Herniation describes an abnormality of the intervertebral disc that is also known as a "slipped," "ruptured," or "torn" disc. This process occurs when the inner core (nucleus pulposus) of the intervertebral disc bulges out through the outer layer of ligaments that surround the disc (annulus fibrosis). This tear in the annulus fibrosis causes pain in the back at the point of herniation. If the protruding disc presses on a spinal nerve, the pain may spread to the area of the body that is served by that nerve. Between each vertebra in the spine are a pair of spinal nerves, which branch off from the spinal cord to a specific area in the body. Any part of the skin that can experience hot and cold, pain or touch refers that sensation to the brain through one of these nerves. In turn, pressure on a spinal nerve from a herniated disc will cause pain in the part of the body that is served by that nerve.
Usually a patient's main complaint is a sharp, cutting pain. In some cases there may be a previous history of episodes of localized low back pain, which is present in the back and continues down the leg that is served by the affected nerve. This pain is usually described as a deep and sharp pain, which gets worse as it moves down the affected leg. The onset of pain with a herniated disc may occur out of the blue or it may be announced by a tearing or snapping sensation in the spine that is thought to be the result of a sudden tear of part of the annulus fibrosis.
A patient with a herniated disc will usually complain of low back pain that may or may not radiate into different parts of the body. They will often demonstrate a limitation in range of motion when asked to bend forward or lean backwards, and they may lean to one side as they try to bend forward. Patients will sometimes walk with an "antalgic" or painful gait, flexing the affected leg so as not to put too much weight on the side of the body that hurts. Straight leg raising may be positive indicating tension on the nerve root.
Abnormalities in the strength and sensation of particular parts of the body that are found with a neurological examination performed by a doctor provide the most objective evidence of nerve root compression. There are no laboratory tests that can detect the presence or absence of a herniated disc, but they may be helpful in the diagnosis of unusual causes of nerve root pain and irritation. An EMG or electromyographic test may help to determine which nerve root in particular is being pinched or is not working normally in the situation where several nerve roots may be involved. An MRI is the test of choice for diagnosis of a herniated disc, but a CT scan (CAT scan) may often be helpful because it provides better visualization of the bony anatomy of the spinal column, indicating where the source of pressure on the nerve root is located.
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