The lumbar spine refers to the lower back, where the spine curves inward toward the abdomen. It starts about five or six inches below the shoulder blades, and connects with the thoracic spine at the top and extends downward to the sacral spine. There are many structures in the lumbar spine that can cause pain. Any irritation to the nerve roots that exit the spine, joint problems, the discs themselves, the bones and the muscles – can all be a source of pain. Visit our Your Spine page for more information on the most common causes of low back pain.