Referencing the trochlear groove based on three-dimensional computed tomography imaging improves the reliability of the measurement of the tibial tuberosity-trochlear groove distance in patients with higher grades of trochlea dysplasia.

Abstract

To determine whether 3D-CT imaging technique is valid and reproducible compared to conventional CT measurement technique (CCT) for the detection of a femoropatellar instability. Patients who had undergone surgery for femoropatellar instability (patellar instability group) between 2010 and 2016 (n = 37 knees of 35 patients) were retrospectively enrolled. For the matched control group, patients who had acute anterior cruciate ligament injury (<4 weeks previously; n = 30) were recruited. Preoperative CT data had been obtained in all patients. Inter-rater reliability was calculated for both measurement protocols, and inter-method reliability was calculated between the two imaging modalities. The results are reported using intraclass correlation coefficients (ICCs) and Bland-Altman 95% limits of agreement. All patients in the patellar instability group had femoral trochlear dysplasia (Dejour types A: four, B: 19, C: seven, and D: six), but no dysplasia was noted in the control group. In the patellar instability group, the CCT technique showed a poor inter-rater agreement (ICC = 0.74), and the 3D-CT technique still showed excellent inter-rater agreement (ICCs = 0.91). In the sub-analysis of the patellar instability group according to the trochlear dysplasia grade, ICCs were markedly decreased with severe trochlear dysplasia when using CCT technique; however, the 3D-CT technique could provide excellent reliability even with severe trochlear dysplasia. The 3D-CT imaging technique for the measurement of the TT-TG distance can be suggested as a better measurement technique for patellar instability patients with bone abnormality.