Spondylolisthesis means slippage of the spine. Discs in the spine tend to lose some of their water content and become dehydrated as they age. As this occurs, the disc height decreases resulting in mild loss of overall patient height. The narrowed disc bulges on the sides much like a partially flat tire. The aging disc is less firm, allowing some shifting of the neighboring vertebra (degenerative spondylolisthesis).
The forward/backward shifting of the vertebra often irritates the spinal nerves and causes bone spurs and enlarged spinal ligaments. The combination of vertebral shifting, disc bulging, bone spurs and enlarged ligaments also can lead to a narrowed spinal canal or spinal stenosis.
Stress Fracture Spondylolisthesis
Spondylolisthesis can also be caused by a stress fracture in the lower back that occurred in childhood but never completely healed. In most cases, this bone defect does not cause ongoing symptoms and is often unrecognized until later in life. The fracture produces weakness within the spinal column and in some cases leads to premature disc degeneration at the base of the spine. As the disc wears out, the fractured vertebra shifts forward out of alignment.
Typically, the slip occurs between the lowest lumbar vertebra (L5) and the sacrum, but can occur at other levels within the spine. The disc degeneration and associated arthritic changes often cause nerve compression and irritation.
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