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Magnetic resonance imaging was used to analyse the patellofemoral relationships during the first 3O' of knee fiexion in women with recurrent patellar dislocation. The patellofemoral joints were imaged both sagittally and axially with the knee flexed O , 1O , 200, and 3 O At the beginning of knee flexion the sulcus angle was greater than in unaffected women, the lateral patellofemoral angle was smaller, the patella displaced further laterally, tilted more laterally and the congruence angle was directed more laterally. At 34 O of knee flexion these differences were less marked than at O to 1O. Logistic regression analysis showed that the sulcus angle at 10' of knee flexion was the most diagnostic feature, indicating that there is an anatomical predisposition to recurrent dislocation and that pathological patellar tracking starts from the beginning of flexion. Traditional sunrise radiographic films taken at 25#{176} to 300 knee flexion clearly miss diagnostically important information.