Reliability of the Tibial Tubercle–Roman Arch Distance for Evaluating Tibial Tubercle Malposition and Predicting Patellar Dislocation via Magnetic Resonance Imaging

Abstract

Background: The tibial tubercle (TT)–trochlear groove (TT-TG) distance has low reproducibility in patients with a dysplastic trochlea, whereas the clinical value of the TT–posterior cruciate ligament (TT-PCL) distance remains controversial. Purposes: To establish a method to assess the position of the TT on magnetic resonance imaging (MRI) scans using the TT–Roman arch (TT-RA) distance, compare this method with the TT-TG and TT-PCL distance, and provide the pathological threshold value of the TT-RA distance in patients with patellar dislocation. Study Design: Cross-sectional study; Level of evidence, 3. Methods: The TT-RA distance, TT-TG distance, and TT-PCL distance were measured on MRI scans in 70 patients with a history of patellar dislocation and 70 healthy individuals. Inter- and intraobserver reliability of each measurement parameter were evaluated. The discriminatory capacity and the interrelationship of the 3 measurement parameters were investigated using Pearson correlation and the receiver operating characteristic curve. The pathological threshold values of these measurements were calculated according to the data of healthy individuals. Finally, logistic regression analysis was performed using these values. Results: Patients with patellar dislocation had a greater TT-RA distance compared with healthy individuals (18.05 ± 4.16 vs 13.86 ± 2.90 mm; P < .001). The TT-RA distance had a stronger diagnostic capacity, with an area under the curve of 0.802 compared with 0.625 for TT-PCL distance. Excellent reproducibility was seen for TT-RA distance measurement at any degree of trochlear dysplasia (all intraclass correlation coefficients [ICCs] >0.90). The inter- and intraobserver ICCs of the TT-TG distance measurements were extremely low for Dejour type D dysplasia (ICC, 0.509 and 0.616, respectively). The pathological TT-RA distance threshold was calculated as 19.5 mm. Logistic regression showed that patients with a TT-RA distance >19.5 mm were 11.7 times more likely to sustain patellar dislocation than were those with TT-RA distance less than this value. Conclusion: The TT-RA distance was a more reliable parameter with which to evaluate TT position than was TT-TG distance in patients with trochlear dysplasia. The TT-PCL distance was the least reliable among the 3 parameters studied.

Pure and Mixed Imaging Tests, Precision, and Sex Dependence in Patellofemoral Imaging: Letter to the Editor

“…although the aim was to have the knee extended in the MRI scanner, the actual knee angle was not measured." 3 Could this be a glimpse that rotational issues might have a bearing in the threshold difference? Unfortunately, this was not investigated.…”

Pure and Mixed Imaging Tests, Precision, and Sex Dependence in Patellofemoral Imaging: Response

“…Therefore, the role of true tibial tubercle lateralization in the evaluation of patellar dislocation patients warrants further assessment. As mixed imaging tests, the TT-RA distance (AUC ¼ 0.8) and TT-TG distance (AUC ¼ 0.8) had higher capacity than TT-PCL distance (AUC ¼ 0.6) to distinguish patients with patellar dislocation from healthy individuals, 5,6 which indicate that the mixed imaging tests would be more suitable to evaluate patellar dislocation.As for the question of the accuracy of the TT-RA distance. We used the intraclass correlation coefficient to evaluate the precision of the measurements, and found that the TT-RA distance showed higher inter-and intraobserver reliability than the TT-TG distance (Table 2 of our study 6 ), especially in patients with patellar dislocation (Figure 6 of our study 6 ).…”

“…Therefore, the role of true tibial tubercle lateralization in the evaluation of patellar dislocation patients warrants further assessment. As mixed imaging tests, the TT-RA distance (AUC ¼ 0.8) and TT-TG distance (AUC ¼ 0.8) had higher capacity than TT-PCL distance (AUC ¼ 0.6) to distinguish patients with patellar dislocation from healthy individuals, 5,6 which indicate that the mixed imaging tests would be more suitable to evaluate patellar dislocation.…”

“…

We thank Dr Nizic ´for his interest for our recently published study. 6 The tibial tubercle-Roman arch (TT-RA) distance has landmarks on the tibia and femur. Therefore, the translation of the tibia or the rotation of knee joints would alter the value of TT-RA distance.

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“…4 We found that the value of TT-RA distance is affected by the rotation or flexion of the knee joint, which is also the case for the current gold standard tibial tubercle-trochlear groove (TT-TG) distance. 1,4,6 Therefore, the TT-RA distance is a mixed imaging test.We do agree with Dr Nizic ´that a test of tibial tuberosity lateralization that is independent of femorotibial rotation may be a more reliable assessment. Some measurements such as tibial tuberosity-tibial intercondylar midpoint (TT-TIM) distance, 2 or tibial tubercle-posterior cruciate ligament (TT-PCL) distance 3 can evaluate pure tibial tubercle lateralization.…”