Ultrasound-guided ulnar nerve block at the wrist is useful in the management of the pain subserved by the ulnar nerve. This technique serves as an excellent adjunct to brachial plexus block and for general anesthesia when performing surgery at the wrist or below and is seeing increased utilization to provide anesthesia for reduction of fractures and dislocations of the fifth metacarpals and phalanges (Fig. 67.1). Ultrasoundguided ulnar nerve block at the wrist with local anesthetic may be used to palliate acute pain emergencies, including postoperative pain, pain secondary to traumatic injuries of the distal radius, and portions of the wrist and carpal bones innervated by the distal ulnar nerve, as well as cancer pain, while waiting for pharmacologic, surgical, and antiblastic methods to become effective.

Ultrasound-guided ulnar nerve block can also be used as a diagnostic tool when performing differential neural blockade on an anatomic basis in the evaluation of distal upper extremity pain as well as in a prognostic manner to determine the degree of neurologic impairment the patient will suffer when destruction of the ulnar nerve is being considered or when there is a
possibility that the nerve may be sacrificed during surgeries in the anatomic region of the ulnar nerve at the level of the wrist. This technique may also be useful in those patients suffering symptoms from compromise of the ulnar nerve due to ulnar tunnel syndrome. Ultrasound-guided ulnar nerve block at the wrist may also be used to palliate the pain and dysesthesias associated with stretch injuries to the ulnar nerve.

The ulnar nerve at the wrist is susceptible to trauma during surgery for ulnar tunnel syndrome or may be damaged by wrist fractures or compressed by mass or tumor (Fig. 67.2). Entrapment neuropathy of the ulnar nerve at the wrist as the ulnar nerve passes through Guyon canal is known as ulnar or Guyon tunnel syndrome and is much rarer than ulnar nerve entrapment at the elbow (Figs. 67.3 and 67.4). How ulnar tunnel syndrome
presents clinically depends on at what point in its course through Guyon canal the ulnar nerve is compromised. If the ulnar nerve is compromised in the proximal portion of the canal before the bifurcation of the motor and sensory components of the nerve, the patient will experience both motor and sensory symptomatology with pain, dysesthesias, and numbness, which radiate into the ulnar aspect of the palm and dorsum of the hand, the little finger and the ulnar half of the ring finger, and paralysis of the intrinsic muscles of the hand. These symptoms may also radiate proximal to the level of nerve entrapment into the distal forearm. If only the deep palmar branch of the ulnar nerve passes through Guyon canal, a pure motor neuropathy results manifesting as painless paralysis of the intrinsic muscles of the hand. If only the more distal superficial branch of the ulnar nerve is compressed, a pure sensory neuropathy will result.

Physical findings associated with entrapment or trauma of the ulnar nerve at the wrist include a positive Tinel sign over the ulnar nerve at the site of injury. Decreased sensation in the distribution of the ulnar nerve of the palm and dorsum of the hand and the little finger and the ulnar half of the ring finger is common. A positive spread sign test is highly suggestive of the diagnosis of ulnar tunnel syndrome. The spread sign test is performed by having the patient relax the hand on the examination table and then spread his or her fingers as far apart as possible. The sign is considered positive if the patient is unable to spread two or more fingers apart. The little finger is often spared (Figs. 67.5 and 67.6).