Bone Infection

Diagnosis

Bone infection, also called osteomyelitis, is an infection of the bone. Figure 01. Osteomyelitis occurs in both children and adults, and can affect any bone in the body. If untreated, it can cause permanent bone deformity. Children usually have an acute form of the disease, while adults are more likely to have chronic osteomyelitis. Treatment for both forms of osteomyelitis includes high doses of antibiotics to rid the body of bacteria. Additional treatment such as draining an open wound or abscess, or surgery to remove infected or dead bone tissue, may be necessary for some people.
Figure 01. Bone infection (Cross-section)

The bacteria or other microorganisms that cause osteomyelitis can enter the bone through an injury, or can be carried through the bloodstream to the bones from another infection in the body. Although bones are usually well-protected against infection, they can become infected in several ways. Bacteria can enter the bone through an open fracture, penetration by a sharp, contaminated object (such as a nail that pierces through a shoe), orthopedic surgery, or a human bite. Poorly controlled diabetics who develop serious skin infections in their feet are prone to develop osteomyelitis. The infection can also be carried to the bones in the bloodstream from another part of the body where an infection is present. This type of infection is known as hematogenous osteomyelitis, and is the most common form of the disease in children.

Staphylococcus aureus is the bacterial organism that causes most cases of osteomyelitis.
S. aureus is the primary cause of osteomyelitis among people of all ages, although other bacteria can be involved, including Group A and B Streptococcus, Hemophilus influenzae, Enterobacteriaceae, Escherichia coli, and Salmonellae. In some cases, more than one type of bacteria is found during the laboratory culture of blood or tissue samples. Although it is less common than bacterial infection, fungal infection can also cause osteomyelitis. Chronic osteomyelitis also can be caused by tuberculosis.

Fever, bone pain, swelling, and redness over the infection site are symptoms of acute osteomyelitis Table 01. A fever is one of the early symptoms of osteomyelitis, and may precede or follow the pain that develops in the infected area of bone. Swelling, redness, warmth, and tenderness also occur over the infected bone, and may occur in nearby joints such as the knee, making movement painful. Back pain is a symptom of vertebral osteomyelitis. Other symptoms of acute osteomyelitis may include vomiting, chills, and a feeling of general illness or lack of energy. A blood test may show a high white blood cell count, indicating that your body has launched a counterattack against invading organisms. An open, draining wound over the infected site is also a sign of osteomyelitis, but is more likely to occur later in the progression of the disease, or as a symptom of chronic osteomyelitis.

Pain is the foremost symptom of chronic osteomyelitis Table 01. Chronic osteomyelitis can persist for weeks, months, or years, although there will be times when the patient does not experience any symptoms. When symptoms are present, they include bone pain, fatigue, general discomfort or an ill feeling, recurring infections in the soft tissue above the bone, and an open, draining wound caused when pus formed in the infected bone breaks through the surface of the skin.

Table 1.  Symptoms of Osteomyelitis

People who are diabetic or who have had a recent trauma have an increased risk of developing osteomyelitis. Trauma such as an injury or a wound provides an opportunity for bacteria to enter the body and cause an infection that may spread to the bones. Diabetic patients are especially susceptible to foot injuries and sores that can become infected, leading to osteomyelitis.

Osteomyelitis occurs in both sexes, but is twice as common in males as in females. Osteomyelitis can occurs at all ages in both males and females.

Acute osteomyelitis is most common in rapidly growing children. Most children are too young to have had the repeated, ongoing episodes that characterize chronic osteomyelitis. In addition, the pattern of blood vessels in children makes their long bones (i.e., arm and leg bones) more susceptible to osteomyelitis.

Orthopedic surgery and the use of orthopedic prosthetic devices such as an artificial knee or hip can also increase the risk of osteomyelitis. Surgery involving bones and joints increases the risk of osteomyelitis because of the possibility of introducing bacteria from the hospital setting. Introducing a foreign object into the body (i.e., a bullet, or a tool during surgery) poses an additional risk.

