[Radiologic and computerized tomography evaluation of pedicle screw placement in lumbar spondylodesis]. / Radiologische und computertomographische Beurteilung der Pedikelschraubenlage bei lumbalen Spondylodesen.

PURPOSE: To determine the accuracy of a standard roentgenogram for the placement control of pedicle screws following spinal fusion. METHOD: From 1995 to 1997 we performed computed tomography (CT) after material removal following lumbar and lumbosacral spinal fusion in 16 patients. We compared the placement of the 76 pedicle screws in plain X-rays after spinal fusion with their appearance on CT. A correct placement was defined as no penetration of the pedicle cortex, no contact of the lateral or ventral cortex of the vertebral body or joint, and a sufficient screw length. RESULTS: We found correct placement of 58 screws (76.3%) on the standard roentgenogram, whereas by CT only 46 (60.5%) were placed correctly. The results of both radiological examinations correlated (correct/incorrect placement) for only 54 screws (71.1%). A penetration of the ventral cortex of the vertebral body in 21 cases (27.6%) was identified in only 11 screws (14.5%) on the postoperative X-rays. The two radiological methods in this instance correlated for 62 screws (81.6%). CONCLUSION: The value of postoperative standard roentgenogram for the placement control of pedicle screws following spinal fusion is low. By this method possible contact with the aorta, vena cava, dura or vertebral joint cannot sufficiently be excluded.