Routes of infection

Your bones are usually resistant to infection. But there are some circumstances where a bacterial or fungal infection can infect your bones. There are a number of ways a bone can become infected:

• A pre-existing infection in the blood may spread to a bone.
• A bone may become infected as a result of an injury, such as a bone fracture, or as a complication of a surgical operation, such as a hip replacement.
• A bone can become infected due to a pre-existing health condition such as diabetes. This often occurs because the bone is not getting a steady supply of blood (more specifically, a supply of infection-fighting white blood cells).

Blood infections that spread to the bone are more common in children than adults. This may be because children’s bones are not fully grown, so they may be more vulnerable to this type of blood-borne infection than adult bones.

What happens during a bone infection?

Once a bacterial or fungal infection develops inside the bone, the immune system will attempt to stop it by sending specialised, infection-fighting white blood cells, known as neutrophils, to the source of the infection.

The neutrophils will attempt to kill the bacteria, or fungi cells, that are causing the infection, but are sometimes unable to do so. If the infection is not treated, a collection of dead nuetrophoils will build up inside the bone, forming a pocket of pus known as an abscess.

In cases of chronic osteomyelitis, abscesses can block the blood supply to the bone, which will eventually lead to the death of the bone.

Risk factors

There are a number of risk factors that can make people more vulnerable to developing osteomyelitis. These are described below.

Weakened immune system

If your immune system is weakened (immunocompromised) it's more likely that an infection that develops in one part of your body will then spread to a bone.

Reasons why your immune system may be weakened include:

• A health condition that weakens the immune system, such as HIV or AIDS.
• Treatments that weaken the immune system, such as chemotherapy, radiotherapy or a long-term dose of oral steroids.
• Poor diet.

Poor circulation

People with health conditions that affect the blood flow are at greater risk of developing osteomyelitis. This is because their bones may not be getting a steady supply of infection-fighting white blood cells.

Conditions that are known to cause poor circulation include:

• diabetes (both type 1 and type 2),
• sickle-cell anaemia, and
• arteriosclerosis (narrowing of the arteries that is usually caused by smoking and/or a high-fat diet).

Diabetes and foot injury

People with diabetes are particularly vulnerable to osteomyelitis because they have an associated risk of developing foot injuries.

As increased levels of glucose in the blood can cause nerve damage, people with poorly controlled diabetes may begin to lose sensation in their feet. This means that small cuts or injuries to the feet may not be noticed. As a result of poor circulation, a serious infection can quickly develop in the feet and then spread to the bone.

See Useful links for more advice and information about caring for your feet if you have diabetes.

Injury and trauma

If you break a bone, or have a serious puncture injury that exposes deep tissue to germs, there's a chance that you'll develop osteomyelitis. This risk is increased if you also have a weakened immune system and/or poor circulation.

Orthopaedic surgery

If you have orthopaedic surgery (surgery involving the bones or joints), or have had an artificial implant, such as a hip,or knee joint replacement, there's a small chance that you may develop osteomyelitis.

It is estimated that 0.5-2% of people who have orthopaedic surgery will develop osteomyelitis.

Intravenous drug abuse

People who regularly inject themselves with illegal drugs, such as heroin or methamphetamine (crystal meth), have an increased risk of developing osteomyelitis.

Recurring chronic osteomyelitis

The underlying factors that often cause chronic osteomyelitis, such as poor circulation or a weakened immune system, can be difficult to treat, particularly if you have severe diabetes or HIV.

Therefore, if you have experienced a previous episode of chronic osteomyelitis, there is a chance that it could return.

Risk factors can vary depending on your individual circumstances. It may be possible to reduce the risk by making lifestyle changes, such as lowering the amount of saturated fat in your diet, and by taking precautions against infection. See Prevention, above, for more information about this.

Amputation

People who are in a very poor state of health, such as those who are very old or those in the latter stages of an HIV infection, may not be able to withstand the affects of surgical debridement for chronic osteomyelitis.

