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The bones of the knee, the distal femur, the proximal tibia, and the patella depend on supporting ligaments, the joint capsule, and the menisci to provide stability for the joint.

A. Menisci and Joint Capsule

The menisci, or semilunar cartilages, are C-shaped fibrocartilaginous structures that provide shock absorption, allow for increased congruency between joint surfaces, enhance joint stability, and aid in distribution of synovial fluid.

The medial and lateral menisci provide a concave surface with which the convex femoral condyles can articulate. If the menisci are not present, the convex femoral condyles articulate with the relatively flat tibial plateaus, and the joint surfaces are not congruent. This decreases the surface area of contact and increases the pressure on the articular cartilage of the tibia and femur, which may lead to rapid deterioration of the joint surface. The medial meniscus is firmly attached to the joint capsule along its entire peripheral edge. The lateral meniscus is attached to the anterior and posterior capsule, but there is a region posterolaterally where it is not firmly attached (Figure 4–1). This results in the medial meniscus being less mobile than the lateral meniscus and more susceptible to tearing when trapped between the femoral condyle and tibial plateau. The lateral meniscus is larger than the medial meniscus and carries a greater share of the lateral compartment pressure than the medial meniscus carries for the medial compartment.

Figure 4–1.

The medial and lateral menisci with their associated intermeniscal ligaments. Note: The lateral meniscus is not attached in the region of the popliteus tendon. (Reprinted with permission, from Scott WN. Ligament and Extensor Mechanism Injuries of the Knee: Diagnosis and Treatment. New York: Mosby-Year Book; 1991.)

B. Ligaments

Within the knee, the anterior cruciate ligament (ACL) prevents anterior translation and rotation of the tibia on the femur (Figure 4–2). The posterior cruciate ligament (PCL) prevents posterior subluxation of the tibia on the femur. (Figure 4–3). On the medial side, the medial collateral ligament has superficial and deep portions (Figure 4–4), which stabilize the knee to valgus stresses. The lateral collateral or fibular collateral ligament runs from the lateral femoral condyle to the head of the fibula. It is the main stabilizer against varus stress (Figure 4–5). The lateral collateral ligament is part of the posterolateral “complex” or “corner” of the knee that also resists external rotation. An important component is the popliteofibular ligament, present in 90% of knees, that runs from the tendon of the popliteus muscle to the styloid on the posterior fibular head.

Figure 4–2.

Drawing of the anterior cruciate ligament with the knee in extension, showing the course of the ligament as it ...

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