BONE INFECTION

( OSTEOMYELITIS )

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What is a Bone Infection ?

A bone infection occurs when bacteria is traveling thru our body within the blood stream and gets stuck within the bone.  Our bone is not hard rock, but rather a living thing like a tree - which is very hard and needs nutrients to survive.  Our bone survives on nutrients provided by the blood, and therefore we have blood vessels that travel thru the bone, and the speed of blood flow slows down once its within the bone to allow all of the nutrients to get of the train and enter the bone.  One problem with this, is that bacteria can also get off, and cause an infection in the bone - aka osteomyelitis.

Bone Infections are painful because the bacteria kicks out the normal cells living in the bone and trashes the place, causing inflammation and pain.

Most cases of osteomyelitis occur when the bacteria travels thru the blood stream, however, a deep cut can also allow bacteria to crawl onto the bone from the outside.  Thats why its so important to clean cuts with soap and water. 

The most common type of bacteria involved with osteomyelitis is "Staph. aureus", and MRSA is a particularly mean type of staph.aureus.  Kingella is another type of bacteria that can cause this infection.  

How do you diagnose a bone infection (osteomyelitis) ?

When a doctor sees a child with a fever and pain putting weight on their leg, they think of many things that could cause these symptoms, but they immediately put Osteomyelitis and Septic Arthritis (see talk) at the top of the list.  

An infection in the bone is important to diagnose quickly to prevent the infection from spreading into the joints, or elsewhere in the body.

Doctors look at blood tests and x-rays to begin their diagnosis of this condition (and to rule out other things).

Blood tests look for signs that major inflammation is occurring within the body.  The blood test cannot say where its occurring, it just says that its somewhere (usually by examining the child, a doctor can localize the site of infection).  These blood tests are called CRP - which is elevated in 98% of people with osteomyelitis within 6 hours of the infection starting.  The other blood test is ESR - which is not as good, but still its elevated in 90% of people within 3 - 5 days of the infection starting.  

X-rays are not very helpful because it can take 7 days or more before the bacteria affect the bone enough for abnormalities to be seen on x-ray.  

MRI is a much better test.  Its 90 - 100% accurate, and it shows inflammation within the bone.  Adding dye to the MRI (called gadolinium) makes the MRI even more accurate in finding the infection.

How do you treat osteomyelitis ( bone infection )?

Bone infections are always treated with antibiotics.  Sometimes they also need a surgery.

Doctors will often place a needle into the area of infection (using an x-ray to confirm that the needle is in the correct place) to get a sample of the type of bacteria causing the infection.  Remember that infections can be caused by different types of bacteria, and different types of bacteria are treated with different types of antibiotics.  However, this needle sample only captures bacteria 50% of the time (not great).  

Many doctors dont think a sample is necessary and will just treat the bone infection with antibiotics that target the usual suspects.  This antibiotic is usually clindamycin (sometimes its vancomycin if the infection is severe).

Because our blood stream flows thru our bones, the antibiotics are delivered to the site of infection and the infection will be cleared after 3 - 4 weeks of antibiotics.  Doctors will often order blood tests before stopping the antibiotic to confirm that the infection is gone.

Surgery is performed when there are signs that the bacteria has walled itself off (this is called an abscess) and the antibiotics cannot reach the bacteria.  Surgery is used to decompress the abscess (like popping a pimple) and this allows antibiotics to invade the area.  The presence of an abscess can be determined with the MRI.

Surgery is also performed if it looks like the bacteria has spread out beyond the bone and entered into a joint (such as the hip joint).  If doctors diagnose the joint as infected (or have a high suspicion for infection) the joint (ie hip) needs to be "washed out" (cleaned) with sterile fluid.

What is the long term outcome?  

The patients do great when the infection is identified quickly and treated.  Delayed diagnosis (typically greater than 4 days) can lead to worse outcomes.