Pinched ulnar nerve

When the ulnar nerve, one of the three main nerves of the hand, becomes pinched, it develops into a compression lesion called mononeuropathy of the upper limb; its ICD-10 code is G56.2. Compression neuropathy is one of the most interesting, but also most challenging aspects of hand surgery. Compression or entrapment neuropathy occurs when a nerve becomes compressed or pinched at some point along its course in the upper limb. This can lead to altered function and, if left untreated, can result in significant limitation of hand function. Therefore, it is important to diagnose and treat these conditions early. [ 1 ]

Epidemiology

Ulnar nerve entrapment at the elbow is the second most common compression neuropathy in the arm. The condition can seriously interfere with daily life and work. However, epidemiological studies that take risk factors into account are rare. [ 2 ]

The exact incidence of ulnar nerve compression is unknown, but clinical experience suggests that compression of the ulnar nerve at the elbow is the second most common cause of upper extremity neuropathy. However, Mondelli conducted a retrospective study using electromyography and estimated the standardized annual incidence of ulnar nerve compression at the elbow to be 20.9 per 100,000.[ 3 ] The prevalence of ulnar nerve compression is estimated to be 1% in the United States.[ 4 ]

Experts note that among peripheral mononeuropathies, the most common is the carpal tunnel syndrome, which occurs when the median nerve of the hand is pinched; the second is the cubital tunnel syndrome, which occurs when the ulnar nerve is pinched in the elbow joint.

Causes ulnar nerve entrapment

When identifying the main causes of ulnar nerve (nervus ulnaris) entrapment, neurologists emphasize, for the most part, its traumatic origin due to damage at the level of the forearm (code S54.0 according to ICD-10), which is classified as a peripheral nerve injury. Pinching can also be a consequence of a shoulder girdle injury; a fracture of the condyle or epicondyle of the humerus; a severe elbow bruise (especially a direct blow to its inner part); dislocation or fracture of the elbow joint; wrist injuries.

Often, local scars form after injuries; due to improper healing of the fracture, bone structures are deformed, and post-traumatic contractures of soft tissues along the nerve occur.

Common causes of compression include prolonged flexion of the elbow and excessive mechanical stress – repeated flexion of the elbow or wrist (intense repetitive motion); leaning on the elbow (pressure on the ulna) for long periods of time.

If a nerve becomes pinched in the elbow joint - in the tunnel behind the inside of the elbow - it is diagnosed as cubital tunnel syndrome. [ 5 ]

Specialists take into account the presence of congenital and acquired deformations of the elbow joint - valgus or varus elbow, predisposing to pinching of the ulnar nerve. Cubitus valgus is a deformation in which the forearm extended along the body deviates from it (by 5-29°). Congenital valgus elbow is observed in Turner or Noonan syndrome, and acquired can be a complication of a fracture of the lateral condyle of the humerus. The cubitus varus deformation is expressed in the deviation of part of the extended forearm toward the midline of the body.

Chronic entrapment of the ulnar nerve as it passes through the wrist results in ulnar tunnel syndrome, Guyon's canal syndrome, or ulnar carpal tunnel syndrome.

By the way, both syndromes can be idiopathic. Read more:

• Types of Ulnar Neuropathy
• Tunnel syndromes

Risk factors

Some risk factors for ulnar nerve impingement include:

• rheumatoid arthritis;
• elbow arthritis, osteoarthritis or deforming arthrosis;
• swelling of the elbow joint;
• inflammation of the tendons (tendinitis);
• synovial chondromatosis;
• synovial cyst (hygroma or ganglion) in the wrist area;
• presence of supracondylar osteophytes;
• osteoma, cortical hyperostosis, lipoma and other malformations;
• the presence of muscle anomalies of the upper limbs, for example, 12-15% of people have an additional short muscle, the anconeus epitrochlearis, passing over the ulnar nerve, crossing the ulnar nerve posterior to the cubital tunnel.
• Male gender and elbow fracture predispose to the development of ulnar nerve compression in the elbow joint. [ 6 ], [ 7 ]
• Smoking has been found to be a risk factor for the development of ulnar nerve compression.[ 8 ]

Pathogenesis

The anatomical and topographic features of the ulnar nerve, which is one of the five terminal branches of the brachial plexus (the middle bundle of the subclavian part), largely explain the pathogenesis of its pinching, since there are areas of potential compression along the course of the nerve.

