Tibial Tuberosity-Tibial Intercondylar Midpoint Distance Can Be Interchangeably Measured on Axial CT and MRI: Retrospective Cross-Sectional Comparative Study.

: It is unknown whether the tibial tuberosity-tibial intercondylar midpoint (TT-TIM) distance can be interchangeably measured on axial computed tomography (CT) and magnetic resonance imaging (MRI). The objective of this retrospective cross-sectional comparative study was to evaluate the intermethod agreement of the TT-TIM distance on axial CT and MRI and its bias towards tibial rotation (TR), age, sex, and body side. : On axial CT and MRI of 15 consecutive knee pairs where each pair belonged to the same patient with no pathology affecting the tibial circumference and tibial tuberosity, TT-TIM distance and TR were measured by two blinded radiologists at 2-week intervals. Upon checking the symmetry of distributions (Shapiro-Wilk test), differences between matched knee pairs (Wilcoxon signed-rank test), intermethod (Bland-Altman plot) and interrater agreement (intraclass correlation coefficient [ICC]), and correlations (Spearman rank correlation) were assessed. : The mean intermethod difference in TT-TIM distance was not statistically significant (-0.4 mm [-1.82, 0.96]; = 0.52). The TT-TIM distance did not differ between knee pairs ( = 0.68), its interrater agreement was almost perfect (ICC > 0.81), and no bias towards TR ( > 0.66), age ( > 0.14), sex ( = 0.66), and body side ( > 0.37) was found. : The TT-TIM distance can be interchangeably measured on axial CT and MRI with almost perfect interrater agreement, unbiased towards TR, age, sex, and body side.