BLOCK AT A GLANCE
Block of the terminal nerves of the brachial plexus at the level of the axilla.
Indications: Elbow, forearm, and hand surgery
Goal: Local anesthetic (LA) spread around the axillary artery next to the median, ulnar, radial, and medial antebrachial cutaneous nerves. Separate injection often required for the musculocutaneous nerve (between the biceps and coracobrachialis muscle).
Local anesthetic volume: 15 to 20 mL
The axillary brachial plexus block is a well-established, widely used regional anesthesia technique for procedures of the upper extremity at and below the elbow. The superficial location of the terminal nerves at this level, in the same sheath as the axillary artery, simplifies the technique and reduces the risk of complications compared with more proximal brachial plexus blocks. Ultrasound (US) monitoring of the LA spread has improved the success rate of the axillary block, including the musculocutaneous nerve. This is because the musculocutaneous nerve separates from the neurovascular bundle proximal to the level of injection and presents numerous anatomical variations. A perivascular technique, consisting of two injections anterior and posterior to the artery, results in a similar success rate and shorter procedural time than the perineural approach, which relies on identification and injections next to each individual nerve. However, the latter may result in faster block onset. The quality of US view and the relative disposition of the vascular and neural structures will dictate the best option in each case.
The terminal nerves of the brachial plexus emerge from the cords proximally in the axillary fossa and travel distally toward the upper extremity surrounding the axillary artery, passing superficial tand anterior o the insertion of the conjoint tendon on the humerus (Figure 17-1). The radial nerve originates from the posterior cord, runs posterior to the artery in close contact with the conjoint tendon, and turns deep posterior to enter the spiral groove of the humerus. The median nerve is formed by fascicles of the medial and lateral cords and it is located typically anterior and lateral to the artery. The ulnar nerve is the continuation of the medial cord and travels along the medial side of the artery. The musculocutaneous nerve arises proximally from the lateral cord and it is located at a variable distance from the artery in the fascial plane between the coracobrachialis and the biceps muscles or the body of the coracobrachialis.
Terminal nerves of the brachial plexus. AA, axillary artery; McN, musculocutaneous nerve; MN, median nerve; UN, ulnar nerve; RN, radial nerve; CNA, cutaneous nerve of arm; ICBN, intercostobrachial nerve.
CROSS-SECTIONAL ANATOMY AND ULTRASOUND VIEW
The neurovascular bundle is located superficially at the junction of the arm and the axilla, contained in a triangular space limited by the conjoint tendon (posterior), the biceps ...