The accuracy of magnetic resonance imaging (MRI) in detecting meniscal pathology

The purpose of this study was to determine the accuracy of Magnetic Resonance Imaging (MRI) scanning in the detection of meniscal pathology in a district general hospital.

We retrospectively analysed a single-surgeon series of 240 knee arthroscopic investigations for all indications. The arthroscopic reports included an outline diagram of the meniscus upon which the surgeon could record his operative findings. 112 of these patients had also had a recent MRI scan. We compared the MRI findings with the arthroscopy findings.

66 patients had a positive MRI scan. 64 of these were found to have a meniscal tear at surgery. 37 MRI scans were reported as "no tear", of which four were found to have a meniscal tear at surgery. Nine MRI scans were descriptive, e.g. "signal change, possible tear", or "tear cannot be ruled out." These tended to correspond with equivocal arthroscopic findings of "degeneration" or "fibrillation". In our series of 112 patients with meniscal pathology, MRI scanning was 90.5% sensitive, 89.5% specific and 90.1% accurate.

False positive MRI scans may lead to unnecessary surgery. Patients with negative MRI scans had a mean delay to surgery of 33 weeks compared to 18 weeks for patients with positive MRI scans. Patients with false negative MRI results may wait longer for their surgery. Two of the false negative MRI scan reports clearly showed meniscus tears, which were not identified by the reporting radiologist. In our series, the MRI scan itself was more accurate than the reporting. It is important to have an experienced musculoskeletal radiologist to minimise the number of missed meniscal tears. It is also important for the surgeon to review the MRI scan itself, as well as the report.