Chapter 31G. Ultrasound-Guided Wrist Block
A wrist block can best be performed:
A. At the wrist crease. At this level, the median nerve is easier to access as it is located superficial to the tendons, just below the retinaculum.
B. 5–10 cm proximally to the wrist crease, to ensure the blockade of the palmar branches of median and ulnar nerves
C. At the elbow crease, to cover the deep motor branch of the radial nerve
D. In-plane so the nerves can be blocked with just one puncture
B is correct. An ultrasound-guided “wrist” block is often performed 5–10 cm proximally to the wrist crease. This location ensures the blockade of the palmar branches of the median and ulnar nerves, which take off a few centimeters proximally to the wrist crease.
A is incorrect. At the wrist crease, it is easy to confuse the tendons for the nerve and vice versa; for this reason, it is recommended to slide the transducer 5–10 cm proximally to the volar side of the forearm, to confirm the location of the nerve.
C is incorrect. The radial nerve divides just above the elbow crease into the superficial (sensory) and deep (motor) branches. Only the superficial branch needs to be blocked for anesthesia of the hand.
D is incorrect. For each of the blocks, the needle may be inserted either in-plane or out-of-plane. Ergonomics often dictates which is more effective.
The easiest way to recognize the median nerve is:
A. By using neurostimulation, searching for flexion of the digits
B. By searching at the lateral side of the brachial artery in the elbow crease
C. By sliding the transducer up and down the arm and tilting the transducer slightly
D. By increasing the depth to at least 5 cm
C is correct. As the median nerve exhibits pronounced anisotropy, tilting the transducer slightly will make the nerve appear alternately brighter or darker with respect to the background.
A is incorrect. Neurostimulation of the median nerve will give flexion of the digits. This can be used when there is doubt about the median nerve. Nevertheless we prefer to avoid placing the needle tip that close to the nerve.
B is incorrect. The median nerve crosses the elbow medial to the brachial artery.
D is incorrect. The median nerve assumes an increasingly superficial position in the forearm. Mostly it is no deeper than 3 ...