A greenstick fracture occurs when a bone bends and cracks, instead of breaking completely into separate pieces. The fracture looks similar to what happens when you try to break a small, "green" branch on a tree.
Most greenstick fractures occur in children younger than 10 years of age. This type of broken bone most commonly occurs in children because their bones are softer and more flexible than are the bones of adults.
Even mild greenstick fractures are usually immobilized in a cast. In addition to holding the cracked pieces of the bone together so they can heal, a cast can help prevent the bone from breaking all the way through if the child falls on it again.