Accuracy of Imaging the Menisci on an In-Office, Dedicated, Magnetic Resonance Imaging Extremity System*

Magnetic resonance imaging effectively defines and characterizes musculoskeletal pathologic lesions, par ticularly meniscal tears. Most studies comparing the efficacy of magnetic resonance imaging and arthro scopic evaluation have been performed on high-field (1.5-T) systems. The effectiveness of a low-field (0.2- T), dedicated, extremity magnetic resonance imaging device in diagnosing meniscal tears was studied pro spectively on 35 patients with knee symptoms who subsequently had arthroscopic evaluation. Magnetic resonance imaging examinations were performed be fore surgery and were read by an experienced radiol ogist who was blinded to the results of the arthroscopic evaluations. Specificity was 100% for both the medial and lateral menisci. Sensitivity was 86% for the medial menisci, 89% for the lateral menisci, and 87% for both. Accuracy was 91 % for the medial menisci, 97% for the lateral menisci, and 94% overall. The positive predic tive values were 100% for the medial menisci, 100% for the lateral menisci, and 100% for both. The nega tive predictive values were 81 % for the medial menisci, 96% for the lateral menisci, and 91 % for both. The low-field magnetic resonance imaging system provided specificity and sensitivity that were equal to or better than previous reports with high-field systems. In par ticular, this low-field system eliminated the problem of false-positive results that has been found in some stud ies using high-field systems.