Low back pain is one of the most common reasons for visiting a doctor. Most North Americans will experience low back pain at some time in their lives. Back pain is costly to the health care system and is a common reason for time away from work.
The lower back consists of the vertebrae of the spine, muscles, and ligaments. The spine contains intervertebral discs, a kind of cushion made of cartilage that fits between two vertebrae (bone segments). Injury or disease of the muscles, ligaments, or discs of the lower back can cause back pain.
The risk of low back injury is higher for people who are overweight, have poor posture, or have weak back and abdominal muscles.
For most people with back pain, a specific cause can't be found. But the most common cause of low back pain is muscle or ligament strains. If back pain comes on suddenly, it's usually a sign of a muscle tear, sprained ligament, or disc problem. A slipped disc occurs when pressure on a disc causes it to bulge or rupture, pushing cartilage sideways. The cartilage presses on the spinal cord nerves, causing intense pain.
Many conditions such as osteoporosis, osteoarthritis, fibromyalgia, ankylosing spondylitis, and spinal stenosis can cause back pain. Pregnancy can also cause back pain because of the extra body weight, because of changes in muscle and ligament firmness, and because the baby's head can compress the mother's spinal nerves. Overweight people are also more prone to back pain due to poorer posture and the extra strain that increased body weight places on discs and muscle.
Some medical problems (e.g., gallbladder disease, stomach problems) cause back pain. When pain is felt at a place in the body different from the injured or diseased part where the pain is expected to be, it is called "referred pain."
Although uncommon, there are some potentially serious causes of low back pain that don't involve injury to the back. These can include pneumonia, gallbladder disease, kidney infections, stomach problems (e.g., ulcer, appendicitis), abdominal aortic aneurysm, infection of the spine, or tumors.