Which of the following injuries is categorized as an open wound?

An avulsion is categorized as an open wound because it involves the tearing away of skin or tissue, which creates a break in the skin's surface. This type of injury leads to direct exposure of underlying tissues and blood vessels to the external environment, making it distinct from other types of injuries. Open wounds can lead to infections and require careful management to promote healing and prevent complications.

In contrast, a contusion is a closed injury that involves bruising without breaking the skin, swelling refers to an accumulation of fluid that may result from various injuries but does not involve skin integrity, and a strain is a soft tissue injury resulting from overstretching or tearing of muscles or tendons, which also does not affect the skin. Each of these other injuries does not create a breach in the protective barrier of the skin, which is why they are classified differently.