How common is back pain?
By the faculty of Harvard Medical School for The Harvard Medical School Adviser

Q: How can I tell whether my low-back pain is just a strain or something more serious?

A: Back pain is very common but rarely serious. About 75 percent of adults say they've suffered through at least one bout of moderate to severe low-back pain (see illustration). But nine times out of 10, low-back pain results from mechanical problems that don't need special tests or sophisticated treatment.

Ordinary back pain will resolve as quickly (or as slowly) without medical attention as with a doctor's care. In most cases, you can take care of your back yourself. The trick is to know what to do and to recognize symptoms that really do call for prompt medical tests and treatments.

Back pain can start gradually, with a nagging ache that builds slowly. Or it can hit abruptly with quite a bang. Some people can point to a single event that sets it off, such as lifting a heavy object or making a sudden movement. Often, it's much less dramatic -- a simple sneeze or bending to tie a shoe can set off a bout of back pain. But in many cases, the pain begins without rhyme or reason.

Most of the time, there's no specific mechanical cause. Doctors often blame muscle inflammation and spasms, strains or sprains, pinched nerves, bulging discs and poor posture. It's likely that ordinary acute low-back pain is caused by a combination of these factors -- by a cycle of pain, muscle spasm, inflammation and nerve irritation. About 70 percent of cases fall into this nonspecific category.

But some people have specific problems that can be identified. About 10 percent of cases are cause by degenerated discs and arthritis of the joints between the vertebrae. Most common in older people, these problems typically cause persistent, nagging, mild to moderate pain. In about 4 percent, a "slipped" disc causes relatively severe pain in the back or pain that radiates into the buttocks or down a leg, known as sciatica.

Spinal stenosis, a problem that usually affects only the elderly, occurs when the bony spurs of arthritis narrow the spinal canal enough to put pressure on the nerves. It can cause back, buttock and leg pain, which often flares with walking but not with biking or other activities that flex the spine. It accounts for about 3 percent of all low-back pain.

Compression fractures of the vertebrae are slightly more common, accounting for about 4 percent of back problems. These fractures, which cause abrupt, severe pain, occur most often in older women who have thin, weakened bones (osteoporosis).

Other less common causes include infections, tumors and disorders of the abdomen, rectum, pelvis or prostate that refer pain to the back. You don't have to know them all, but you should know the "red flags" that suggest serious problems needing prompt medical attention. They include:

-- First episode before age 20 or after age 55

-- Recent major trauma, including motor-vehicle accidents, falls and severe sports injuries

-- Radiation of pain down a leg, particularly if accompanied by:

-- Numbness or loss of sensation

-- Weakness or loss of muscular strength

-- Impaired bowel or bladder control

-- Pain that is constant and not affected by motion

-- Pain in the upper back or chest

-- Pain that increases at night or when lying down

-- Unexplained weight loss of 10 pounds or more

-- Unexplained fever

-- A previous diagnosis of cancer

-- Use of corticosteroids or other immunosuppressive drugs

-- History of drug abuse

-- History of a major chronic medical illness

Every back patient should know about these warning signs. But few people will experience any of them. And the things that worry patients most are not on the list of things that worry doctors. The severity of pain is not related to the seriousness of the problem. Patients with terrible pain are no more likely to have complications than those with mild to moderate pain. Similarly, the inability to straighten up and stand or walk normally is not a cause for alarm. Of course, it certainly causes major distress. If you have any of the above warning signs, see your doctor. You may need X-rays and a few simple lab tests.

If you don't have any red flags, chances are you'll get better without any special therapy. But it takes time to recover. About 30 percent of patients are much better in just a week, but another 60 percent take up to eight weeks to get better. And about 40 percent will have another bout of pain within six months of the first. It doesn't mean they have "bad backs" that will plague them for life, but it does mean they need good, commonsense back care. Watch for those recommendations in a future column.

Copyright 2006 the President and Fellows of Harvard College. Developed by Harvard Health Publications (www.health.harvard.edu). Distributed by UFS. Submit questions to harvard_