Fig. 3

A young male patient of symptomatic bilateral spondylolysis repaired by autogenous iliac crest graft and temporary intersegmental pedicle screw fixation. a–c Preoperative CT scan showed L5 bilateral pars defect (CT classification Type II). d The signals of lumbar intervertebral discs were normal in T2-weighted sagittal MRI. e, f The ROM of L5S1 segment was 16.2° in dynamic lateral X-ray. g Lateral X-ray after surgery. h–j Bony continuity at the pars defect in axial and sagittal CT scan 12 months postoperatively. k, l There was 12.9° ROM of L5S1 segment with 79.6% motion preservation at 1 year after surgery. m–o Solid bone union showed in CT scan after fixation removal