Ulnar Nerve Entrapment - An Overview

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?

The ulnar nerve runs around or near the ulna bone (long bone found in the upper forearm). The ulnar nerve is a single nerve network in the peripheral nervous system that carries information from the brain through the spinal cord. The ulnar nerve helps in moving the little and ring fingers and helps in grasping objects. It also transfers sensory information, such as pain, temperature, and touch.

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 Ulnar Nerve Entrapment Types?

The types of ulnar nerve entrapment include the following:

• Guyon’s Canal Syndrome - This type is when the ulnar nerve entrapment occurs in the wrist area.
• Cubital Tunnel Syndrome - This type is when the ulnar nerve is stretched or pulled in the elbow region. It is the second most common type of peripheral neuropathy.

What Causes Ulnar Nerve Entrapment?

Ulnar nerve entrapment can occur due to excess force given on the ulnar nerve. Depending on the type, the causes vary. In cubital tunnel syndrome, the ulnar nerve entrapment occurs in the elbow region. The causes include:

• Elbow Injury - While playing a sport, driving a vehicle, falling on the elbow side, and sleeping with elbows bent.
• Bone and Joint Disease - One of the most common types of bone and joint disease is osteoarthritis. It is a very common type of arthritis that causes the cartilage cushions of the bones to wear down over time.
• Repeated Bending or Leaning - When an individual bend or lean continuously due to old age or day-to-day activities.
• Diabetes - Diabetic patients are more prone to weaker bones which leads to ulnar nerve entrapment.
• Hereditary Neuropathy with Pressure Palsies (HNPP) - It is an inherited condition that causes tingling and numbness in the limbs and muscles. The peripheral nerves are affected.

In Gyon’s canal syndrome, the wrist is affected, and the causes include:

• Laceration - Laceration refers to open cuts or skin wounds. In some lacerations, the soft body tissue is torn, and peripheral nerves are damaged, which leads to ulnar nerve entrapment.
• Ganglion Cyst - It is a noncancerous fluid sac that generally occurs around the wrist. Around 40 percent of the Guyon canal syndrome cases are due to this condition.
• Direct Trauma - Sudden or direct trauma to the wrist due to an accident or lifting heavy weights can affect the ulnar nerve.

What Are the Risk Factors of Ulnar Nerve Entrapment?

The risk factors for ulnar nerve entrapment are:

• Shallow positioning of the nerve.

• An extended course of the nerve or a location prone to trauma.

• Nerve pathways pass through notches or openings.

• Intrinsic factors like smoking, education, and work experiences.

• Occupational factors involve repetitive tasks, significant force, mechanical stress, and exposure to vibration and temperature.

• Sustained elbow or wrist flexion.

• Pressure on the nerve during elbow flexion against a surface.

• Work-related musculoskeletal disorders like medial epicondylitis, carpal tunnel syndrome, and radial tunnel syndrome.

• Activities that exert prolonged pressure on the hypothenar compartment of the hand, such as cycling.

• Significant joint deformities (varus or valgus).

• Medial collateral ligament deficiency.

• Repeated subluxation of the nerve.

• Trauma to the elbow or areas near Guyon’s canal.

• Iatrogenic causes during ligamentous reconstruction surgery.

• 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:

• Gradual onset of symptoms, unless associated with trauma.

• Numbness and paresthesia in the ulnar aspect of the hand, fifth digit, and medial half of the fourth digit.

• Worsens with elbow flexion, particularly at night.

• Pain is not a prominent feature, but some may experience forearm flexor pain.

• Progressive symptoms may lead to muscle weakness, loss of skill, and claw hand.

Ulnar Neuropathy at the Wrist:

• Symptoms can range from pure sensory to motor deficits.

• Types I, II, and III distinguish ulnar neuropathy at the wrist.

• Type I involves mixed motor and sensory deficits.

• Type II results in a pure motor deficit.

• Type III causes sensory deficits in specific hand areas.

How to Diagnose Ulnar Nerve Entrapment?

Some of the diagnostic methods for ulnar nerve entrapment are listed below:

• Physical Examination - Some of the basic physical examinations, such as Froment's test, in which the doctor will ask the patient to hold a piece of paper between the index finger and thumb which will help in observing the flexing at the interphalangeal joint of the thumb if a nerve injury is there. Another test is Tinel’s test, in which the doctor examines the elbow’s funny bone or the ulnar nerve to see an extreme shock-like sensation in the little finger.
• Magnetic Resonance Imaging (MRI) - It is done to see the compressed nerves and other abnormalities like arthritis. A healthcare professional will ask the patient to lie down on the bed of the machine. Once the patient is settled, the expert will operate the machine in a different chamber. The machine will take several scans, which take around half an hour to complete.
• Electromyography (EMG): It is done to see how well the signals from the nerves stimulate the muscles.

What Is the Treatment of Ulnar Nerve Entrapment?

There are two main conservative treatments for ulnar neuropathy:

1. 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.

2. 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.