The joints in the human body are the connections between bones, and the connections between bones are divided into direct connections and indirect connections, and joints are a form of indirect connections. There are no specific statistics on how many joints there are in the human body, but there are 78 joints with clear names, and some very small joints do not have names, so the number is not certain. The statistics are relatively clear that there are 206 bones in the human body, and this number is not constant. The bones of children are different from those of adults, because during the growth and development of children, some bones will fuse into one, such as the ilium, pubic bone, and sit bones, and the pelvis formed after growth and development, the number of bones will change, and the number of joints will also change. joint capsule and joint cavity. Articular cartilage exists on the joint surface to reduce friction between joints. The joint capsule is the encapsulation and fixation structure of the joint, and the synovial layer inside the joint secretes synovial fluid to reduce friction. According to the different characteristics of joints, joints can be divided into three categories: immobile joints, semi-articular joints, and dynamic joints. The immobile joints are the joints between the skull bones, and the mobility between the joints is very small; the movable joints are the joints of typical limb bones, such as the shoulder, elbow, and wrist; the semi-movable joints are transitional connections between the movable and immobile joints, characterized by the bones being connected to each other in the form of cartilage, and the range of movement is relatively small, such as the pubic symphysis.