Background/Objectives: The aim of our study was to identify the most reliable MRI measurements associated with patellar dislocation. Methods: MRI scans from 86 knees (48 controls and 38 with a history of patellar dislocation) were retrospectively analyzed. The following parameters were measured: lateral trochlear inclination (LTI) and its modified version, sulcus angle (SA), trochlear depth (TD), tibial tubercle–trochlear groove distance (TT–TG), patellar tendon–lateral trochlear ridge distance (PT–LTR), and PT–LTR horizontal, a novel modification. Inter-rater reliability was assessed using intraclass correlation coefficients (ICCs), and diagnostic accuracy was evaluated using ROC analysis. Results: All measurements significantly differed between the groups (p < 0.05). SA and TD were highly discriminative (AUC > 0.8) but demonstrated lower inter-rater agreement. PT-LTR horizontal strongly correlated with PT-LTR and was equally sensitive and specific for patellar dislocation as PT-LTR (81.6% and 87.5%, respectively) when in line or extending more laterally than the lateral trochlear ridge (AUC = 0.896, p < 0.001). LTI demonstrated the highest diagnostic performance with a sensitivity of 89.5% and a specificity of 97.9% for a cut-off ≤12.85° (AUC = 0.981), with excellent inter-rater agreement. LTI modified also performed well (AUC = 0.937), with a sensitivity and specificity of 81.6% and 93.7%, respectively. Conclusions: LTI, PT–LTR, and their modified versions demonstrated the highest reliability and diagnostic performance among the MRI measurements evaluated. Given their reproducibility and ease of application, these parameters may be useful in the imaging assessment of patellar dislocation. Further prospective studies are recommended to confirm their clinical utility in broader populations.