Medial meniscus ramp lesion injury increases extrusion and meniscal mobility

Background: Medial meniscus ramp lesions, involving the posterior horn and its meniscocapsular attachments, occur in up to 40% of anterior cruciate ligament (ACL) reconstructions. While these injuries are associated with increased rotatory laxity and anterior tibial translation in ACL-deficient knees, their specific impact on meniscal kinematics and extrusion under axial loading remains insufficiently characterized. Objective: This cadaveric study aimed to quantify and compare medial meniscal mobility and extrusion between intact knees and those with grade 4 ramp lesions using 7-Tesla MRI and digital volume correlation (DVC) under varying axial loads. Key Points: Two cadaveric specimens were subjected to axial loads of 0N, 750N, and 1500N in full extension. Following the creation of a grade 4 ramp lesion via a posteromedial arthroscopic approach, DVC analysis of 33,619,968 data points demonstrated significant increases in meniscal displacement. At 1500N, the mean lateromedial displacement (extrusion) increased from 2.11–2.81 voxels in native knees to 4.48–4.71 voxels in injured knees. Similarly, mean anteroposterior displacement increased from 0.48–2.11 voxels to 3.29–7.31 voxels post-injury. These findings indicate that disruption of the meniscotibial and meniscocapsular attachments significantly compromises the stabilizing "hoop" function of the medial meniscus. Conclusion: Grade 4 medial meniscus ramp lesions significantly increase meniscal extrusion and posterior mobility during axial compression, even in ACL-intact states. Because meniscal extrusion is a known precursor to compartment hyper-pressure and cartilage degeneration, these results suggest that surgical repair of ramp lesions may be necessary to restore joint kinematics and prevent secondary osteoarthritis.