Medial meniscus extrusion is a specific condition affecting the knee joint, involving the displacement of a crescent-shaped cartilage structure. This displacement can lead to altered mechanics within the knee, impacting its normal function. Understanding this condition involves recognizing how this internal knee component moves from its usual position.
Understanding Medial Meniscus Extrusion
The medial meniscus is a C-shaped fibrocartilage disc located on the inner side of the knee, between the medial femoral condyle (thigh bone) and tibial plateau (shin bone). It functions as a shock absorber, distributing forces across the joint and enhancing knee stability by deepening the tibial surface for articulation with the femur. The medial meniscus covers approximately 50-60% of the articular surface between these bones.
Extrusion occurs when the medial meniscus moves radially, or outward, beyond its normal boundary with the tibial plateau. This displacement means the meniscus is no longer fully positioned to cushion the joint or distribute weight effectively, compromising its ability to bear load and maintain knee stability. A displacement of 3 millimeters or more is considered significant.
Common Causes
Medial meniscus extrusion often results from a disruption of the circumferential collagen bundles within the meniscus. Tears, particularly those involving the posterior root of the meniscus or large radial tears extending over 50% of the meniscal width, can destabilize the meniscus and lead to extrusion.
Degenerative changes, often age-related, contribute to the weakening and fraying of the meniscus over time, making it more susceptible to extrusion. Chronic instability within the knee joint or conditions like varus malalignment, where the knee bows outward, can also increase the load on the medial compartment and promote extrusion. Repetitive stress or certain activities can also contribute.
Diagnosis and Symptoms
Individuals experiencing medial meniscus extrusion report pain on the inside of the knee, which may worsen with activity. Swelling, clicking or popping sensations within the knee, and a feeling of instability or the knee “giving way” are also reported. These symptoms arise from the compromised function of the displaced meniscus.
Medical professionals diagnose medial meniscus extrusion through a physical examination, assessing the knee’s range of motion, stability, and tenderness along the joint line. Imaging techniques are also employed, with Magnetic Resonance Imaging (MRI) being the primary tool. MRI provides detailed images of soft tissues, allowing for clear visualization and accurate measurement of meniscal displacement from the tibial margin.
Treatment Options
Treatment for medial meniscus extrusion involves both non-surgical and surgical approaches, depending on the severity of the extrusion, presence of associated tears, and patient symptoms. Conservative management begins with rest, ice application, compression, and elevation (RICE) to reduce pain and swelling. Pain relief can also be achieved with non-steroidal anti-inflammatory drugs (NSAIDs).
Physical therapy plays a significant role in conservative treatment, focusing on strengthening the muscles surrounding the knee to improve joint stability and support. Exercises to restore range of motion and proprioception are also included. For persistent symptoms or significant extrusion, especially if associated with a meniscal tear, surgical intervention may be considered.
Surgical options include arthroscopic partial meniscectomy, which involves removing the damaged portion of the meniscus, preserving healthy tissue. In some cases, particularly for younger patients with tears in the well-vascularized “red zone” of the meniscus, meniscal repair may be attempted to preserve the meniscus and its load-bearing function. Another procedure, meniscus centralization, aims to reposition the extruded meniscus and secure it back to its normal anatomical location, often through repairing the meniscotibial ligaments or capsule. This technique helps restore the meniscus’s ability to share load across the knee compartment.
Implications for Joint Health
Medial meniscus extrusion has long-term implications for knee joint health. When the meniscus moves out of its normal position, its ability to distribute load across the knee joint is compromised. This altered biomechanics leads to increased stress and concentrated pressure on the articular cartilage of the knee.
This increased stress can accelerate the wear and tear of the cartilage, potentially leading to the development and progression of osteoarthritis. Studies indicate that meniscal extrusion is strongly associated with cartilage loss, bone marrow lesions, and joint space narrowing. Early diagnosis and appropriate management of medial meniscus extrusion are therefore important to help preserve knee health and slow down degenerative changes.