Abstract:
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Purpose: Lumbar fusion cages are a popular method to augment interbody arthrodesis. Previous studies has shown metal cages may obscure information within and around the cage confounding assessments of fusion. Even with limitations, CT has potential to be a valuable tool for evaluating arthrodesis. The purpose of this study was to 1) demonstrate intra-metal cage lucencies can be produced by CT reconstruction artifacts and 2) validate CT for density evaluations within metal cages.
Methods and Materials: An anthropomorphic lumbar spine phantom was utilized. Dual cages were inserted into 6 anterior-middle column inserts and filled with 10, 100, or 400 mg/cc HA equivalent material. The inserts were composed of either fibrous tissue or trabecular bone equivalent material. Inserts were placed within the phantom and CT scanned. Direct axial and reformatted sagittal and coronal images were evaluated for artifact and ROI analysis performed for intra-cage density.
Results: Lucent streaking within and adjacent to cages was similar to clinical images. CT values within cages overestimated the intra-cage materials' true values (paired t test, p<0.001). Intra-cage CT values calculated from axial, sagittal, and coronal images were directly related to the true CT values of the materials (r=0.99, p<0.0001). Thus, intra-cage values were correctable and could be converted to bone mineral content values. Intra-cage CT values were not effected by anterior-middle column material differences (fibrous tissue versus trabecular bone) (paired t test, p>0.05).
Conclusion: Interbody fusion cage artifacts are compatible with beam hardening, edge, and metal CT reconstruction artifacts and simulate fragmentation and lack of fusion. However, even in the presence of these artifacts, densitometry may be performed within cages to assist evaluations of cage augmented arthrodesis.
Robertson MD, PhD, D,
Fusion within Lumbar Interbody Cages: CT Evaluation. Radiological Society of North America 2003 Scientific Assembly and Annual Meeting, November 30 - December 5, 2003 ,Chicago IL.
http://archive.rsna.org/2003/3105282.html
