Low back pain is one of the most frequently encountered conditions in clinical practice. Up to 84 percent of adults have low back pain at some time in their lives, and over one-quarter of U.S. adults report recent (in the last 3 months) low back pain.  Low back pain can have major adverse impacts on quality of life and function. Low back pain is also costly: total U.S. health care expenditures for low back pain in 1998 were estimated at $90 billion.  Since that time, costs of low back pain care have risen at a rate higher than observed for overall health expenditures.  In addition to high direct costs, low back pain is one of the most common reasons for missed work or reduced productivity while at work, resulting in high indirect costs.