Transplantation of tissue from animals to humans is called xenotransplantation. There is grave concern about the risk of transmitting deadly infections from animals to humans.
Nonhuman primates are now considered an unsafe source of donor organs. Pigs and cows are the most commonly used meniscal tissue in experiments. Both of these animals have thicker menisci compared to humans. The stiffness and therefore the strength is much greater than in humans.
Physicians are already successfully using various pig components (e.g., heart valves, clotting factors, islet cells, brain cells) to treat human diseases. Researchers are now breeding genetically manipulated donor pigs whose cells, tissues, and organs could be permanently transplanted into humans without being destroyed by the human immune system.
On the other hand, a new branch of science called tissue engineering is looking at ways to regenerate tissue. Small bits of normal cartilage are harvested or removed from the body and grown in a lab.
Bioengineered articular cartilage is already available in some clinical settings. Collagen meniscus implants (CMI) may be used to regenerate or regrow new meniscus-like tissue. The goal is to slow down and prevent degenerative joint disease. The implants may also improve joint stability, provide pain relief, and return people to activities at their desired level.
We're still a long way from having these types of transplants ready for everyday use. Surgeons are trying to repair torn menisci as often as possible in young adults. When there is already joint degeneration (as in the older adult), repair may not be possible. The torn cartilage is removed and the edges smoothed down to prevent further fraying.