To understand how degenerative disc disease unfolds, it is helpful to know more about the anatomy of the spine. Spinal anatomy includes strong bones, flexible ligaments and tendons, large muscles and sensitive nerves. Its most notable feature is the vertebral column, also called the spinal column. It is made up of block-shaped bones called vertebrae that typically total 33 at birth but later become 26 bones because some of the lower vertebrae fuse to become the sacrum and the tailbone (coccyx).

An intervertebral disc (also called spinal disc) separates each of the vertebrae, except the first and second cervical vertebrae. These discs are made up of tough fibrocartilaginous material that is nonetheless elastic. They act as shock absorbers between the vertebrae, shielding the bones from the impact of activities such as jumping from heights or certain forms of exercise. They also add stability to the spine while still allowing for movement between the bones. Each disc is composed of a core of jelly-like material (nucleus pulposus) surrounded by a covering of tough, fibrous material (annulus fibrosis).

Degenerative disc disease is associated with aging. Typically, symptoms related to the disorder first begin to affect people in their 30s or 40s. From the moment a person gets out of bed in the morning, the spine is continuously called upon to support a person’s body weight. Over a period of years, this creates daily stresses and minor injuries that begin to accumulate and wear down the discs of the spine. The role of the discs between the vertebrae is to absorb these stresses so that bones are not injured.

Usually, the first part of the disc to be injured is the outer portion (annulus). Excessive pressure on or injury to the annulus can cause tears. Scar tissue forms in the annulus to repair the tears, but this tissue is not as strong as normal. As more scar tissue forms, the annulus becomes weaker, which can lead to damage of the inner disc (nucleus pulposus). Damage to the nucleus pulposus may result in a loss of water within the disc, which weakens the disc's ability to absorb stress. Damage to the nucleus pulposus can allow the contained proteins to leak out, which inflames nerves and causes pain.