The entire spine has many components, including the cervical, thoracic, lumbar, sacral, and caudal vertebrae, except that as we age, the entire caudal vertebrae gradually degenerate and the sacral vertebrae gradually fuse into one large bone. In addition to these bony structures, there are many ligaments or accessory structures that connect the bones to each other, such as the ligamentum flavum, the posterior longitudinal ligament, the anterior longitudinal ligament, the interspinous ligament, the supraspinous ligament, and the small joints between the vertebrae. There are some special parts like the cervical vertebrae and the skull, where there are no intervertebral discs in the middle, and they are firmly connected to each other by ligaments, so that the rotational movement of the head is greater. For example, after the degeneration of the caudal vertebrae, there is no obvious interdiscal and ligament interconnection structure.