Diagnosis and Treatment of Work-Related Ulnar Neuropathy at the Elbow

Ulnar neuropathy at the elbow (UNE) is the second most common entrapment neuropathy after carpal tunnel syndrome and occurs most commonly at the elbow due to mechanical forces that produce traction or ischemia to the nerve. The primary symptom associated with UNE is diminished sensation or dysesthesias in the fourth or fifth digits, often coupled with pain in the proximal medial aspect of the elbow. Treatment may be conservative or surgical, but optimal management remains controversial. Surgery should include exploration of the ulnar nerve throughout its course around the elbow and release of all compressive structures.

Key points

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Ulnar neuropathy at the elbow (UNE) is the second most common entrapment neuropathy after carpal tunnel syndrome (CTS). UNE occurs most commonly at the elbow due to mechanical forces that produce traction or ischemia to the nerve.
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Electrodiagnostic (EDX) studies can help to objectively locate, confirm, and quantify the severity of ulnar nerve compression.
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Management should include modification of activities that exacerbate symptoms, night-time splinting, and/or padding the elbow to prevent direct compression. Surgical treatment should be considered if the condition does not improve despite conservative treatment and the condition interferes with work or activities of daily living.

Introduction

It is well known that work-related upper limb musculoskeletal disorders, particularly nerve entrapment, remain a difficult and costly problem in industrialized countries. Upper extremity entrapment neuropathies may be misdiagnosed as lateral or medial epicondylitis, de Quervain disease, among many others. Ulnar nerve entrapment occurs most commonly at the elbow due to mechanical forces that produce traction, compression, or ischemia to the ulnar nerve. However, it may be misdiagnosed as CTS, radial tunnel syndrome, and cervicobrachial neuralgia. Despite the high frequency of work-related musculoskeletal disorders, the relation between work conditions and ulnar nerve entrapment at the elbow has not been the object of much research. Predictive factors associated with the onset of ulnar nerve entrapment at the elbow are not yet well delineated. Ulnar nerve entrapment at the elbow is typically associated with biomechanical risk factors (ie, holding a tool in position, repetitively).

For the sake of clarity regarding nomenclature, ulnar neuropathy at the elbow is now considered the preferred term and is used in this article. Terms such as cubital tunnel syndrome or ulnar neuritis are still used by clinicians and may yet be seen in the literature. However, these terms are nonspecific descriptors often used interchangeably for any problem possibly relating to a nerve injury or entrapment near the elbow. After CTS, UNE is the second most common entrapment neuropathy. A differential diagnosis for UNE includes cervical radiculopathy, brachial plexopathy, and compression of the ulnar nerve at the wrist. Potential sites of UNE include Osborne ligament at the cubital tunnel, the arcade of Struthers (particularly after ulnar nerve transposition, when the nerve can be tethered), the medial intermuscular septum, the medial epicondyle, the flexor-pronator aponeurosis, and rarely an accessory muscle, the anconeus epitrochlearis. Entrapment may also occur from soft-tissue structures such as tumors or ganglions, bony abnormalities due to fractures, osteophytes (bone spurs), or subluxation of the ulnar nerve over the medial epicondyle with elbow flexion. A tardy ulnar nerve palsy may be seen in association deformities of the elbow secondary to a supracondylar fracture of the humerus. This condition may occur when the ulnar nerve becomes entrapped by scar tissue, which may produce anterior displacement of the nerve with elbow flexion, which may then spontaneously reduce back into the ulnar nerve groove with elbow extension. In general, work-relatedness and appropriate symptoms and objective signs must be present to establish a legitimate claim. EDX studies, including nerve conduction velocity (NCV) studies and needle electromyography (EMG), should be scheduled immediately to corroborate the clinical diagnosis.

