Spinal stenosis is a condition in which one or more areas of the spine narrow, pressuring the spinal cord or the roots of the nerves that branch off it. This impingement causes pain and other symptoms for many patients.

The spine is made up of 33 bones (vertebrae) held together by fibrous bands (ligaments). There are seven cervical vertebrae in the neck and 12 thoracic vertebrae in the middle of the back. The five large lumbar vertebrae in the lower back carry most of the body’s weight. Below the lumbar vertebrae are the sacrum, made from five fused vertebrae, and the coccyx (tailbone). Together, these bones are referred to as the spine, spinal column or vertebral column.

The spine supports the upper body’s weight. It also houses and protects the spinal cord, which along with the brain forms the central nervous system. The spinal cord is made up of nerves and nerve cells that extend the length of the spine. Thirty-one pairs of nerves branch off from the spinal cord and transmit electrical signals between the brain and the nerves in the legs, arms and other areas of the body. The spinal cord extends from the base of the brain to just below the rib cage. A bundle of nerves known as the cauda equina continues from the lumbar region, where the spinal cord ends, and downward. This provides neurologic function to the lower part of the body.

Spinal stenosis is a result of a narrowing of the spine that puts pressure on the spinal cord or nerve roots. It is categorized as one of the following two varieties:

• Primary stenosis. Relatively uncommon, it is the result of congenital disorders (those present at birth), such as being born with a narrow spinal canal.
  
  
• Acquired stenosis. Develops later in life, usually as a result of degenerative changes in the spine that occur with aging. This is the more common source of stenosis.

Spinal stenosis may affect a large or small portion of the spine. It tends to affect one or more of three areas:

• The canal in the center of the spinal column through which the spinal cord and nerve roots run
  
  
• The canals at the base or root of nerves that branch out from the spinal cord
  
  
• The openings between the vertebrae through which the nerves leave the spine on their way to other parts of the body