Spondylolisthesis is the anterior or posterior displacement of a vertebra or the vertebral column in relation to the vertebrae below. The variant “listhesis,” resulting from misdivision of this compound word, is sometimes applied in conjunction with scoliosis. These “slips” (aka “step-offs”) occur most commonly in the lumbar spine. Spondylolysis (a defect or fracture of the pars interarticularis of the vertebral arch) is the most common cause of spondylolisthesis. This is not to be confused with a slipped disc, where one of the spinal discs in between the vertebrae has ruptured.