Most long bones end near the joint in a separate epiphysis which at first consists of cartilage and is later ossified. This epiphysis becomes fused with the shaft of the bone, in most cases only towards the end of puberty. The process is regulated by a number of parallel systemic, cellular and mechanical feedback controls, the complexity of which accounts for its liability to become disordered. The stress acting on the cartilaginous epiphysis is comparable to that in the adult. The relative differences may be attributed to variations in the mechanical relationship and to the hormonal control of the body's growth. The individual epiphyses undergo a characteristic series of events; central calcification, absorption of cartilage and endochondral ossification, the further course of which is definitely determined by the degree of local distortion. This applies to the general shape of the epiphysis as well as to its internal structure. The composition and thickness of the remaining articular cartilage are controlled by these feedback mechanisms throughout the whole of life.