Peripheral Nerve Series – Structure, Function, and Pathology of the Ulnar Nerve: What you need to know

Ulnar Nerve Injury

The ulnar nerve is a mixed sensorimotor nerve that arises from the medial cord (C8-T1 nerve roots) of the brachial plexus and may also have contributions from the C7 nerve root. It passes down the anteromedial aspect of arm lateral to the brachial artery piercing the medial intermuscular septum as it courses from the anterior to the posterior compartment, passing through the arcade of Struthers, a musculofascial band located approximately 8 cm proximal to the medial epicondyle. It then runs posterior to the medial epicondyle through the cubital tunnel as it enters the forearm, where it passes between two heads of flexor carpi ulnaris under a fascial band called Arcade of Osborne. It then descends through forearm between flexor carpi ulnaris and flexor digitorum profundus, innervating both muscles but only the medial half of the flexor digitorum profundus. It then becomes superficial in the distal part of the medial forearm and passes through Guyon’s tunnel, formed by the pisiform, hamate, and pisohamate ligament, at the level of the wrist. It then travels superficial to the flexor retinaculum and carpal tunnel as it enters the hand, where it splits into deep (motor) and superficial (sensory) branches. The deep branch innervates most of the intrinsic muscles of the hand including the hypothenar muscles, adductor pollicis, deep portion of flexor pollicis brevis, medial (3rd and 4th) lumbricals, and dorsal and palmar interossei. The superficial branch supplies the palmaris brevis, skin to the palmar portion of digit 5 & the medial half of digit 4, and the distal medial palm. The dorsal branch of ulnar nerve supplies skin of medial aspect of dorsum of hand and and dorsal aspects of little finger and medial half of ring finger. The palmar cutaneous branch of ulnar nerve supplies skin on the proximal medial palm, overlying the medial carpals.

The ulnar nerve is most vulnerable to injury at two sites, the cubital tunnel at the medial elbow and Guyon’s canal at the wrist. The cubital retinaculum and Arcade of Osborne flattens with elbow flexion, decreasing the volume and and increasing pressure within and around the cubital tunnel, increasing the likelihood that the ulnar nerve will be compressed. Vigorous and repetitive contraction of the flexor carpi ulnaris over time may also compress the nerve. The four major etiological factors for injury of the nerve at the elbow are presented in Table 20-5.

Injury to the ulnar nerve is common in athletes who perform repeated overhead throwing motions, such as baseball pitching, the volleyball spike, the tennis serve, and the javelin throw. During overhead throwing a rise in pressure occurs in the ulnar nerve in the cubital tunnel as the elbow is flexed in combination with wrist extension, shoulder abduction, trunk lateral flexion, and valgus loading. Escamilla et al, 2002; Escamilla et al., 2007; Matsuo et al., 2006 Matsuo et al.Matsuo et al., 2006 reported that abnormal pitching mechanics, such as excessive trunk lateral flexion (approximately 40°) and shoulder abduction (approximately 120°) resulted is approximately twice as much varus torque (approximately 125 N∙m) that is needed to resist valgus loading during normal pitching mechanics, which may increase the strain on the ulnar nerve.

Muscle imbalance, such as excessive strength in the extensor-supinator forearm musculature, which generates a valgus torque, compared to the flexor-pronator forearm musculature, which generates a varus torque may increase valgus loading and strain to the ulnar nerve. Buchanan et al., 1998 Weakness or fatigue in the flexor-pronator forearm musculature may also increase valgus loading and ulnar nerve strain. Therefore, with repetitive throwing it is important to have adequate strength and endurance in the flexor-pronator musculature of the forearm to help control valgus loading and ulnar nerve strain, as well as proper muscle balance between the flexor-pronator and extensor-supinator musculature of the forearm. Over time excessive ligamentous laxity of the ulnar (medial) collateral ligament at the elbow may also increase valgus mobility and further increase excessive strain on the ulnar nerve in the cubital tunnel. Surgical removal of an excessive posteromedial olecranon osteophyte, which may occur in overhead throwing sports like baseball, may result in excessive stretch of both the ulnar collateral ligament and the ulnar nerve due to the loss of valgus restraints.Cain et al, 2010; Levin et al.,2004

In overhead throwing athletes the ulnar nerve should be evaluated for subluxation during elbow flexion and valgus loading. Pain over the ulnar nerve, a positive Tinel’s sign posterior to the medial epicondyle, a positive elbow flexion test, as well as ulnar nerve sensory or motor deficits, all may suggest involvement of the ulnar nerve. Most cases of cubital tunnel syndrome have an insidious onset of medial elbow pain radiating down the medial forearm and numbness and tingling in the ulnar aspect of the forearm and hand. Symptoms are aggravated by continued use. Symptoms can occur in computer users working in excessive elbow flexion, violinists or violists practicing for long periods of time and laborers who perform repeated elbow flexion/extension on the job. Wright et al. reported that the nerve requires 2 cm (1 inch) of unimpeded movement at the elbow and can experience strain values that diminish the circulation to the nerve. Entrapment or inflammation of the nerve lessens the nerve’s ability to tolerate movement or changes in intraneural pressure.

Visible signs of ulnar nerve pathology are “claw hand”, in which the flexor digitorum profundus and extensor digitorum (extrinsic muscles) both pull on the distal phalanx, and without the control of the intrinsic muscles that attach more proximally, the fingers collapse into the zig-zag pattern of MCP hyperextension and PIP & DIP flexion. Another visible sign is sunken interosseous spaces in the dorsum of the hand secondary to atrophy of the dorsal interossei muscles. There may also be noticeable atrophy of the hypothenar eminence. Additional signs include an inability to abduct and adduct the fingers or adduct the thumb.

