Fusion assessment of posterior lumbar interbody fusion using radiolucent cages: X-ray films and helical computed tomography scans compared with surgical exploration of fusion.

BACKGROUND Plain radiographic assessment of posterolateral fusion has been reported as accurate in only two thirds of patients who were found to be healed at surgical exploration. Plain radiographic techniques for fusion assessment of interbody fusion with radiolucent cages are reported to be accurate. A helical computed tomography (CT) scan shows a high sensitivity for pseudarthrosis compared with plain radiography. PURPOSE To determine the accuracy of fusion assessment with plain X-ray films and helical CT scans by comparison to results of surgical exploration of fusion. STUDY DESIGN/SETTING The accuracy and interobserver agreement of plain X-ray films and thin-cut helical CT scans were compared with fusion assessment by surgical exploration in patients with posterior lumbar interbody fusion using a radiolucent carbon fiber reinforced polymer cage (CFRP) and iliac crest bone graft. PATIENT SAMPLE A review of 90 patients who had surgical exploration of the lumbar fusion. OUTCOME MEASURES All patients had plain X-ray films including Ferguson anteroposterior parallel to the interbody space. Fifty-four patients had thin-section helical CT scans. METHODS Fusion assessment by exploration was compared with blinded assessment by plain X-ray films and CT scans. RESULTS Ninety patients had surgical exploration of 172 lumbar interbody and posterolateral fusion levels. At the time of exploration, fusion was determined to be successful in 87 of 90 patients and 168 of 172 (97%) fusion levels. X-ray assessment showed healed interbody fusions in 87% and posterolateral fusion healed in 75%. CT grading of the interbody fusion found healed interbody fusion in 77%, and the posterolateral fusion was fused in 68%. Plain X-ray films and CT scans had a sensitivity of 100% for pseudarthrosis and a negative predictive value of 100% for healed fusion. Specificity was almost 90% and was not significantly different between X-ray films and CT scans. CONCLUSIONS Fusion assessment with plain X-ray films and helical CT scans showed equal accuracy after posterior lumbar interbody fusion confirmed by surgical exploration. Our results indicate that when plain X-ray films show strong evidence of fusion or pseudarthrosis, the helical CT is unlikely to provide useful new information.