Ulnar nerve entrapment
|Ulnar nerve entrapment|
|Classification and external resources|
On its course down the medial upper extremity, the ulnar nerve passes through several small tunnels and outlets. These regions of the nerve are vulnerable to compression or entrapment (a "pinched nerve") when there is a disruption in the normal anatomy. Thus, ulnar entrapments can be classified by location. The most common site of ulnar nerve entrapment is at the elbow, followed by the wrist. A full list of causes includes:
- Problems originating at the neck (thoracic outlet syndrome, disease of the cervical spine, tight anterior scalene muscles)
- Problems originating in the chest (tight pectoralis minor muscles)
- Brachial plexus abnormalities
- Elbow abnormalities (fractures, growth plate injuries, cubital tunnel problems, flexorpronator aponeurosis issues, arcade of Struthers)
- Forearm abnormalities (tight flexor carpi ulnaris muscles)
- Wrist abnormalities (fractures, Guyon canal problems)
- Artery aneurysms or thrombosis
- Infections, tumors, diabetes, hypothyroidism, rheumatism, and alcoholism
Guyon's canal syndrome
Guyon's canal syndrome, sometimes called Guyon's tunnel syndrome, is a common nerve compression affecting the ulnar nerve as it passes through a tunnel in the wrist called Guyon's canal. This problem is similar to carpal tunnel syndrome but involves a completely different nerve. Symptoms include a feeling of pins and needles in the ring and little fingers, and may progress to a burning pain in the wrist and hand followed by decreased sensation in the ring and little fingers. One common cause of this syndrome is from pressure of bicycle handlebars seen with avid cyclists. Another is from hard, repetitive compression against a desk surface while using a computer mouse.
Cubital tunnel syndrome
Cubital tunnel syndrome occurs when the ulnar nerve is obstructed during its path along the cubital tunnel, at the inner edge of the elbow. The cubital tunnel is a channel which allows the ullnar nerve to travel over the elbow. It is bordered 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.Compression of the nerve here, often leads to a tingling or 'pins and needles' sensation in the little and ring fingers. Most cases will be minor and tend to come and go with time. Common causes are sleeping with the arm folded up, so the hand is at the person's neck and the elbow is sharply bent. On waking there is frequently experienced a tingling in the fingers, because the nerve has been pinched or squeezed while asleep. Treatment of these types of causes are straightforward and can involve simply altering sleeping positions to avoid aggravating the elbow area. In more extreme cases however where tingling is persistent, surgery is an option to remove the arm from the elbow down to prevent permanent damage to the nervous system resulting in paralysis and death.
Although the nerve can be entrapped in several places near the elbow, the cubital tunnel is the most common.
Entrapment of the ulnar nerve is most likely caused by extended pressure of the elbow on a hard surface repeatedly over a period of time. For example, the resting of the elbows on the arms of a chair while typing at a work station. This condition is also known as driver's elbow, oftentimes caused by resting or bracing the elbow on the arm rest of vehicles over extended periods of time.
Signs and symptoms
The symptoms of ulnar nerve entrapment depend on where the nerve is being compressed.
Compression at the elbow, known as cubital tunnel syndrome, causes numbness in the small finger (also known as the "pinky"), along the half (lengthwise) of the ring finger closest to the small finger, and the back half of the hand over the small finger. Initially, the numbness is transient and usually 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.
The distinct innervation of the hand allows identifying an impinged nerve straightforward. The ulnar nerve provides sensory and motor innervation to the fourth and fifth—the ring & pinky—fingers. Ulnar neuropathy or damage will result in symptoms of numbness, tingling, or weakness in those fingers. In addition, the ulnar nerve provides motor innervation for various intrinsic muscles of the hand. 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 sign, can be easily performed for assessment of ulnar nerve. However, a complete diagnosis should identify the source of the impingement, and further testing may be necessary to determine which of many possible underlying causes is relevant.
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.
The difference between the ulnar lesion and a median lesion is that in the median nerve lesion the index and middle finger cannot be flexed when the patient is told to make a fist. However, in the ulnar nerve lesion the pinky and ring finger cannot be unflexed if the patient is told to extend fingers.
Some people are affected by multiple nerve compressions, which can complicate diagnosis.
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 in a straight position instead of keeping the elbow tightly bent. A recent example of this is popularization of the concept of cell phone elbow.
Effective treatment generally requires resolving the underlying cause.
Initial conservative therapy includes identifying positions and activities that aggravate symptoms and stopping them. 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.
Physical therapy, occupational therapy, and chiropractic often provide relief. Surgery may be required for some causes, such as ulnar tunnel syndrome, cubital tunnel syndrome thoracic outlet syndrome. Cubital and ulnar tunnel release can be performed wide awake with no general anaesthesia, no regional anaesthesia, no sedation and no tourniquet.
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. 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. The use of vibrating tools at work or other causes of repetitive activities increase the risk, including throwing a baseball.
Damage to or deformity of the elbow joint increases the risk of cubital tunnel syndrome. 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.
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. When diagnosed prior to atrophy, weakness or static numbness, the disease can be arrested with treatment. Mild and intermittent symptoms often resolve spontaneously.
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- AAOS:Ulnar Nerve Entrapment at the Elbow
- Worldwide Awake Hand Surgery Nonprofit Group: helping surgeons transition to wide awake ulnar nerve surgery