Pinched Compression Nerve Syndromes - Why Does Your Back Hurt: Back Pain

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Pinched (compression) nerve syndromes

The next most common category of low back pain consists of conditions involving compressed nerves. Two major examples are disk problems, such as a herniated disk, and spinal stenosis, which occurs when a narrowing of the spinal column puts pressure on nerves in the spine.

Disk abnormalities

Disk abnormalities are more common among people in their middle years or older. As a disk degenerates over time, its gelatinous center tends to dry out. The layers of the outer shell — the annulus — that binds to the adjacent vertebrae often start to tear, thin, and weaken, especially in the parts of the disk closest to the nerve roots. A disk with these changes tends to bulge, looking like an underinflated tire.

Herniation occurs when the inner core of the disk bulges out of the annulus. People commonly refer to a herniated disk as a "slipped disk" or a "ruptured disk." The protruding disk may press on a nearby nerve root. This kind of pressure usually causes inflammation and back pain, often accompanied by sciatica, which is a sharp pain that runs along the path of the sciatic nerve, which passes through the buttock, down the back of the leg, and into the foot. Sciatic pain is often accompanied by a sensation of pins and needles in the affected leg, especially in the foot and toes, and it often causes people with this condition to limit their trunk movements.

The symptoms are worsened by moving, assuming certain positions, coughing or sneezing, or doing anything that pulls on the sciatic nerve, such as bending forward from your waist or flexing your hips while keeping your knees straight. If the pain is constant, it will be difficult to find a comfortable position; if it is occasional, sharp, and shooting, it will feel like an electric shock.

Your symptoms and your doctor's confirming findings during an exam — leg weakness, diminished ankle and knee reflexes, sensory changes, and localized pain — usually help locate where the disk problem lies. Magnetic resonance imaging (MRI) is often used to detect herniated disks. A cautionary note: Although an MRI may reveal a disk problem, don't assume that disk is the cause of your pain. Many people walk about with imperfect disks and have no symptoms. For people who do experience pain and other symptoms, it isn't always obvious which disk is causing the problems.

If the acute sciatic pain persists without any improvement for more than one month, in spite of treatment, further evaluation — and a different treatment approach — are probably necessary.

Spinal stenosis

Spinal stenosis — a narrowing of the spinal canal — most commonly affects people over age 50, since degenerative changes are often the root of the problem. Some people naturally have smaller spinal canals and are thus more prone to such difficulties.

Many different factors can cause the spinal canal to become constricted. For example, disks may degenerate and bulge. Ligaments may thicken. Or small bony growths, known as bone spurs or osteophytes, may develop and protrude into the spinal canal. Other possible causes include displacement of a ligament, thickening of a vertebra's bony plate (the lamina), or Paget's disease.

Lumbar spinal stenosis causes low back pain and usually sciatica when you stand up straight, bend backward, or walk even short distances — as little as 50–100 yards. It's common for people with stenosis to be more comfortable when leaning forward (for example, when pushing a grocery cart).

Your doctor is usually able to diagnose stenosis based on your symptoms, medical history, and physical exam. He or she may also use x-rays, an MRI scan, or a computed tomography (CT) scan to help assess your condition.

Last updated:	January 23, 2007