eMedicine Specialties > Orthopedic Surgery > Hand & Upper Extremity

Ulnar Nerve Entrapment

Author: Mark Stern, MD, Former Chief, Department of Orthopedic Surgery, Cedars-Sinai Medical Center
Coauthor(s): Scott P Steinmann, MD, Assistant Professor of Orthopedics, Mayo Medical School; Consulting Staff, Department of Orthopedic Surgery, Mayo Clinic of Rochester
Contributor Information and Disclosures

Updated: Sep 21, 2009

Introduction

Because of the anatomic positioning of the ulnar nerve, it is subject to entrapment and injury by a wide variety of causes.¹ It is the second most common entrapment neuropathy in the upper extremity (the first being the median nerve and its branches). Because of its superficial position at the elbow, it is often injured by excessive pressure in this area (leaning on the elbow during work or while driving a car). This article discusses the most common type of entrapments of the ulnar nerve, which occur most frequently at the elbow and wrist.^2,3,4

Recent studies

In a study of the validity of the Disabilities of Arm, Shoulder and Hand (DASH) questionnaire for elbow ulnar neuropathy by Zimmerman et al, the DASH questionnaire was confirmed as reflecting the clinical staging of ulnar neuropathy. Levine-Katz questionnaires were correlated with DASH to determine criterion validity, and construct validity was determined by comparing scores and clinical stages and by comparing scores preoperatively and postoperatively. The authors found that there was a high correlation between the DASH scores, severity of symptoms, and functional status. Correlations were identified as significant between DASH and biomechanical measures, but correlation coefficients were lower. All measures showed significant improvement postoperatively.⁵
 
In a retrospective study by Charles et al, 49 patients who underwent ulnar nerve transposition were followed to determine clinical sensory and motor recovery in cubital tunnel syndrome and whether recovery is influenced by such factors as preoperative McGowan stage, age, and symptom duration. Submuscular transposition was used in 25 patients, and subcutaneous transposition was applied in 24 patients. Obvious improvement was reported in 20 of 25 patients in the submuscular group and in 17 of 24 patients in the subcutaneous group. Both groups showed significant improvement in sensory and motor function, with 17 patients in both groups recovering sensory function and with 19 patients in each group recovering motor function. Patients with symptoms lasting more than 6 months had a poor prognosis, regardless of surgical technique used.⁶

Jaddue et al compared operative technique (incision length, operative time), postoperative care (postoperative pain and complications), and outcome between subcutaneous and submuscular surgical techniques for anterior transposition of the ulnar nerve after decompression in moderate cubital tunnel syndrome. Subcutaneous transposition was found to be associated with shorter incision, shorter operative time, less postoperative pain, fewer postoperative complications, and better outcome.⁷

Problem

Pressure or injury to the ulnar nerve along its anatomic course may cause denervation and paralysis of the muscles supplied by that nerve. One of the most severe consequences is loss of intrinsic muscle function in the hand. When the ulnar nerve is divided at the wrist, only the opponens pollicis, superficial head of the flexor pollicis brevis, and lateral 2 lumbricals are functioning.

Frequency

Ulnar nerve entrapment is the second most frequent entrapment neuropathy in the upper extremity. Because of the anatomic arrangement of structures, the area around the elbow is the most common area for entrapment. The wrist at the Guyon canal is the second most common area of entrapment.

Etiology

In a 1998 article, Posner⁸ defined 5 areas of potential compression around the elbow as follows:

• Under the heading intermuscular septum, Posner lists the arcade of Struthers (a musculofascial band about 8 cm proximal to the medial epicondyle), the medial intermuscular septum (which the nerve pierces to reach the olecranon groove), and the medial head of the triceps muscle (which can be hypertrophied or can chronically snap over the medial epicondyle, causing a neuritis).
• The area of the medial epicondyle is a valgus deformity caused by malunion of a condylar fracture, nonunion of a condylar fracture, or an epiphyseal injury to the lateral side of the elbow. These may cause tardy ulnar palsy secondary to chronic stretching of the ulnar nerve.
• The olecranon or epicondylar groove is a fibroosseous tunnel holding the ulnar nerve and its vascular accompaniment. A congenitally shallow groove or a torn fibrous roof can allow the nerve to chronically subluxate or dislocate, causing neuritis and palsy. Fracture fragments and arthritic spurs in or around the groove impinging on the nerve can also cause entrapment and subsequent neuritis. Traumatic hemorrhage, soft tissue tumors, ganglia, infections, osteochondromas, synovitis secondary to rheumatoid diseases, and malposition during work or sleep all may cause entrapment and nerve dysfunction.
• The cubital tunnel is the passage between the 2 heads of the flexor carpi ulnaris, which are connected by a continuation of the fibroaponeurotic covering of the epicondylar groove (Osborne ligament). During elbow flexion, the tunnel flattens as the ligament stretches, causing pressure on the ulnar nerve.^9,10,11
• Flexor-pronator aponeurosis is the fifth topic. As the nerve exits the flexor carpi ulnaris, it perforates a fascial layer between the flexor digitorum superficialis and the flexor digitorum profundus. Entrapment can occur here also. The most common sites of entrapment around the elbow are the olecranon groove and the cubital tunnel.

