When the periosteum is torn, displacement may occur. The plane of separation is horizontal and the germinal cells remain with the epiphysis.

In a type I separation, the epiphysis separates from the metaphysis. Transverse fracture through the growth plate. Table 1: Salter-Harris classification of physeal injuries. When an apparently 'unclassifiable pattern' is encountered, additional imaging may be helpful, including oblique views, an arthrogram, CT or MRI. Another 5% can be classified using one of the more elaborate systems and the final 5% defy classification. About 90% of children with physeal injuries can be classified using the five Salter-Harris classifications from plain x-rays (Table 1). Salter-Harris classification of physeal injuriesР”Р„lthough there are more recent and more complex classifications, the Salter-Harris classification is the most widely used and clinically useful approach to classifying and describing physeal injuries in children. However, due to this anatomy, there is a higher chance of a growth arrest to occur following injury. This is in contrast to the commonly injured distal radial physis that is more linear and rarely arrests.Р”Р‡igure 11: The undulating shape of the distal femoral physis and the presence of mamimillary bodies provides extra stability to the growth plate.

If it does sustain a shear injury there is a higher chance of developing a bony bar across the physis and subsequent growth arrest. This anatomic arrangement locks the physis solidly. Around the knee, the stresses are high and in order to resist shear, the physis interdigitates with surrounding bone in what are known as mammillary bodies. The macroscopic structure of the growth plates varies according to the degree of stress to which it is exposed. Most physeal separations occur through this layer because it is less able to resist shearing stress.Р”Р‡igure 10: Anatomy of the physis (growth plate). The hypertrophic zone is the weakest because it lacks both collagen and calcified tissue. Osteoblasts use the chondrocyte columns as a scaffold for ossification in the zone of provisional calcification. The proliferative zone is where the chondrocytes undergo rapid division by mitosis and is the most metabolically active zone. The cells of the physis are arranged in columns or layers described as the germinal or resting layer, the proliferative zone, the hypertrophic zone and the zone of provisional calcification (Figure 10). The growth plate, or physis, is the translucent, cartilaginous disc separating the epiphysis from the metaphysis and is responsible for longitudinal growth of long bones. Physeal injuries are very common in children, making up 15-30% of all bony injuries. The key difference between the child's bone and that of an adult is the presence of a physis. Salter-Harris classification of physeal injuries.

Salter harris type 3