Spondylolysis of the lumbar spine: demonstration of defects and laminal fragmentation.

Fifty-six cases of spondylolysis were encountered in 1500 lumbar spine reports reviewed. The frequency of detecting isthmus defects on anteroposterior (AP), lateral, 45-degree right and left oblique, 30-degree up-angled AP, and collimated lateral views was determined. The collimated lateral view showed the largest number of pars defects, 84% of cases. The 30-degree up-angled AP view was more sensitive than the AP view, showing 55% versus 32% of cases. A previously unreported sign of spondylolysis, fragmentation of lamina demonstrated on the AP or AP up-angled view, was found in 14.2% of cases of spondylolysis.