Spondylolisthesis occurs when one of the vertebrae slips out of position and essentially dislocates. Stress fractures in the pars articularis portion of the vertebrae can cause this, as can degenerative spinal wear and tear, abnormal spine development, and erosion or damage from tumors, bone conditions, or previous spinal surgery. With this slippage, sciatica pain may come and go based on one's physical position. As the vertebrae move, they compress the sciatic nerve, but when the vertebrae move back, compression releases.

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