Congenital              Child            Congenital dysplasia of S1 superior facet
  Isthmic                   5-50             Most Common; Predisposition leading to
                                                         elongation/Fx of pars (L5-S1)
  Degenerative          Older           Facet arthrosis leading to subluxation- L4/5
  Traumatic               Young          Acute fracture other than pars;
  Pathologic              Any              Incompetence of bony elements
  Post surgical          Adult            Excessive resection of neural arches/facets