Guyon canal

The Guyon canal is the second most common site of entrapment and is located at the wrist. Entrapment may cause purely motor, purely sensory, or a mixed lesion, depending on the site of compression.

Anatomically, the canal is divided into 3 zones. Zone 1 is the area proximal to the bifurcation of the ulnar nerve. Compression in zone 1 causes combined motor and sensory loss. It is most commonly caused by a fracture of the hook of the hamate or a ganglion. Zone 2 encompasses the motor branch of the nerve after it has bifurcated. Compression causes pure loss of motor function to all of the ulnar-innervated muscles in the hand. Ganglion and fracture of the hook of the hamate are the most common etiological factors. Zone 3 encompasses the superficial or sensory branch of the bifurcated nerve. Compression here causes sensory loss to the hypothenar eminence, the small finger, and part of the ring finger, but it does not cause motor deficits. Common causes are an aneurysm of the ulnar artery, thrombosis, and synovial inflammation.

Pathophysiology

Seddon¹² in 1972 and Sunderland¹³ in 1978 classified nerve injuries similarly.

Seddon classified 3 levels of injury as follows:

1. Neuropraxia is a transient episode of complete motor paralysis with little sensory or autonomic involvement. This usually is secondary to a transitory mechanical pressure. Once this is relieved, return of function is complete.
2. Axonotmesis is a more severe injury involving loss of continuity of the axon with maintenance of continuity of the Schwann sheath. Motor, sensory, and autonomic paralysis is complete, and denervated muscle atrophy can be progressive. Recovery depends on a number of factors, including timely removal of the compression and axon regeneration. The time necessary to recover function depends on the distance between the denervated muscle and the proximal regenerating axon. Recovery can be complete.
3. Neurotmesis is the most serious level of injury. It entails complete loss of continuity of the axon and of the Schwann sheath. Recovery rarely is complete, and the amount of loss can only be determined over time; regenerating axons without intact neural tubes reinnervate muscle fibers that were not part of their original network.

Sunderland's classification has 5 degrees of nerve damage. The first degree corresponds to neuropraxia; the second degree corresponds to axonotmesis; and the third, fourth, and fifth correspond to increasingly severe levels of neurotmesis. Axons and Schwann sheaths are disrupted within intact nerve fascicles in a third degree injury. In a fourth degree injury, the perineurium surrounding the fascicles is damaged, as is the endoneurium. In a fifth degree injury, the nerve trunk is severed.

Presentation

Presenting symptoms of ulnar nerve entrapment can vary from mild transient paraesthesias in the ring and small fingers to clawing of these digits and severe intrinsic muscle atrophy.⁵ The patient may report severe pain at the elbow or wrist with radiation into the hand or up into the shoulder and neck. Patients may report difficulty in opening jars or turning doorknobs. Early fatigue or weakness may be noticed if work requires repetitive hand motions. If the patient rests on the elbows at work, increasing numbness and paraesthesias may be noticed throughout the day.¹⁴

A careful clinical history is imperative, noting the time of occurrence of symptoms. Determine whether symptoms are transient or continuous. Determine whether symptoms are related to work, sleep, or recreation. Elicit duration of symptoms and possible relation to trauma.

Begin the clinical examination at the neck and shoulder and move down the affected extremity to the elbow. Pain on neck movement mimicking the patient's symptoms could indicate cervical disc disease; pain on palpation or with shoulder motion could indicate a pathological condition in the brachial plexus or lung. Provocative maneuvers for thoracic outlet syndrome should be assessed. Masses on the medial side of the arm could indicate a soft tissue tumor or hemorrhage compressing the nerve. At the elbow, any deformity is noted, the nerve is palpated, and any abnormal mobility is noted. Masses are discerned, and if any question remains, use the opposite elbow as a standard. The course of the nerve is palpated in the forearm to the wrist.

Flexor capri ulnaris and flexor digitorum profundus strength should be assessed. Intrinsic muscle function is tested by asking the patient to cross the long finger over the index finger (ie, crossed finger test). Only 2 muscles can be tested accurately in the hand, the abductor digiti quinti and the first dorsal interosseous. The tendons or bellies of these muscles can be palpated or visualized. Weakness of thumb pinch may be elicited by the Froment sign. A Martin-Gruber anastomosis in the forearm or a Riche-Cannieu anastomosis in the palm may deceive the examiner by apparent functioning of ulnar-innervated muscles.

