Introduction: The distance between the tibial tuberosity and the trochlear groove (TT–TG) is a key metric in the assessment of patellar instability. Measurements of this distance may differ between computed tomography (CT) scans and magnetic resonance imaging (MRI). The aim of this study was to compare TT–TG distance measurements obtained via CT and MRI, evaluate intra-rater reliability, and assess the level of agreement between these two imaging modalities in patients with patellar dislocation.
Methods: In this retrospective paired study, 20 patients underwent both CT and MRI scans. A radiologist measured the bony distance between the tibial tuberosity and the trochlear groove on two separate occasions, one month apart; the radiologist was blinded to the initial measurement results during the second assessment. Intra-rater reliability was evaluated using the intraclass correlation coefficient (ICC). Paired measurements were compared using a paired t-test and sensitivity analyses. Additionally, the level of agreement between the two imaging methods was examined using Bland–Altman analysis.
Results: The mean age of the patients was 24.50 ± 7.74 years, and 60% were female. During the first measurement session, the mean TT–TG distance was 15.47 ± 4.18 mm on CT scans and 14.15 ± 3.80 mm on MRI scans. Measurements obtained via CT scan were, on average, 1.32 mm greater than those obtained via magnetic resonance imaging (95% confidence interval [CI]: 0.58 to 2.07 mm; p = 0.0014). The intraclass correlation coefficient (ICC) was 0.965 (95% CI: 0.913 to 0.986) for CT scans and 0.955 (95% CI: 0.884 to 0.982) for magnetic resonance imaging. For the first set of measurements, the limits of agreement ranged from -1.79 mm to 4.44 mm. Based on the average of two sets of measurements, the mean bias was 1.58 mm, with limits of agreement ranging from -1.88 mm to 5.04 mm.
Conclusion: Measurements of the distance between the tibial tubercle and the trochlear groove yielded higher values ​​when performed via CT scan compared to magnetic resonance imaging, although both methods demonstrated high intra-rater reliability. The limits of agreement at the patient level indicate that these two methods cannot be considered interchangeable.