Comparing Tibiofemoral Rotation Measurements Between Computed Tomography and Magnetic Resonance Imaging in Patients With Patellofemoral Instability

Background: Tibiofemoral rotation is an emerging parameter, especially in assessing patellofemoral instability. However, reference values in the literature are inconsistent regarding the used imaging modality and do not consider the effect of knee flexion during image acquisition. Purpose: To analyze the differences in tibiofemoral rotation measurements between computed tomography (CT) and magnetic resonance imaging (MRI). Study Design: Cross-sectional study; Level of evidence, 3. Methods: A total of 78 knees in 72 patients were included. All patients underwent surgery for patellofemoral instability at our institution and preoperative CT and MRI were available. Tibiofemoral rotation was measured on axial CT and MRI, whereas the respective knee flexion angle (KFA) was measured on sagittal images. Tibiofemoral rotation values in which the tibia was externally rotated to the femur were handled as positive values. Differences between CT and MRI measurements were calculated and the association between KFA and tibiofemoral rotation was evaluated using Pearson correlation and the Mann-Whitney U test. Results: The mean tibiofemoral rotation was 8.7°± 5.5° in CT and 4.2°± 6.7° in MRI ( P < .001). The mean KFA was 2.4°± 3.1° in CT and 14.9°± 6.4° in MRI ( P < .001). The difference in the KFA between CT and MRI moderately correlated with the difference in tibiofemoral rotation between imaging modalities ( r = 0.529; P < .001). Conclusion: Tibiofemoral rotation measurements significantly differed between CT and MRI, with larger values observed in CT. The difference between imaging modalities correlated with the degree of knee flexion during image acquisition. This observation should be considered when assessing tibiofemoral rotation, as current reference values in the literature are inconsistent regarding the used imaging modality.