Ultrasound-guided injection for ulnar tunnel syndrome is useful in the management of the symptoms associated with ulnar tunnel syndrome. Because the ulnar nerve is contained within a relatively noncompliant space as it passes through the ulnar tunnel, the addition of ultrasound guidance allows for more accurate needle placement within the borders of the canal while at the same time avoiding needle-induced trauma to the ulnar nerve. Furthermore, the ability to observe the actual flow of the injectate within this closed space utilizing real-time ultrasound imaging allows the clinician to identify any further compression of the nerve as the injection proceeds.

Entrapment neuropathy of the ulnar nerve at the wrist is known as ulnar tunnel syndrome and is much less common than carpal tunnel syndrome (Fig. 69.1). The clinical
presentation of ulnar tunnel syndrome is dependent on the point at which the motor and sensory branches of the ulnar nerve are compromised (Fig. 69.2). 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 and 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 (see Fig. 65.3). A failure to treat ulnar tunnel syndrome can result in permanent functional disability and deformity (Fig. 69.3).

The key landmark when performing ultrasound-guided ulnar nerve block at the elbow is ulnar artery at the wrist, which lies in proximity to the ulnar nerve (Fig. 69.4). Arising from fibers from the C8-T1 nerve roots of the medial cord of the brachial

plexus, the ulnar nerve lies anterior and inferior to the axillary artery in the 3:00 o’clock to 6:00 o’clock quadrant as it passes through the axilla. As the ulnar nerve exits the axilla, it passes inferiorly adjacent to the brachial artery. At the middle of the upper arm, the ulnar nerve turns medially to pass between the olecranon process and medial epicondyle of the humerus. Continuing its downward path, the ulnar nerve passes between the heads of the flexor carpi ulnaris moving radially along with the ulnar artery. At a point ˜1 inch proximal to the crease of the wrist, the ulnar nerve divides into the dorsal and palmar branches. The dorsal branch provides sensation to the ulnar aspect of the dorsum of the hand and the dorsal aspect of the little finger and the ulnar half of the ring finger (Fig. 69.5). The palmar branch provides sensory innervation to the ulnar
aspect of the palm of the hand and the palmar aspect of the little finger and the ulnar half of the ring finger.