Numbness usually precedes motor loss. Muscle wasting and clawing of the ring and small digits are indicative of a chronic compressive syndrome.

Differential diagnosis usually includes the following:

• Cervical disc disease
• Brachial plexus abnormalities, thoracic outlet syndrome, Pancoast tumor
• Elbow abnormalities, epicondylitis
• Infections, tumors, diabetes mellitus, hypothyroidism, rheumatoid diseases, and alcoholism
• Wrist fractures
• Ulnar artery aneurysms or thrombosis at the wrist

Indications

Indications for surgery for ulnar nerve entrapment are the following:

• No improvement in presenting symptoms after 6-12 weeks of conservative treatment
• Progressive palsy or paralysis
• Clinical evidence of a long-standing lesion (eg, muscle wasting, clawing of the fourth and fifth digits)

Relevant Anatomy

The ulnar nerve is the terminal portion of the medial cord of the brachial plexus, after the medial head of the median nerve has separated from it, with fibers from C8-T1. Initially, it lies medial to the axillary artery and then to the brachial artery to the middle of the arm. It pierces the intermuscular septum at this point and follows the medial head of the triceps muscle to the groove between the olecranon process and the medial epicondyle. It gives off no branches in the arm. It then crosses the elbow, giving off articular branches and branches to the flexor carpi ulnaris and the medial half of the flexor digitorum profundus. It slips between the 2 heads of the flexor carpi ulnaris and continues into the forearm between this muscle and the flexor digitorum profundus.

In the distal half of the forearm, it is joined on its lateral side by the ulnar artery. Proximal to the wrist, the nerve gives off a large dorsal branch, sensory in nature. The ulnar nerve continues into the hand via the Guyon canal. It then splits into a superficial or sensory portion and a deep or motor portion. The dorsal branch supplies sensation to the dorsum of the wrist and the ulnar side of the hand.

The superficial branch in the Guyon canal supplies the palmaris brevis and the skin of the hypothenar eminence and digital nerves to the small and ulnar side of the ring finger. The deep branch passing between the abductor digiti quinti and the flexor digiti quintus brevis, with the deep branch of the ulnar artery, perforates the opponens digiti quinti and follows the deep volar arch across the interossei. It supplies the 3 small muscles of the small finger, the third and fourth lumbricales, the volar and dorsal interossei, the adductoris pollicis, and the deep head of the flexor pollicis brevis.

Two nerve anomalies must be noted because, in ulnar neuropathy, these anomalies may confuse the diagnosis. The first is the Martin-Gruber anastomosis in the forearm. In this anomaly, fibers that supply the intrinsic muscles are carried in the median nerve to the middle of the forearm where they leave the median nerve to join the ulnar nerve. Functioning intrinsic muscles could be observed with injury above this anastomosis, although the ulnar nerve dysfunction is proximal. The second is the Riche-Cannieu anastomosis, in which the median and ulnar nerves are connected in the palm. Even with an injury at the wrist, some intrinsic function occurs.

Contraindications

Progressive palsy with increasing muscle weakness is an indication that conservative treatment for ulnar nerve entrapment should be terminated and surgery carried out.

If a fracture of the hook of the hamate is noted in the wrist, cast immobilization or splinting is required for 4-6 weeks. Surgery is indicated if symptoms progress during this time. On the other hand, as swelling subsides, pressure on the nerve may abate and symptoms may disappear. Nonsteroidal anti-inflammatory medications are also valuable to reduce swelling in the tunnel.

Contraindications to each of the operative procedures used to decompress the nerve are the following:

• Decompression in situ should not be used in cases of severe posttraumatic neuropathy with scarring, chronic subluxation, or dislocation of the ulnar nerve from the epicondylar groove and soft tissue masses in the epicondylar groove.
• Medial epicondylectomy is not used when double crush syndrome with entrapment at the distal end of the cubital tunnel or soft tissue masses in the epicondylar groove are suspected.
• Subcutaneous transposition does not release the ulnar nerve completely, leaving the distal course from the cubital tunnel as a possible site of compression. It may not be the best choice for transposition in a thin person who lacks significant adipose tissue at the site of transposition because of the possibility of repeated trauma to the nerve at the elbow.⁶
• Intramuscular transposition is the most controversial of the procedures because of the claim of severe postoperative scarring.
• Submuscular transposition is contraindicated when scarring of the joint capsule or irregularity of the elbow joint due to malunited fracture or severe arthritis is present.

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