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 fourth lumbar spine vertebra (L4) is located towards the bottom of the lumbar section, near the sacral vertebrae at the bottom of the spine. Like the other lumbar spinal bones, L4 primarily provides protection to the spinal cord. Also, it features a number of processes and grooves where muscles attach. This includes the spinous, transverse, and the inferior and superior articular processes. Like the rest of the spinal vertebrae, L4 articulates, or connects, with other spinal vertebrae through circular cartilage, called annulus fibrosus discs.