Five (or in some cases, six) vertebrae make up the lumbar spine, which provides support for much of the upper body and is rather flexible. Lumbar vertebrae are larger than the thoracic or cervical vertebrae, as they have to bear the weight of the spine and the head. The fifth lumbar spine vertebrae (L5) is part of the greater lumbar region. To the human eye, this is the curve just above the buttocks, which is also commonly referred to as the small of the back.
The L5 is larger than its counterparts located in the thoracic and cervical regions. The L5 is the lowest with the lumbar region, as it is the closest to the sacrum and the pelvis. Like other lumbar vertebrae, the L5 primarily protects the spinal column. This is the case for most individuals; however, there have been some anatomical variations that have been discovered. Some people have been born without a L5, while others have been born with an additional, or sixth, lumbar vertebrae. One of the more common conditions that affects the L5 is a type of stress fracture called spondylolysis.