Final answer:
An open skull fracture involves a break in the bone along with an external wound that communicates with the brain or cranial cavity, increasing infection risk.
Step-by-step explanation:
For a skull fracture to be termed "open," two specific injuries must occur. First, the bone must break, causing a fracture that disrupts the continuity of the skull. Second, there must be some form of communication with the external environment, typically in the form of a laceration in the scalp or facial tissues that exposes the brain or cranial cavity to the outside. This can happen when one end of the fractured skull bone tears through the soft tissues and skin. An open skull fracture carries a higher risk of infection because of the exposure to bacteria and foreign material from the environment.