Anatomy of a Disc
What exactly is the disc that lies between the bones of our back? Actually they are soft yet durable pads that lie in between the bones or vertebrae that make up the spine. The human spine has six disc in the cervical or neck, twelve in the thoracic or mid-back and five in the lumbar or low-back regions of the spine. Discs that lie in between the vertebra are designed as shock absorbers that assist in decreasing the forces impounding the spinal column.
Anatomically, there are three components that make up a disc in the back:
- The Nucleus Pulposus – this is the center portion of the disc which is a gelatinous structure and water rich in content. This portion of the disc withstands the tremendous pressures of the spine from gravity and movement patterns. The purpose of the nucleus pulposus is to bear weight and act as a pivot for movement as well as serves as a ligamentous structure to the disc;
- The Annulus Fibrosus – this structure is more fibrous as it contains a high collagen content called Lamellae that forms rings around the highly pressurized nucleus pulposus. The annulus fibrosus therefore contains the nucleus pulposus from squirting out. The annulus fibrosus is highly innervated with nerve fibers; and
- The Vetebral Body End Plate that lie above and below the annulus fibrosus. These structures attach the discs to the bony vertebra they lie between as well as serve as a mechanism for nutrition to the inner two-thirds of the annulus fibrosus and the entire nucleus pulposus. This is an area often plagued by bone spurs that are quite painful.
What types of things can cause problems with the discs in the back?
A well hydrated disc is strong yet pliable. The nucleus pulposus has to be well hydrated in order to take on the high pressure of axial loading it withstands. As a disc dehydrates it loses its ability to support axial loading to which it is exposed. The disc consequently then begins to decompose biomechanically. This biomechanical change within the disc causes abnormal pressures of the nucleus pulposus causing unequal pressures to shift. The shifting pressure gradient within the nucleus pulposus leads to abnormal stressors to the annular fibrosus. When the lamellae begin to lose their stability within the annulus fibrosus, the result is a tear of the annular ring. If too much repeated abnormal forces continue the nucleus pulposus will literally get squeezed out between the layers of the lamellae of the annulus fibrosus.
Thusly, one will experience the dreaded ‘herniated disc’ syndrome, which as well all know, is a painful experience. Realize that there are degrees of the abnormal pressure gradient to the disc anatomy. The ultimate result of too much abnormal pressure within the nucleus pulposus is what causes the herniated disc. The pain comes from the nucleus pulposus getting pushed outside of its containment area and onto a nearby nerve rootlet exiting from the spinal cord. When this happens the pain felt will be to the region of anatomy that the nerve rootlet supplies.
Jean McConnell, MS, PT, ATC is the owner of Pinnacle Health Concepts physical therapy located in Boardman, OH. You may reach her at 330-480-9362.