As people age, their spines usually undergo gradual changes.  The inter-vertebral disks “degenerate.” Disk degeneration involves the alteration of disk proteins (proteoglycans), loss of water content (de-hydration), disruption of internal disk architecture (annular tears), ingrowth of scar tissue (disk fibrosis) and, eventually, disk resorption.  All of these changes result in a reduction in disk height.

Flexion extension XRays of the cervical spine with degeneration at C5-6

Bone spurs (osteophytes) develop at the vertebral body edges (end-plates) and around the small joints (zygapophyseal joints) of the vertebrae.  Spinal ligaments and joint capsules around the small joints of the spine may develop looseness (laxity).  With ligamentous looseness and loss of disk height, disk bulges often develop.  Occasionally, portions of the inner part of a disk may dislodge and slip (herniate) through cracks (fissures) in the fibrous ring (annulus fibrosus), which surrounds the central portion of the disk (nucleus pulposus).

As a result of these degenerative changes, the alignment of vertebrae may be affected to the point where they are no longer normally aligned, one on top of the other.  Vertebral mal-alignment (spondylolisthesis) results.  This may further stimulate the enlargement of osteophytes and the thickening of ligaments (ligamentum flavum hypertrophy).  The degree of spondylololisthesis sometimes does not change with body movement (fixed spondylolisthesis).  Occasionally,  there is abnormal movement of vertebrae in relation to each other with body movement, resulting in spinal instability.

Spaces, which are normal occupied by the spinal cord (central spinal canal) and the spinal nerve roots (neural foramina) can become narrowed by degenerative tissue. Such narrowing may result in spinal cord or nerve root compression.  Depending on the locasion of disk bulges, fragments of herniated disks, thickened joint capsules, bone spurs (osteophytes) or ligament different areas of the spinal cord or different nerve rootsmay get compressed and stop to function properly.

Lumbar spondylolisthesis L5-S1 with endplate sclerosis and osteophytes

The speed, with which degenerative changes of the spine develop is often very slow, lasting years or decades.  The resulting conditions are often gradual in onset.  Spinal degenerative conditions, including lumbar or cervical spinal stenosis are more commonly seen in people in their 60s or older.  Occasionally, conditions like rheumatoid arthritis and other connective tissue disorders can lead to onset of problems at a younger age.  The worsening of pain and spinal cord or nerve function may be rapid, if the space, which had been occupied by spinal cord and nerve tissue had been narrowed by degenerative tissue for a long period of time and when only a minor additional compression occurs.

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