 branches are the most common targets for BP repair. Understanding the anatomy means better surgical planning and better patient outcomes.