Spondylolysis/Spondylolisthesis

What Are Spondylolysis and Spondylolisthesis?

Spondylolysis is a defect or fracture of part of the vertebral bones called the pars interarticularis. It usually occurs in the fifth lumbar vertebra and, less commonly, in the fourth lumbar vertebra. Spondylolisthesis is a slippage of one vertebral body on top of another.