Phases of Disc Degeneration

Intervertebral discs are comprised primarily of water. They tend to lose water content with progressive age. This gradual process of desiccation typically starts to become noticeable at approximately 30 years of age at which time the outer layers of the annulus fibrosis begin to degenerative and crack forming regions of annular fiber discontinuity or fissures.  The phases of disc degeneration can generally be classified into four phases or stages. 

phase 1 usually occurs between the ages of 20 and 30. Dysfunction of movement is the earliest sign.  This phase is characterized by minor pathology resulting in abnormal function of the posterior facet joints and intervertebral disc. The gel-like center of the disc referred to as the nucleus pulposis begins to lose some water content, although typically minimal. In general the disc is still quite normal in many aspects.  Phase 2 disc degeneration usually occurs between 30 and 40 years of age and is characterized by stiffening of the outer annular fibers that begin to lose continuity and internal fissures begin to develop in the disc. This is often referred to as the unstable phase.  This phase is characterized by progressive degeneration due to repeated trauma resulting in laxity of the posterior joint capsule and the intervertebral disc. The development of fissures allows the more fluid nucleus of the disc to migrate into the paths of least resistance, causing disc herniation.  During phase 2 the water content of the disc, particularly within the nucleus continues to diminish.  Phase 3 usually occurs between the ages of 40 and 50. Phase 3 is characterized by fibrosis, tissue thickening, scar tissue development involving the posterior facet joints and early spur development.  It is also characterized by a loss of disc volume and vertical disc height. The inner layers of the annulus become further compromised and continue to fissure. The fourth phase of degeneration, occurs between 50 and 70 years of age. The disc becomes progressively dehydrated and thinner causing the nucleus to continue to shrink in volume. These combined changes lead to progressive loss of disc approximation of the adjacent vertebral bodies their facet joints and stiffening of the vertebral segment. With this late phase, there is bony hypertrophy or enlargement of the facet articular processes and development of osteophytes.  This combined process may lead to lateral and/or central stenosis.

Facet Arthrosis (Hypertrophic Disease)

The aging spine is leads to greater prevalence of spinal joint degeneration.  Under normal circumstances the facet surfaces do not touch one another but glide in relationship to each other. As the intervertebral disc volume decreases the facet joints bear more weight contributing to wearing away of the cartilage surfaces.  As the cartilage wears away, the joint space becomes narrower and excess bone is formed in the area of the compromised cartilage.  This can lead to bone spur formation.  The process of enlargement of the bony aspects of the joint (facet) is often referred to as facet hypertrophy or arthrosis.