We analyzed angles of defect planes of spondylolysis from coronal plane using axial computed tomography to identify the problem of 45° oblique plain radiograph by which we routinely has used and to suggest an appropriate radiological diagnostic tool for spondylolysis.

From January 2001 to July 2002, 84 cases of spondylolysis from 44 patients were studied. The diagnosis of spondylolysis was confirmed with axial computed tomography in all cases and angles of isthmic defect from coronal plane were measured. We intended to assess the distribution of angles of isthmic defect and analyzed the result of plain radiographs which were obtained in the direction parallel to the angle of the mean value.

Although angles of lumbar isthmic defects have a wide distribution, the mean value was 20.9± 9.5° which was nearer to coronal plane than 45° oblique plane. Fifty eight cases were distributed within 23° from coronal plane. A diagnostic sensitivities were 88.1% in lateral view, 78.6% in 45° oblique view and 100% in 20° oblique view, so a 20° oblique view seemed to be more sensitive in diagnosis of lumbar isthmic defect.

Because the mean angle of lumbar isthmic defects from coronal plane was about 21°, obliqueview with 20° was more appropriate and sensitive diagnostic tool for spondylolysis than oblique view with 45° which have been used routinely.