Medial meniscal stabilizers, variants, and injuries of the knee

The stability and function of the medial meniscus is linked to the complex anatomy and biomechanics of the medial, posteromedial, and posterior knee capsuloligamentous structures, including the superficial medial collateral ligament, deep medial collateral ligament, posterior oblique ligament, semimembranosus tendon and its expansions including the oblique popliteal ligament, and the meniscocapsular and meniscotibial ligaments. These components provide static and dynamic stability against valgus stress, tibial rotation, and anterior tibial translation. Injuries to these structures can contribute to meniscal pathology including extrusion, ramp lesions, early cartilage degeneration, and failure of cruciate ligament reconstructions. MRI plays a crucial role in the evaluation of these structures, aiding in diagnosis and allowing for an understanding of injury patterns. However, anatomic variations and differences in classification schemes may create challenges, particularly with regard to ramp lesions which occur at the posteromedial meniscocapsular junction. These lesions are frequently associated with anterior cruciate ligament tears and are often underdiagnosed without careful imaging evaluation or special attention during arthroscopy. In this article, we will discuss the anatomy (including historical and contemporary perspectives) and injury patterns of the medial supporting structures, posteromedial corner, and posterior capsular junction of the medial meniscus of the knee with a focus on MRI. Recognition of nuanced anatomy and pathology of these stabilizing structures is essential for appropriate treatment planning and optimization of patient outcomes. Key Points 1) Medial meniscal stability relies on complex interactions between the superficial medial collateral ligament (sMCL), deep medial collateral ligament (dMCL), posterior oblique ligament (POL), semimembranosus tendon, and posteromedial meniscocapsular structures resisting valgus, rotational, and translational forces. 2) sMCL injuries often co-occur with anterior cruciate ligament (ACL) and posteromedial corner tears and precise localization is key. Proximal tears are most common, while distal tears may require surgery due to potential soft tissue interposition. 3) The semimembranosus tendon and expansions contribute to posteromedial knee stability and mobilization of the posterior horn of the medial meniscus during knee flexion, preventing meniscal impingement and tears. 4) Ramp lesions at the posteromedial meniscocapsular junction frequently accompany ACL tears and are difficult to detect without careful analysis on MRI and arthroscopy.