Bones and the fluid and tissues of joints can become infected. Such infections include osteomyelitis and infectious arthritis.
Osteomyelitis
Osteomyelitis is a bone infection usually caused by bacteria but sometimes by a fungus.
When a bone is infected, the soft, inner part (bone marrow) often swells. As the swollen tissue presses agninst the rigid outer wall of the bone, the blood vessels in the marrow may be compressed, reducing or cutting off the blood supply to the bone. Without an adequate blood supply, parts of the bone ray die. The infection also can spread outward from the bone to form collections of pus (abscesses) in adjacent soft tissues, such as the muscle.
Causes
Bones, which usually are well protected from infection, can become infected through three routes: the bloodstream, direct invasion, and adjacent soft tissue infections.
The bloodstrean may cany an infection from another part of the body to the bones. An infection usually occurs in the ends of leg and arm bones in children and in the spine (vertebrae) in adults. People who undergo kidney dialysis and those who inject illegal drugs are particularly susceptible to an infection of the vertebrae (vertebral osteomyelitis). Infections also may occur where a piece of metal has been attached to a bone, as is done to repair hip or other fractures.The bacteria that cause tuberculosis also can infect the vertebrae (Pott's disease).
Organisms may invade the bone directly through open fractures, during bone surgery, or from contaminated objects that pierce the bone. An infection in an artificial joint, usually acquired during surgery, can spread to adjacent bone.
An infection in the soft tissues around a bone may spread to the bone after several days or weeks. A soft tissue infection may start in an area damaged by an injury, radiation therapy, or cancer or in a skin ulcer caused by poor circulation or diabetes. A sinus, gum, or tooth infection may spread to the skull.
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