Meniscus Injuries

The meniscus is a C-shaped shock absorber located between the tibia and femur within the knee joint. There are two menisci in each knee joint: the medial meniscus located on the inner side, and the lateral meniscus, positioned on the outer side of the knee. When viewed as a cross-section, they are wedge shaped.  Their wedge shape allows them to create a perfect fit between the round end of the femur and the flat edge of the tibia within the joint. This fit allows for an even distribution of forces and minimizes regions of high contact pressure. In doing so, the menisci serve a vital role in preventing excessive wear and tear on the articular cartilage. Additionally, the menisci help provide rotational stability to the joint. The menisci have many important roles in the knee, but their ability to absorb forces between the thigh bone and shin bone is the most crucial.

The menisci have a unique composition of protein fibers that allow them to absorb forces. They have parallel fibers that expand circumferentially. They also have fibers that intersect these circumferential fibers at a 90-degree angle. Together, this creates a mesh-like honeycomb network. When you walk, the femur presses down on the tibia. The menisci are between the two and will get compacted, or squeezed, whenever weight is applied to the leg. When the menisci are being compressed, a portion of the force is pushed outwards away from the knee joint due to the unique protein fiber configuration of the menisci. By reducing the amount of force that is transmitted from the femur to the tibia, the menisci will protect the cartilage in the knee. Over years and decades, this cumulative protective effect is crucial, as it will delay or prevent the onset of severe symptomatic osteoarthritis.

Meniscus tears can be acute, meaning they happen suddenly from a single injury, or degenerative, meaning they happen gradually over time with general wear and tear.

Acute meniscus tears are frequently the result of traumatic injuries and can occur during high-risk sports, including soccer, tennis, pickleball, football, or basketball. Typically, injury mechanisms involve aggressive movements in which the knee twists or rotates during pivoting, kneeling, or squatting. Tears can also result from hyperflexion when the knee is flexed beyond its normal range of motion (excessive bending). Everyday activities including getting in and out of a car, using stairs, squatting, or heavy lifting, can also cause tears.

Degenerative tears occur from chronic wear and tear of the meniscus cartilage that accumulates with age. As patients age, the cartilage can become stiff and brittle, leading to degenerative tearing or fraying of the menisci.

Acute meniscus tears are very common knee injuries that frequently affect active individuals. It is not uncommon to suffer a meniscus tear in the setting of a ligamentous injury. In contrast, degenerative meniscus tears are more common in older individuals, affecting 6 out of 10 patients over age 65.

Common symptoms of a meniscus injury include a popping sensation, localized pain and swelling on the inside or outside of the knee depending on the location of the tear. Other symptoms include stiffness, clicking, catching, or locking of the knee. Patients can also report instability, reduced range of motion, and difficulty walking.

Sometimes after 4-6 weeks from the injury, the knee will recover, and symptoms will improve. However, knee pain may return during daily activities including walking, running, and climbing stairs. This recurrent pain may also be associated with symptoms of intermittent swelling, instability, and locking of the knee. Over time, a torn meniscus can predispose the affected knee to the development of osteoarthritis.