MR-IMAGING OF ANTERIOR CRUCIATE LIGAMENT INJURY - INDEPENDENT VALUE OF PRIMARY AND SECONDARY SIGNS

OBJECTIVE. The purpose of this blinded study was to test the value of primary and secondary signs, independent of each other, for diagnosis of a tear of the anterior cruciate ligament (ACL) by means of MR imagi ng. MATERIALS AND METHODS, MR images of the knee in 74 patients who ha d the status of the ACL confirmed arthroscopically were blindly review ed for status of the ACL three times: with primary signs masked, with secondary signs masked and with no signs masked. On the basis of the o bserved signs at each session, the status of the ACL was predicted and the confidence in that prediction was noted. The MR imaging predictio ns were compared with the arthroscopic findings, The results were anal yzed with receiver operating characteristic curves and stepwise discri minant analysis. RESULTS. We found no difference in diagnostic perform ance when only primary signs were used and when both primary and secon dary signs were used. When using primary signs only, our observers per formed significantly better than when using secondary signs alone. How ever, with secondary signs alone, our observers pet-formed better than if left to chance for predicting ACL status. Of the secondary signs, our statistical analysis found bone contusion, anterior translation of the tibia, and an uncovered posterior horn of the lateral meniscus to be the most useful for diagnosis. CONCLUSION. Secondary signs do have value for deciding ACL status independent of primary signs. However, our observers performed much better when using primary signs instead o f secondary signs. In the clinical setting, secondary signs do not hel p significantly in the diagnosis of ACL tears by means of MR imaging.