Which type of fracture describes a bone that cracks under pressure but does not break completely?

The correct answer is greenstick fracture. This type of fracture occurs when a bone bends and partially cracks, similar to how a green twig would break. Instead of breaking fully into separate pieces, a greenstick fracture results in an incomplete fracture where the bone remains partially intact. This commonly occurs in children because their bones are more flexible and less brittle than those of adults.

In contrast, other types of fractures do not fit this description. An impacted fracture involves one fragment of bone being driven into another and typically results in a complete break. A simple fracture, also known as a closed fracture, refers to a complete break in the bone without puncturing the skin but does not address the specific nature of a crack under pressure. Finally, a comminuted fracture is one in which the bone is broken into multiple pieces, indicating a more severe level of fracture than a simple crack.