Introduction:
Ulnar nerve entrapment is a relatively common syndrome, ranking second in prevalence only to Carpal tunnel syndrome. Potential locations for entrapment include the brachial plexus, cubital tunnel, and Guyon’s canal. This condition is more prevalent in individuals experiencing pregnancy, diabetes, rheumatoid arthritis, and those with jobs involving prolonged periods of elbow flexion or wrist dorsiflexion. Cyclists are especially prone to Guyon’s canal neuropathy. Patients typically begin with sensory issues in the palm’s fourth and fifth digits, followed by motor symptoms such as reduced pinch strength and difficulties with tasks like buttoning shirts or opening bottles.
Ulnar nerve entrapment can occur at various points along its path. While the elbow is the most common site of compression, the wrist, forearm, and upper arm can also lead to ulnar nerve injury. Early detection and treatment are crucial for a favorable prognosis, as once the nerve sustains axonal damage, the treatment outcomes are often unsatisfactory.
What Is Ulnar Nerve Entrapment?
Ulnar nerve entrapment, or Cubital tunnel syndrome, occurs when the ulnar nerve in the arm experiences compression or irritation. This nerve, one of the major nerves in the arm, originates in the neck and extends down to the hand, with various locations along its course where compression can occur, including beneath the collarbone and at the wrist. The elbow’s inner part is the most common site for nerve compression in this condition.
Ulnar nerve entrapment commonly occurs at two key locations in the arm: the cubital tunnel near the elbow and Guyon’s canal at the wrist. The specific site of compression influences the symptoms experienced by the individual.
Anatomy: The ulnar nerve starts from the brachial plexus’s medial cord, runs along the inner side of the upper arm, and passes through the arcade of Struthers near the elbow. It enters the forearm through the cubital tunnel, formed by the medial collateral ligament and Osborne’s ligament.
In the forearm, the ulnar nerve runs between the Flexor Carpi Ulnaris (FCU) and the Flexor Digitorum Profundus (FDP) muscles, controlling finger joint flexion. At the wrist, it enters Guyon’s canal, bordered by ligaments and bones. Guyon’s canal is divided into three zones, each affecting motor or sensory functions. The ulnar nerve is vital for hand muscle control and sensory feedback from specific hand areas to the central nervous system.
What Are the Causes of Ulnar Nerve Entrapment?
Ulnar nerve entrapment commonly occurs at two sites: the cubital tunnel and Guyon’s canal (ulnar tunnel). In the cubital tunnel, compression can result from factors such as Osborne’s ligament, leading to forearm and hand compressive neuropathy.
Within Guyon’s canal, the location of compression dictates the symptoms.
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Zone 1 compression at the canal’s proximal end leads to a mixed motor and sensory deficit, often caused by ganglia or hook of the hamate fractures.
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Zone 2 compression, occurring after the nerve’s bifurcation and surrounding the deep motor branch, causes an isolated motor deficit.
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Zone 3 compression surrounding the superficial sensory branch results in an isolated deficit, commonly due to issues like ulnar artery thrombosis or aneurysms.
Ulnar nerve entrapment at the elbow is the second most common upper extremity neuropathy. At the elbow, the ulnar nerve lacks protective covering in the ulnar groove, making it susceptible to external compression. Factors like repetitive elbow movement, arthritis, valgus deformities, and nerve subluxation during flexion can increase the risk of injury.
In some cases, pressure on the ulnar nerve may exceed 200 mm Hg during elbow flexion. Repetitive movements that stress the ulnar wrist and hypothenar eminence can also predispose the ulnar nerve to neuropathy. Additionally, wrist fractures and mass lesions can lead to ulnar neuropathy at the wrist.
What Are the Risk Factors of Ulnar Nerve Entrapment?
The risk factors for ulnar nerve entrapment are:
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Shallow positioning of the nerve.
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An extended course of the nerve or a location prone to trauma.
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Nerve pathways pass through notches or openings.
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Intrinsic factors like smoking, education, and work experiences.
