What Is Entrapment Neuropathy?
Entrapment neuropathy is a condition in which a nerve becomes compressed, or entrapped, between two other structures in the body. Usually, the nerve is compressed between a ligament and a bone.
Repetitive motion can cause the ligament and bone to press or rub against the nerve. Over time, this damages the myelin sheath, which is a layer of tissue that covers the outside of the nerve. The myelin sheath helps the nerve transmit electrical signals, so when it is damaged, the nerve can’t function as well. The nerve’s reduced ability to transmit signals causes symptoms of numbness, tingling, burning, or weakness in the fingers or other extremities.
Although usually not serious, entrapment neuropathy can be painful and can seriously affect function if not treated.
Types of Entrapment Neuropathy
Entrapment neuropathy can be acute or chronic.
Acute entrapment neuropathy is usually caused by an injury, such as a sprain or a fracture, that moves bones or ligaments and causes them to compress the nerve.
Chronic entrapment neuropathy is usually caused by repetitive motion that affects an area where a nerve travels through a narrow space. These types are named for the area they impact.
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Carpal Tunnel Syndrome
Carpal tunnel syndrome is the most common type of entrapment neuropathy. It involves compression of the median nerve, which runs through the arm and controls movement in the thumb and first three fingers (all but the pinky). The nerve is compressed inside a passage called the carpal tunnel, which runs between the carpal bones (the bones in the back of your hand) and the transverse carpal ligament (which connects those bones). In carpal tunnel syndrome, a tendon or muscle inside the carpal tunnel becomes inflamed by repetitive use. Because the ligament and bones cannot move or expand, the inflammation puts pressure on the median nerve. -
Cubital Tunnel Syndrome
Cubital tunnel syndrome occurs when the ulnar nerve is compressed in the cubital tunnel, which is under a bone in the elbow. The ulnar nerve controls feeling in the pinky finger and part of the ring finger. In the elbow, the ulnar nerve runs close to the skin surface, so bumping the elbow can cause tingling in those fingers (this is often referred to as the “funny bone”). The ulnar nerve can be compressed when the elbow is bent, so repetitive bending of the elbow, or frequently leaning on the elbows, can cause inflammation and entrapment of this nerve. -
Sciatic Compression
Sciatic compression, or sciatica, is the most common type of entrapment neuropathy in the back or legs. The sciatic nerve runs from the lower back down the back of the legs, ending at the knee. The most common cause of sciatica is a herniated disc. Discs lie between each vertebra in the back to cushion the spine, and pressure on the spine can cause a bulge, or herniation, in one area of the disc wall. This hernia can push against the sciatic nerve, causing compression. Sciatic compression causes tingling, pain, and numbness in the lower back, legs, or feet. -
Peroneal Nerve Entrapment
The peroneal nerve in the knee, which branches off of the sciatic nerve, controls movement and feeling in the front of the lower legs and the top of the feet. Compression of this nerve can cause foot drop, which is an inability to raise the foot up at the ankle.
Other less common types of entrapment neuropathy include suprascapular nerve entrapment, which affects the nerve that controls the shoulder; meralgia paresthetica, which involves the nerve that supply the skin over the outer and the upper leg; and radial nerve entrapment, which affects the back of the forearm and hand.
What Causes Entrapment Neuropathy?
Entrapment neuropathy is usually caused by repetitive motion in a joint, leading to inflammation that compresses a nerve. However, it can also be a symptom of other conditions:
- A traumatic injury can cause swelling or shift bones and ligaments, compressing a nerve.
- Tumors or cysts can press against a nerve.
- Pregnancy hormones cause ligaments to loosen and stretch, which can result in nerve compression.
- Rheumatoid arthritis causes inflammation in the joints, which can lead to nerve entrapment.
A full assessment is necessary to determine whether symptoms of entrapment neuropathy are caused by a more serious condition.
Entrapment Neuropathy Diagnosis
Diagnosis of entrapment neuropathy begins with a physical examination of symptoms. There are specific physical tests that can support a diagnosis of nerve entrapment in particular areas of the body. For example:
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Phalen’s Test
A positive Phalen’s test indicates carpal tunnel syndrome. For this test, you’ll raise your arms so your elbows are bent straight out, and press the backs of your hands against each other so your wrists are bent down at a 90-degree angle. After holding this position for 60 seconds, tingling in your fingers indicates carpal tunnel syndrome. -
Tinel Test
A Tinel test involves the doctor tapping lightly on the front of the wrist or the elbow. This will cause tingling if the nerve is irritated. A positive Tinel’s sign could indicate carpal tunnel syndrome or cubital tunnel syndrome. -
Neurological Exam
Neurological tests can include testing the ability to:- Feel light touch, such as a cotton swab
- Feel sharp touch, such as a toothpick
- Distinguish between cold and heat in the affected area
- Imaging
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Electromyogram or Nerve Conduction Study
Both of these tests use electrical stimuli to determine how well your nerves can conduct signals and how effectively your muscles respond to those signals. These tests can help pinpoint the location of the nerve compression, and they can indicate the extent of any damage.
Entrapment Neuropathy Treatment
The nerves in the arms and legs can recover from damage over time, so most of the time, people with entrapment neuropathy can experience a full recovery.
The first line of treatment is to stop the mechanical injury to prevent further damage. This could mean using a brace or other tools to prevent the movement causing the damage. It could also mean changing the way one does activities to avoid damaging movement in the future. For example, using an ergonomic keyboard and changing the way a desk is set up can improve carpal tunnel syndrome that is caused by repetitive typing.
If these changes aren’t effective, surgery may be needed.
Entrapment neuropathy surgery involves cutting the ligament that is compressing the nerve to widen the area where the nerve passes. The ligament is still able to function since it remains attached to the bone. This surgery is very effective, and most people regain full function with no further pain.