From its starting point, the ulnaris nerve runs down the medial surface of the humerus; in the middle of the arm, the nerve passes through the medial intermuscular septum (called the arcade of Struthers) and runs inside the triceps brachii. Occasionally, the ulnar nerve may become pinched here, as it is anchored in the lower part of the arm by the triceps.

In the elbow joint area, the nerve can be pinched as it passes through the supracondylar groove (sulcus nervi ulnaris). And very often, the pinching occurs in the ulnar canal (canalis ulnaris) or cubital tunnel: in Latin, ulna is the ulna bone, and cubitus is the elbow.

This tunnel is located between the medial epicondyle of the humerus and the olecranon and has an elastic "roof" of a tendinous arch - myofascial trilaminar ligament (fascia of the ulnar canal or Osborn's ligament). When the arm is bent at the elbow, the shape of the canal changes and it narrows by half, which leads to dynamic compression of the ulnar nerve.

Descending along the forearm through the flexor muscles of the wrist and the pronators of the forearm, the nervus ulnaris enters the hand through the fibrous-osseous tunnel of the wrist up to 4 cm long - Guyon's canal, and this is also a typical localization of compression of the ulnar nerve. Pinching in this canal is the result of its excessive compression from the outside when the wrist is bent. However, the mechanism of pinching of the ulnar nerve in the wrist area is different in the presence of an aberrant long muscle of the palm (musculus aberrant palmaris longus).

Symptoms ulnar nerve entrapment

The ulnar nerve supplies the little finger, half of the ring finger, and sensory innervation of the skin in the hypothenar region (the muscular eminence on the palm of the hand (below the little finger)) and the dorsal region of the hand. It also controls most of the small muscles of the hand (involved in flexion and extension of the medial and distal phalanges of the fingers) and the two large muscles of the anterior forearm that flex and abduct the hand at the wrist and support the grasping forces of the upper limbs.

Therefore, as a result of its pinching, motor, sensory or mixed - motor-sensory symptoms arise. In this case, the very first signs are sensory, which manifest themselves in the loss of sensitivity of the ring finger and little finger and paresthesia, that is, numbness or tingling (especially pronounced when the elbow is bent).

Motor symptoms include muscle weakness (weakening of grip) and difficulty coordinating the fingers innervated by the ulnar nerve. When it is pinched in the elbow joint, neuralgic pain of varying intensity and duration occurs in the elbow area, often radiating to the shoulder. Compression within the Guyon canal leads to muscle weakness and loss of sensitivity on the outer lateral and dorsal side of the hand.

Categories of nervous dysfunction (McGowan [ 9 ] and Dellon [ 10 ])

• Mild nerve dysfunction involves intermittent paresthesias and subjective weakness.
• Moderate dysfunction is accompanied by intermittent paresthesias and measurable weakness.
• Severe dysfunction is characterized by persistent paresthesias and measurable weakness.

More information in the article: Symptoms of damage to the ulnar nerve and its branches.

Complications and consequences

Regardless of the localization of the ulnar nerve entrapment, the consequences may be partial closed damage to the fibers of its trunk (axonotmesis) or more serious open damage to the entire trunk, perineurium and epineurium (neurotmesis). Depending on this, complications such as:

• ulnar neuropathy;
• ischemia and fibrosis of the ulnar nerve;
• damage to the myelin sheath of axons, leading to the cessation of transmission of nerve impulses.

Late paralysis of the ulnar nerve (and paralysis of the limb) and irreversible muscle wasting – muscle atrophy (amyotrophy) of the hand are also possible.

Diagnostics ulnar nerve entrapment

The diagnosis of this injury begins with anamnesis, physical examination of the patient and analysis of the existing symptoms. A number of special neurodynamic tests are used to assess the degree of impairment of mobility of various parts of the limb and the level of sensory deficit.

