Ulnar Nerve Block at the Elbow

Indications and Clinical Considerations

Cubital tunnel syndrome is caused by compression of the ulnar nerve by an aponeurotic band that runs from the medial epicondyle of the humerus to the medial border of the olecranon ( Fig. 58.1 ). This entrapment neuropathy manifests as pain and associated paresthesias in the lateral forearm that radiate to the wrist and ring and little fingers. If the condition remains untreated, progressive motor deficit and ultimately flexion contracture of the affected fingers can result. The onset of symptoms usually occurs after repetitive elbow motions or from repeated pressure on the elbow, such as that from using the elbows to rise from bed. Direct trauma to the ulnar nerve as it enters the cubital tunnel also may result in a similar clinical presentation.

Physical findings include tenderness over the ulnar nerve at the elbow. A positive Tinel sign over the ulnar nerve as it passes beneath the aponeuroses is usually present ( Fig. 58.2 ). Weakness of the intrinsic muscles of the forearm and hand that are innervated by the ulnar nerve may be identified with careful manual muscle testing ( Table 58.1 ). Manual muscle testing that assesses the strength of the adductor pollicis includes the Froment and Jeanne signs ( Fig. 58.3 ). Manual muscle testing that tests the interosseous muscles includes the crossed finger test, the finger flexion test, and the Egawa sign ( Fig. 58.4 ). Manual muscle testing that assesses the strength of the lumbar innervated lumbrical muscles includes the Duchenne and André Thomas signs. Manual muscle testing that assesses the strength of the hypothenar muscles includes the Wartenberg, Masse, and Pitres–Testut signs ( Fig. 58.5 ). There is always the possibility that a patient with cubital tunnel syndrome may also have additional ulnar, median, or radial nerve lesions distal to the elbow that may confuse the clinical picture. Furthermore, the clinician should be aware that early in the course of the evolution of cubital tunnel syndrome, the only physical finding other than tenderness over the nerve may be the loss of sensation on the ulnar side of the little finger.

Cubital tunnel syndrome often is misdiagnosed as “golfer’s elbow,” and this accounts for the many patients whose golfer’s elbow fails to respond to conservative measures. Cubital tunnel syndrome can be distinguished from golfer’s elbow in that in cubital tunnel syndrome the maximal tenderness to palpation is over the ulnar nerve 1 inch below the medial epicondyle, whereas in golfer’s elbow the maximal tenderness to palpation is directly over the medial epicondyle (see Fig. 58.1 ). Cubital tunnel syndrome also should be differentiated from cervical radiculopathy involving the C7 or C8 roots and golfer’s elbow. Furthermore, it should be remembered that cervical radiculopathy and ulnar nerve entrapment may coexist as the so-called “double crush” syndrome, which is seen most often with median nerve entrapment at the wrist or with carpal tunnel syndrome.

Electromyography helps distinguish cervical radiculopathy and cubital tunnel syndrome from golfer’s elbow. Plain radiographs, ultrasound imaging, and magnetic resonance imaging (MRI) are indicated for all patients with cubital tunnel syndrome to rule out occult bony disease and to confirm the clinical diagnosis ( Fig. 58.6 ). On the basis of the patient’s clinical presentation, additional testing may be indicated, including complete blood count, uric acid, sedimentation rate, and antinuclear antibody testing. MRI and/or ultrasound imaging of the elbow is indicated if joint instability is suspected. The injection technique described later serves as both a diagnostic and a therapeutic maneuver.

Clinically Relevant Anatomy

The ulnar nerve is made up of fibers from the C6-T1 spinal roots. The nerve lies anterior and inferior to the axillary artery in the 3 o’clock to 6 o’clock quadrant. Exiting the axilla, the ulnar nerve descends into the upper arm along with the brachial artery. At the middle of the upper arm, the nerve courses medially to pass between the olecranon process and medial epicondyle of the humerus. It is at this point that the entrapment of the ulnar nerve responsible for cubital tunnel syndrome occurs. The nerve then enters the cubital tunnel and passes between the heads of the flexor carpi ulnaris muscle, continuing downward, moving radially along with the ulnar artery. At a point approximately 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, the dorsal aspect of the little finger, and the ulnar half of the ring finger. The palmar branch provides sensory innervation to the ulnar aspect of the palm of the hand, the palmar aspect of the little finger, and the ulnar half of the ring finger.