Defining the role of TT-TG and TT-PCL in the diagnosis of lateralization of the Tibial tubercle in recurrent patellar dislocation.

BACKGROUND: The radiological indicators can help doctors determine whether to make tibial tubercle transfer. But which indicator is better is still in question.
METHODS: 117 knees in 103 patients who had undergone patellar surgery and 60 knees in 58 patients who had no history of patellar dislocation from 2014 to 2019 were analyzed. Significant differences of tibial tubercle-trochlear groove (TT-TG) on CT and tibial tubercle-posterior cruciate ligament (TT-PCL) on MRI between the case group and the control group were estimated by an unpaired t test. Significant differences between TT-TG on CT and TT-TG on MRI were estimated by a paired t test. The correlation between TT-PCL on MRI and tibial width was estimated by Pearson test. Receiver operating characteristic (ROC) curves and the area under the ROC curve (AUC) were measured to assess the diagnostic accuracy of TT-TG and TT-PCL on MRI.
RESULTS: The intraclass correlation coefficient (ICC) for TT-TG between CT and MRI evaluated by two raters was were 0.566. When comparing TT-TG on CT with that on MRI, the mean difference was 2.5 mm (p< 0.001). The mean TT-TG difference on CT between the case group and the control group was 5.3 mm, which was significantly bigger than the mean TT-PCL difference on MRI of 1.2 mm(p< 0.001). AUC of TT-TG on CT and TT-PCL were 0.838 and 0.580 (P< 0.001). TT-PCL correlated with tibial width (r=0.450, P< 0.001).
CONCLUSION: A statistically significance and a fair ICC proved that TT-TG could not be used interchangeably. The bigger mean difference between the case group and the control group and better AUC proved that TT-TG on CT might be an indicator more suitable for measuring the lateralization of the tibial tubercle. And TT-PCL should be considered as an individual parameter because of the significant correlation between TT-PCL and tibial width.