Atlas of pathophysiology, 2 Edition

Part II - Disorders

Neurologic disorders

Herniated intervertebral disk

A herniated disk, also called a ruptured or slipped disk or a herniated nucleus pulposus, occurs when all or part of the nucleus pulposus—the soft, gelatinous, central portion of an intervertebral disk—protrudes through the disk's weakened or torn outer ring (anulus fibrosus).

Herniated disks usually occur in adults (mostly men) older than age 45. About 90% of herniated disks are lumbar or lumbosacral; 8%, cervical; and 1% to 2%, thoracic. Patients with a congenitally small lumbar spinal canal or with osteophyte formation along the vertebrae may be more susceptible to nerve root compression and more likely to have neurologic symptoms.

Age Alert

A herniated disk occurs more frequently in middle-age and older men.

Causes

·         Severe trauma or strain

·         Intervertebral joint degeneration

Age Alert

In older patients whose vertebral disks have begun to degenerate, even minor trauma may cause herniation.

Pathophysiology

An intervertebral disk has two parts: the soft center called the nucleus pulposus and the tough, fibrous surrounding ring called the anulus fibrosus. The nucleus pulposus acts as a shock absorber, distributing the mechanical stress applied to the spine when the body moves.

Physical stress, usually a twisting motion, can tear or rupture the anulus fibrosus so that the nucleus pulposus herniates into the spinal canal. The vertebrae move closer together and in turn exert pressure on the nerve roots as they exit between the vertebrae.

Herniation occurs in three steps:

·         protrusion—the nucleus pulposus presses against the anulus fibrosus

·         extrusion—the nucleus pulposus bulges forcibly though the anulus fibrosus, pushing against the nerve root

·         sequestration—the anulus gives way as the disk's core bursts and presses against the nerve root.

Signs and symptoms

·         Severe lower back pain to the buttocks, legs, and feet; usually unilaterally

·         Sudden pain after trauma, subsiding in a few days, and then recurring at shorter intervals and with progressive intensity

·         Sciatic pain following trauma, beginning as a dull pain in the buttocks (Valsalva's maneuver, coughing, sneezing, and bending intensify the pain, which is commonly accompanied by muscle spasms)

·         Sensory and motor loss in the area innervated by the compressed spinal nerve root and, in later stages, weakness and atrophy of leg muscles

Diagnostic test results

·         Straight-leg raising test is positive only if the patient has posterior leg (sciatic) pain, not back pain.

·         Lasgue's test reveals resistance and pain as well as loss of ankle or knee-jerk reflex, indicating spinal root compression.

·         Myelogram, computed tomography scan, and magnetic resonance imaging show spinal canal compression as evidenced by herniated disk material.

Treatment

·         Heat applications

·         Exercise program

·         Nonsteroidal anti-inflammatory drugs such as aspirin; rarely, corticosteroids such as dexamethasone; muscle relaxants, such as diazepam, methocarbamol, or cyclobenzaprine

·         Surgery, including laminectomy to remove the protruding disk, spinal fusion to overcome segmental instability, or both to stabilize the spine

P.141

HERNIATION AND PAIN IN DISK INJURY

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