Provocative tests: [ 11 ]

• Tinel's test along the ulnar nerve
• Elbow flexion test.
• Pressure provocation test (where direct pressure is applied to the cubital tunnel for 60 s) and
• Combined elbow pressure bending test.

A positive Tinel test is only 70% sensitive, while the elbow flexion test is 75% sensitive at 60 s. However, at 60 s, the pressure test is 89% sensitive, and the combined elbow flexion and pressure test is 98% sensitive. These examination results can be used in combination to better diagnose cubital tunnel syndrome.

Predisposing causes:

• Childhood supracondylar fracture (late ulnar nerve palsy)
• Chronic hallux valgus stress
• Elbow fractures that are treated without ulnar nerve grafting (olecranon fractures, distal humerus fractures, medial supracondylar fractures).

Instrumental diagnostics are performed: X-ray of the elbow or wrist (to detect abnormalities of bone structures); ultrasound of the nerves; electromyography (study of nerve conduction). [ 12 ]

Differential diagnosis

Differential diagnosis should take into account the presence of similar neurological symptoms in: carpal tunnel syndrome associated with compression of the median nerve of the hand; radial nerve entrapment (with the development of supinator syndrome or Froese syndrome); Kylo-Nevin syndrome; medial epicondylalgia (golfer's elbow); radiculopathy and spondylosis of the cervical spine; brachial plexopathy; peripheral polyneuropathy; thoracic outlet syndrome (scalene muscle syndrome); amyotrophic lateral sclerosis; Pancoast-Tobias syndrome in lung cancer, primary bone tumors.

Treatment ulnar nerve entrapment

Mild cubital tunnel syndrome can often be treated conservatively. There is a tendency for spontaneous recovery in patients with mild and/or intermittent symptoms if provoking causes can be avoided and adequate rest is used.

According to the Cochrane Database Syst Review (2016), treatment of ulnar nerve entrapment primarily requires removing physical loads from the affected limb and immobilizing it with a brace. It may be necessary to limit professional activity if the symptoms of tunnel syndromes worsen during work. [ 13 ]

Medicines for ulnar nerve entrapment are used to relieve pain and swelling, and are usually nonsteroidal anti-inflammatory drugs. All the details are in the materials:

• Pills for neuralgia
• Treatment of neuropathy of the upper extremities
• Treatment of neuropathic pain

Although corticosteroids are very effective, their injections are generally not used due to the high risk of nerve damage.

Massage for pinched ulnar nerve is aimed at its decompression and is effective in relieving symptoms. In particular, massage of tense and shortened muscles followed by stretching to lengthen them helps relieve nerve compression.

To prevent stiffness in the elbow and wrist, therapeutic exercises for pinched ulnar nerves are used, that is, special exercises to maintain muscle tone and expand the range of motion, which are taught to patients by a physical therapy specialist. The entire complex of physiotherapy is important for restoring motor function and gradually increasing lost muscle strength. More details in the publication - Physiotherapy for neuritis and neuralgia of peripheral nerves.

In severe cases, as a last resort, they resort to surgical intervention (widening of the cubital tunnel, decompression with nerve transposition, epicondiectomy, etc.). [ 14 ]

Treatment with folk remedies includes applying ice to the elbow or wrist (for pain and swelling), as well as taking water infusions or alcohol extracts of plants with antioxidant and neuroprotective activity, such as ginkgo biloba, sage (Salvia officinalis) and basil (Ocimum basilīicum).

Prevention

Measures to prevent ulnar nerve entrapment include avoiding prolonged stress on the elbow joints and wrists, periodically interrupting monotonous movements involving these anatomical structures (straightening the arms), sleeping with straight elbows, feasible physical activity (to increase muscle strength), and promptly contacting a doctor if at least one of the symptoms listed above appears.

Forecast

The dependence of the prognosis on the degree of compression of the nerve and a timely visit to a neurologist is unconditional. Thus, if the symptoms of pinching are mild, then in almost 90% of patients, timely conservative therapy leads to their removal and restoration of all functions of the ulnar nerve. With more pronounced symptoms and delay in seeking medical help, treatment brings a positive result in only 38% of cases.