Abstract
The purpose of this study was to determine the accuracy of MRI scan for the detection of meniscal pathology in our unit. There are published data which show that both sensitivity and specificity can approach 90% when compared to arthroscopic findings.
We retrospectively analysed a single surgeon series of 240 scopes for all indications The arthroscopic reports included an outline diagram of the meniscus upon which the surgeon recorded operative findings. 112 of these patients had also had recent MRI.
We looked at whether the MRI report showed a tear, and this was graded Y/N. The arthroscopic report was graded for tear: Y/N. 66 patients had a positive scan. 64 of these were found to have a tear at surgery. 37 scans were reported as “no tear”, of which 4 were found to have a tear at surgery. Nine scans were not easy to classify as they were descriptive.
In our series of 112 knees, MRI was 90.5% sensitive, 89.5% specific and 90.1% accurate.
When a definite diagnosis of “tear”, or “no tear” was made at scan, there were two false positives and four false negatives. False positives may be unnecessarily exposed to the risks of surgery. Patients with negative scans had a mean delay to surgery of 33 weeks compared to 18 weeks for patients with positive scans. False negatives may wait longer for their surgery. Two of the false negative scans clearly showed meniscus tears which were missed by the reporting radiographer. In our series the scan itself was more accurate than the reporting. It is important to have an experienced musculoskeletal radiologist to minimise the number of missed tears. It is also important for surgeon to check the scan as well as the report.
