In a study of 72 rabbits, four, eight, twelve and 16 weeks old, the mechanical resistance of the distal radius and ulna epiphyseal plate against shear strength has been examined. On one side the extremity has been freed of all soft-tissue attachments except the periosteum, on the other side the periosteum of the epiphyseal plate additional has been removed. The mechanical strength of the epiphyseal cartilage increases with age. A decrease of the resistance during sexual maturation has not been observed. In all age groups the stability of the epi-metaphyseal junction is significantly higher with the periosteum. In younger animals it is more marked than in older ones. The biomechanical behaviour of the periosteum can be explained with the principle of a "traction strap": the fibrous periosteum, firmly attached at the perichondrial ring, is stretched from epiphysis to epiphysis and fixes the epiphysis to the metaphysis. The periosteum and its continous tension takes not only part in regulating the longitudinal growth but also increases the resistance of the growth cartilage against shear strength. The dominated influence of the periosteum on the integrity of the epiphyseal cartilage is also supported by corresponding results dealing with the occurrence of Salter and Harris-type I or II fractures in absence or presence of the periosteum.
