What is spondylolisthesis and spondylolysis? Name the two major causes and the key imaging findings.
Spondylolisthesis is displacement of one vertebral body with respect to the vertebral body below. Anterolisthesis, which is anterior displacement of a vertebral body relative to the one located more inferiorly, is more common than retrolisthesis, which involves posterior displacement. The most common causes are spondylolysis (bilateral fractures through the pars interarticularis of the vertebra) and degenerative facet joint disease. Spondylolysis is recognized by lucency through the pars interarticularis and occurs most commonly at L5. Loss of posterior vertebral body height relative to anterior vertebral body height is also strongly suggestive of bilateral spondylolysis.
