Definition
A bruise (contusion) is an extravasation of blood into tissues due to rupture of blood vessels caused by blunt force trauma, without breach of the skin surface.
Mechanism of production
1. Direct impact — blunt force ruptures blood vessels beneath the skin; blood escapes into surrounding tissues producing discoloration.
- Examples: blow by fist, stick injury, fall on hard surface.
2. Compression against bone — soft tissues are crushed between the blunt object and underlying bone; vessels rupture producing contusion.
- Examples: scalp bruises, shin bruises.
3. Traction or stretching of tissues — sudden stretching tears blood vessels; produces bruising even without a direct blow.