Spondylolysis is a stress fracture or defect in the pars interarticularis, the small bony bridge between the upper and lower facets of a vertebra, most commonly seen in the lumbar spine. If left untreated or aggravated, it may progress to Spondylolisthesis, a condition in which one vertebra slips forward (anterolisthesis) or backward (retrolisthesis) over the vertebra below it.

These conditions are common in children and adolescents, particularly those active in high-impact or extension-heavy sports like football, gymnastics, and weightlifting.