Orientation of lumbar pars defects - Implications for radiological detection and surgical management

Lateral oblique radiographs are considered important for the identification of spondylolytic lesions, hut these projections will give a clear view only when the radiological beam is in the plane of the defect, We studied the variation in orientation of spondylolytic lesions on CT scans of 34 patients with 69 defects. There was a wide variation of angle: only 32% of defects were orientated within 15 degrees of the 45 degrees lateral oblique plane. Lateral oblique radiographs should not he considered as the definitive investigation for spondylolysis. We suggest that CT scans with reverse gantry angle are now more appropriate than oblique radiography for the assessment of spondylolysis. Variation in the angle of the defect mag also need consideration when direct repair is being planned.