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Occupational factors involve repetitive tasks, significant force, mechanical stress, and exposure to vibration and temperature.
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Sustained elbow or wrist flexion.
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Pressure on the nerve during elbow flexion against a surface.
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Work-related musculoskeletal disorders like medial epicondylitis, carpal tunnel syndrome, and radial tunnel syndrome.
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Activities that exert prolonged pressure on the hypothenar compartment of the hand, such as cycling.
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Significant joint deformities (varus or valgus).
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Medial collateral ligament deficiency.
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Repeated subluxation of the nerve.
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Trauma to the elbow or areas near Guyon’s canal.
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Iatrogenic causes during ligamentous reconstruction surgery.
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Prolonged pressure on the ulnar nerve in anesthetized patients due to the postoperative elbow flexion position.
What Are the Symptoms of Ulnar Nerve Entrapment?
The symptoms include:
Ulnar Neuropathy at the Elbow:
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Gradual onset of symptoms, unless associated with trauma.
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Numbness and paresthesia in the ulnar aspect of the hand, fifth digit, and medial half of the fourth digit.
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Worsens with elbow flexion, particularly at night.
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Pain is not a prominent feature, but some may experience forearm flexor pain.
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Progressive symptoms may lead to muscle weakness, loss of skill, and claw hand.
Ulnar Neuropathy at the Wrist:
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Symptoms can range from pure sensory to motor deficits.
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Types I, II, and III distinguish ulnar neuropathy at the wrist.
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Type I involves mixed motor and sensory deficits.
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Type II results in a pure motor deficit.
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Type III causes sensory deficits in specific hand areas.
How to Diagnose Ulnar Nerve Entrapment?
The diagnosis of ulnar neuropathy typically relies on the patient’s clinical history, physical examination, electrodiagnostic tests such as electromyography (EMG), and Nerve Conduction Velocity (NCV). Combining EMG and NCV tests can improve diagnostic accuracy by identifying the specific location of pathological ulnar nerve compression.
Ultrasound is recommended for screening and follow-up imaging in cases of ulnar neuropathy at the elbow. It is effective in detecting morphological changes and assessing the extent of ulnar nerve lesions. MRI (Magnetic Resonance Imaging) scan can measure the cross-sectional areas of the ulnar nerve, taken one centimeter proximal to the medial epicondyle. It can differentiate between patients with and without ulnar neuropathy using a defined threshold of 11.0 mm.
The ulnar nerve-swelling ratio and other sonographic indicators, such as intra-neural vascularity, increased flattening ratio, and an enlarged intra-neural hypoechoic fraction, have been proposed as supplementary tools for diagnosing ulnar neuropathy at the elbow.
What Is the Treatment of Ulnar Nerve Entrapment?
There are two main conservative treatments for ulnar neuropathy:
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Reducing External Compression and Elbow Flexion: This approach aims to decrease stress on the ulnar nerve. It involves using elbow splints, pads, sleeves, and physical therapy to limit external compression and maintain the elbow joint flexibly. Conservative treatment is suitable for patients with mild to moderate symptoms.
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Injection Procedure: Injection procedures, such as corticosteroid injections guided by ultrasound, have been suggested for treatment.
For patients with persistent symptoms, sensory changes, and muscle atrophy, surgical treatment becomes a consideration. Various surgical methods are available, including decompression, anterior transposition techniques, and medical epicondylectomy. A systematic review found that both simple decompression and decompression with transposition are equally effective in idiopathic ulnar neuropathy at the elbow.
Conclusion:
Ulnar nerve entrapment is a common condition that can lead to discomfort, weakness, and loss of function in the arm and hand. It typically occurs at the elbow or wrist, with various causes and risk factors. Diagnosing ulnar neuropathy relies on clinical evaluation and diagnostic tests. It has a spectrum of treatment approaches, from conservative methods to surgical interventions for cases that do not respond to non-operative approaches. Timely diagnosis and effective management are crucial for achieving the best outcomes for individuals with ulnar nerve entrapment.
