Use of the "two-slice-touch" rule for the MRI diagnosis of meniscal tears.

OBJECTIVE: We reviewed our experience with knee MRI to determine if using the "two-slice-touch" rule increased our positive predictive value for diagnosing meniscal tears. This rule classifies a meniscus as torn if there are two or more MR images with abnormal findings and as possibly torn if there is only one MR image with an abnormal finding. We also compared our sensitivity and specificity using fast spin-echo imaging with previously reported studies.
MATERIALS AND METHODS: We reviewed the medical records of 174 patients who had knee MR examinations and correlative knee arthroscopy to determine our accuracy when we diagnosed menisci as torn, possibly torn, or intact using knee arthroscopy as the gold standard.
RESULTS: Our positive predictive value increased from 91% to 94% (p = 0.37) for medial meniscal tears and from 83% to 96% (p = 0.02) for lateral meniscal tears when using the two-slice-touch rule compared with the standard criterion of diagnosing a meniscus as torn if one or more images are abnormal. When using the standard criterion, we had 95% sensitivity and 85% specificity for diagnosing medial meniscal tears and 77% sensitivity and 89% specificity for diagnosing lateral meniscal tears.
CONCLUSION: When using the two-slice-touch rule, we had an increased positive predictive value for diagnosing menisci as torn, which was statistically significant for the lateral meniscus. Our accuracy using the standard criterion with fast spin-echo imaging was comparable to that reported in previous studies with spin-echo imaging.