What is the primary characteristic of avulsion fractures?

Avulsion fractures are primarily characterized by a small piece of bone being pulled away from its usual location by a tendon or ligament. This type of injury often occurs when a strong force is exerted on a joint, causing a ligament or tendon to pull off a fragment of bone where it attaches. This mechanism differentiates avulsion fractures from other types of fractures, such as complete breaks, which involve a full fracture through the bone, or those caused by high impact trauma, which may not necessarily involve the pulling mechanism related to tendons or ligaments. Additionally, avulsion fractures can occur without external wounds, but that detail is not what primarily defines them. Therefore, the pulling away of the bone from its usual location is the key characteristic of avulsion fractures, highlighting the role of soft tissue structures in this injury mechanism.