How serious is spondylolysis?

Spine defect. Spondylo means spine and lysis means crack. These can be congenital variety which is genetic in origin occuring in 6% of population or after trauma which can be repetitve particularly in certain high level athletes: swimmers, gymnasts, pitchers, football linemen to name a few. Most are treated non operatively. They will not cause usually anything more than some pain in back & occasionally legs.