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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.

X-rays were reviewed after callus distractions (50 cases) and distraction epiphysiolysis (10 cases) in 45 patients. With the aid of a computerized digitization system for analogue films, the relative x-ray density of the distraction area was determined in the medial, lateral, ventral and dorsal surface areas, and in the median line of the callus tissue. Bone formation became evident within 21.7 +/- 3.7 days post-distraction in the thigh and 25.4 +/- 4.9 days in the shank. The lowest density values were found at the end of the distraction phase followed by a continual increase in x-ray density in the fixation phase. There was a significant decrease in callus x-ray density in the shank from lateral to medial and from dorsal to ventral, and in the thigh from medial to lateral and from dorsal to ventral. When the corticotomized callus distraction is compared to the distraction epiphysiolysis without corticotomy it becomes apparent that the differences between lateral-medial x-ray densities and dorsal-ventral x-ray densities were significantly greater in the group with callus distraction. The deminished bone formation in the ventromedial area of the shank and the ventrolateral area of the thigh seems to be due to soft tissue damage and disturbances in local bone blood supply after the operative approach for corticotomy.

Knowledge of the physiology of the epiphyseal cartilage, respectively epiphyseal plate, is essential for an understanding of defective growth and abnormal modeling of the long bones. The epiphyseal cartilage develops from the embryonal, cartilaginous long bone structure. The histology of the epiphyseal cartilage is characterised by definable zones representing the individual differentiation steps from the reformation of cartilage to chondrolysis. Modeling of the ends of the long bones is also influenced by a transversal and longitudinal direction of growth in the epiphyseal cartilage. The intercellular substance mainly contains collagin, proteoglycanes and non-collagenic proteins. These macromolecules are compounded by means of physicochemical bonds and are responsible for the special mechanical qualities of the hyaline cartilage. The process of mineralisation at the base of the epiphyseal cartilage is an essential differentiating step for the ossification processes which take place in the metaphysis. Two pathogenetic principles at the epiphyseal cartilage appear to be important for the defective growth of the long bones. On the one hand, the flowing equilibrium between the differentiation steps of cartilage reformation, transformation of the hyaline cartilage into a mineralised cartilaginous tissue and chondrolysis is changed, whereas on the other hand the turnover of these differentiation steps is retarded or accelerated.

Rotation of the radius about the fixed ulna is analysed radiographically in an anatomic specimen. While rotating the styloid process of the radius migrates in relation to the ulna. Compared to the prone position supination leads to a more distal position of the styloid process.