A joint is an indirect connection between bone and bone that plays an important role in maintaining the body’s active function. The basic structure of the joint includes the joint surface, the joint capsule, the joint cavity, and other accessory structures. The articular surface is the surface of contact between bone and bone, with one side being more prominent and the other side being relatively depressed, forming the joint socket, which plays an important role in maintaining the stability of the joint. The joint surface is covered with a layer of smooth cartilage tissue that reduces friction in the joint during movement, and the cartilage tissue is elastic and can relieve vibration or shock during movement. The joint capsule is a connective tissue that firmly links two adjacent bones. The joint capsule is divided into two layers: the outer layer is the fibrous layer, which mainly plays a fixed role, and the inner layer is the synovial layer, which can secrete synovial fluid and play a role in reducing friction within the joint during movement. The joint cavity is a cavity enclosed by articular cartilage and the joint capsule, which normally contains a small amount of synovial fluid secreted by the synovial capsule. In pathological conditions, the amount of fluid in the joint cavity increases, creating a joint effusion. There are also other structures attached to the joint, such as ligaments that increase the stability of the joint; there may be joint discs or menisci, seed bones, etc., which are more conducive to relieving the impact of external forces on the joint during exercise, increasing the stability of the joint, reducing friction between joints, and protecting tendons. The joints are among the more easily injured human structures, but also play an important role in all human movements, so in daily life and work, to carefully protect the joints.