Tibial tuberosity‐trochlea groove distance is dependent on flexion angle and intra‐articular version in different magnetic resonance imaging recording techniques

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Abstract Purpose The purpose of this study was to compare the tibial tuberosity‐trochlea groove distance (TT‐TG) and the tibial tuberosity‐posterior cruciate distance (TT‐PCL) between conventional and rotatory magnetic resonance imaging (MRI). It was hypothesised that the TT‐TG varies between the investigated techniques, due to differences in knee flexion angle and intra‐articular version. Variations in TT‐TG could lead to misdiagnoses and consequently result in inappropriate surgical indications. Methods Twenty‐five patients with both a conventional knee MRI and a rotatory MRI (which allows full knee extension) due to recurrent patellar dislocation were included. TT‐TG and TT‐PCL, knee flexion angle and intra‐articular version (external rotation) were determined in each scan. Inter‐rater reliability was assessed using the intraclass correlation coefficient (ICC). Between‐group differences were assessed using the Wilcoxon matched‐pairs signed‐rank test. Spearman's correlation coefficient was used to detect correlations between the TT‐TG and TT‐PCL with flexion angle and intra‐articular version. Results The TT‐TG was significantly ( p < 0.05) higher in rotatory MRI (median: 18.4 mm, interquartile range [IQR]: 7.3 mm), in comparison to conventional MRI (median: 12 mm, IQR: 5.7 mm), while no significant differences were observed for TT‐PCL. Knee flexion angle was significantly higher in the conventional MRI (median: 21.4°, IQR: 8.6°) compared to rotatory MRI (median: 3.1°, IQR: 3.4°, p < 0.0001). The intra‐articular version was significantly lower in the conventional MRI (median: 2°, IQR: 6.3°) compared to the rotatory MRI (median: 9°, IQR: 7.3°, p < 0.0001). Measurements showed excellent interrater agreement (ICC: 0.87−0.94). Conclusion TT‐TG measurements are dependent on flexion angle and intra‐articular version, which vary with differing MRI techniques. Extension of the knee with a simultaneous higher intra‐articular version in the rotatory MRI technique, suggests increased TT‐TG close to extension, due to the screw‐home mechanism. This should be considered to avoid misdiagnosis due to the TT‐TG. Level of Evidence Level III.

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