CT as a feasible tool for quantifying anterior knee fibrosis volume following ACL reconstruction

PurposeKnee joint fibrosis after anterior cruciate ligament (ACL) reconstruction causes dysfunction and requires precise quantification. Magnetic resonance imaging (MRI) is the primary method but has limitations like high cost and long scan times. Computed tomography (CT) offers better accessibility and speed, but its reliability remains unverified. This study compares CT and MRI for quantifying fibrosis volume post-ACL reconstruction.Methods18 fibrosis patients underwent same-day CT (1.0-mm and resliced 3.5-mm) and MRI (3.5-mm). Two observers measured fibrotic volume via three-dimensional (3D) reconstruction. Standardized regions of interest (ROI) were delineated to measure total and regional fibrotic volumes across three imaging modalities: 1.0-mm CT, 3.5-mm CT, and 3.5-mm MRI. Statistical analyses included intraclass correlation coefficient (ICC), Pearson's correlation coefficient, Bland-Altman analysis, one-way ANOVA, and paired-sample t-tests.ResultsBoth Pearson correlation coefficients and ICC values between the two observers exceeded 0.9, indicating excellent correlation and agreement. Bland-Altman analysis showed low mean inter-observer differences (-1.29% to 2.78%). For comparisons between imaging modalities with identical slice thickness (3.5-mm CT vs 3.5-mm MRI), the mean differences were minimal (-3.02% to 1.06%) with Pearson correlation coefficients >0.9. ANOVA analysis revealed no significant differences, demonstrating excellent agreement between CT and MRI. Although 1.0-mm CT did not show statistically significant differences in ANOVA analysis compared to the other two modalities, its thinner slice thickness provided more detailed visualization, resulting in significantly higher volume measurements in Bland-Altman analysis. Nevertheless, it maintained excellent correlation (Pearson's > 0.9) with both 3.5-mm CT and MRI.ConclusionThis study provides a method to quantify anterior knee fibrosis. CT is a feasible tool with performance comparable to MRI. Further studies are needed for multi-regional assessment and integration with other imaging or functional parameters.