Introduction

It is well known that work-related upper limb musculoskeletal disorders, particularly nerve entrapment, remain a difficult and costly problem in industrialized countries. Upper extremity entrapment neuropathies may be misdiagnosed as lateral or medial epicondylitis, de Quervain disease, among many others. Ulnar nerve entrapment occurs most commonly at the elbow due to mechanical forces that produce traction, compression, or ischemia to the ulnar nerve. However, it may be misdiagnosed as CTS, radial tunnel syndrome, and cervicobrachial neuralgia. Despite the high frequency of work-related musculoskeletal disorders, the relation between work conditions and ulnar nerve entrapment at the elbow has not been the object of much research. Predictive factors associated with the onset of ulnar nerve entrapment at the elbow are not yet well delineated. Ulnar nerve entrapment at the elbow is typically associated with biomechanical risk factors (ie, holding a tool in position, repetitively).

For the sake of clarity regarding nomenclature, ulnar neuropathy at the elbow is now considered the preferred term and is used in this article. Terms such as cubital tunnel syndrome or ulnar neuritis are still used by clinicians and may yet be seen in the literature. However, these terms are nonspecific descriptors often used interchangeably for any problem possibly relating to a nerve injury or entrapment near the elbow. After CTS, UNE is the second most common entrapment neuropathy. A differential diagnosis for UNE includes cervical radiculopathy, brachial plexopathy, and compression of the ulnar nerve at the wrist. Potential sites of UNE include Osborne ligament at the cubital tunnel, the arcade of Struthers (particularly after ulnar nerve transposition, when the nerve can be tethered), the medial intermuscular septum, the medial epicondyle, the flexor-pronator aponeurosis, and rarely an accessory muscle, the anconeus epitrochlearis. Entrapment may also occur from soft-tissue structures such as tumors or ganglions, bony abnormalities due to fractures, osteophytes (bone spurs), or subluxation of the ulnar nerve over the medial epicondyle with elbow flexion. A tardy ulnar nerve palsy may be seen in association deformities of the elbow secondary to a supracondylar fracture of the humerus. This condition may occur when the ulnar nerve becomes entrapped by scar tissue, which may produce anterior displacement of the nerve with elbow flexion, which may then spontaneously reduce back into the ulnar nerve groove with elbow extension. In general, work-relatedness and appropriate symptoms and objective signs must be present to establish a legitimate claim. EDX studies, including nerve conduction velocity (NCV) studies and needle electromyography (EMG), should be scheduled immediately to corroborate the clinical diagnosis.

Establishing work-relatedness

Work-related activities may also cause or contribute to the development of UNE. Establishing work-relatedness requires all of the following:

1.

Exposure: Workplace activities that contribute to or cause UNE
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Outcome: A diagnosis of UNE that meets the diagnostic criteria given in section Making The Diagnosis
3.

Relationship: Generally accepted scientific evidence, which establishes on a more probable than not basis (greater than 50%) that the workplace activities (exposure) in an individual case contributed to the development or worsening of the condition (outcome)

Although the exact incidence and prevalence are uncertain, UNE is second only to CTS as the most common peripheral nerve entrapment. From 1995 to 2000, approximately 2800 claims for work-related UNE were reported to the Washington State Department of Labor and Industries. Approximately one-quarter of these patients received surgical treatment, whereas the remainder was treated conservatively. Time loss payments were paid to 93% of the surgery group and 61% of the conservatively treated group.

Certain work-related activities have been associated with UNE, such as activities requiring repetitive or sudden elbow flexion or extension, intensive use of hand tools, or repeated trauma or pressure to the elbow. Jobs in which these activities occur may include but are not limited to the following: repetitive lifting, leaning on elbows at desk or work bench, working in tight places, shoveling, digging, hammering, using hand saws or large power machinery, and operating boring and punching machines. Several specific occupations have been associated with UNE, including carpenter, painter, glass cutter, musician, seamstress, packaging worker, assembly line worker, shoe and clothing industry worker, and food industry worker. This list is not exhaustive and is meant only as a guide in the consideration of work-relatedness.

