The Meniscus: Location, Structure, Functions, and Injuries

Where is the Meniscus?

The meniscus is a crucial C-shaped piece of fibrocartilage located inside the knee joint, positioned between the distal end of the femur (thigh bone) and the proximal end of the tibia (shin bone), acting primarily as a shock absorber and stabilizer.

Introduction to the Knee Joint and the Meniscus

The knee is one of the body's most complex and vital joints, responsible for supporting body weight, enabling locomotion, and facilitating a wide range of movements such as walking, running, jumping, and squatting. Its intricate structure comprises bones, ligaments, tendons, and cartilage, all working in concert to provide stability and mobility. Among these critical components are the menisci, often overlooked until they become a source of pain or dysfunction. Understanding their precise location is the first step toward appreciating their profound importance in knee health and performance.

Precise Anatomical Location

The menisci are situated within the tibiofemoral joint, which is the primary articulation of the knee, formed by the meeting of the femur and the tibia. More specifically, they sit atop the tibial plateau, which is the flattened top surface of the tibia.

There are two menisci in each knee:

• Medial Meniscus: Located on the inner side of the knee (closer to the midline of the body).
• Lateral Meniscus: Located on the outer side of the knee (away from the midline of the body).

These C-shaped structures effectively deepen the relatively flat tibial plateau, creating a more congruent surface for the rounded condyles of the femur to articulate with. They are firmly anchored to the tibia by various ligaments and to the joint capsule, ensuring their stable position during movement.

Structure and Types of Menisci

Both menisci are composed of fibrocartilage, a tough, rubbery tissue that is more resilient than hyaline cartilage (which covers the ends of bones in joints). This composition allows them to withstand significant compressive and shear forces.

While both are C-shaped, there are distinct differences:

• Medial Meniscus:
  • Typically larger and more C-shaped.
  • It is more firmly attached to the medial collateral ligament (MCL) and the joint capsule, making it less mobile. This reduced mobility contributes to its higher incidence of injury compared to the lateral meniscus.
• Lateral Meniscus:
  • Generally smaller and more O-shaped or nearly circular.
  • It is less firmly attached to surrounding structures (it doesn't directly attach to the lateral collateral ligament, LCL, but rather has a tendon of the popliteus muscle passing between it and the LCL), granting it greater mobility. This increased mobility helps it adapt to movements and potentially makes it less prone to tearing from rotational forces.

The blood supply to the menisci is limited. The outer third (known as the "red zone") receives a direct blood supply from the surrounding joint capsule, allowing for some healing capacity. The inner two-thirds (the "white zone") are avascular, meaning they rely on synovial fluid for nutrition, and thus have very limited healing potential if injured.

Function of the Meniscus

The strategic location and unique structure of the menisci enable them to perform several critical functions essential for optimal knee performance and longevity:

• Shock Absorption: The menisci act as crucial shock absorbers, distributing compressive forces across a larger surface area of the articular cartilage. This reduces peak stresses on the underlying bone and articular cartilage, protecting them from wear and tear.
• Joint Stability: By deepening the tibial plateau, the menisci enhance the congruence between the femoral condyles and the tibia, improving the knee's stability, especially during rotational movements.
• Load Transmission: They transmit approximately 50% of the compressive load across the knee joint in extension and up to 85% in 90 degrees of flexion.
• Joint Lubrication and Nutrition: They assist in the circulation of synovial fluid, which lubricates the joint and provides nutrients to the articular cartilage.
• Proprioception: Recent research suggests that the menisci contain nerve endings, contributing to proprioception (the body's sense of position and movement), which is vital for coordination and balance.

Common Meniscus Injuries

Given their vital role and anatomical position, the menisci are susceptible to injury, particularly tears. These can occur acutely from sudden twisting motions, deep squats, or direct impact, often seen in sports. Degenerative tears can also develop gradually due to age-related wear and tear or repetitive stress. Symptoms typically include pain, swelling, stiffness, and mechanical symptoms like clicking, popping, or locking of the knee joint.

Conclusion

The meniscus, despite its relatively small size, is an indispensable component of the knee joint. Its precise location between the femur and tibia, combined with its unique fibrocartilaginous structure, allows it to perform critical roles in shock absorption, joint stability, and load distribution. Understanding where the meniscus is and what it does is fundamental to appreciating its importance in maintaining a healthy, functional knee throughout life, whether for daily activities or high-level athletic performance.