Osteomyelitis

Overview

Osteomyelitis is an infection in a bone. Infections can reach a bone by traveling through the bloodstream or spreading from nearby tissue. Osteomyelitis can also begin in the bone itself if an injury exposes the bone to germs.

In children, osteomyelitis most commonly affects the long bones of the legs and upper arm, while adults are more likely to develop osteomyelitis in the bones that make up the spine (vertebrae). People who have diabetes may develop osteomyelitis in their feet if they have foot ulcers.

Symptoms

Sometimes osteomyelitis causes no signs and symptoms or has signs and symptoms that are difficult to distinguish from other problems.

Signs and symptoms of osteomyelitis include:

• Fever or chills
• Irritability or lethargy in young children
• Pain in the area of the infection
• Swelling, warmth and redness over the area of the infection
• Nausea
• General discomfort, uneasiness, or ill feeling (malaise)
• Drainage of pus through the skin (in chronic osteomyelitis)

Causes

Most cases of osteomyelitis are caused by staphylococcus bacteria, a type of germ commonly found on the skin or in the nose of even healthy individuals. Bone infection can also be caused by 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.

Germs can enter a bone in a variety of ways, including:

• Via the bloodstream. Germs in other parts of your body — for example, from pneumonia or a urinary tract infection — can travel through your bloodstream to a weakened spot in a bone. In children, osteomyelitis most commonly occurs in the softer areas, called growth plates, at either end of the long bones of the arms and legs.
• From a nearby infection. Severe puncture wounds can carry germs deep inside your body. If such an injury becomes infected, the germs can spread into a nearby bone.
• Direct contamination. This may occur if you have broken a bone so severely that part of it is sticking out through your skin. Direct contamination can also occur during surgeries to replace joints or repair fractures.

Risk factors:

Your bones are normally resistant to infection. For osteomyelitis to occur, a situation that makes your bones vulnerable must be present.

Recent injury or orthopedic surgery

A severe bone fracture or a deep puncture wound gives infections a route to enter your bone or nearby tissue. Surgery to repair broken bones or replace worn joints also can accidentally open a path for germs to enter a bone. Deep animal bites also can provide a pathway for infection.

Circulation disorders

When blood vessels are damaged or blocked, your body has trouble distributing the infection-fighting cells needed to keep a small infection from growing larger. What begins as a small cut can progress to a deep ulcer that may expose deep tissue and bone to infection. Diseases that impair blood circulation include:

• Poorly controlled diabetes
• Peripheral arterial disease, often related to smoking
• Sickle cell disease

Problems requiring intravenous lines or catheters

There are a number of conditions that require the use of medical tubing to connect the outside world with your internal organs. However, this tubing can also serve as a way for germs to get into your body, increasing your risk of an infection in general, which can lead to osteomyelitis. Examples of when this type of tubing might be used include:

• Dialysis machines
• Urinary catheters
• Long-term intravenous tubing, sometimes called central lines

Conditions that impair the immune system

If your immune system is affected by a medical condition or medication, you have a greater risk of osteomyelitis. Factors that may suppress your immune system include:

• Chemotherapy
• Poorly controlled diabetes
• Having had an organ transplant
• Needing to take corticosteroids or drugs called tumor necrosis factor (TNF) inhibitors.

For unclear reasons, people with HIV/AIDS don't seem to have an increased risk of osteomyelitis.

Illicit drugs

People who inject illicit drugs are more likely to develop osteomyelitis because they typically use nonsterile needles and don't sterilize their skin before injections.

 

Prevention

Certain people who have artificial joints or metal components attached to a bone should take preventive antibiotics before surgery, including dental surgery, because these people may be at increased risk of infection from bacteria normally present in the mouth and other parts of the body. People can ask their health care practitioner for expert, detailed recommendations regarding preventive antibiotics. People undergoing surgical or dental procedures should tell their surgeon, orthopedist, or dentist that they have an artificial joint or metal component attached to a bone so that preventive antibiotics can be taken.

Diagnosis

A combination of tests and procedures is necessary to diagnose osteomyelitis and to determine which germ is causing the infection.

Blood tests

Blood tests may reveal elevated levels of white blood cells and other factors that may indicate that your body is fighting an infection. If your osteomyelitis was caused by an infection in the blood, tests may reveal what germs are to blame. No blood test exists that tells your doctor whether you do or do not have osteomyelitis. However, blood tests do give clues that your doctor uses to decide what further tests and procedures you may need.

Imaging tests

• X-rays. X-rays can reveal damage to your bone. However, damage may not be visible until osteomyelitis has been present for several weeks. More detailed imaging tests may be necessary if your osteomyelitis has developed more recently.
• Computerized tomography (CT) scan. A CT scan combines X-ray images taken from many different angles, creating detailed cross-sectional views of a person's internal structures.
• Magnetic resonance imaging (MRI). Using radio waves and a strong magnetic field, MRIs can produce exceptionally detailed images of bones and the soft tissues that surround them.

Bone biopsy

A bone biopsy is the gold standard for diagnosing osteomyelitis, because it can also reveal what particular type of germ has infected your bone. Knowing the type of germ allows your doctor to choose an antibiotic that works particularly well for that type of infection. An open biopsy requires anesthesia and surgery to access the bone. In some situations, a surgeon inserts a long needle through your skin and into your bone to take a biopsy. This procedure requires local anesthetics to numb the area where the needle is inserted. X-ray or other imaging scans may be used for guidance.

Prognosis

The prognosis for people with osteomyelitis is usually good with early and proper treatment. However, sometimes, chronic osteomyelitis develops, and a bone abscess may recur weeks to months or even years later.

Treatment

The most common treatments for osteomyelitis are antibiotics and surgery to remove portions of bone that are infected or dead. Hospitalization is usually necessary.

Medications

A bone biopsy will reveal what type of germ is causing your infection, so your doctor can choose an antibiotic that works particularly well for that type of infection. The antibiotics are usually administered through a vein in your arm for at least four to six weeks. Side effects may include nausea, vomiting and diarrhea. An additional course of oral antibiotics may also be needed for more-serious infections.

Surgery

Depending on the severity of the infection, osteomyelitis surgery may include one or more of the following procedures:

• Drain the infected area. Opening up the area around your infected bone allows your surgeon to drain any pus or fluid that has accumulated in response to the infection.
• Remove diseased bone and tissue. In a procedure called debridement, the surgeon removes as much of the diseased bone as possible, taking a small margin of healthy bone to ensure that all the infected areas have been removed. Surrounding tissue that shows signs of infection also may be removed.
• Restore blood flow to the bone. Your surgeon may fill any empty space left by the debridement procedure with a piece of bone or other tissue, such as skin or muscle, from another part of your body. Sometimes temporary fillers are placed in the pocket until you're healthy enough to undergo a bone graft or tissue graft. The graft helps your body repair damaged blood vessels and form new bone.
• Remove any foreign objects. In some cases, foreign objects, such as surgical plates or screws placed during a previous surgery, may have to be removed.
• Amputate the limb. As a last resort, surgeons may amputate the affected limb to stop the infection from spreading further.

Hyperbaric oxygen therapy

In people with very difficult-to-treat osteomyelitis, hyperbaric oxygen therapy may help get more oxygen to the bone and promote healing. Hyperbaric oxygen therapy is a means of delivering more oxygen than is normally available in the atmosphere. This is done using a pressure chamber that resembles a large, clear tube.