Both high body mass index (BMI) and low BMI have been reported as risk factors for UNE. Landau and colleagues retrospectively analyzed the EDX records of subjects with UNE. The BMI was calculated for 50 patients with a sole diagnosis of UNE and compared with the BMI of 50 patients with CTS and 50 control subjects. The difference in BMI between patients with UNE and normal patients was significant ( P <.01). In the control groups, increasing BMI directly correlated with increasing ulnar motor NCV across the elbow but not with forearm NCV. The results suggested that across-elbow (AE) ulnar motor NCV may be falsely increased in patients with a high BMI, probably because of distance measurement factors. Slender individuals seem to have comparatively slower AE ulnar NCVs and may also be at increased risk for developing UNE.

Making the diagnosis

For the purposes of this article, the case definition of confirmed UNE includes appropriate symptoms, objective physical findings (signs), and abnormal results on EDX studies. A provisional diagnosis of UNE may be made based on appropriate symptoms and objective signs, but confirmation of the diagnosis requires abnormal results on EDX studies. The anatomy of the ulnar nerve and areas of entrapment are illustrated in Fig. 1 .

Symptoms and Signs

The primary symptom associated with UNE is diminished sensation or dysesthesias in the ring and small fingers (fourth and fifth digits), often coupled with pain in the proximal medial aspect of the elbow. Motor symptoms may include progressive weakness, with inability to separate fingers, loss of power grip, and poor dexterity. Nonspecific symptoms (eg, pain without sensory loss, “dropping things”) by themselves are not diagnostic of UNE. Symptoms of UNE may worsen at night. Symptom provocation has been described with Tinel sign (tapping over the cubital tunnel) or by sustained (60 seconds) elbow flexion with or without manual compression of the ulnar nerve at or proximal to the cubital tunnel. Alone, these findings are neither sensitive nor specific for the diagnosis of UNE.

Objective findings on physical examination should be localized to muscles supplied by the ulnar nerve or sensory impairment in an ulnar distribution. In the forearm, the muscular branch of the ulnar nerve innervates the flexor carpi ulnaris and the flexor digitorum profundus (medial half). In the hand, the deep branch of the ulnar nerve innervates the hypothenar muscles (opponens digiti minimi, abductor digiti minimi [ADM], flexor digiti minimi brevis), the adductor pollicis, the flexor pollicis brevis (deep head), the third and fourth lumbrical muscles, and the dorsal and palmar interossei. In the hand, the superficial branch of the ulnar nerve innervates the palmaris brevis.

Weakness of the hand intrinsic muscles may be tested by looking for a positive Froment sign, which is a contraction of flexor pollicis longus to compensate for a weak adductor pollicis. Testing involves having the patient attempt to hold a flat object (ie, a piece of paper) between the index finger and thumb. The examiner then tries to pull the object out of the patient’s hands. A normal individual is able to maintain a hold on the object without difficulty. Because of weakness in the ulnar nerve–innervated adductor pollicis muscle, a patient with an ulnar nerve lesion has difficulty maintaining a hold on the object and compensates by contracting the flexor pollicis longus muscle to achieve a grip.

In more advanced cases, intrinsic muscle atrophy becomes visibly evident (eg, first dorsal interosseous [FDI]). In severe cases, hand opening reveals a characteristic ulnar claw posture, with hyperextension of the metacaropophalangeal joints and flexion of the interphalangeal joints. This posture should not be confused with the median neuropathy benediction sign seen with hand closing. Ulnar sensory impairment can be demonstrated using Semmes-Weinstein monofilaments and should be localized to the ulnar side of the ring finger and the small finger and ulnar aspect of the hand. There seems to be a high frequency of diagnostic imprecision for cases handled within the workers’ compensation system. In the general population, UNE typically occurs as an isolated mononeuropathy, with coincidence of UNE and CTS being uncommon. However, in the workman compensation setting, approximately 60% of UNE surgical patients have a concomitant diagnosis of CTS, usually made before a diagnosis of UNE. Every effort should be made to objectively verify the diagnosis of UNE before considering surgery.

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