Spondylolysis is a unilateral or bilateral defect in the region of the pars interarticularis, which may or may not be accompanied by the vertebral body slippage. It is most commonly the sequelae of repetitive trauma to the growing immature skeletal architecture among a genetically susceptible individuals.  The pars interarticularis is considered the isthmus or bone bridge between the inferior and superior articular surfaces of a single vertebra.