The Alarming Facts If you are among those who have already experienced a bout with lower back pain, you know how debilitating it can be. In the western world, 80% of the population will experience disabling low back pain during their lives. Back pain is the second most common reason patients visit doctors, and costs the U.S. economy $25 billion per year. Low back pain clearly represents the single greatest and most inefficient expenditure of health care resources in our society today. Understanding the anatomy of the back will help you under- stand why and how back problems occur. The spine is composed of 24 bones called vertebrae. The lower back or lumbar spine has five vertebrae whose functions are to bear weight and provide a protective covering for the spinal cord. Between each pair of vertebrae are cushions called discs. The main responsibility of the disc is to absorb the compressive forces to which the spine is subjected. Most back pain is preventable and is often caused by too little exercise, overuse, poor exercise or work positioning, lack of flexibility, and poor posture. Smoking can cause decreased blood flow to the spine as well as a loss of bone density. Even obesity can be a cause of low back pain due to the increased pressure the excess weight puts on the spinal discs. All of the above may result in arthritic or degenerative changes in the spine, disc herniations ("slipped discs"), muscle spasms, spinal joint irritation, dysfunction, and nerve irritation (sciatica). Over time, spinal arthritis may develop. The discs narrow, wear out, and the vertebrae crumble, often forming spurs which narrow and compress the area through which the spinal cord and nerves pass. A disc herniation (see below) occurs when the outer wall of the disc weakens and the jelly like middle causes the outer wall to bulge out. This bulging may "pinch" the nerve exiting from the spinal cord or the spinal cord itself.