Figure 6-1. Brachial plexus anatomy.
Figure 6-2. A very limited dissection demonstrating how the brachial plexus lies in the neck as transverse from its origin of individual roots from the cervical spine to somewhat join into divisions and group into cords. The divisions travel in a similar plane at this level and are organized in a parallel fashion to each other. The plexus is framed by the sternocleidomastoid at the superior edge of the triangle until it gives way to the anterior border of the anterior scalene. At times the anterior scalene is not prominent as in this specimen. The inferior border is the clavicle. The triangle is completed by the posterior border in the middle scalene muscle.
Figure 6-3. The brachial plexus and its surrounding structures. In this dissection the sternocleidomastoid and the internal jugular vein have been reflected away so that the surrounding structures could be better visualized. The close proximity to the phrenic can be appreciated as well as the relatively close internal carotid artery and vagus nerve. Of note in this specimen is an example of how small in diameter the phrenic nerve can be and how close. At the upper end of the origin of the brachial plexus they are almost side by side. This is often demonstrated during performance of an interscalene block with just a very small change in needle direction causing a phrenic nerve stimulation of the diaphragm or the desired twitch of stimulation of the brachial plexus.
Figure 6-4. Terminal branches (anterior plan).
Figure 6-5. Upper limb innervation.
Figure 6-6. Topographic anatomy.
Figure 6-7. Frontal dissection of the brachial plexus demonstrating its course from the interscalene area to the beginning of the axilla. The pectoralis major and minor have been removed. The plexus exits the interscalene region, passes under the clavicle, and surrounds the artery. The axillary artery has been retracted by the blue band to show the posterior cord of the plexus or it would not have been seen at all. The medial cord is too deep to be shown in this frontal view. The vein is quite inferior and if it is punctured by the needle, the needle should be removed and reentered 1 to 2 cm superiorly. Note in this section the boundaries of the lung as seen by the edges of the intercostal muscles and why it is possible to enter the lung with both the vertical infraclavicular block and the coracoid infraclavicular block.
Figure 6-8. Sagittal section of the infraclavicular area. This dissection is a sagittal section of the right side demonstrating the relationship of the brachial plexus below the clavicle. The pectoralis major and minor are virtually the only muscles above the plexus. The lung is not visible and has not been violated. At the level of a vertical infraclavicular block, the lung would be visible. The axillary vein is prominently seen inferior to the plexus, which surrounds the axillary artery. The fascicles of the lateral cord (which contains one-half of the median nerve) is virtually laying on the artery. The posterior cord (which contains 100% of the radial nerve) is actually superior but is deeper than the artery from the surface of the skin. It is large and round in this specimen compared with the lateral cord, which is flattened and surrounds the upper surface of the artery. The medial cord (which contains the other part of the median nerve and the ulnar nerve) is just under the artery and is the deepest cord to the skin.