W e have all been taught to draw the brachial plexus (BP) with the anterior division (A) of the upper trunk (UT) more cranial than the posterior division (P). 4,5,7,9,[14][15][16]18 For the peripheral nerve surgeon familiar with BP reconstruction, this is anatomically incorrect; the correct arrangement should be P cranial to A. Dealing with BP trauma is already challenging because of scar tissue that sometimes masks the normal anatomy. Without the knowledge of normal anatomical concepts, one may be grafting into the wrong targets. In an effort to better understand the relationship of the divisions of the UT, 20 BPs were dissected in embalmed cadavers, looking specifically at the branching pattern of the UT.
MethodsTen embalmed cadavers were used for this project.Both sides (20 BPs) were dissected, mostly via an anterior approach. A skin incision was made along the posterior border of the sternocleidomastoid (SCM) muscle or horizontally. The platysma was opened. The omohyoid, suprascapular, and transverse cervical vessels were transected. The supraclavicular pad of fat was reflected laterally from the posterior border of SCM. The trunks of the BP were then identified between the anterior and middle scalenes. Special attention was devoted to identifying the branches and divisions of the UT. They were also followed proximally to their origin from the C-5 and C-6 spinal nerves.Infraclavicular exposure was achieved through the deltopectoral groove. The pectoralis minor was transected, which allowed exposure of the cords of the BP and the axillary artery. For full exposure of the divisions, the clavicle was either retracted or transected. 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 The clavicle was retracted or resected to identify the divisions of the BP.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.