What is meant by “The Aging Spine”?

Many people, as they grow older, have no symptoms from their neck or back. However, there are several processes which are characteristic of the spine as it ages. These include disc degeneration and osteoarthritis. At times, these can cause symptoms of pain in the back, buttocks or legs. Two common conditions which are caused by degeneration are: lumbar spinal stenosis, and facet syndrome (osteoarthritis).

What is disc degeneration?

The bones of the spine are called vertebrae. The cervical spine or neck has seven vertebrae. The thoracic spine has twelve vertebrae and the lumbar spine (low back) has five vertebrae. There are additional five fused vertebrae in the sacrum (supporting the pelvis). Between each two vertebrae there is softer material called the intervertebral disc. These discs acts as “shock absorbers” and “bear the weight” of the body and the stresses of motion and posture. As the spine ages, the elasticity and fluidity of these discs decreases and the discs become stiffer and less flexible. With age, there is also “cracking” of the outer protective rings of the disc, called the annulus fibrosis. There is loss of the inner gelatin-like material, called the nucleus pulposus. There is a resultant loss of height of each disc, and this results in some loss of height for the aging individual. This can be on the order of a couple of inches.

Is disc degeneration the same as a “slipped disc”?

Interestingly, the incidence of a “slipped disc” or herniated nucleus pulposus, decreases with age after about age forty. Although it is certainly not uncommon for older adults to experience a “slipped disc,” it is more common for the disc to degenerate without actual herniation. Disc degeneration in and of itself is generally not a painful process. Even when painful, the pain is felt primarily in the back, rarely causing pain down the leg (sciatica). Thus, although x-rays show progressive degeneration of the disc from decade to decade, so that people in their seventies virtually all have evidence of disc degeneration, statistically the incidence of significant low back pain decreases with age after age forty!

What is osteoarthritis?

Osteoarthritis is the most common form of arthritis and results when the cartilage which cushions the bones in one'’ joints get worn out. When this happens, then the surfaces of the bones get roughened; in fact, the bones may compensate by “thickening,” resulting in spur formation—little sharp points which develop along the surface of the bone. When spurs form, motion often becomes painful. Secondary to this, consciously or unconsciously, there is decreased motion. Inflexibility, stiffness after immobility, and localized pain are all results of this process. Although osteoarthritis is common in joints throughout the body, it is most common in weight-bearing joints, including the spine. Osteoarthritis is seen on x-ray more commonly as we age; that is, in people in their seventies, it is the rule and not the exception. Yet, the presence of osteoarthritis on x-ray or examination does not correlate well with the incidence of pain or stiffness. In fact, often the symptoms from osteoarthritis are as much due to surrounding ligaments and tendons as they are to the joints themselves, and ligaments and tendons are not visualized on x-ray at all.

Is there an association between disc degeneration and osteoarthritis?

It is felt that these two processes are closely interrelated. The combined process has been called the “degenerative cascade.” The disc bears approximately 80 per cent of the weight of the vertebral column above it, the other 20 per cent being borne by the facet joints of the spine. As disc degeneration occurs, the ability of the disc to adequately bear weight is reduced. As a result, increased weight-bearing is shifted to the facet joints. Consequently, the facet joints begin to degenerate as well and osteoarthritis results. Hence, the initial disc degeneration leads to facet osteoarthritis. This “degenerative cascade” can ultimately lead to spinal stenosis.