Computational analysis of factors contributing to patellar dislocation.

Treatment for an initial incidence of patellar dislocation is usually conservative management; however, almost half of patients experience a subsequent, or multiple, dislocation(s). Patients often undergo multiple procedures which fail to treat the underlying anatomic abnormalities. The objective of this study was to evaluate interactions between key predisposing anatomic factors to patellar dislocation and identify combinations of abnormal factors which increase the risk of recurrent lateral dislocation. Four factors associated with lateral patellar dislocation were identified (sulcus angle, Insall-Salvati ratio, tibial tubercle-trochlear groove distance, and femoral anteversion). A finite element model of the patellofemoral joint was developed and parameterized so that a value for each factor could be applied and the model geometry/alignment would be modified accordingly. 100 combinations of the four factors were generated in separate computational simulations and resulting kinematics and forces of the patellofemoral joint were recorded. Sulcus angle was the most impactful factor on constraint. Multiple abnormal factors were generally required to produce the extremes of patellar alignment observed in this analysis. Understanding the underlying anatomic factors, and their effect on joint mechanics, for patients with recurrent lateral patellar dislocation will aid in determining optimal treatment pathways on a patient-specific basis.