Cubital tunnel syndrome is a common entrapment neuropathy of the ulnar nerve at the elbow that 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. 55.1). Patients suffering from cubital tunnel syndrome will experience pain and dysesthesias radiating from the elbow to the lateral forearm and into the wrist and ring and little finger. The onset of cubital tunnel syndrome can be insidious and is usually the result of misuse or overuse of the elbow joint although direct trauma to the nerve as it passes through the cubital tunnel may also result in a similar clinical scenario. If this entrapment neuropathy is not treated, pain and functional disability may become more severe, and, ultimately, permanent numbness and flexion contractures of the ring and little finger may result.

Physical findings in patients suffering from cubital tunnel syndrome will exhibit weakness of the intrinsic muscles of the forearm and hand that are innervated by the ulnar nerve. A Tinel sign will be present at the point where the ulnar nerve passes through the cubital tunnel and the nerve will be tender to palpation (Fig. 55.2). Weakness of the adductor pollicis muscles can be demonstrated by performing the Froment and Jeanne test (Fig. 55.3). Weakness of the interosseous muscles can be demonstrated by performing the crossed finger, finger flexion, little finger adduction, and Egawa tests (Fig. 55.4). Weakness of the hypothenar muscles can be demonstrated by performing the Wartenberg, Masse, and Pitres-Testut tests. It should be remembered that the ulnar nerve is the largest unprotected nerve in the body and that it is subject to trauma or entrapment at many points along its course and that more than one ulnar nerve lesion may coexist.

Cubital tunnel syndrome often is misdiagnosed as golfer’s elbow and can be distinguished from golfer’s elbow by determining the site of maximal tenderness to palpation. Patients suffering from cubital tunnel syndrome will experience maximal tenderness to palpation over the ulnar nerve 1 inch below the medial epicondyle, whereas patients suffering from golfer’s elbow will experience maximal tenderness to palpation directly over the medial epicondyle. 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. The double crush syndrome is seen most commonly with median nerve entrapment at the wrist or with carpal tunnel syndrome but has been reported with the ulnar nerve.

Electromyography and nerve conduction velocity testing are useful in helping in the differentiation of cubital tunnel syndrome from cervical radiculopathy and golfer’s elbow. Plain radiographs, ultrasound imaging, and magnetic resonance imaging are indicated in all patients who present with cubital tunnel syndrome in order to rule out occult bony pathology involving the cubital tunnel and to identify occult fractures, masses, tumors, and abnormalities of the ulnar nerve that may be responsible for compromise of the ulnar nerve (Figs. 55.5 and 55.6). Based on the patient’s clinical presentation, additional testing may be indicated, including complete blood count, uric acid, sedimentation rate, and antinuclear antibody testing. The ultrasound-guided injection technique described below serves as both a diagnostic and therapeutic maneuver.

The key landmarks when performing ultrasound-guided cubital tunnel syndrome are the medial epicondyle and olecranon process. Arising from fibers from the C8 to 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 where it passes beneath an aponeurotic band and is subject to entrapment (Fig. 55.7). 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. 55.8). 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.