Back pain is one of the most common human ailments, and it can be caused by everything from bad posture to a
cancerous growth. The most common problems include muscle strains, arthritis and herniated discs.

However, if these conditions have been ruled out, your aching back may be caused by one of these less common problems:

Spinal stenosis

Your vertebrae protect the delicate tissues in your spinal cord and its nerve roots. Sometimes, however, the openings
in the vertebrae are too small and these tissues get pinched. This condition is called spinal stenosis.

Some people are born with this problem, while others develop it over time. As you get older, the discs between your
vertebrae dehydrate and shrink. The bones and ligaments in your spine thicken and become less pliable. Discs may also
protrude into the spinal canal. Such changes may narrow the space occupied by the spinal cord and its nerve roots.

Signs and symptoms can include an ache in your buttock, thigh and calf, pain radiating from your lower back to your
calf, progressive numbness or weakness in a leg, and bladder- and bowel-control problems. Symptoms often worsen when
you stand or walk, particularly downhill, but subside when you sit for a few minutes or bend forward from the waist.

Over-the-counter pain medications often can control pain in the early stages of spinal stenosis. Some patients
benefit from physical therapy and cortisone injections. In severe cases, surgeons can widen the space inside the
affected vertebrae.

Ankylosing spondylitis

A form of arthritis, ankylosing spondylitis (ang-kuh-LOE-sing spon-duh-LI-tis) causes the joints and ligaments in the
spine to become inflamed. Eventually, the vertebrae can actually fuse. Signs and symptoms include chronic pain and
lack of motion in the lower back, typically starting where the spine is joined to the pelvis.

Both women and men get ankylosing spondylitis, but the disease primarily affects young men. A specific gene seems to
be linked to the condition, although not everyone with the gene develops ankylosing spondylitis. Treatment can include
exercise, medications, posture management and, sometimes, surgery.

Infections and tumors

In rare circumstances, infections can develop in the spine. Cancer also may spread to the spine from a tumor in
another part of the body, such as the breast, prostate or lung. Tumors rarely originate in the spine. Most that do are
benign.

Referred pain

Sometimes your brain mistakes pain signals from other organs as pain originating in your back. Bladder infections and
kidney stones can cause back pain, as can endometriosis, ovarian cysts and ovarian cancer.