Pathophysiology of nerve entrapment

Overview

Cross section of normal and atrophied nerve

The pathophysiology of nerve entrapment involves the compression or irritation of a peripheral nerve as it travels through a narrow anatomical passageway. This condition can lead to a variety of symptoms, including pain, numbness, and muscle weakness. Nerve entrapment syndromes are common and can affect any peripheral nerve, but some of the most frequently involved nerves include the median nerve, ulnar nerve, and sciatic nerve.

Anatomy and Physiology of Nerves

Structure of a neuron

Peripheral nerves are composed of bundles of axons that are surrounded by connective tissue layers. These layers include the endoneurium, perineurium, and epineurium. The axons are the long, slender projections of neurons that transmit electrical impulses. The health and function of these nerves depend on adequate blood supply and the absence of mechanical compression.

Mechanisms of Nerve Entrapment

Nerve entrapment occurs when a nerve is compressed or irritated, often within a confined anatomical space. This can be due to:

• **Anatomical variations**: Some individuals have anatomical structures that predispose them to nerve compression.
• **Repetitive movements**: Activities that involve repetitive motion can lead to inflammation and swelling, compressing the nerve.
• **Trauma**: Direct injury to a nerve or surrounding tissue can cause entrapment.
• **Systemic conditions**: Conditions such as diabetes mellitus can predispose individuals to nerve entrapment due to metabolic changes.

Common Nerve Entrapment Syndromes

Carpal Tunnel Syndrome

Carpal Tunnel Syndrome

Carpal Tunnel Syndrome is one of the most common nerve entrapment syndromes, involving compression of the median nerve as it passes through the carpal tunnel in the wrist. Symptoms include numbness, tingling, and weakness in the hand, particularly affecting the thumb, index, and middle fingers.

Ulnar Nerve Entrapment

Ulnar nerve entrapment often occurs at the elbow, known as cubital tunnel syndrome, or at the wrist, known as Guyon's canal syndrome. Symptoms include numbness and tingling in the ring and little fingers, and weakness in the hand.

Sciatic Nerve Entrapment

Fibrovascular entrapment of the sciatic nerve

Sciatic nerve entrapment can occur due to compression by the piriformis muscle, known as piriformis syndrome, or due to herniated discs in the lumbar spine. Symptoms include pain radiating from the lower back down the leg, known as sciatica.

Pathophysiological Changes

Entrapment of a nerve leads to several pathophysiological changes:

• **Ischemia**: Compression can reduce blood flow to the nerve, leading to ischemia and subsequent nerve damage.
• **Demyelination**: Prolonged compression can cause the myelin sheath surrounding the nerve fibers to degenerate, impairing nerve conduction.
• **Axonal degeneration**: Severe or chronic compression can lead to degeneration of the axons themselves, resulting in permanent nerve damage.

Diagnosis and Management

Diagnosis of nerve entrapment is based on clinical examination, patient history, and diagnostic tests such as nerve conduction studies and electromyography. Management may include:

• **Conservative treatment**: Rest, splinting, and anti-inflammatory medications.
• **Physical therapy**: Exercises to improve range of motion and strengthen surrounding muscles.
• **Surgical intervention**: Decompression surgery may be necessary in severe cases.

Related Pages

• Peripheral neuropathy
• Nerve injury
• Neuroanatomy