The lower part of the back, also called the lumbar spine, is made up of five bones called vertebrae which are given the labels L1 through L5. The lumbar spine is located between the chest, or thoracic area, and the lowest portion of the spinal column, known as the sacrum. Lumbar is a word that was taken from a Latin word that means “lion.”
The lumbar spine usually curves just slightly inward. This curve is called lordosis. The curve of the lumbar spine, as well as the other spinal curves, helps provide balance and also protection from vibrations and shocks as the body moves.
The lumbar spine area contains muscles that are quite large. These provide support for the back and they allow the body’s trunk to move. A common reason for low back pain is muscle spasms that occur when these large muscles are strained.
Special joints called “facet” connect the five bones (vertebrae) of the lumbar spine. These allow the lumbar spine to twist, extend backward and bend forward. The lowest segments of the lumbar spine have the most mobility. These segments are also responsible for carrying the most weight, so they are at increased risk of being injured.
Intervertebral discs lie between the vertebrae of the lumbar spine. These provide support and cushioning for the bones. The intervertebral discs found in the lower or lumbar spine are more likely to degenerate and then herniate or bulge than other discs of the spine. This is because they move more, so wear out more quickly. A bulging or herniated disc, or one that is degenerated, can cause inflammation and pressure on the nerves. This can be a reason for low back pain, and it can also be a reason for pain that travels down into the buttocks and radiates to the back of the thighs and down the legs into the feet - sciatica. Pain related to compressed nerves is sometimes called radiculopathy.
The spinal cord starts at the base of the skull and ends at the point where the lumbar spine and the thoracic spine meet. The cauda equina is found here, which is a group or bundle of nerve roots branching out from the spinal cord.
The cauda equina was named for its similarity in appearance to the tail of a horse. There are many nerves in this bundle, extending from the lumbar spine to provide nerve function to the feet, legs and buttocks. Since the spinal cord itself does not pass through the lumbar spine, spinal cord damage rarely result from injury or insult to the lower back. Cauda equina syndrome is a very serious condition however.