Key Functions of the Meniscus
The knee joint relies on two crescent-shaped pieces of cartilage called menisci. These structures are positioned between the thigh bone (femur) and the shin bone (tibia). Each knee contains a medial meniscus on the inner side and a lateral meniscus on the outer side.
Shock Absorption and Load Distribution
The menisci play a significant role in managing the forces placed upon the knee during daily activities. They function to distribute the body’s weight evenly across the surface of the knee joint. This action helps to spread the load over a larger area, reducing concentrated pressure on the articular cartilage that covers the ends of the bones. When the knee bears weight, the menisci help increase the contact area between the femur and tibia, which can decrease stress on the cartilage by 50% to 70%.
During movements such as walking, running, or jumping, the menisci help to absorb and dissipate forces. Their ability to expand under compressive forces and increase contact area remains important for protecting the joint from damage and stress. The medial meniscus can transmit up to 50% of the load on its side, and the lateral meniscus can transmit up to 70% of the load on its side, with these percentages increasing during knee flexion.
Joint Stability
The C-shaped menisci enhance the mechanical fit between the relatively flat shin bone and the rounded thigh bone. They effectively deepen the surface of the tibia, creating a more congruent articulation for the femoral condyles. This improved fit helps to prevent excessive movement and misalignment between the bones, contributing to the overall stability of the knee joint.
The menisci also contribute to knee stability by being attached to surrounding ligaments and the joint capsule. This attachment system provides mechanical support, particularly during rotational movements of the knee.
Lubrication and Nutrition
Beyond their mechanical roles, the menisci also contribute to the health of the articular cartilage. They assist in the distribution of synovial fluid, a natural lubricant found within the joint. This fluid helps reduce friction between the joint surfaces during movement, allowing for smooth and effortless motion.
Synovial fluid also provides essential nutrients to the articular cartilage, which lacks its own direct blood supply. The menisci aid in circulating this fluid, ensuring that the cartilage receives the nourishment it requires to remain healthy.
Implications of Meniscus Health
When the meniscus is injured or its functions are compromised, the consequences can significantly affect knee health and function. A torn meniscus is a common injury that can result from sudden twisting movements or from age-related degeneration.
A meniscus injury often leads to immediate symptoms such as pain and swelling in the knee joint. Individuals may also experience stiffness, difficulty fully straightening or bending the knee, or a sensation of the knee catching, locking, or giving way.
Without the proper load distribution and cushioning provided by a healthy meniscus, the articular cartilage within the knee experiences increased stress. This heightened pressure can accelerate the wear and tear on the smooth cartilage lining the ends of the bones. The damage to articular cartilage can lead to ongoing pain and impaired joint function.
Over time, this increased stress and degeneration of the articular cartilage can contribute to the development or progression of osteoarthritis in the knee. Meniscal injuries are associated with a higher risk of developing knee osteoarthritis, a degenerative joint disease. Studies indicate that meniscal tears can increase the risk of knee osteoarthritis by a significant margin.
A compromised meniscus can also lead to feelings of instability in the knee. The joint may feel as though it is “giving way” or buckling, impacting a person’s ability to move confidently and safely. This instability, combined with pain and swelling, can limit the knee’s range of motion and overall functional capacity.