Final answer:
The separation of articular surfaces at a joint is termed a dislocation and is typically caused by an injury, leading to pain and immobility in the affected area.
Step-by-step explanation:
The separation of articular surfaces at a joint is called a dislocation. A dislocation occurs when there is an abnormal separation in the joint, where two or more bones meet. This is often the result of a sudden impact or injury and can lead to immobility and pain in the affected joint. A dislocation differs from a sprain, which involves the ligaments, a strain, which involves the muscles or tendons, and a fracture, which involves a crack or break in the bone itself. These conditions can have different implications for the joint's structure, function, and treatment.