Any illness that lowers the body's resistance to infection increases the risk of developing osteomyelitis. Conditions such as AIDS and sickle cell anemia are potential risk factors because they decrease your body's innate ability to fight the invading bacteria that can cause osteomyelitis. Intravenous drug use, alcoholism, kidney dialysis, malnutrition, and advanced age are also risk factors, as they all decrease your immune response.

Your doctor will take a medical history to help diagnose osteomyelitis. Early diagnosis is important for preventing chronic illness and bone tissue death. Your doctor will ask about your symptoms, including whether you have recently had a fever, chills, or pain and tenderness of a limb or joint. The doctor will also ask if you have had any recent injuries, infections, surgery, or other illnesses.

Your physician will examine you for bone tenderness, swelling, and redness. If osteomyelitis is suspected, your doctor will need to verify and identify the bacteria that are present. In a child, pain in the upper or lower leg bone or the arm bones suggests osteomyelitis. In an adult, the pain is more likely to occur in the pelvis or spine.

Blood tests will be run if your physician suspects osteomyelitis. Two of the most common tests for osteomyelitis are a white blood cell count (WBC) and a red blood cell (erythrocyte) sedimentation rate (ESR). A high WBC or an elevated ESR may indicate osteomyelitis. For both tests, blood is drawn through a needle inserted in a vein. The blood samples are then sent to a laboratory for analysis, and the results will be available within a few days.
Another blood test that may be used to diagnose osteomyelitis is the C-reactive protein test. This test checks for the presence of C-reactive protein, a high level of which may indicate various inflammatory diseases or an infection such as osteomyelitis.
Your doctor may also take samples of pus, joint fluid, bone, or bone tissue, or order a laboratory blood culture to identify causative organisms. Once the bacteria have been identified, the doctor can prescribe an antibiotic that targets the responsible organism.

Various imaging devices can also be used to diagnose osteomyelitis. An x-ray is often the first diagnostic technique used when osteomyelitis is suspected. However, because an x-ray may not show changes in the bone until several weeks after an infection has begun, other imaging devices are often used as well. An MRI is effective in distinguishing osteomyelitis from bone tumors or dead tissue; however, it is an expensive technology that may not be appropriate in all cases. CT scans can also be performed, although the results are sometimes less specific than those obtained with MRI.
A radionuclide bone scan is especially useful for revealing metabolic changes in the bone caused by fractures or disease well before they could be detected with a conventional x-ray. This test may produce positive results in as little as 24 to 48 hours after symptoms begin. A bone scan is performed by giving the patient an intravenous injection of a radioactive material called technetium. Scanning images are taken several hours later when the technetium becomes concentrated in the bones and tissue.
Since many factors can influence the accuracy of these imaging techniques, the results of any one test should not be the sole basis for the diagnosis.

A bone biopsy is one of the most reliable methods of diagnosing osteomyelitis. In suspected cases of osteomyelitis, an orthopedic surgeon may remove a sample of bone for examination. This may be done under local or general anesthetic, and is sometimes performed during surgery. Another approach is needle aspiration or needle biopsy, which may be performed by an orthopedic surgeon or radiologist. In this procedure, the doctor obtains samples by using one or more hollow needles. Following either procedure, the samples will be sent to a laboratory to determine if bacteria are present.

Any bacterial infection should be promptly and thoroughly treated to lessen the chance that osteomyelitis will spread to the bones. If you have a bacterial infection, appropriate diagnosis and treatment should prevent the bacteria from spreading to the bones. Since osteomyelitis may also be caused by a direct infection from an injury, effective wound management also helps to prevent the disease. This is particularly true in people with diabetes who have a high risk of foot ulcers that do not heal properly. If you have a diabetic foot ulcer, ask your doctor about a referral to a wound clinic to help your foot ulcer heal properly.