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Value of knee MRI in the diagnosis and management of knee disorders.

The primary objectives of this study were to determine how frequently knee magnetic resonance imaging (MRI) changes (1) diagnosis, (2) diagnostic confidence, and (3) management. A secondary objective was to correlate these changes with specific patient/physician characteristics and develop a prediction model using these characteristics. Six orthopedic specialists prospectively completed surveys when ordering knee MRI (n=93). Pre-MRI surveys recorded history, symptoms, signs, diagnosis, diagnostic confidence, and planned management. Post-MRI surveys recorded diagnosis, confidence, and planned management. Changes in diagnosis, management, and diagnostic confidence were correlated with patient/physician characteristics using chi-square and logistic regression tests. A multiple variable model was created with the most significant variables from the univariate analysis, and a c-index was used for cross-validation. Magnetic resonance imaging changed diagnosis in 29.3% and management in 25.3% of cases. Confidence in diagnoses after MRI increased, on average, by 10.6%. Change in diagnosis was significantly correlated with lateral joint line pain (P=.012) and tenderness (P=.006). The 3 most significant predictors for change in management were ligament pathology (P=.017), medial-sided pain/tenderness (P=.051), and age (P=.133). A 3-variable model using these predictors was significantly better than chance alone at predicting management changes (c-index: model=0.766; cross-validation=0.661). Magnetic resonance imaging frequently changed diagnosis and management and improved diagnostic confidence in a large minority of patients with internal derangement of the knee, even after evaluation by subspecialized physicians. A statistical model using specific patient characteristics can be created to predict when MRI will change management.