Anatomy of the knee menisci
The menisci are cartilage-like structures located between the articular surfaces of the knee joint — the tibial plateau and the femoral condyles. Each meniscus consists of an anterior horn, a posterior horn, and a body connecting them.
The lateral meniscus has a more regular, rounded shape and resembles the letter O. Its anterior horn attaches anterior to the lateral intercondylar eminence, and the posterior horn attaches posterior to the lateral intercondylar eminence. The medial meniscus is less round, elongated, and resembles the letter C: its anterior horn is fixed anterior to the medial intercondylar eminence, and the posterior horn is fixed posterior to it. Along its entire arc, each meniscus is attached to the joint capsule of the knee.
Functions of the menisci
The main functions of the menisci are shock absorption and stabilization of the knee joint. Additionally, they are credited with a proprioceptive function and participation in synovial fluid metabolism due to their well-developed vascular network.
In the sagittal plane, the femoral condyle acts as a sphere resting on the flat surface of the tibial plateau. The capsuloligamentous apparatus can be compared to a cylinder, which on its own is incapable of fully stabilizing the joint. The space between the sphere, the plane, and the cylinder is filled by the meniscus, which has a triangular shape on a sagittal slice. It is precisely thanks to this "hoop" that joint surface congruency and load distribution are ensured.
Areas of blood supply
Three blood supply zones are distinguished in each meniscus:
- The red zone is the pericapsular region with the best blood supply;
- The red-white zone is a transitional region with moderate blood supply;
- The white zone is the inner part of the meniscus with poor blood supply.
The clinical significance of these zones is fundamental for treatment tactics: tears in the red zone have a good regenerative potential, can be repaired with sutures, and heal well. Injuries in the white zone have an extremely low regenerative potential, so such fragments are subject to resection to prevent entrapment between the articular surfaces.
Connections of the menisci with surrounding structures
The meniscus is not a freely floating structure, but a closely integrated element of the joint. In the anterior section, the anterior horns are connected by the transverse ligament, and fibrous bands extend from the patella to attach to the outer and inner surfaces of the anterior horns.
In the posterior section, the medial meniscus is connected by bundles of fibrous fibers to the medial collateral ligament and the tendon of the semimembranosus muscle. The lateral meniscus interacts with the tendon of the popliteus muscle and the posterior cruciate ligament, which sends a bundle of fibers to it, forming the meniscofemoral ligament (ligament of Wrisberg).
Biomechanics during flexion and extension
During flexion of the knee joint, the contact point of the articular surfaces shifts posteriorly, and both menisci move posteriorly. This is facilitated by a passive factor — the pressure of the femoral condyles, and active factors — the contraction of the popliteus and semimembranosus muscles, which pull the menisci along with them. The anterior and posterior horns remain firmly fixed in the intercondylar region, which is why the menisci inevitably deform during movement.
During extension of the knee joint, the femoral condyles push the menisci anteriorly, assisted by fibrous bands extending from the patella. During forced extension (e.g., kicking a ball hard in soccer players), the menisci may fail to keep up with the condyles, leading to injuries of the anterior horns, transverse tears, or complete detachment.
Biomechanics of rotation and mechanisms of injury
Rotation of the lower leg is possible in the knee joint. During external rotation, the lateral meniscus shifts anteriorly and the medial meniscus shifts posteriorly; during internal rotation, the picture is mirrored. The lateral meniscus is more mobile and shifts by an average of 12 mm, whereas the medial meniscus shifts by only 6 mm.
During forced rotation, especially when combined with axial and lateral loads, the meniscus can become caught between the articular surfaces "like between two millstones." In such cases, longitudinal tears and bucket-handle tears occur. Entrapment of a damaged fragment can cause locking of the knee joint. Such injuries are typical for soccer players, miners, and workers whose activities involve prolonged forced postures.
Key points
- The menisci are cartilage-like structures between the femoral condyles and the tibial plateau; they consist of an anterior horn, body, and posterior horn.
- The lateral meniscus is O-shaped and more mobile; the medial meniscus is C-shaped and more firmly fixed.
- Main functions: shock absorption, stabilization, proprioception, synovial fluid metabolism.
- Red, red-white, and white blood supply zones are distinguished; tears in the red zone are repaired, while those in the white zone are resected.
- The anterior horns are connected by the transverse ligament; the lateral meniscus is connected to the ligament of Wrisberg and the tendon of the popliteus muscle.
- During flexion, the menisci shift posteriorly, and during extension, anteriorly; forced movements lead to tears.
- Rotational injury with axial loading is a typical mechanism for longitudinal and bucket-handle tears.
- Entrapment of a meniscus fragment causes locking of the knee joint and requires surgical correction.