Complex sentence: Spondylolysis (a defect or fracture of the pars interarticularis of the vertebral arch) is the most common cause of spondylolisthesis, which should not be confused with a slipped disc, where one of the spinal discs in between the vertebrae has ruptured.
Split into simpler sentences: 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.