the menisci. MRI is widely accepted as the optimal imaging modality because of superior soft tissue contrast. On cross-sectional MRI, the normal meniscus appears as a uniform low-signal (dark) triangular structure (Figure 9). A meniscal tear is identified by the presence of an increased intrameniscal signal that extends to the surface of this structure. Several studies have evaluated the clinical utility of MRI for meniscal tears. In general, MRI is highly sensitive and specific for tears of the meniscus. The sensitivity of MRI in detecting meniscal tears ranges from 70% to 98%, and the specificity, from 74% to 98%.48,62,105,107,117 The MRI of 1014 patients before an arthroscopic examination had an accuracy of 89% for pathology of the medial meniscus and 88% for the lateral meniscus.48 A meta-analysis of 2000 patients with an MRI and arthroscopic examination found 88% sensitivity and 94% accuracy for meniscal tears.105,107 There have been discrepancies between MRI diagnoses and the pathology identified during arthroscopic examination. Justice and Quinn reported discrepancies in the diagnosis of 66 of the 561 patients (12%).86 In a study of 92 patients, discrepancies between the MRI and arthroscopic diagnoses were noted in 22 of the 349 (6%) cases.106 Miller conducted a
single-blind prospective study comparing clinical examinations and MRI in 57 knee examinations.117 He found no significant difference in sensitivity between the clinical examination and MRI (80.7% and 73.7%, respectively). Shepard et al assessed the accuracy of MRI in detecting clinically significant lesions of the anterior horn of the meniscus in 947 consecutive knee MRI154 and found a 74% false-positive rate. Increased signal intensity in the anterior horn does not necessarily indicate a clinically significant lesion.154
conclUsions The menisci of the knee joint are crescent-shaped wedges of fibrocartilage that provide increased stability to the femorotibial articulation, distribute axial load, absorb shock, and provide lubrication to the knee joint. Injuries to the menisci are recognized as a cause of significant musculoskeletal morbidity. Preservation of the menisci is highly dependent on maintaining its distinctive composition and organization.
AcKnoWledgment We wish to thank Tom Cichonski for his assistance in the formatting of this manuscript.
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