Tissue Engineering of the Meniscus

The meniscus is crucial in bearing and distributing loads, absorbing shock, lubricating, and stabilizing the knee. Injuries to the meniscus are some of the most common injuries seen in orthopaedics and often lead to osteoarthritis and degradation of articular cartilage. More promising means to repair meniscal tears or synthesize an artificial meniscus are necessary, because the meniscus has a limited regenerative capability and injuries often occur in the interior, avascular region of the meniscus. Tissue engineering offers new treatment possibilities for meniscal repairs and replacements.

The phenotype of the meniscal tissue is similar to fibro-cartilage in the avascular region and is fibrous in the vascular region, consisting predominantly of type I collagen and glycosaminoglycans. Scaffolds that are biocompatible and biodegradable, allow unrestricted cell growth and free diffusion of nutrients, can be used as a carrier for growth factors, and maintain structural integrity while supporting the joint on the knee are qualifications for an ideal scaffold material. Scaffolds based on collagen molecules are the most promising, because of their optimal load-bearing capacity and the control of pore creation for new tissue ingrowth. Using whole tissues or isolated tissue components as scaffold material are often disadvantageous, because they cannot often bear large loads. The use of synthetic polymer-based scaffolds is currently being investigated because of the ability to control the porosity, the degradation rate, and other mechanical properties of polymers. In polymer design, the adhesive potential of the polymer scaffold to the host tissue is of key importance.

Other potential cells for investigation in scaffold associated studies involve nondifferentiated progenitor cells or fibroblasts, which have differentiated into fibro-cartilage-like cells in previous studies. Additionally, growth factors which stimulate synthesis and inhibit the degradation of the ECM have been studied for their effects on cultured meniscal cells or meniscus explants. Such growth factors include TGF-β, PDGF, IGF-I, which stimulate glycosaminoglycan production, proliferation of meniscal cells, and production of cartilage matrix molecules, respectively. As for replacing a meniscus with an autologous allograft, problems occur because of poor initial mechanical properties of the materials, preventing the allograft from lasting long-term. Donor menisci implants have associated problems, such as immunological reactions, disease transfer, and reshaping of the implant to fit the patient. More importantly, such implants often induce high friction in the knee joint, resulting in damage to the cartilage.

Meniscal injuries are exceedingly common in athletes, particularly soccer players and runners. If the meniscus degenerates or is removed, the remaining cartilage in the knee joint slowly wears away, leading to increasing pain in the joint, osteoarthritis, and severe joint degeneration. At this point, artificial joint replacement seems to be the most promising way to relieve the pain of osteoarthritis. However, there are numerous problems with this painful procedure, especially the length of time the implant lasts, usually around ten years, and the stresses on the bone that the implant places. Repairing the meniscus or offering new treatments using synthetic tissue engineering, provides these athletes with a remedy for their knee problems, enabling them to live with less pain, avoid artificial joint replacements, and possibly return to their sport. Currently recovering from my second meniscal tear, I am especially interested in new technologies and research into synthetic menisci and more effective treatments for meniscal repairs.