COMPARISON OF PLAIN RADIOGRAPHS WITH CT TO EVALUATE THE INTERBODY FUSION FOLLOWING THE USE OF TITANIUM INTERBODY CAGES AND PEDICLE SCREW INSTRUMENTATION.

Abstract

Objectives: To determine if high quality, thin slice (1–3)mm CT scan images would allow proper evaluation of interbody fusion through titanium cages in view of the fact that there are no universally accepted radiological criteria. ¹

Design: Patients undergoing interbody lumbar fusion were prospectively evaluated with a CT scan and plain radiographs six months following surgery. These were blindly and independently evaluated by a consultant radiologist and a research fellow. They were assessed for bridging bony trabeculation both through and surrounding the cages as well as for changes at the cage endplate interface.

Subjects: Fifty-three patients (156 cages) undergoing posterior lumbar interbody fusion using titanium inter-body cages were evaluated. Posterior elements were used to pack the cages and no graft was packed outside the cages.

Outcome Measures: Kappa co-efficient and chi-squared analysis.

Results: On the CT scan both observers noted bridging trabeculation in 95%of the cages-Kappa 0.85, while on radiographs they were present in only 4%-Kappa 0.74. Both observers also identified bridging trabeculation surrounding the cages on the CT scans in 90%-Kappa 0.82, while on the radiographs this was 8%-Kappa 0.86. Radiographs also did not identify all the loose cages.

Conclusions: High quality CT scan images can demonstrate bridging bony trabeculation following the use of titanium interbody cages. It also demonstrated consistent bone growth outside the cages inspite of not using any bone graft.