Magnetic Resonance Imaging Characteristics of the Medial Patellofemoral Ligament Lesion in Acute Lateral Patellar Dislocations Considering Trochlear Dysplasia, Patella Alta, and Tibial Tuberosity-Trochlear Groove Distance

Purpose: The objective of this study was to analyze the injury patterns of the medial patellofemoral ligament (MPFL) in acute lateral patellar dislocations (LPDs) considering the anatomically relevant factors of patellar instability. Methods: Knee magnetic resonance images were collected from 73 patients within 7 weeks after LPD, and the injury patterns of the MPFL were evaluated for trochlear dysplasia, for patellar height, and for the tibial tuberosity-trochlear groove (TT-TG) distance. Results: Injury to the MPFL was found in 98.6% of the patients (72 of 73) after the acute LPD, with a complete tear in 51.4% (37 of 72), most frequently localized at the femoral attachment site, and a partial tear in 48.6% (35 of 72). Injury to the femoral origin (Fem), to the midsubstance (Mid), and to the patellar insertion (Pat) of the MPFL was found in 50.0% (36 of 72), 13.9% (10 of 72), and 13.9% (10 of 72), respectively. More than 1 site of injury was found in 22.2% (16 of 72), most frequently as a combined injury at the femoral origin and at the patellar insertion sites (Pat+Fem) (13 of 16). The study population, as well as the Pat, Fem, and Pat+Fem subgroups, showed significantly different values of trochlear dysplasia and patellar height when compared with the control group, whereas the data of the Mid group were not significantly different. In addition, injury at the patellar insertion (Pat) was accompanied by a significantly increased TT-TG distance when compared not only with the control group but also with the Fem, Mid, and Pat+Fem groups. Conclusions: The data from our study indicate that patterns of MPFL injury depend on trochlear dysplasia, patellar height, and TT-TG distance. They show a new aspect in the complex interplay between active, passive, and static stabilizers of the patellofemoral joint. Level of Evidence: Level IV, diagnostic case-control study.