Spondylolysis of the upper lumbar spine. Radiological features.

To elucidate the radiological features of spondylolysis of the three upper lumbar vertebrae, review of radiology reports during an 8-year period was performed. Among 17 levels of defects in 14 patients, nine were unilateral. Among 25 defects, nine had an atypical course. In eight of nine atypical defects, the direction was vertical at the inferolateral aspect, and horizontal at the superomedial aspect. The spondylolysis of the upper lumbar spine is often unilateral and the course of the defect is frequently atypical.