a b s t r a c t Objective: To determine the contribution of magnetic resonance imaging (MRI) in evaluating patelofemoral instability. Methods: 39 patients (45 knees) with patellar instability underwent knee magnetic resonance images between October 2009 and July 2011, at the Rede Lab's D'Or, in the city of Rio de Janeiro, State of Rio de Janeiro, were included. MRI were analyzed for the presence of bone, hyaline cartilage and soft-tissue abnormalities, as well as anatomic variants that may contribute to chronic patellar instability. Results: The authors found, of the 45 knees analysed, bone changes in 44%, cartilaginous injuries in 64%, disruption of the medial patellofemoral ligament (MPFL) in 29% and joint morphology abnormalities in 73% patients. Meniscal tears were also identified in 2 (4%) patients and fibular fracture in one (2%) patient. Conclusion: MRI allowed the detection of predisposing factors that may contribute to the development of patellofemoral instability and the diagnosis of bone, hyaline cartilage, ligamentous and meniscal abnormalities.

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