Which type of fracture is characterized as incomplete?

The type of fracture characterized as incomplete is the greenstick fracture. This type of fracture typically occurs in children whose bones are still flexible and not fully ossified. In a greenstick fracture, the bone bends and cracks, but does not break all the way through. This results in a fracture on one side of the bone while the other side remains intact, similar to how a green twig may bend and fracture without breaking completely.

In contrast, other types of fractures such as comminuted, transverse, and spiral are all categorized as complete fractures. A comminuted fracture involves the bone breaking into multiple fragments, a transverse fracture consists of a straight break that crosses the bone at a right angle, and a spiral fracture occurs due to twisting forces, which fully breaks the bone. Thus, the greenstick fracture is distinct in that it does not constitute a complete break, making it the correct answer.