It 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.
The Lumbar Spine has several distinguishing characteristics:
* The lower the vertebra is in the spinal column, the more weight it must bear. The five vertebrae of the lumbar spine (L1-L5) are the biggest unfused vertebrae in the spinal column, enabling them to support the weight of the entire torso.
* The lumbar spine’s lowest two spinal segments, L4-L5 and L5-S1, which include the vertebrae and discs, bear the most weight and are therefore the most prone to degradation and injury.
* The lumbar spine meets the sacrum at the lumbosacral joint (L5-S1). This joint allows for considerable rotation, so that the pelvis and hips may swing when walking and running.
* The spinal cord travels from the base of the skull through the spinal column and ends at about T12-L1 – where the thoracic spine meets the lumbar spine. At that point numerous nerve roots from the spinal cord continue down and branch out, forming the “cauda equina,” named for its resemblance to a horse’s tail. These nerves extend to the lower extremities (buttocks, legs and feet). Because the spinal cord does not run through the lumbar spine, it is quite rare that a lower back problem would result in spinal cord damage or paralysis.
* The lower spine curves slightly inward, toward the abdomen. This inward curve of the spine is called lordosis.