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Osteomyelitis is a bone infection usually caused by bacteria, mycobacteria, or fungi.
Bacteria, mycobacteria, or fungi can infect bones by spreading through the bloodstream or, more often, by spreading from nearby infected tissue or a contaminated open wound.
People have pain in one part of the bone, fever, and weight loss.
Blood tests and imaging tests are done, and doctors remove a sample of bone for tests.
Antibiotics are given for weeks, and surgery may be needed.
Osteomyelitis occurs most commonly in young children and in older people, but all age groups are at risk. Osteomyelitis is also more likely to occur in people with serious medical conditions.
When a bone becomes infected, the soft, inner part (bone marrow) often swells. As the swollen tissue presses against the rigid outer wall of the bone, the blood vessels in the bone marrow may become compressed, which reduces or cuts off the blood supply to the bone. Without an adequate blood supply, parts of the bone may die. These areas of dead bone are difficult to cure of infection because it is difficult for the body’s natural infection-fighting cells and antibiotics to reach them. The infection can also spread outward from the bone to form collections of pus (abscesses) in nearby soft tissues, such as the muscle. Abscesses occasionally drain spontaneously through the skin.
Bones, which usually are well protected from infection, can become infected through three routes:
Injury, foreign bodies, and a decrease in the blood supply to organs or tissues (ischemia) may cause osteomyelitis. Osteomyelitis may form under deep pressure sores (see Pressure Sores). Most osteomyelitis results from direct invasion or infections in nearby tissues.
When organisms that cause osteomyelitis spread through the bloodstream, infection usually occurs in the ends of leg and arm bones in children and in the spine (vertebrae) in adults, particularly older people. Infections of the vertebrae are referred to as vertebral osteomyelitis. People who are older, are debilitated (such as people living in nursing homes), have sickle cell disease, undergo kidney dialysis, and inject drugs using nonsterile needles are particularly susceptible to vertebral osteomyelitis. Staphylococcus aureus is the bacteria most commonly responsible for causing osteomyelitis that spreads via the bloodstream. Mycobacterium tuberculosis (the main cause of tuberculosis) and fungi can spread the same way.
Bacteria or fungal spores may also infect the bone directly through open fractures, during bone surgery, or from contaminated objects that pierce the bone.
Osteomyelitis may also occur where a piece of metal has been surgically attached to a bone, as is done to repair hip or other fractures. Also, bacteria or fungal spores may infect the bone to which an artificial joint (prosthesis—see Figure: Replacing a Knee) is attached. The organisms may be carried into the area of bone surrounding the artificial joint during the operation in which the joint is installed, or the infection may occur later.
Osteomyelitis may also result from an infection in nearby soft tissue. The infection spreads to the bone after several days or weeks. This type of spread is particularly likely to occur in older people. Such an infection may start in an area damaged by an injury or surgery, radiation therapy, or cancer or in a skin ulcer (particularly a foot ulcer) caused by poor circulation or diabetes. A sinus, gum, or tooth infection may spread to the skull.
Infections of the leg and arm bones cause fever and, sometimes days later, pain in the infected bone. The area over the bone may be sore, red, warm, and swollen, and movement may be painful. The person may lose weight and feel tired.
Infections of the vertebrae usually develop gradually, causing persistent back pain and tenderness when touched. Pain worsens with movement and is not relieved by resting, applying heat, or taking analgesics. Fever, usually the most obvious sign of an infection, is often absent.
When osteomyelitis results from infections in nearby soft tissues or direct invasion by an organism, the area over the bone swells and becomes painful. Abscesses may form in the surrounding tissue. These infections may not cause fever. Infection around an infected artificial joint or limb typically causes persistent pain in that area.
Chronic osteomyelitis may develop if osteomyelitis is not treated successfully. It is a persistent infection that is very difficult to eradicate. Sometimes, chronic osteomyelitis is undetectable for a long time, causing no symptoms for months or years. More commonly, chronic osteomyelitis causes bone pain, recurring infections in the soft tissue over the bone, and constant or intermittent drainage of pus through the skin. Such drainage occurs when a passage (sinus tract) forms from the infected bone to the skin surface and pus drains through the sinus tract.
Symptoms and findings during a physical examination may suggest osteomyelitis. For example, doctors may suspect osteomyelitis in a person who has persistent pain in part of a bone with or without a fever and feels tired much of the time.
If doctors suspect osteomyelitis, they do a blood test for inflammation by measuring the person's erythrocyte sedimentation rate (ESR—a test that measures the rate at which red blood cells settle to the bottom of a test tube containing blood) or level of C-reactive protein (a protein that circulates in the blood and dramatically increases in level when there is inflammation). Inflammation is usually present if the ESR and C-reactive protein level are increased. Also, blood tests often indicate elevated levels of white blood cells. However, these blood tests are not sufficient to diagnose osteomyelitis, although normal results, which suggest there is little or no inflammation, make osteomyelitis less likely.
An x-ray may show changes characteristic of osteomyelitis, but sometimes not until 2 to 4 weeks after the first symptoms occur. Computed tomography (CT) and magnetic resonance imaging (MRI) can also identify the infected areas and reveal abscesses. The infected area almost always appears abnormal on bone scans (images of bone made after injecting radioactive technetium), except in infants, because scans do not reliably indicate abnormalities in growing bones. However, a bone scan cannot always distinguish infections from other bone disorders. White blood cell scans (images made after radioactive indium–labeled white blood cells are injected into a vein) can help distinguish between infection and other disorders in areas that are abnormal on bone scans.
To diagnose a bone infection and identify the organisms causing it, doctors may take samples of blood, pus, joint fluid, or the bone itself to test. Usually, for vertebral osteomyelitis, samples of bone tissue are removed with a needle or during surgery.
For children and adults who have recently developed bone infections through the bloodstream, antibiotics are the most effective treatment. If the bacteria causing the infection cannot be identified, then antibiotics that are effective against Staphylococcus aureus and many types of bacteria (broad-spectrum antibiotics) are used. Depending on the severity of the infection, antibiotics may be given by vein (intravenously) for about 4 to 8 weeks but then may be given by mouth later. Some people have chronic osteomyelitis and need months of antibiotic treatment.
If a fungal infection is identified or suspected, antifungal drugs are required for several months. If the infection is detected at an early stage, surgery is usually not necessary.
For adults who have bacterial osteomyelitis of the vertebrae, the usual treatment is antibiotics for 4 to 8 weeks. Sometimes bed rest is needed, and the person may need to wear a brace. Surgery may be needed to drain abscesses or to stabilize affected vertebrae (to prevent the vertebrae from collapsing and thereby damaging nearby nerves, the spinal cord, or blood vessels).
When osteomyelitis results from a nearby soft-tissue infection (such as a foot ulcer caused by poor circulation or diabetes), treatment is more complex. Usually, all the dead tissue and bone are removed surgically, and the resulting empty space is packed with healthy skin or other tissue. Then the infection is treated with antibiotics. Broad-spectrum antibiotics are taken for more than 3 weeks after surgery.
When an abscess is present, it usually needs to be drained surgically. Surgery may also be needed for people with persistent fever and weight loss.
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