Also called a ruptured or slipped disk or a herniated nucleus pulposus, a herniated disk occurs when all or part of the nucleus pulposus—the soft, gelatinous, central portion of an intervertebral disk—is forced through the disk’s weakened or torn outer ring (anulus fibrosus).
When this happens, the extruded disk may impinge on spinal nerve roots as they exit from the spinal canal or on the spinal cord itself, resulting in back pain and other signs of nerve root irritation. Herniated disks usually occur in adults (mostly men) under age 45.
Herniated disks may result from severe trauma or strain or may be related to intervertebral joint degeneration. In older patients, whose disks have begun to degenerate, minor trauma may cause herniation. About 90% of herniated disks occur in the lumbar and lumbosacral regions, 8% occur in the cervical area, and 1% to 2% occur in the thoracic area.
Patients with a congenitally small lumbar spinal canal or with osteophyte formation along the vertebrae may be more susceptible to nerve root compression with a herniated disk and more likely to have neurologic symptoms.
Signs and symptoms
The overriding symptom of lumbar herniated disk is severe lower back pain that radiates to the buttocks, legs, and feet, usually unilaterally. When herniation follows trauma, the pain may begin suddenly, subside in a few days, and then recur at shorter intervals and with progressive intensity.
Sciatic pain follows, 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. A herniated disk may also cause sensory and motor loss in the area innervated by the compressed spinal nerve root and, in later stages, weakness and atrophy of leg muscles.
Obtaining a careful patient history is vital because the mechanisms that intensify disk pain are diagnostically significant. The following test results support the diagnosis:
The straight-leg-raising test and its variants are perhaps the best tests for diagnosing a herniated disk. For this test, the patient lies in a supine position while the examiner places one hand on the patient’s ilium, to stabilize the pelvis, and the other hand under the ankle and then slowly raises the patient’s leg. The test is positive only if the patient complains of posterior leg (sciatic) pain, not back pain.
In Lasegue’s test, the patient lies flat while the thigh and knee are flexed to a 90-degree angle. Resistance and pain as well as loss of ankle or knee-jerk reflex indicate spinal root compression.
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