Coloured 3D computed tomography (CT) scan of the lumbar and sacral spine. The lumbar spine is made up of five vertebrae (cylindrical individual bones of the spine) known as L1 to L5, although it is not unusual to have six. This part of the spine bears most of the body's weight and allows for the most movement, which can lead to back problems. The sacral region, located beneath the lumbar spine, is composed of five bony sections called S1 to S5. These sections fuse together to form the triangular-shaped bone that serves as the base of the spine and contributes to the pelvis. At the very bottom of the spine lies the coccyx, which is made up of four small bones and is commonly known as the tailbone. Both the sacrum and the coccyx play a crucial role in walking, running, and sitting.