Osteomyelitis

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What is osteomyelitis?

Osteomyelitis is an infection of a bone. Many different types of bacteria can cause osteomyelitis. However, infection with a bacterium called Staph. aureus is the most common cause. Infection with a fungus is a rare cause.

How do you get osteomyelitis?

If some bacteria settle on a small section of bone, they can multiply and cause infection. Bacteria can get to bone:

• Via the bloodstream. This is the common cause in children. Bacteria sometimes get into the blood from an infection in another part of the body and then travel to a bone. Even if you are healthy, bacteria can sometimes get into the blood from the nose or bowel (gut).
• Following an injury. Bacteria can spread to bone if you have a deep cut on the skin. In particular, if you have a broken bone which you can see through the cut skin.

Anyone at any age can develop osteomyelitis. However, you have an increased risk if you:

• Have recently fractured (broken) a bone.
• Have a bone prosthesis (such as an artificial hip, a screw in a bone following surgery, etc).
• Have recently had surgery to a bone.
• Have a poor immune system. For example, if you have AIDS; if you are taking chemotherapy; if you are seriously ill with another disease; etc.
• Inject street drugs which can be contaminated with bacteria.
• Have had a previous episode of osteomyelitis.
• Have certain types of blood disorders. For example, sickle cell disease.
• Have reduced skin sensation. This can lead to damage and infection of the skin which can spread to the blood or to local bone. For example, some people with diabetes have reduced sensation in their feet.
• Have regular kidney dialysis.

Which bones can be affected?

The long bones of the leg (femur, tibia and fibula) are the most commonly affected. However, osteomyelitis can affect any bone (although it is very rare in some bones).

What are the symptoms of osteomyelitis?

• Pain and tenderness over an area of bone.
• A lump may develop over a bone which is usually very tender.
• Redness of overlying skin may then develop.
• Feeling generally unwell with fever (high temperature) is common as the infection develops.

If osteomyelitis develops following a fracture to a bone then the symptoms include increasing redness, swelling, and pain around the fracture site. Pus may come out from a skin wound over a fracture.

Are any tests needed?

Tests to confirm the diagnosis
If you have typical symptoms coming from an infection of a leg bone then the diagnosis may be fairly clear. However, pain coming from 'deeper' bones such as the spine or pelvis can be due to a number of causes. A scan of the bone will help to confirm the diagnosis. (A plain x-ray is not so useful in the early stages of osteomyelitis as an x-ray can be normal for up to a week or so after the infection starts.)

Tests to find which bacterium is causing the infection
The blood often contains some bacteria from the bone infection. Samples of blood are sent to the 'lab' to identify which type of bacterium is causing the infection. This is important as it will help to decide which is the best treatment. (Some bacteria are 'resistant' to some antibiotics.)

If the blood tests do not show any bacteria, then a biopsy (small sample) of the affected bone is needed to send to the lab.

What is the outlook (prognosis)

If the infection is treated promptly, then there is a good chance of a complete cure. (In the days before antibiotics, osteomyelitis was a very serious illness which sometimes caused death, and often caused severe disability.)

Possible complications are listed below. As a rule, there is more risk of developing complications if the infection develops after a serious bone injury, or after surgery to a bone.

• If the infection is left untreated, an abscess (ball of pus) may develop in the bone and surrounding tissue. In time, this may burst onto the skin and leave a track (sinus) between the infected bone and surface of the skin.
• Blood infection (septicaemia) which can cause serious illness.
• If the infection follows a bone fracture, then there is a chance that the fracture will not heal ('non-union of fracture').
• Compression of other structures next to the infection.
• Some bone infections are caused by a bacterium called MRSA (Methicillin Resistant Staph. Aureus) which is difficult to clear with antibiotics.
• Persistent infection of the bone ('chronic osteomyelitis') sometimes develops which can be difficult to clear.

Once you have had one bout of osteomyelitis, your risk of a further bout is higher than average. Therefore, if you have had a previous bout of osteomyelitis, see a doctor quickly if you develop the symptoms described above.

What is the treatment for osteomyelitis?

Antibiotics
An antibiotic is usually started as soon as possible. The initial antibiotic chosen is one that is likely to kill the bacteria which commonly causes osteomyelitis. However, the antibiotic is sometimes changed to a different one when the results of the tests confirm which bacterium is causing the infection. (Some bacteria are resistant to some antibiotics.)

The symptoms may settle quite quickly after you start taking an antibiotic. However, you need to continue taking the antibiotic for several weeks. This is to make sure all infection has gone from the bone.

Surgery
You will usually need an operation if:

• An abscess develops. The pus in an abscess needs to be drained.
• The infection presses on other important structures. For example, an infection in the spine may press on the spinal cord.
• The infection has become 'chronic' (persistent) and some bone has been destroyed. Dead and infected bone may need to be removed to allow the infection to clear. Sometimes plastic surgery is needed at the same time to cover any wound to give the best chance of cure.

Hyperbaric oxygen
This may be considered if the infection does not clear. It involves going into a chamber where the pressure of oxygen you breathe is higher than normal. This raises the amount of oxygen in your blood which helps in various conditions. Some evidence suggests that surgery and antibiotics combined with hyperbaric oxygen may help in cases of persistent (chronic) osteomyelitis that have not been helped by surgery and antibiotics alone. Further research is needed to clarify this.

© EMIS and PIP 2006   Updated: February 2006

The authors and editors of this article are employed to create accurate and up to date content reflecting reliable research evidence, guidance and best clinical practice. They are free from any commercial conflicts of interest. Find out more about updating.

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