The prone position for CT of the lumbar spine.

In scanning the L5-S1 disk space, the known technical difficulty is limitation of the gantry angle. A prone scanning technique used to examine the lumbar spine may help to overcome or lessen this problem. A prospective CT scanning of the L5-S1 level was performed in both the prone and supine positions on 25 patients who had low back pain and who had not undergone previous laminectomy or fusion. The angle between the S1 vertebral end plate and maximum tilted gantry line (15 degrees on the G.E. 8800) was measured in the supine position and compared with the same angle in the prone position. In 20 of 25 cases (80%), significant improvement in alignment was noted in the prone position. The prone scanning technique is also more desirable if CT is performed with metrizamide. Finally, printed images from the prone technique allow easier image-patient orientation for viewing in the operating room.