Background: The tibial tubercle to trochlear groove (TT-TG) distance is currently considered as an indication for tibial tubercle osteotomy. While the influence of femoral condylar morphology on such measurement remains unclear. Methods: A total of 86 patients with patellar dislocation (PD) and 86 healthy individuals were enrolled. Femoral condylar morphology and the TT-TG distance measured by anatomical transepicondylar axis (TT-TGa), by surgical transepicondylar axis (TT-TGs), and by posterior condylar reference line (TT-TGp) were assessed by MRI. Unpaired t-test, Spearman, and Pearson correlation analysis were conducted. We determined the pathological value of the parameters and established a binary regression model. Results: The interclass correlation coefficients of all the TT-TG distances were greater than 0.75 in all types of trochlear dysplasia. The lateral/posterior femoral condyle was shorter and the medial/posterior condyle was longer in the study group (28.5 ± 3.3 and 35.2 ± 2.8, respectively) than in the control group (30.9 ± 2.7 and 33.5 ± 2.3, respectively). In the study group, the TT-TGp distance was greater than TT-TGs and TT-TGa distance (p < 0.001). The pathological value of the TT-TG distance was 13.0 mm. Each TT-TG distance revealed a significant OR with regard to PD. Conclusion: The TT-TGa, TT-TGs, and TT-TGp distance can be reliably measured by MRI even in patients with trochlear dysplasia. While the TT-TGp distance may overestimate the lateralization deformity of the tibial tubercle. Posterior femoral condylar dysplasia may be a reason for such overestimating. These findings have not been correlated to clinical outcomes and further studies are required.

Background and Objectives: Various predisposing factors for lateral patellar dislocation (LPD) have been identified, but the relation between femoral rotational deformity and the tibial tubercle–Roman arch (TT-RA) distance remains elusive. Materials and Methods: We conducted this study including 72 consecutive patients with unilateral LPD. Femoral anteversion was measured by the surgical transepicondylar axis (S-tAV), and the posterior condylar reference line (P-tAV), TT-RA distance, trochlear dysplasia, knee joint rotation, patellar height, and hip–knee–ankle angle were measured by CT images or by radiographs. The correlations among these parameters were analyzed, and the parameters were compared between patients with and without a pathological TT-RA distance. Binary regression analysis was performed, and receiver operating characteristic curves were obtained. Results: The TT-RA distance was correlated with S-tAV (r = 0.360, p = 0.002), but the correlation between P-tAV and the TT-RA distance was not significant. S-tAV had an AUC of 0.711 for predicting a pathological TT-RA, with a value of >18.6° indicating 54.8% sensitivity and 82.9% specificity. S-tAV revealed an OR of 1.13 (95% CI [1.04, 1.22], p = 0.003) with regard to the pathological TT-RA distance by an adjusted regression model. Conclusions: S-tAV was significantly correlated with the TT-RA distance, with a correlation coefficient of 0.360, and was identified as an independent risk factor for a pathological TT-RA distance. However, the TT-RA distance was found to be independent of P-tAV.