Lateral meniscal stabilizers, variants, and injuries of the knee

The lateral meniscus (LM) has unique anatomic and biomechanical features. Several anatomic areas of LM may represent diagnostic challenges on MRI. This article reviews the LM anatomy that pertains to accurate analysis of the LM and its stabilizers on clinical MRI. Anterior and posterior LM root attachments reside in immediate proximity to the ACL and PCL footprints. Meniscofemoral ligaments contribute to the stability of the LM in the setting of LM posterior root tears and serve as secondary restraints against posterior tibial translation in the PCL deficient knee. Congenital deficiency or traumatic injury to the popliteomeniscal fascicles can lead to hypermobile LM that can be associated with knee pain and locking. Injuries to the anterior LM often do not carry clinical significance and may represent pseudotears. LM posterior root injuries are seen in 12-15% of patients undergoing ACL reconstruction and are of great biomechanical significance. MRI diagnosis of LM posterior root tears requires a high index of suspicion. MRI signs aiding detection of LM posterior root tears include coronal cleft, sagittal ghost, axial radial defect, and sagittal truncated triangle signs. Meniscus on a string refers to a radial tear of the LM posterior root with intact meniscofemoral ligament that serves as a sole remaining posterior horn stabilizer. Deep lateral femoral notch sign has almost 40% prevalence in patients with ACL tears and concomitant LM posterior root tears. Several classifications of LM posterior root tears have been introduced recently. Lateral meniscal oblique radial tear (LMORT) Type 4 represents the most common tear pattern.