CT and MRI measurements of tibial tubercle lateralization in patients with patellar dislocation were not equivalent but could be interchangeable

Purpose To compare the values and the relationship of tibial tubercle lateralization measurements between computerized tomography (CT) and magnetic resonance imaging (MRI). Methods Sixty patients with patellar dislocation who underwent both CT and MRI of the same knee joint from November 2021 to February 2022 were included in our study. The intraclass correlation coefficient (ICC) and Bland–Altman analysis were performed to evaluate the reliability of tibial tubercle–trochlear groove (TT–TG), tibial tubercle–Roman arch (TT–RA), and tibial tubercle–posterior cruciate ligament (TT–PCL) distance measurements. The values of CT and MRI measurements using the same bony landmarks were compared for the difference. Pearson correlation analysis and linear regression analysis were performed to assess the correlation between CT and MRI measurements. Finally, the estimated values obtained from the regression equation were compared with the actual values obtained from the radiological measurement to evaluate the accuracy of the equations. Results A total of 60 patients with patellar dislocation who underwent both CT and MRI of the same knee joint were included in this study. The included measurements showed excellent agreement with ICCs > 0.9. TT–TG distance measured on CT (19.5 ± 5.1 mm) had a mean of 7.1 mm higher than that on MRI (12.4 ± 4.7 mm) ( P < 0.001). The mean value of TT–RA distance was 22.5 ± 3.7 mm on CT and 16.7 ± 4.9 mm on MRI ( P < 0.001), showing a mean difference of 5.8 mm. The values of TT–TG distance measured by CT and MRI were significantly correlated ( R = 0.5, P < 0.001). The values of TT–RA distance between these two modalities showed a better correlation than that of TT–TG distance ( R = 0.6, P < 0.001). The interchange values of TT–TG distance and TT–RA distance between CT and MRI can be obtained using regression equations (TT–TG distance: y = 0.6x + 12.3; TT–RA distance: y = 0.5x + 14.4). Conclusion The values of tibial tubercle lateralization measured by MRI may be underestimated compared with those measured by CT. Although the values measured on CT and MRI are not equivalent, the value in the other modality can be estimated. Therefore, an additional CT scan for tibial tubercle lateralization evaluation may not be necessary. Level of evidence Level II.