Spondylolysis is a stress fracture of vertebra that may progress into spondylolisthesis, a condition of displacement of vertebrae from the spinal column. Spondylolysis is the cause for frequent low back pain in children. It is more common among children and teenagers who participate actively in sports such as football, weightlifting and gymnastics. Spondylolysis occurs as a result of a defect or stress fracture in the pars interarticularis, the part of the lumbar spine joining the upper and lower joints. Genetic factors may have a role.