The Lateral Meniscal Oblique Radial Tear: MRI Identification of a Biomechanically Important Tear Pattern Associated With Anterior Cruciate Ligament Injury

BACKGROUND. The lateral meniscal oblique radial tear (LMORT) is a recently described, biomechanically important tear pattern associated with anterior cruciate ligament (ACL) injury. OBJECTIVE. The purposes of this study were to assess the utility of MRI for distinguishing LMORT lesions from other posterior lateral meniscal tears in patients undergoing primary ACL reconstruction, using an arthroscopic reference standard, and to assess potential independent predictors of LMORT lesions on MRI. METHODS. An arthroscopic database of 568 ACL reconstructions (December 2022-December 2023) included 140 lateral meniscal posterior horn or posterior root tears meeting the inclusion criteria. An orthopedic surgeon, blinded to the original arthroscopic report, reviewed the arthroscopic images for LMORT presence and type. Three musculoskeletal radiologists, also blinded to the original arthroscopic report, independently reviewed posterior lateral meniscal tears for LMORT presence, lesion type based on treatment, the presence of a meniscofemoral ligament tear, presence of meniscal extrusion, and presence of the "meniscal sail" sign. Sensitivity and specificity were calculated for each reader, and the kappa coefficient assessed interreader agreement. Univariate regression analysis assessed for independent imaging predictors of LMORT lesions using a p value of less than .05. RESULTS. Arthroscopic review identified 51 LMORT lesions (9.0% of ACL reconstructions, 36.4% of lateral meniscal posterior tears; 19 female patients, 32 male patients; mean age, 28.1 years; age range, 14-50 years). MRI had a sensitivity of 76.5-80.4% and specificity of 54.9-88.2% for all LMORT lesions, with moderate to substantial interreader agreement (0.443-0.747). MRI showed a higher sensitivity for the classification of LMORT type 3 and 4 lesions (82.6-91.3%) than for the classification of type 1 (12.5-25.0%) or type 2 (0-27.3%) lesions. Lateral meniscal extrusion was an independent predictor of LMORT presence (p = .049). CONCLUSION. MRI can be used to distinguish LMORT lesions from other posterior lateral meniscal tears, and lateral meniscal extrusion may serve as a useful feature in the identification of LMORT lesions on MRI. CLINICAL IMPACT. The LMORT lesion is a biomechanically important meniscal tear pattern that should be included in the MRI search pattern of patients with ACL tears.