Comparison of plain radiography, computed tomography, and magnetic resonance imaging in the evaluation of bone tunnel widening after anterior cruciate ligament reconstruction

Bone tunnel widening poses a problem for graft fixation during revision anterior cruciate ligament (ACL) reconstruction. Large variability exists in the utilization of imaging modalities for evaluating bone tunnels in pre-operative planning for revision ACL reconstruction. The purpose of this study was to identify the most reliable imaging modality for identifying bone tunnels and assessing tunnel widening, and specifically, to validate the reliability of radiographs, MRI, and CT using intra- and inter-observer testing. Data was retrospectively collected from twelve patients presenting for revision ACL surgery. Five observers twice measured femoral and tibial tunnels at their widest point using digital calipers in coronal and sagittal planes. Measurements were corrected for magnification. Tunnel identification, diameter measurements, and cross-sectional area (CSA) calculations were recorded. A categorical classification of tunnel measurements was created to apply clinical significance to the measurements. Using kappa statistics, intra- and inter-observer reliability testing was performed. CT demonstrated excellent intra- and inter-observer reliability for tunnel identification. Intra- and inter-observer reliability was significantly less for MRI and radiographs. CT revealed superior reliability versus either radiographs or MRI for CSA analysis. Intra-observer kappa scores for tibial CSA using CT, radiographs, and MRI were 0.66, 0.5, and 0.37, respectively. Inter-observer kappa scores for tibial CSA using CT, radiographs, and MRI were 0.65, 0.39, and 0.32, respectively. Our results demonstrate CT is the most reliable imaging modality for evaluation of ACL bone tunnels as proven by superior intra- and inter-observer testing results when compared to MRI and radiographs. Radiographs and MRI were not reliable, even for simply identifying the presence of a bone tunnel.