COMPARISON OF PLAIN RADIOGRAPHS AND CT SCANS IN INSTRUMENTED POSTERIOR LUMBAR INTERBODY FUSION

The success of posterior lumbar interbody fusion has been analyzed pri marily by plain radiography. There are no widely accepted criteria for fusion, except for lack of motion, which can be obviated by instrumen tation, and the appearance of continuous bridging bone in the interspa ce. To determine the accuracy of plain radiography in detecting poster ior lumbar interbody union, the radiographs of instrumented posterior lumbar fusion performed at 22 levels were compared with reformatted co mputed tomography (CT) scans. Results revealed that although 17 of 22 interbody levels were classified as fused by radiograph, 10 of these 1 7 demonstrated a nonunion by reformatted CT scans taken an average of 13.8 months postoperatively. Only progressively increased density by r adiograph correlated with a solid fusion by CT scan. We therefore conc lude that plain radiographs are unreliable in reporting the results of posterior lumbar interbody fusion and that CT scanning may be more ap propriate.