Spondylolisthesis

Spondylolisthesis is displacement of one vertebra relative to the vertebra below it, usually forward. It can result from a defect, degeneration, trauma, or another spinal condition.

Pars interarticularis: A short segment of bone connecting the upper and lower articular processes of a vertebra. A defect here can let a vertebral body slip forward, producing isthmic spondylolisthesis.
Vertebral column: The segmented bony column that supports the trunk and protects the spinal cord. Spondylolisthesis is displacement within this stacked structure.
Lumbar spine radiography: X-ray imaging of the lower spine, sometimes performed with the patient standing or bending. Standing images can show a slip that is less apparent when lying down.
Isthmic spondylolisthesis: Spondylolisthesis associated with a defect or fracture in the pars interarticularis. It is the subtype most directly linked to spondylolysis.
Spondylolysis: A stress fracture or defect in the pars interarticularis, most often in the lower lumbar spine. It is the bony defect underlying many cases of isthmic spondylolisthesis.
Lumbar spine: The five vertebrae in the lower back, between the thoracic spine and sacrum. Most clinically recognized spondylolisthesis occurs in this region.
Magnetic resonance imaging: An imaging method that uses magnetic fields and radio waves to produce detailed images of internal tissues. MRI can show nerve compression and soft-tissue changes associated with a slip.
Degenerative spondylolisthesis: Spondylolisthesis caused by age-related degeneration of spinal discs and joints, without a pars defect. It contrasts with slips caused by a pars lesion.
Intervertebral disc degeneration: Age-related breakdown of the cushioning discs between vertebrae. Disc and facet-joint degeneration can destabilize a spinal segment and permit vertebral slippage.
Retrolisthesis: Backward displacement of one vertebra relative to the vertebra below it. It contrasts with the forward displacement that defines the usual meaning of spondylolisthesis.

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