MENISCAL TEARS MISSED ON MR-IMAGING - RELATIONSHIP TO MENISCAL TEAR PATTERNS AND ANTERIOR CRUCIATE LIGAMENT TEARS

OBJECTIVE. MR imaging of the knee is a valuable technique for diagnosi ng meniscal tears, but some tears found at arthroscopy are not shown o n MR imaging. The purpose of this study was to determine whether or no t tears were more frequently missed in the presence of an anterior cru ciate ligament tear or when tears had certain locations or configurati ons. MATERIALS AND METHODS. We reviewed the original MR reports and su rgical records of 400 patients who had both an MR examination and arth roscopy of the knee. Using chi2 analysis, we examined how the sensitiv ity for detecting meniscal tears varied with the presence of a tear of the anterior cruciate ligament, with the location of the tear within the meniscus, and among six configurations of meniscal tears. We also studied whether sensitivity decreased with an increasing delay between MR examination and arthroscopy. RESULTS. In the presence of a tear of the anterior cruciate ligament, the sensitivity decreased from 0.97 t o 0.88 (p =.016) for medial meniscal tears and from 0.94 to 0.69 (p = .0005) for lateral tears. The overall sensitivity for lateral meniscal tears was significantly less for posterior (p = .001) and peripheral (p = .005) tears than for other tear locations or configurations. The sensitivities did not significantly differ between tear locations and configurations in the medial meniscus or with an increasing delay unti l arthroscopy. Patients with a torn anterior cruciate ligament were mo re likely to have peripheral tears of the medial meniscus (p = .00004) and posterior (p = .0004) and peripheral (p = .04) tears of the later al meniscus. CONCLUSION. Because of their location and configuration, meniscal tears associated with an anterior cruciate ligament injury ar e more difficult to detect on MR images than are tears in knees with a n intact ligament. If a tear of the anterior cruciate ligament is dete cted, special attention should be given to the subtle peripheral tears that may be present in either meniscus, but most commonly in the post erior horn of the lateral meniscus. These tears are especially difficu lt to detect on MR images.