The Salter-Harris classification of epiphyseal fractures is generally regarded as the most commonly used classification when assessing pediatric fractures of the growth plate. The epiphyseal or growth plate is the part of the long bones where eventual growth and length come from in the developing child. These growth plates generally do not finish closing until puberty.
The importance here is that trauma to the growth plate (epiphyseal plate) can lead to deformed growth of the affected bone. Either the fractured bone, if it is a long bone, like a metatarsal bone, may continue to grow, but at an angle instead of straight, or, with damage to the growth plate, there can be stunting of future growth.
In the case of fractures, children are not merely small adults. A force applied to an adult bone is the same as that to a pediatric patient; the difference is that the surrounding ligaments are generally stronger than the epiphyseal plate so the force of the trauma ends up going through the epiphyseal plate. In an adult, since there is no longer an epiphyseal plate, the force of the trauma will tend to tear the adjacent ligament.
Looking at the above picture, the red line represents the fracture through the bone. The gray dotted (clouded) area represents the epiphyseal plate (growth plate).
A. Salter I, where the fracture extends along the epiphyseal plate but does not extend into the metaphysis (the area above the epiphyseal plate) nor does it extend into the epiphysis itself (area below the epiphyseal plate). Injury here will open the epiphyseal plate but many times it will self reduce. Complications are rare.
B. Salter II, where the fracture extends along the epiphyseal plate and also involves the metatphysis.
C. Salter III, where the fracture goes through the epiphyseal plate and extends into the epiphysis and may extend into the joint.
D. Salter IV, where the fracture extends through the joint, the epiphysis, across the epiphyseal plate and into the metataphysis.
E. Salter V, where the velocity of the fracture crushes the epiphyseal plate.
As a rule of thumb, less than 2mm of displacement of the fractured section of bone is considered acceptable and all that is needed is a cast. Length of time that the cast has to be worn and whether or not the child can be weight bearing depends on which particular bone is broken.
In instances where there is more than 2mm of displacement, the displaced portion of bone may be re-positioned through the use of closed reduction, usually under anesthesia.