What Is Spondylolisthesis?

The spine is made up of 33 bones called vertebrae and divided into four regions: cervical (neck), thoracic (mid back), lumbar (lower back), and sacrum. Spondylolisthesis refers to the improper positioning of a vertebra and occurs in two ways: anterolisthesis, in which the vertebral body is positioned forward in relation to the vertebra it sits above, and retrolisthesis, in which the vertebral body is positioned backward from the vertebra it is positioned above. Spondylolisthesis can be either dynamic, fixed, or glacial. Fixed spondylolisthesis indicates misalignment of one vertebral body on top of another, but that this structure does not move during motion of the spine, such as bending forward. Dynamic spondylolisthesis refers to a misaligned vertebral segment that moves when the spine moves, during flexion and extension (bending forward and bending backward). Dynamic Spondylothesis may mask misalignment because the vertebrae may seem aligned in either the flexion or the extension positions. Glacial spondylolisthesis refers to an increasing misalignment over time. Spondylolisthesis is given a grade based on its severity; the grade is determined by the distance that the vertebral body is misaligned.

There are multiple types of spondylolisthesis including isthmic, degenerative, and iatrogenic. Isthmic spondylolisthesis means that there is a defect or fracture in the area of the vertebrae that makes up the facet joints, called the pars interarticularis. This usually occurs during childhood due to stress on the spine as the part interarticularis has a poor blood supply and therefore does not heal well. The symptoms don’t manifest till adulthood so it is commonly undiagnosed until that time. Degenerative spondylolisthesis refers to degeneration of the disc, joints, and ligaments of the spinal column due to aging and wear and tear. As these parts of the spine weaken, their ability to hold the spine in alignment diminishes and may result in the slip of a vertebra. The term iatrogenic refers to any medical treatment that directly results in a complication. Iatrogenic spondylolisthesis commonly occurs as a complication or result of spine surgery.

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