8 Distal Upper Extremity Block
Ulnar, Median, and Radial Block at the Elbow
Placement
At the Elbow
Anatomy
Of the three major nerves at the elbow—radial, median, and ulnar—the ulnar is most predictable in location. As illustrated in Figure 8-1, the ulnar nerve is located in the ulnar groove, which is a bony fascial canal between the medial epicondyle of the humerus and the olecranon process. This area is extremely well protected by fibrous tissue and, although it may seem at first like an easy site to carry out block, the nerve is well protected (and potentially vulnerable) in the ulnar groove. The median nerve at the elbow lies medial to the brachial artery, which lies just medial to the biceps muscle. Conversely, the radial nerve has a somewhat variable course; it pierces the lateral intramuscular septum on its way to the forearm, and lies between the brachialis muscle and the brachioradialis muscle in the distal aspect of the upper arm. It is more effectively blocked in the axilla than at the elbow.
Position
All three of these nerves are blocked with the patient in the supine position and the arm supinated and abducted at the shoulder at a 90-degree angle. In addition, when the ulnar nerve block is performed, the forearm is flexed on the upper arm to more easily identify the ulnar groove (as illustrated in Fig. 8-3).
Needle Puncture: Median Nerve Block
A line should be drawn between the medial and lateral epicondyles of the humerus (at the level of the “pane of glass” shown in Fig. 8-1). Immediately medial to the brachial artery, the needle is inserted in the plane of the pane of glass, and a paresthesia is sought or a nerve stimulator or ultrasonographic guidance is used to direct the needle (Fig. 8-2). After the needle is positioned, 3 to 5 mL of solution is injected medial to the brachial artery.