Excerpt from Cubital Tunnel Syndrome

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History of the Procedure

Feindel and Stratford (1958) were the first to use the term cubital tunnel. They emphasized that the ulnar nerve is compressed at the elbow because of anatomic peculiarities to that region. In 1898, Curtis performed the first published case of management for ulnar nerve neuropathy at the elbow, which consisted of a subcutaneous anterior transposition.

Problem

Affected patients often experience numbness and tingling along the little finger and the ulnar half of the ring finger. This discomfort is often accompanied by weakness of grip and, rarely, by intrinsic wasting.

Frequency

The elbow is the most common site of compression of the ulnar nerve. Cubital tunnel syndrome is the second most common compressive neuropathy (after carpal tunnel syndrome). Cubital tunnel syndrome affects men 3-8 times as often as women.

Etiology

Cubital tunnel syndrome may be caused by constricting fascial bands, subluxation of the ulnar nerve over the medial epicondyle, cubitus valgus, bony spurs, hypertrophied synovium, tumors, ganglia, or direct compression. Occupational activities may aggravate cubital tunnel syndrome secondary to repetitive elbow flexion and extension. Certain occupations are associated with the development of cubital tunnel syndrome; however, a definite relationship with occupational activities is not well defined.

Pathophysiology

As the elbow moves from extension to flexion, the distance between the medial epicondyle and the olecranon increases 5 mm for every 45° of elbow flexion. Elbow flexion places stress on the medial collateral ligament (MCL) and the overlying retinaculum. The shape of the cubital tunnel changes from a round to an oval tunnel, with a 2.5-mm loss of height, because the cubital tunnel rises during elbow flexion and the retrocondylar groove on the inferior aspect of the medial epicondyle is not as deep as the groove is posteriorly. The cubital tunnel's loss in height with flexion results in a 55% volume decrease in the canal, which further results in the mean ulnar intraneural pressure increasing from 7 mm Hg to 14 mm Hg. A combination of shoulder abduction, elbow flexion, and wrist extension results in the greatest increase in cubital tunnel pressure, with ulnar intraneural pressure increasing to about 6 times normal.

Traction and excursion of the ulnar nerve also occur during elbow flexion, as the ulnar nerve passes behind the axis of rotation of the elbow. With full range of motion (ROM) of the elbow, the ulnar nerve undergoes 9-10 mm of longitudinal excursion proximal to the medial epicondyle and 3-6 mm of excursion distal to the epicondyle. In addition, the ulnar nerve elongates 5-8 mm with elbow flexion.

Within the cubital tunnel, the measured mean intraneural pressure is significantly greater than the mean extraneural pressure at elbow flexion of 90° or more. With the elbow flexed 130°, the mean intraneural pressure is 45% higher than the mean extraneural pressure. At this amount of flexion, significant flattening of the ulnar nerve occurs; however, with full elbow flexion, no evidence exists of direct focal compression, suggesting that traction on the nerve in association with elbow flexion is responsible for the increased intraneural pressure. In addition, studies have shown that the intraneural and extraneural pressures within the cubital tunnel are lowest at 45° of flexion. As a result of these studies, 45° of flexion is considered to be the optimum position for immobilization of the elbow to decrease pressure on the ulnar nerve.

Subluxation of the ulnar nerve is a common finding. Childress (1975) looked at 2000 asymptomatic elbows. None of the patients were aware of ulnar nerve subluxation; however, 16.2% of these patients had subluxation of the ulnar nerve following flexion past 90°. Of the 325 patients with subluxation of the ulnar nerve, only 14 had unilateral subluxation. Although subluxation is a common finding and does not appear to cause cubital tunnel syndrome, the friction generated with repeated subluxation may cause inflammation within the nerve, and in the subluxed position, the nerve may be more susceptible to inadvertent trauma.

Sunderland (1987) described the internal topography of the ulnar nerve at the medial epicondyle. The sensory fibers and intrinsic muscle nerve fibers are located superficially. In contrast, the motor fibers to the flexor carpi ulnaris (FCU) and flexor digitorum profundus (FDP) are located deep within the nerve. The central location protects the motor fibers and explains why weakness of the FCU and FDP is not typically seen in ulnar neuropathy.

