Osteomyelitis / bone infection

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.

Who is at risk of developing osteomyelitis?

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.

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

The goal of treatment is to get rid of the infection and reduce damage to the bone and surrounding tissues.

Antibiotics are given to destroy the bacteria causing the infection.

• • You may receive more than one antibiotic at a time.

  • Often, the antibiotics are given through an IV (intravenously, meaning through a vein) rather than by mouth.

  • Antibiotics are taken for at least 4 - 6 weeks, often through an IV at home.

Surgery may be needed to remove dead bone tissue if you have an infection that does not go away.

• • If there are metal plates near the infection, they may need to be removed.

  • The open space left by the removed bone tissue may be filled with bone graft or packing material. Doing this promotes the growth of new bone tissue.

Infection that occurs after joint replacement may need surgery to remove the replaced joint and infected tissue around the area. A new prosthesis may be implanted in the same operation. More often, doctors wait until the infection has gone away.

If you have diabetes, it will need to be well controlled. If there are problems with blood supply to the infected area, such as the foot, surgery to improve blood flow may be needed to treat the infection.

Expectations (prognosis)

With treatment, the outcome for acute osteomyelitis is usually good.

The outlook is worse for those with long-term (chronic) osteomyelitis. Symptoms may come and go for years, even with surgery. Amputation may be needed, especially in those with diabetes or poor blood circulation.

The outlook for those with an infection of the prosthesis depends, in part, on:

• • The patient's health

  • The type of infection

  • Whether the infected prosthesis can be safely removed

Calling your health care provider

Call your health care provider if:

• • You develop symptoms of osteomyelitis

  • You have osteomyelitis and the symptoms continue despite treatment

References

• 1. Matteson EL, Osmon DR. Infections of bursae, joints, and bones. In: Goldman L, Schafer AI, eds. Cecil Medicine. 24th ed. Philadelphia, Pa: Saunders Elsevier; 2011:chap 280.

  2. Berbari BF, Steckelberg JM, Osmon Dr. Osteomyelitis. In: Mandell GL, Bennett JE, Dolin R, eds. Principles and Practice of Infectious Diseases. 7th ed. Philadelphia, Pa: Elsevier Churchill Livingstone; 2009:chap 103.

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.