Meniscus tissue engineering and repair

The knee is the largest joint in the human body that permits flexion/extension movements and partial internal/external rotation. The knee contains four major structural tissues that maintain the integrity of the joint: bone, ligament, cartilage, and meniscus. The meniscus is the least studied of these tissues. The word meniscus is derived from the Greek term, mēniskos, which means “crescent” that alludes to the half-moon shape of this tissue. This tissue is fibrocartilaginous and it exists between the femoral condyle and the tibial plateau of the knee. The meniscus not only provides shock absorption and mechanical stability to the knee, but increasing evidence indicates that it also has indispensable biological functions that are essential for maintaining a healthy knee joint. The many mechanical functions of the meniscus tissue are accomplished by its unique composition, shape, and anatomy. Unlike articular cartilage and bone, which have fixed positions relative to other tissues, the menisci is relatively mobile during knee flexion/extension. Evolutionarily, evidence of the meniscus can be traced back more than 1.3 million years when the hominid lineage (that led to homo sapiens) developed complete bipedal locomotion and the patellofemoral joint came into existence. In homo sapiens, the structural variation in the meniscus indicates the evolutionary consequences of full knee extension movements during bipedal locomotion. Menisci were once described as vestigial organs or functionless remnants of embryonic development and they were often removed surgically, when injured, as a strategy to subside acute inflammation and to prevent resulting knee degeneration. However, the meniscus is now recognized as a vital component of the healthy joint, and its injury or removal is shown to correlate with the onset of osteoarthritis.