The long bones of the extremities mainly include the humerus, ulna, radius, femur, tibia and fibula. The long bones are tubular in shape, mainly distributed in the extremities, and can be divided into one and two ends. The body part is also called the long bone stem, which has an internal marrow cavity to accommodate the bone marrow and 1-2 trophoblastic pores on the surface of the stem for vascular access. The two ends of the long bones are called epiphyses, which have smooth articular surfaces and form joints with the adjacent articular surfaces. The epiphyseal cartilage is called epiphyseal cartilage, and epiphyseal cartilage cells continue to divide, proliferate, and ossify, making the bone lengthen. In adulthood, the epiphyseal cartilage ossifies and the epiphysis becomes one with the epiphysis, leaving an epiphyseal line behind.