Osteomyelitis

What is osteomyelitis?

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

How do you develop osteomyelitis?

If some germs (bacteria) settle on a small section of bone, they can multiply and cause osteomyelitis. Bacteria can get to a 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 gut (bowel).
• 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.

Who is at risk of developing osteomyelitis?

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

• Have recently broken (fractured) a bone.
• Have a bone prosthesis (an artificial hip, a screw in a bone following surgery, etc).
• Have recently had surgery to a bone.
• Have diabetes, especially if also have a foot ulcer.
• 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 germs (bacteria).
• Are dependent on alcohol.
• 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.
• Take steroids regularly.

Which bones can be affected by osteomyelitis?

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 high temperature (fever) as the infection develops.

If osteomyelitis develops following a break (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 for osteomyelitis?

Tests to confirm the osteomyelitis 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. An MRI 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 germ (bacterium) is causing the infection

The blood often contains some bacteria from the bone infection. Samples of blood are sent to the laboratory 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 antibiotic medicines.) If the blood tests do not show any bacteria, then a small sample (biopsy) of the affected bone is needed to send to the laboratory.

If the infection from a bone tracks through to the skin, any discharging pus can be sent off for culture. Fluid drawn off from an infected joint can also be analysed to identify the type of bacteria.

What is the treatment for osteomyelitis?

Antibiotic medicines

An antibiotic is usually started as soon as possible. The initial antibiotic chosen is one that is likely to kill the germs (bacteria) which commonly cause 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.)

Osteomyelitis symptoms may settle quite quickly after you start taking an antibiotic. You may have to take the medication for 4-6 weeks but, if you have a severe infection, the course may last up to twelve weeks. This is to make sure all infection has gone from the bone.

To control pain you may be given painkillers and if you have infection in a long bone (such as an arm or leg) you may be fitted with a splint to restrict movement.

Surgery

You will usually need an operation if:

• A ball of pus (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 persistent (chronic) 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.

Rarely, surgical removal (amputation) of a foot or leg is needed if infection persists in a leg bone and does not clear with any other treatment.

What is the outlook (prognosis)?

If the osteomyelitis infection is treated promptly, there is a good chance of a complete cure. The best outcome occurs if you have treatment within 3-5 days of the start of infection. (In the days before antibiotic medicines, 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 osteomyelitis develops after a serious bone injury, or after surgery to a bone:

• If the infection is left untreated, a ball of pus (abscess) may develop in the bone and surrounding tissue. In time, this may burst on to the skin and leave a track (sinus) between the infected bone and the surface of the skin.
• Blood infection (sepsis) which can cause serious illness.
• If the infection follows a bone break (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 germ (bacterium) called meticillin-resistant S. aureus (MRSA) which is difficult to clear with antibiotics.
• Persistent infection of the bone (chronic osteomyelitis) sometimes develops and 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.