Background: Recurrent patellar instability (RPI) is strongly influenced by osseous morphology of the patellofemoral joint, yet population-specific data from South Asia remain scarce. This study evaluated magnetic resonance imaging (MRI) parameters of trochlear and patellar geometry in Nepalese patients with RPI compared with matched controls.

Methods: In this hospital-based case-control study, 72 patients with clinically confirmed RPI and 72 age- and sex-matched controls without patellofemoral pathology underwent standardized knee MRI at 15–20° flexion. Patellar tilt angle (PTA), sulcus angle (SA), and lateral trochlear inclination (LTI) were measured independently by two blinded orthopedic surgeons, and mean values were compared using independent-sample t-tests (p < 0.05).

Results: Patients with RPI demonstrated significantly greater PTA (25.8 ± 5.7° vs. 14.3 ± 4.8°), larger SA (143.6 ± 6.5° vs. 135.1 ± 5.3°), and smaller LTI (9.2 ± 3.3° vs. 15.6 ± 4.1°) than controls (p < 0.001 for all). These morphologic deviations indicate a shallow trochlear groove and increased lateral patellar tilt, both predisposing to recurrent lateral displacement.

Conclusion: MRI assessment confirmed that increased patellar tilt and sulcus angle with reduced lateral trochlear inclination are key morphologic correlates of recurrent patellar instability in the Nepalese population. Integrating these quantitative MRI parameters into diagnostic and preoperative planning may improve risk stratification and guide surgical decision-making, particularly in resource-limited settings where population-specific normative data are essential.

Keywords: Patellofemoral joint, Recurrent patellar instability, Lateral trochlear inclination, Sulcus angle, Patellar tilt, Magnetic resonance imaging, Nepalese population