Proximal compression of a nerve trunk, such as that which occurs with cervical radiculopathy, may lead to increased vulnerability to nerve compression in a distal segment. This "double crush" condition can affect the ulnar nerve and results from disruption in normal axonal transport.

Histologically, severe demyelination of the nerve may occur in ulnar neuropathy. Demyelination may be located in the bulbous swelling just proximal to the entry of the nerve into the cubital tunnel.

McGowan (1950) established the following classification system:

• Grade I - Mild lesions with paresthesias in the ulnar nerve distribution and a feeling of clumsiness in the affected hand; no wasting or weakness of the intrinsic muscles
• Grade II - Intermediate lesions with weak interossei and muscle wasting
• Grade III - Severe lesions with paralysis of the interossei and a marked weakness of the hand

Clinical

Patients who are affected with cubital tunnel syndrome often experience numbness and tingling along the little finger and ulnar half of the ring finger, usually accompanied by weakness of grip. This frequently occurs when the patient rests upon or flexes the elbow. Patients may experience pain and tenderness at the level of the cubital tunnel, which may radiate proximally or distally. Symptoms vary from a vague discomfort to hypersensitivity at the elbow, and they may be intermittent at first and then become more constant. Nocturnal symptoms, especially with elbow flexion, may be quite disturbing. Patients with chronic ulnar neuropathy may complain of loss of grip and pinch strength and loss of fine dexterity. Rarely, patients with severe prolonged compression present with intrinsic muscle wasting and clawing or abduction of the little finger.

The physical examination should include the following steps:

• Check elbow ROM and examine the carrying angle; examine for areas of tenderness or ulnar nerve subluxation.
  • A positive Tinel sign finding is typically present in cubital tunnel syndrome; however, up to 24% of the asymptomatic population present with a positive Tinel sign finding.
  • The elbow flexion test is the best diagnostic test for cubital tunnel syndrome. The test involves the patient flexing the elbow past 90°, supinating the forearm, and extending the wrist. Results are positive if discomfort is reproduced or paresthesia occurs within 60 seconds. The addition of shoulder abduction may enhance the diagnostic capacity of this test.
• Palpate the cubital tunnel region to exclude mass lesions.
• Examine for intrinsic muscle weakness.
• Examine for clawing or abduction of the small finger with extension (Wartenberg sign).
• Assess ability to cross the index and middle fingers.
• Check for a Froment sign with key pinch.
• Check grip and pinch strength.
• Check vibratory perception and light touch with Semmes-Weinstein monofilaments. This is more important than static and moving 2-point discrimination tests, which reflect innervation density, as the initial changes in nerve compression affect threshold.
• Check 2-point discrimination.
• Evaluate sensation, especially the area on the ulnar dorsum of the hand supplied by the dorsal ulnar sensory nerve; hypesthesia in this area suggests a lesion proximal to the Guyon canal.
• Exclude other causes of dysesthesias and weakness along the C8-T1 distribution, such as cervical disk disease or arthritis; thoracic outlet syndrome; or ulnar nerve impingement at the Guyon canal.

Differential diagnoses include the following:

• Systemic - Diabetes, renal disease, multiple myeloma, amyloidosis, chronic alcoholism, malnutrition, leprosy, others
• Compression
  • Extrinsic – Postoperative; tourniquet; occupational or recreational activities requiring repetitive flexion or prolonged use of vibrating tools; recurrent trauma; others
  • Intrinsic - Supracondylar process, ligament of Struthers, anconeus epitrochlears, medial head of the triceps, arcuate ligament, Osborne ligament, nerve subluxation
• Valgus ligament instability
• Elbow injury and deformities - Fractures and dislocations; cubitus valgus or varus; trochlear hypoplasia
• Space occupying lesions - Ganglia, tumors, osteophytes, bursae
• Perineural adhesions
• Burns and heterotopic bone
• Arthritic conditions - Osteophytes, synovitis
• Conditions that mimic cubital tunnel - Syringomyelia, cervical disc disease, thoracic outlet syndrome, Pancoast tumor, double crush, entrapment of the nerve at the Guyon canal

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