Anatomy of the Knee Joint: Ligaments, Menisci, and Bony Articulations

Key Ligamentous Stabilizers

The stability of the knee is primarily governed by four major ligaments, conventionally divided into the central intracapsular cruciates and the peripheral extracapsular collaterals. Understanding their exact anatomical attachments is vital for interpreting knee MRI studies.

• Anterior Cruciate Ligament (ACL): Originates from the anterior intercondylar area of the tibia and ascends posterolaterally to attach to the medial aspect of the lateral femoral condyle. Its primary biomechanical function is to prevent anterior translation of the tibia relative to the femur. It is the most commonly torn knee ligament, typically injured during pivoting, decelerating, or jumping mechanisms.
• Posterior Cruciate Ligament (PCL): Originates from the posterior intercondylar area of the tibia and ascends anteromedially to attach to the lateral aspect of the medial femoral condyle. It is significantly thicker and mechanically stronger than the ACL. Its primary function is to prevent posterior translation of the tibia. Isolated injuries are rare and typically occur via severe direct trauma, such as a 'dashboard injury' during a motor vehicle collision.
• Medial Collateral Ligament (MCL): A broad, flat, fan-shaped band that extends from the medial epicondyle of the femur to the medial condyle and superior surface of the tibia. Crucially, the deep fibers of the MCL are firmly attached to the periphery of the medial meniscus. It actively resists valgus (abduction) stress.
• Lateral Collateral Ligament (LCL): A distinct, round, cord-like structure that extends from the lateral epicondyle of the femur to the head of the fibula. Unlike the MCL, it is entirely independent of the lateral meniscus, separated from it by a small bursa and the tendon of the popliteus muscle. It primarily resists varus (adduction) stress.

Meniscal Anatomy and Function

The menisci are crescent-shaped wedges of fibrocartilage interposed between the femoral condyles and tibial plateaus. They serve critically to deepen the articular surfaces, absorb shock, distribute weight-bearing forces, and contribute to joint lubrication.

• Medial Meniscus: Forms a larger, slightly open 'C' shape. Because it is firmly tethered to the deep fibers of the medial collateral ligament and the joint capsule over a broad area, it is relatively immobile. This rigid fixation makes it significantly more susceptible to traumatic tearing compared to the lateral meniscus.
• Lateral Meniscus: Forms a tighter, more closed 'O' shape. It is highly mobile and entirely separate from the lateral collateral ligament. This relative mobility allows it to glide posteriorly during knee flexion, sparing it from many classic shearing injuries.