Comparison of methods for determining the presence and extent of anterior lumbar interbody fusion

Study Design. Titanium alloy interbody fusion devices with autogenous bone were placed in the L5-L6 disc space of 31 adult pig-tailed monkeys through an anterolateral ( retroperitoneal) approach. Anteroposterior and lateral radiographs, CT imaging, and histologic analysis of the specimens were performed. Objectives. This study compared the accuracy of plain film radiographs and CT imaging for determining bony fusion of a titanium interbody device implanted in a non-human primate model. The accuracy of the assessments was determined by comparison to histologic analysis. Summary of Background Data. Interbody fusion assessment is often difficult to compare in clinical studies because of differences in definition of fusion criteria. In addition, the accuracy of plain film radiographs and CT imaging assessments of fusion are debated because of device material radiopacity and introduction of artifacts. Methods. A uniform grading system evaluating both the presence and extent of bony fusion was applied to all evaluation techniques. Matched-pair nonparametric t tests were used to determine differences in scoring. Results. The radiographic and histologic presence of fusion grades was equivalent in only 13 of 29 cases (45%), while the CT imaging was equivalent to histologic assessment in 24 of 29 cases (83%). However, the extent of bony fusion in CT imaging and histologic assessment was equivalent in only 4 of 29 cases (14%). Grading of CT images significantly overestimated the extent of fusion. Conclusions. This study demonstrated CT imaging techniques to be superior to plain film radiographs in determining the presence of bony fusion. However, CT imaging did not accurately determine the extent of bony fusion present as confirmed by histologic analysis.