Critical analysis of the macro- and sonographic anatomy of the brachial plexus

Abstract

Various institutions and government hospitals in South Africa, still perform nerve blocks using anatomical landmarks to approximate the precise position of the targeted nerve(s). Although this technique has been reported to be successful, variation does occur within the South African population therefore increasing the risk of complications. Thus causing surgeons and anaesthesiologist’s to employ sonography-guided techniques. Sonography allows the visualisation of structures in real time. This technique provides adequate coverage of the needle insertion site and its surrounding structures, to allow for readjustment in order to obtain a successful block in the event of a variation. The aim of this study was to investigate the sonographic anatomy of the brachial plexus at the three common areas in which brachial plexus nerve blocks are performed, i.e. the interscalene groove, supraclavicular fossa and the infraclavicular space. The anatomy of the brachial plexus was also studied on 60 cadavers and then further compared to the anatomy seen on the sonographic screen. Bilateral dissections were done on 60 embalmed cadavers, comprising of 43 males and 17 females, from the Department of Anatomy in the School of Medicine at the Faculty of Health Sciences of the University of Pretoria, South Africa. The use of these cadavers was in accordance with the South African National Health Act 61 of 2003. Dissection was done to expose the brachial plexus in situ. The various segments of the brachial plexus were evaluated. The root contributions, branching patterns and relationships were noted. Upper limb sonographic scans were done bilaterally for the 3 approaches to measure the distance of surrounding structures to the brachial plexus, the skin to structure distances and to determine the ideal placement of the probe for each approach. A full step-by-step guideline was recorded. Variations found in the cadaveric component of the study include the following: a direct branching of the C5 cord into the suprascapular nerve; the direct branching of the medial cutaneous nerve of the arm distinctly as a larger single branch; a communicating branch forming between the musculocutaneous and median nerve; abnormal formation of the median nerve from two lateral roots from the lateral cord and one medial root from the medial cord and; a post fixed brachial plexus. In the interscalene approach, the roots of the brachial plexus were found lying in a horizontal plane between the anterior and middle scalene muscles or the roots were found lying anterior to the anterior scalene muscle yet posterior to the sternocleidomastoid muscle. In the supraclavicular approach the brachial plexus was situated between the subclavian artery and vein and in the infraclavicular approach, the cords of the brachial plexus were found at variable angles to the subclavian artery/axillary artery. This study focused on variations that may be present, each of which are important to note if any clinical or surgical procedures are to be performed in the area. The most prevalent variation found was the direct braching of the suprascapular nerve from the C5 root instead of the superior trunk. The study aimed to improve “blind”, as well as sonographic-guided, nerve blocks that may be performed in a South African population.