As joint bodies, the menisci (singular: meniscus) compensate for the anatomical differences between the tibia and femoral pulleys. Together with the cruciate ligaments, they stabilize the knee and act as shock absorbers that protect the articular cartilage.
What is the meniscus?
Schematic diagram showing the anatomy and structure of the meniscus. Click to enlarge. The meniscus is a cartilaginous tissue structure within the knee joint that assists in the transfer of forces and loads between the femur (thigh bone) and tibia (shin bone) by compensating for differences in shape between the femoral condyle (femoral condyle or distal articular processes) and tibia. Each knee joint has a meniscus medialis (inner meniscus) and a meniscus lateralis (outer meniscus). During external rotation, the medial meniscus is loaded, and during internal rotation, the lateral meniscus is loaded. Depending on the blood supply, the menisci are further divided into a red zone near the capsule (well supplied with blood), a red-white zone (restricted blood supply) and a white zone (no blood supply). Injuries such as tears generally affect the less perfused, peripheral zones of the menisci.
Anatomy and structure
In each of the two knee joints, the meniscus medialis and meniscus lateralis are located between the femur and tibia. In addition, the ‘menisci are divided into the three parts: anterior meniscus (anterior third), pars intremedia (middle third), and posterior meniscus (posterior third). The meniscus is composed of connective tissue and elastic fibrocartilage, through which it can adapt to the movements and motor function of the corresponding knee joint. Formally, the meniscus is adapted to the surface shape of the tibial plateau and the femoral condyle in order to be able to realize its buffer function. The meniscus medialis has a C- or crescent-shaped appearance and is firmly fused to the capsula articularis (connective tissue joint capsule) and the ligamentum collaterale mediale (medial collateral ligament), making it less mobile and more susceptible to trauma-related injuries. The meniscus lateralis has a nearly round shape and is only partially fused to the capsula articularis, making it more flexible and less susceptible to injury.
Function and Tasks
The primary function of the menisci is to compensate for differences in shape between the tibia and femoral condyle in order to relieve and appropriately protect the articular cartilage. Since the femur and tibia, which are joined by the knee joint, have different articular surfaces and accordingly would have minimal contact area if in direct contact, they would be very unstable and non-functional without the intervening menisci. Accordingly, the menisci in the knee joints act as a kind of “washers” that increase the contact area and thus protect the femoral and tibial cartilages from friction and wear via better pressure distribution. A stabilizing function is assigned in particular to the meniscus posterior horn, which fulfills the function of a “brake block” or buffer and prevents the head of the tibia (caput tibiae) from sliding away. In addition, the elastic tissue structure of the menisci ensures that forces and impacts acting on the femur and tibia are buffered (buffer function). The menisci also ensure better distribution of synovial fluid.
Diseases, complaints, and disorders
Both genetic disorders and degenerative processes increase the risk of impairment of the menisci, with meniscal tears being the most common damage. For example, chronic overuse, including from sports activities, can lead to microtrauma (fine tears in the menisci), causing the cartilaginous tissue structures to become unstable and tear or pinch even during normal everyday movements. In miners and tile setters, this so-called meniscopathy (meniscal damage) is recognized as an occupational disease. Acute damage can cause proportional displacement of the affected meniscus, which can lock the knee joint. Chronic structural changes to the meniscus generally cause a permanently increased load on the cartilage, which in turn promotes degenerative processes (signs of wear) and correspondingly knee joint arthrosis. Load-dependent pain is characteristic of chronic meniscopathy.Since the menisci are only supplied with blood in their peripheral zones, they also have a low potential for regeneration. In most cases, the more common damage to the medial meniscus involves injury to the posterior horn of the meniscus. Degenerative processes at the cartilaginous structures are further associated with an increased risk for the manifestation of cysts, fluid-filled cavities. In general, cysts form on the lateral meniscus, which may be manifested by an external protrusion. Cysts in turn promote meniscopathies by entrapment and/or tearing. Meniscopathies can also be caused by anatomical anomalies such as a meniscus disciformis (disc meniscus). The affected meniscus is weakened and correspondingly more susceptible to injury-related damage.
