How does platelet rich plasma work to improve cartilage?

The most basic explanation is that human blood plasma and platelets contain cells which cartilage uses for healing. Since cartilage is a poorly healing tissue on its own, it has been shown that providing the injured area with increased availability of these different cells can increase the ability of the cartilage to heal itself. More specifically plasma contains about 200 different types of proteins, which are involved in tissue healing, hormones, and human growth factors; the most significant one being IGF-1 which has been shown to assist in cartilage healing. Platelets also contain several types of growth factors and other bioactive molecules. There is also frequently addition of leukocytes, which are a source of cytokines and enzymes, which help prevent infection. Leukocytes also secrete molecules into the area of healing including interleukins, proteins, growth factors and interferon, which can help signal the bodies healing processes.