MR DIAGNOSIS OF TEARS OF ANTERIOR CRUCIATE LIGAMENT OF THE KNEE - IMPORTANCE OF ANCILLARY FINDINGS

OBJECTIVE. Detection of tears of the anterior cruciate ligament with M R is usually based on the appearance of the ligament. However, other M R findings may be useful to establish the diagnosis. We assessed the u tility of these ancillary MR findings for detecting tears and for diff erentiating partial from complete tears of the anterior cruciate ligam ent. MATERIALS AND METHODS. MR images of 68 patients who had arthrosco pic correlation were retrospectively reviewed by two radiologists who did not know the arthroscopic findings. The reviewers noted the presen ce and location of bone bruises (nonlinear low signal in the bone marr ow on T1-weighted images), assessed posterior displacement of the post erior horn of the lateral meniscus, and measured the posterior cruciat e ligament angle. At arthroscopy, 39 patients had tears of the anterio r cruciate ligament (24 complete, 15 partial) and 29 had intact anteri or cruciate ligaments. RESULTS. The presence of bone bruising in the p osterolateral tibial plateau had sensitivities of 50% and 46%, with co rresponding specificities of 97% and 97% for the two reviewers. Poster ior displacement of the posterior horn of the lateral meniscus had a s ensitivity of 56% for both reviewers, with 100% and 97% specificities. An angle of the posterior cruciate ligament less than 105 degrees had sensitivities of 72% and 74%, with corresponding specificities of 79% and 86%. The prevalence of these findings was similar in patients wit h partial tears and those with complete tears. CONCLUSION. Ancillary M R imaging findings may be helpful for diagnosing tears of the anterior cruciate ligament when diagnosis based on the MR appearance of the li gament is equivocal. Ancillary findings cannot be used to differentiat e patients with partial tears from those with complete tears. The pres ence of bone bruising in the posterior aspect of the tibial plateau an d posterior displacement of the posterior horn of the lateral meniscus are highly specific for a torn anterior cruciate ligament; therefore, the presence of either of these findings should be considered strong evidence of a tear of the anterior cruciate ligament.