What type of force typically causes an avulsion fracture?

An avulsion fracture occurs when a fragment of bone is pulled away from the main bone mass, usually due to the forceful contraction of a muscle or a sudden, powerful twist or stretch. This type of injury is often associated with athletic activities where rapid movements and changes in direction occur. In such instances, the muscles and tendons that attach to the bone exert a strong pull, which can lead to the bone breaking away where these structures attach.

This mechanism highlights why a sudden twist or stretch is particularly relevant in causing avulsion fractures, contrasting with other forces such as a direct blow, which typically results in different types of fractures, or a repetitive stress force, which is more likely to lead to stress fractures. Gradual degeneration of the bone pertains more to conditions like osteoporosis rather than acute injury scenarios like an avulsion fracture. Thus, recognizing the specific nature of the force involved helps in understanding the mechanics that lead to avulsion fractures.