Most doctors refer to back pain as acute (generally severe, but short-lived), subacute or chronic (long-lasting or occurring often). Acute back pain usually lasts from one to seven days. Pain may be mild or severe and occasionally may be caused by an accident or injury. About 80 percent of all back pain is acute. Subacute back pain usually lasts from seven days to seven weeks and usually is mild; occasionally it's severe. This pain generally is unrelated to other illnesses you may have. About 10 to 20 percent of all back pain is subacute. Chronic back pain usually lasts more than three months and maybe mild or severe. It may be related to other illnesses you may have or may have no identifiable cause. About five to 10 percent of all back pain is chronic.

Incidence and risk factors

Back pain is one of the most common health problems in the United States, yet its cause is generally unidentified.

It is estimated that 50 to 80 percent of adults have had back pain at some time and that 10 percent of all Americans have back pain in a given year. Back pain can occur at any age in both men and women. However, it may occur slightly more often in women beginning at middle age, probably due to osteoporosis.

The back is held upright by muscles attached to the backbone. Doctors often refer to the backbone as the spine, spinal column, or vertebral column. The backbone isn't one long bone, but actually 24 separate bones called vertebrae. These 24 vertebrae are stacked one on top of another to form the backbone.

The points where two vertebrae or bones fit together are called joints. They make it possible for the spine to move and turn in many different directions. Look at the backbone and find the discs located between each vertebra. These discs are made of cartilage, which is a soft, elastic material. Discs act as cushions, or shock absorbers, much like the shock absorbers in your car. Their main job is to protect the joints from wearing out. Most joints contain a slippery substance called synovial fluid that keeps them moving smoothly.

The spinal cord is very important because it transmits electrical signals between the brain and the nerves in your legs, arms, back, and other parts of your body. The spinal cord runs through a hole in each vertebra of the upper and middle parts of your backbone, much like a piece of string through a beaded necklace. The space it runs through is called the spinal canal. At times, a message might signal pain or discomfort. The pain signal is an important one, because pain tells you that some part of your body needs attention.

A serious injury to the neck or upper back runs the risk of damaging the spinal cord, causing paralysis of the parts of the body below the injury. It should be noted that the spinal cord is not present in the lower part of your backbone. Here the spinal canal contains a sack of nerves, the cauda equina.
Your backbone, with all its parts, cannot hold itself upright. It needs strong muscles, tendons, and ligaments for support. Muscles help you move or hold your position. Tendons fasten muscles to bones. And ligaments stretch from one bone to another to hold bones together.

Immediate medical attention

If your back pain is accompanied by any of the following, see a doctor today:

• weakness or numbness in one or both legs
• pain going down one leg below the knee
• back pain from a fall or injury
• back pain accompanied by fever without flu-like aches
• pain that continues to interrupt sleep after three nights
• or back pain that remains after six weeks of home treatment