BLOCK AT A GLANCE
Block of the median and ulnar nerves (and superficial branch of the radial nerve) at the level of the forearm.
Indications: Hand and finger surgeries not involving the deep structures of the dorsum of the hand and thumb
Goal: Injection of local anesthetic (LA) within the vicinity of the median, ulnar, and the superficial branch of the radial nerve (if needed)
Local anesthetic volume: 3 to 5 mL per nerve
The wrist block is a commonly used technique for hand and finger surgeries, in particular for short procedures involving soft tissues on the palmar side. The main advantage of the block is that it provides effective anesthesia (and eventually, long-lasting analgesia) while preserving the mobility of the wrist. The landmark-based technique relied on the superficial location of the nerves running in between the flexor tendons (median nerve) or next to the artery (ulnar nerve), and was often complemented with subcutaneous infiltrations according to the incision site. Ultrasound (US) guidance allows for precise identification of the nerves along their course in the forearm and the most convenient level for a reliable injection within the spaces that contain the nerves. However, the complex innervation of the wrist and hand, involving branches of five different nerves overlaping between them, is responsible for the variability observed in the distribution of anesthesia after a wrist block.
The wrist block does not result in a complete block of the hand and fingers. For instance, the territory of the deep branch of the radial nerve (deep structures on the dorsum of the hand, and first-to-third fingers) will not be blocked. To anesthetize this area, it is necessary to block the radial nerve proximal to the elbow crease (see Chapter 19). Likewise, the skin over the wrist crease is not completely anesthetized, as it is also supplied by the lateral and medial antebrachial cutaneous nerves, the superficial branch of the radial nerve, and occasional contribution from the interosseous nerves. For carpal tunnel surgery, for instance, a subcutaneous infiltration at the level of the wrist crease is necessary to block all these small terminal branches.
When using small-gauge (e.g., 25-gauge) needles, special attention should be given in order to avoid intraneural injection, even more so when nerve stimulation is not used. Care must be taken when performing ulnar and radial nerve blocks, because they are intimately associated with arteries, to avoid inadvertent arterial puncture and injection.
Below the elbow, the median nerve courses toward the wrist deep to the pronator teres and flexor digitorum superficialis muscles. Commonly, there is a communicating branch with the ulnar nerve at this level (anastomosis of Martin-Gruber). The palmar branch of the median nerve takes off 3 to 8 cm proximally to the wrist crease and exits ...