Patellofemoral instability: Quantitative evaluation of predisposing factors by MRI

Objective: To determine the contribution of MRI in evaluating patellofemoral instability (PFI) and to compare the underlying predisposing factors between the study and control groups. Materials and methods: We enrolled knee MRI scans of 38 patients with lateral patellar dislocation (LPD) and 38 control subjects. All MRI scans were examined for LPD and patellofemoral joint (PFJ) morphological abnormalities. The lateral trochlear inclination angle, sulcus angle and trochlear depth were the MR measures for trochlear dysplasia (TD), patellar height ratio was used for evaluation of patella alta, the patellar tilt angle, and the tibial tuberosity-trochlear groove (TT-TG) distance were also measured. Results: MRI confirmed PFI in 84.2% of study group and detected abnormal PFJ morphological factors in all cases. The prevalences and mean values of all MR parameters showed significant differences (p < 0.001) between the study and control groups. MR parameters for TD had the highest sensitivity of 57.9%, while the TT-TG distance was the most specific 97.4% for PFI. The prevalence of combined PFJ abnormal morphological factors was 36.8% in the study group. Conclusion: MRI was useful in quantitative measuring of the predisposing factors contributing to PFI resulting in significant difference in all MR parameters between the study and control groups.