Various tests for lesions along the path of the ulnar nerve have been described in the literature. Buehler and Thayer suggested using the elbow flexion test as a clinical test for cubital tunnel syndrome. A positive response to the test consists of reproduction of paresthesias along the ulnar border of the forearm and hand. Butler’s upper limb neurodynamic test with an ulnar nerve bias (ULNT 3) is similar but increases the tensile stress on the brachial plexus and proximal portion of the ulnar nerve by adding shoulder girdle depression, glenohumeral abduction, and external rotation (this test has been described elsewhere as the ULTT 3 or ULTT 4). Although the test originally was described with the forearm in supination, pronation of the forearm often makes the test more provocative of symptoms. Cervical lateral flexion away from the extremity being tested can also be added.

Responses to Butler’s ULNT 3 have been studied in normal patients, Martinez et al, 2014 and in symptomatic patients. In most normal subjects, symptoms of tingling or numbness occurred in the medial forearm and hand. Subjects also frequently reported a sensation of pressure at the medial elbow. Some normal subjects had no symptomatic response to the test. In 18 subjects with a variety of upper extremity or cervical spine symptoms, all subjects had some response to the test. They had more frequent reports of medial upper arm pain (44% versus 18% in healthy subjects) and occasional symptoms in the contralateral extremity.

Twenty-five percent of the subjects tested in the patient group had an onset of symptoms before the addition of shoulder abduction, something that never occurred in asymptomatic subjects. When the range of shoulder abduction at the onset of symptoms in the remaining symptomatic arms was compared with that in healthy subjects, the difference was not statistically significant. Clinically, this seems to indicate that provocation of symptoms in the early stages of the ULNT 3 or with the elbow flexion test is a better measure of the presence of abnormality than the degree of abduction available before the onset of symptoms in the ULNT 3. It should be noted that the sequencing of the components of the test impacts the onset of symptoms. In a recent study when the test was performed with wrist and finger extension then forearm pronation, elbow flexion, shoulder ER, scapular depression and shoulder abduction followed by cervical lateral flexion towards the opposite side, 52% of patients felt symptoms with wrist and finger extension alone. Martinez et al, 2014

Treatment for cubital tunnel syndrome consists initially of rest, ice, and anti-inflammatory medications. The patient should also be examined for any problems in the cervical spine or shoulder that may be contributing to the symptoms. Altering the mechanics of throwing may help minimize stress on the elbow in the athlete. Computer keyboard height should be adjusted to place the elbow in less than 90° flexion during prolonged computer use. A soft splint worn at night can help symptoms by preventing prolonged elbow flexion during sleep.

If conservative treatment fails, surgical treatment should be considered. Surgical options include (1) release of the ligament at the cubital tunnel, (2) transposition of the ulnar nerve to the anterior surface of the elbow joint and (3) removal of the medial epicondyle. Rettig and Ebben retrospectively reviewed the cases of 20 athletes who underwent anterior subcutaneous transfer of the ulnar nerve. The average length of time between surgery and return to sports was 12.6 weeks (range, 6 to 43 weeks), and 19 of 20 athletes returned to their preinjury level of athletic activity.

Injury to the ulnar nerve at the wrist can cause sensory disturbances in the medial hand and motor weakness in the intrinsic muscles of the hand. It is vulnerable during surgical procedures on the the triangular fibrocartilage complex (TFCC), ulnar styloid or carpal tunnel.Zhang et al, 2011 Compression of the ulnar nerve is a common problem for cyclists due to prolonged pressure on the medial hand and wrist.   Fernald studied the incidence of overuse injuries in elite cyclists and found that 21% had sensory changes in the upper extremities. The abnormality may result from acute or chronic compression of the ulnar nerve in Guyon’s canal (tunnel) as a result of prolonged weight bearing on the hands or a fall. It also can be caused by traction on the nerve produced by the extended wrist position on the handlebars. Normally cyclists bear approximately 45% of their weight on the upper extremities; therefore the combination of compression and vibration from the road increases the likelihood of neurogenic symptoms.

Strategies to prevent irritation to the nerve at the wrist include changing the position of the hands frequently while riding, using padded gloves and handlebars to increase surface area and decrease pressure, using modified handlebars, and adjusting the overall “fit” of the bike to reduce weight bearing on the hands.

Ulnar Nerve (C7-T1): Cubital Tunnel Lesions

Cause/Site Signs and Symptoms
Traction injuries caused by increased valgus forces: Medial elbow pain radiating to the medial forearm
    Prior fracture or injury to the growth plate
    Disruption of the ulnar (medial) collateral ligament (UCL)
Entrapment under:

    Thickened arcuate ligament

Numbness and tingling in the ulnar aspect of the forearm and hand (medial 1 and ½ fingers)
    Hypertrophic medial head of triceps, anconeus, or flexor carpi ulnaris muscle
    Postoperative scar or bony callous formation
Irregularities in the ulnar groove (cubital tunnel) caused by osteophytes may prevent sliding of the ulnar nerve Atrophy in intrinsic muscles of hand; claw fingers
Subluxation or dislocation of the nerve over the medial epicondyle (usually as a result of laxity of soft tissue restraints) leads to a friction fibrosis
Modified from Drye C, Zachazewski JE: Peripheral nerve injuries. In Zachazewski JE, Magee DJ, Quillen WS, editors: Athletic injuries and rehabilitation, p 450, Philadelphia, 1996, WB Saunders.

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