FNDC5 and osteoarthritis: Irisin has been shown to promote osteoblast differentiation and proliferation in bone, increase bone density, improve bone quality, and enhance the mechanical support of cartilage by subchondral bone; on the other hand, irisin promotes chondrocyte proliferation, reduces the secretion of inflammatory factors and matrix metalloproteinases in chondrocytes, inhibits chondrocyte apoptosis, and strengthens the stability of the extrachondral matrix, which has great potential in the prevention and treatment of osteoarthritis.