What is osteomyelitis?
Osteomyelitis is infection of the bone, usually by a pus-forming bacteria. All bacterial osteomyelitis starts as acute infection. If untreated or unsuccessfully treated after 6 weeks, by definition, it becomes chronic osteomyelitis. Bone infections may occur at any age. Certain conditions increase the risk of developing such an infection, including sickle cell anemia, injury, the
presence of a foreign body (such as a bullet or a screw placed to hold together a broken bone), intravenous drug use (such as heroin), diabetes, kidney dialysis, surgical procedures to bony areas, untreated infections of tissue near a bone (for example, extreme cases of untreated sinus infections have led to osteomyelitis of the bones of the skull).
The infection that causes osteomyelitis often is in another part of the body and spreads to the bone via the blood. Affected bone may have been predisposed to infection because of recent trauma. In children, the long bones are usually affected. In adults, the vertebrae and the pelvis are most commonly affected. Bone infection can be caused by bacteria or by fungus. When the bone is infected, pus is produced within the bone, which may result in an abscess. The abscess then deprives the bone of its blood supply. Chronic osteomyelitis results when bone tissue dies as a result of the lost blood supply. Chronic infection can persist intermittently for years. Risk factors are recent trauma, diabetes, hemodialysis, and intravenous drug abuse. People who have had their spleen removed are also at higher risk for osteomyelitis.
Osteomyelitis may occur as a result of a bacterial bloodstream infection, sometimes called bacteremia, or sepsis, that spreads to the bone. This type is most common in infants and children and usually affects their long bones such as the femur (thighbone) or humerus (upper arm bone). When osteomyelitis affects adults, it often involves the vertebral bones along the spinal column. The source of the blood infection is usually Staphylococcus aureus, although it may be caused by a different type of bacteria or fungal organism. Osteomyelitis can also occur from a nearby infection due to a traumatic injury, frequent medication injections, a surgical procedure, or use of a prosthetic device. In addition, individuals with diabetes who develop foot ulcers are more susceptible. In any of these situations, the organism has a direct portal of entry into the affected bone. Individuals with weakened immune systems are more likely to develop osteomyelitis. This includes individuals with sickle cell disease, human immunodeficiency virus (HIV), or individuals receiving immunosuppressive medications such as chemotherapy or steroids.
Osteomyelitis affects about two out of every 10,000 people. If allowed untreated, the infection can become chronic and cause a loss of blood supply to the affected bone. When this happens, it can lead to the eventual death of the bone tissue. Osteomyelitis can affect children or adults. The bacteria or fungus that may cause osteomyelitis, however, differs among age groups. When osteomyelitis affects children, the infection usually affects the adjacent ends of long bones. Long bones are large, dense bones that provide strength, structure and mobility such as the femur and tibia in the legs and the humerus and radius in the arms. In adults, however, osteomyelitis can often affect the vertebrae and the pelvis.