Normal Aging and Bone Remodeling

The bone is a living tissue with numerous cells and its own blood supply.  It is always changing in response to health and the stress placed upon it.  The process of chemical and related structural changes is sometimes referred to as tissue remodeling.  There are specialized cells in bone called osteoblasts that help to create new bone. There are specialized cells called osteoclasts that break down bone.  The process of bone remodeling is strongly influenced by the balance of activity between these two cell types. The bone remodeling process affects both the mass and the internal architecture of bone.  The majority of normal age-related changes occur with the superior and inferior aspects of the vertebral body.  The cartilage end-plates and dense outer lining of bone is vulnerable to failure resulting in weakening of both structures. 

Aging and the Intervertebral Disc

The intervertebral disc exhibits the greatest degree of age-related changes of all the musculoskeletal tissues.  These changes have become even more obvious with the use of magnetic resonance imaging (MRI).  One of the most common complaints from the elderly patients is the reporting of localized stiffness and discomfort of the neck and low back.  This in part, may be attributed to aging and degeneration of the intervertebral disc.

Normal aging of the disc is accompanied by a loss of the water content inside the disc as well as decrease in the concentration of a chemical building block referred to as proteoglycans.  Water content decreases with age in the center (nucleus) and outer aspects of the disc (annular fibers/matrix).  The water content in the disc drops from approximately 85% in preadolescence to about 70% in middle age.  This subsequent loss of water results in desiccation of the intervertebral disc and a loss of volume and vertical height of the disc.  The loss of disc volume results in abnormal stress on spinal joints (facets) and stretching of the joint capsule.  The loss of vertical disc height and the subsequent changes associated with this is sometimes referred to as rostrocaudal subluxation or rostrocaudal subluxation degeneration.