Ulnar nerve entrapment

Ulnar nerve entrapment is a condition where the ulnar nerve becomes trapped or pinched due to some physiological abnormalities.

Anatomy of Ulnar Nerve

Classification

Ulnar nerve entrapment is classified by location of entrapment. The ulnar nerve passes through several small spaces as it courses through the medial side of the upper extremity, and at these points the nerve is vulnerable to compression or entrapment—a so-called "pinched nerve". The nerve is particularly vulnerable to injury when there has been a disruption in the normal anatomy. The most common site of ulnar nerve entrapment is at the elbow, followed by the wrist.^[1]

Causes or structures which have been reported to cause ulnar nerve entrapment include:^[2]

• Problems originating at the neck: thoracic outlet syndrome, cervical spine pathology, compression by anterior scalene muscles
• Problems originating in the chest: compression by pectoralis minor muscles
• Brachial plexus abnormalities
• Elbow pathology: fractures, growth plate injuries, cubital tunnel syndrome, flexorpronator aponeurosis, arcade of Struthers^[3]
• Forearm pathology: tight flexor carpi ulnaris muscles^[4]
• Wrist pathology: fractures, ulnar tunnel syndrome, hypothenar hammer syndrome
• Artery aneurysms or thrombosis
• Other: Infections, tumors, diabetes, hypothyroidism, rheumatism, and alcoholism

Cubital tunnel syndrome

Ulnar nerve impingement along the cubital tunnel, at the medial edge of the elbow, is known as cubital tunnel syndrome. It is the most common site of ulnar nerve impingement in the elbow.^[5] The tunnel is formed by the medial epicondyle of the humerus, the olecranon process of the ulna and the tendinous arch joining the humeral and ulnar heads of the flexor carpi ulnaris muscle.^[6] While most cases of injury are minor and resolve spontaneously with time, chronic compression or repetitive trauma may cause more persistent problems. Commonly cited scenarios include:

• Sleeping with the arm folded behind neck, elbows bent.
• Pressing the elbows upon the arms of a chair while typing.
• Resting or bracing the elbow on the arm rest of a vehicle.
• Bench pressing.
• Intense exercising and strain involving the elbow.

Guyon's canal syndrome

Ulnar nerve impingement along an anatomical space in the wrist called Guyon's canal is known as Guyon's canal syndrome, or ulnar tunnel syndrome.^[7] Recognized causes of ulnar nerve impingement at this location include local trauma, fractures, ganglion cysts,^[8] and classically avid cyclists who experience repetitive trauma against bicycle handlebars.^[9] This form of ulnar neuropathy comprises two work-related syndromes: so-called "hypothenar hammer syndrome," seen in workers who repetitively use a hammer, and "occupational neuritis" due to hard, repetitive compression against a desk surface.^[8]

Signs and symptoms

In general, ulnar neuropathy will result in symptoms affecting the fourth and fifth — the ring and little — fingers, as well as various intrinsic muscles of the hand. The proximal aspect of the nerve consists of mixed sensory and motor innervation; more distally, the ulnar nerve separates into distinct motor and sensory branches in the hand. Thus, symptoms of ulnar neuropathy may be either motor, sensory, or both depending on the location of nerve injury. Motor symptoms consistent of weakness of the muscles normally controlled by ulnar nerve. Sensory symptoms or paresthesias consist of numbness or tingling in the areas of the hand that receive sensory input from the ulnar nerve.

Compression at the elbow (e.g. cubital tunnel syndrome) causes numbness in the fifth (pinky) finger, along the half (lengthwise) of the fourth (ring) finger closest to the fifth finger, and the back half of the hand over the fifth finger. Initially, the numbness is transient and primarily occurs in the middle of the night or in the morning. The sensation is similar to hitting one's "funny bone," but lasts a bit longer. Over time, the numbness is there all of the time, and weakness of the hand sets in. The "ulnar claw," or a position where the small and ring fingers curl up, occurs late in the disease and is a sign the nerve is severely affected.

The claw hand is worse for Guyon canal stenosis, or nerve compression at the wrist. This is an example of the ulnar paradox. Also, if the nerve is compressed at the wrist, the back of the hand will have normal sensation.

Diagnosis

The distinct innervation of the hand usually enables diagnosis of an ulnar nerve impingement by symptoms alone. Ulnar nerve damage that causes paralysis to these muscles will result in a characteristic ulnar claw position of the hand at rest. Clinical tests such as the card test for Froment's sign, can be easily performed for assessment of ulnar nerve. However, a complete diagnosis should identify the source of the impingement, and radiographic imaging may be necessary to determine or rule-out an underlying cause.

