Tearing of internal tissue and blood vessels, causing haemorrhage, by a blow from a blunt instrument whereby the skin remains intact. Because all that is visible from the surface is discoloration of the skin, there is a danger that the seriousness of the internal injuries might not be recognized. The symptoms are pain and swelling caused by the haemorrhage, and accumulation of fluid in the damaged tissue (oedema). In bone contusion there can be haemorrhage between the bone and the periosteum, which can cause local bone death, because the periosteum is normally a source of bone nutrition. Contusion of a joint often causes extra production of synovial fluid, and thus severe swelling. Muscle is rich in blood vessels, so muscular contusion can cause severe haemorrhage within the muscle. Because jt is surrounded by fibrous connective tissue (the fascia) pressure in the muscle is increased, reducing the blood supply and possibly leading to muscle death; dead muscular tissue is replaced by connective tissue, which can shrivel to cause contracture. To avoid this the fascia should be cut as soon as possible after muscular contusion to give the muscle more room and prevent pressure increases.