Dynamic Kine-mri in Patellofemoral Instability in Adolescents- an Aid in the Diagnosis

Purpose: The impact of kinematic-MRI (KINE-MRI) in the patellofemoral instability and anterior knee pain of the adolescents is rarely reported.Interest was to evaluate the patellofemoral joint biomechanics with KINE-MRI in adolescents with affected and unaffected knees in a case-control study.Methods: KINE-MRI was performed in 29 adolescents (affected knee group, AKG, n=29 and n=26 unaffected knee group, UAKG, n=26) aged 11-16 years with unilateral patellofemoral instability. For the control group invvestigators enrolled ten healthy age- and sex-matched volunteers (healthy knee group, HKG, n=19 ).The study parameters, Bisect Offset (BSO), Lateral Patellar Displacement (LPD), Patellar Tilt Angle (PTA), Sulcus Angle and Insall-Salvati ratio at 0, 10, 20 and 30 degrees of flexion-extension, were measured for the AKG patients (n=29), and UAKG patients (n=26) and the HKG subjects (n=19). Results: In a comparison between the AKG patients and the HKG subjects there was a significant difference in the BSO-ratio, LPD-test and PTA-test. In these parameters the difference between the AKG patients and the HKG subjects progressively increased towards the full extension of the knee. In the AKG and UAKG patients BSO-ratio at 0 degree ranged between 0.5 and 1.2 in both groups, whereas the BSO-ratio in the HKG subjects ranged between 0.33 and 0.75 (P < .001). At the zero degree the LPD-test ranged between 0 and 10 mm in the AKG patients and between 0 and 35 mm in the UAKG patients, whereas the lateral displacement-test ranged between 0 and 5 mm in the HKG subjects (P = .003). Patellar tilt angle-test ranged between -30 and 20 degrees in the AKG patients and between -30 and 24 degrees in the UAKG patients and in the HKG subjects the PTA-test ranged between 10 and 24 degrees (P < .001).Conclusion: The KINE-MRI could be a feasible method for the evaluation of patellar tracking in adolescents.