Background and Objective: The distance between the tibial tuberosity and the trochlear groove (TT–TG) is an important criterion in the assessment of patellar instability. The measurement of this distance in CT scan and magnetic resonance imaging may differ from each other. The aim of the present study was to compare the measurement of the distance between the tibial tuberosity and the trochlear groove in CT scan and magnetic resonance imaging and to evaluate the intra-rater reliability and the agreement between the two imaging methods in patients with patellar dislocation.
Method: In this retrospective paired study, 20 patients underwent CT scan and magnetic resonance imaging. A radiologist measured the bone distance between the tibial tuberosity and the trochlear groove on two occasions, one month apart, and was unaware of the results of the initial measurement on the second occasion. The intra-rater reliability was assessed using the intraclass correlation coefficient. Paired measurements were compared using paired t-tests and sensitivity analyses. The agreement between the two methods was also examined using Bland–Altman analysis.
Findings: The mean age of the patients was 24.50 ± 7.74 years, and 60% were female. At the first measurement, the mean distance between the tibial tuberosity and the trochlear groove was 15.47 ± 4.18 mm on CT and 14.15 ± 3.80 mm on MRI. The CT measurement was on average 1.32 mm greater than the MRI measurement (95% confidence interval [CI]: 0.58 to 2.07 mm; p = 0.0014). The ICC for CT was 0.965 (95% confidence interval: 0.913 to 0.986) and for MRI was 0.955 (95% confidence interval: 0.884 to 0.982). In the first measurement, the range of agreement was -1.79 to 4.44 mm. In the averaged measurements from two times, the mean bias was 1.58 mm and the range of agreement was -1.88 to 5.04 mm.
Conclusion: Measurement of the tibial tuberosity-trochlear groove distance with CT was higher than with MRI, although both methods had high intra-rater reliability. The patient-level range of agreement indicates that these two methods cannot be considered interchangeable.