Imaging studies, such as ultrasound or MRI, may reveal anatomic abnormalities or masses responsible for the impingement. Additionally, imaging may show secondary signs of nerve damage that further confirm the diagnosis of impingement. Signs of nerve damage include flattening of the nerve, swelling of the nerve proximal to site of injury, abnormal appearance of nerve, or characteristic changes to the muscles innervated by the nerve.^[10]

Differential diagnoses

Symptoms of ulnar neuropathy or neuritis do not necessarily indicate an actual physical impingement of the nerve; indeed, any injury to the ulnar nerve may result in identical symptoms. In addition, other functional disturbances may result in irritation to the nerve and are not true "impingement". For example, anterior dislocation and "snapping" of ulnar nerve across the medial epicondyle of the elbow joint can result in ulnar neuropathy.^[11]

Entrapment of other major sensory nerves of the upper extremities result in deficits in other patterns of distribution. Entrapment of the median nerve causes carpal tunnel syndrome, which is characterized by numbness in the thumb, index, middle, and half of the ring finger. Compression of the radial nerve causes numbness of the back of the hand and thumb, and is much more rare.

A simple way of differentiating between significant median and ulnar nerve injury is by testing for weakness in flexing and extending certain fingers of the hand. Median nerve injuries are associated with difficulty flexing the index and middle finger when attempting to make a fist. However, with an ulnar nerve lesion, the pinky and ring finger cannot be unflexed when attempting to extend the fingers.

Some people are affected by multiple nerve compressions, which can complicate diagnosis.^[5]

Prevention

Cubital tunnel syndrome may be prevented or reduced by maintaining good posture and proper use of the elbow and arms, such as wearing an arm splint while sleeping to maintain the arm is in a straight position instead of keeping the elbow tightly bent.^[5][12] A recent example of this is popularization of the concept of cell phone elbow.^[12]

Treatment

While pain symptoms may be effectively controlled using medications such as NSAID, amitriptyline, or vitamin B6 supplementation, effective treatment generally requires resolving the underlying cause.

Mild to moderate symptoms, such as pain or paresthesia, are treated conservatively with non-surgical approaches. Physiotherapy treatments can prove effective at treating cubital tunnel syndrome symptoms and can include:

• Joint mobilizations
• Neural flossing/gliding
• Strengthening/stretching exercises
• Activity modification^[13]

It is important to identify positions and activities that aggravate symptoms and to find ways to avoid them.^[5] For example, if the person experiences symptoms when holding a telephone up to the head, then the use of a telephone headset will provide immediate symptomatic relief and reduce the likelihood of further damage and inflammation to the nerve. For cubital tunnel syndrome, it is recommended to avoid repetitive elbow flexion and also avoiding prolonged elbow flexion during sleep, as this position puts stress of the ulnar nerve.^[14]

Surgery is recommended for those who are not improved with conservative therapy or those with serious or progressive symptoms. The surgical approaches vary, and may depend on the location or cause of impingement. Cubital and ulnar tunnel release can be performed wide awake with no general anaesthesia, no regional anaesthesia, no sedation and no tourniquet.^[15]

Epidemiology

People with diabetes mellitus are at higher risk for any kind of peripheral neuropathy, including ulnar nerve entrapments.^[5]

Cubital tunnel syndrome is more common in people who spend long periods of time with their elbows bent, such as when holding a telephone to the head.^[5] Flexing the elbow while the arm is pressed against a hard surface, such as leaning against the edge of a table, is a significant risk factor.^[5] The use of vibrating tools at work or other causes of repetitive activities increase the risk, including throwing a baseball.^[5]

Damage to or deformity of the elbow joint increases the risk of cubital tunnel syndrome.^[5] Additionally, people who have other nerve entrapments elsewhere in the arm and shoulder are at higher risk for ulnar nerve entrapment. There is some evidence that soft tissue compression of the nerve pathway in the shoulder by a bra strap over many years can cause symptoms of ulnar neuropathy, especially in very large-breasted women.^[5]

Prognosis

Most patients diagnosed with cubital tunnel syndrome have advanced disease (atrophy, static numbness, weakness) that might reflect permanent nerve damage that will not recover after surgery.^[16] When diagnosed prior to atrophy, weakness or static numbness, the disease can be arrested with treatment. Mild and intermittent symptoms often resolve spontaneously.^[5]

References

External links

• AAOS:Ulnar Nerve Entrapment at the Elbow
• Worldwide Awake Hand Surgery Nonprofit Group: helping surgeons transition to wide awake ulnar nerve surgery