Radiologic assessment of interbody fusion using carbon fiber cages

Study Design. A comparative study investigated the use of plain static radiographs, flexion-extension radiographs, and thin-section helical computed tomography (CT) scanning in the assessment of anterior lumbar interbody fusion using carbon fiber cages. Objective. To compare plain static radiographs, flexion-extension radiographs, and thin-section helical computed tomography scans in the assessment of lumbar interbody fusion using carbon fiber cages. Summary of Background Data. Lumbar interbody fusion has become a popular procedure for the treatment of discogenic back pain. However, there currently is no universally accepted radiologic assessment tool for determining fusion, and the definitive criteria for diagnosing a successful interbody fusion in the lumbar spine remains controversial. Methods. Plain static radiographs, flexion-extension radiographs, and helical computed tomography scans were performed on 32 patients (49 levels) 5 years after anterior lumbar interbody fusion using carbon fiber cages and autologous bone. A radiologist assessed fusion using the Hutter method to detect movement, whereas a spinal surgeon measured movement in degrees using the Simmons method. Helical computed tomography scans were assessed for the presence of bridging trabecular bone. Results. The fusion rate was 86% on plain radiographs and 84% with the Hutter method. The fusion rate was 74% with the 2degrees cutoff, and 96% with the 5degrees cutoff prescribed by the Food and Drug Administration. Fusion on helical computed tomography scans was observed in 65% of the patients. Conclusions. In the radiologic assessment of interbody fusion using carbon fiber cages, the use of plain radiographs and flexion-extension radiographs produced much higher fusion rates than assessment with thin-section helical computed tomography scans. The thin-section helical computed tomography studies clearly demonstrated the radiographic presence or absence of bridging bone, a property that was not seen with plain static radiographs or flexion-extension radiographs.