OBJECTIVE: To evaluate the diagnostic accuracy of magnetic resonance imaging (MRI) of the knee. MATERIALS AND METHODS: Seventy-two patients have been submitted to MRI previously to arthroscopy of the knee performed by a single surgeon and utilized as a comparative standard method. Sensitivity, specificity, values of likelihood and rate of interobserver agreement have been evaluated. RESULTS: The kappa agreement coefficient between MRI and arthroscopy was very good for lesions in the anterior cruciate ligament (0.84), good for lateral meniscus (0.75), reasonable for medial meniscus (0.50) and poor for chondral lesions (< 0.50). MRI has demonstrated high sensitivity for tears in the anterior cruciate ligament (94%) and in the medial meniscus (92%), good sensitivity for lesions in the lateral meniscus (80%), and low sensitivity for lesions in all of the chondral zones (< 50%), while the specificity has been excellent for all the chondral, and ligamentous structures, besides the lateral menisci analyzed (more than 97%), and reasonable (65%) for the medial meniscus. CONCLUSION: MRI is a useful tool in the clinical diagnosis of intra-articular knee lesions, as already demonstrated by similar results reported both in the Brazilian and international literature.

Keywords: Arthroscopy, Magnetic resonance imaging, Knee, Lesions, Sensitivity, Specificity