In some cases, it may be possible to slow the spread of infection for many years by using antibiotics or antifugnals medicines. However, if the infection threatens to spread from a body part, such as a foot, leg or arm, to the rest of your body, it may be necessary to amputate the affected limb.

Initial diagnosis

In the first stage in confirming a diagnosis of suspected osteomyelitis, your GP will carry out a physical examination of your affected body part, checking for signs of tenderness or swelling.

Your GP will want to know about your recent medical history, such as whether you have recently had an injury or a seemingly unrelated infection.

Your GP may refer you for a blood test. While a blood test cannot be used to diagnose osteomyelitis, a high number of white blood cells in your blood may suggest that you have an infection.

Imaging

If a diagnosis of osteomyelitis is suspected, it is likely that you will be referred for further imaging testing. There are a number of imaging tests that may be able to detect bone damage that is caused by osteomyelitis. These include:

• X-rays (although they can usually only detect osteomyelitis in its later stages),
• computerised tomography (CT) scans,
• ultrasound scans, and
• magnetic resonance imaging (MRI) scans.

Biopsy

If earlier testing suggests that you have osteomyelitis, it is usually necessary to remove a small sample of bone for further testing. This is known as a biopsy.

A biopsy is usually necessary for two important reasons:

• it is usually the most effective way to confirm a diagnosis of osteomyelitis, and
• it should be able to establish exactly what type of bacteria, or fungi, is causing your infection, which can be very useful in deciding on the most effective treatment for you.

If you have an infection in an easily accessible bone, such as your foot, it may be possible to remove a small sample of bone under local anaesthetic using a long needle.

Otherwise, open surgery, carried out under general anaesthetic, will probably be required to obtain a sample of bone.

Osteomyelitis is a medical term that describes an infection inside a bone. It's usually caused by a bacterial infection but the condition can also be the result of a fungal infection.

Types of osteomyelitis

There are three main types of osteomyelitis:

• Acute osteomyelitis, where the bone infection develops within two weeks of an initial infection, injury or the onset of an underlying disease.
• Sub-acute osteomyelitis, where the bone infection develops within one ot two months of an initial infection, injury or onset of an underlying disease.
• Chronic osteomyelitis, where the bone infection develops two months or more after an initial infection, injury or onset of an underlying disease.

Acute osteomyelitis is more common in children than adults and usually develops as a complication of a pre-existing blood infection (haematogenous osteomyelitis).

Sub-acute and chronic osteomyelitis are more common in adults and usually develop as a result of an injury or trauma (contiguous osteomyelitis), such as a fractured bone.

Sub-acute and chronic osteomyelitis can also develop as a complication of a condition that affects the blood supply to the bones, such as diabetes, making the bones more vulnerable to infection.

How common is osteomyelitis?

Acute osteomyelitis is rare in children. It's estimated that one in every 1,000 children under the age of one will develop acute osteomyelitis.

The condition is even less common in children over one, with one in every 5,000 children affected.

At present, there is limited data to accurately estimate how widespread osteomyelitis is in the adult population. The condition is known to be a common complication in certain health conditions.

For example, it's estimated that between 30% and 40% of people with diabetes, who experience a puncture injury to the foot, will develop osteomyelitis. One in every 200 people with sickle cell anaemia (a hereditary blood condition) will develop osteomyelitis in any given year.

Outlook

The outlook for osteomyelitis can vary depending on what type of osteomyelitis is present. Acute osteomyelitis, if detected and treated early enough, tends to have a good prognosis.

Sub-acute and chronic osteomyelitis can be more difficult to correctly diagnose and to treat, and both conditions can result in permanent damage to the bone.

Osteomyelitis can usually be successfully treated using antibiotics or, when appropriate, anti-fungal medicines. In more serious cases, surgery may be required to remove diseased bone and tissue and drain away the pus that can be caused by an infection.

If you have a pre-existing health condition that means you have either poor circulation, a weakened immune system or both, it is still possible for you to reduce the risk of developing osteomyelitis.

Weakened immune system

If you have a weakened immune system, you should take extra precautions to prevent exposure to infection and to boost your immune system. These are the steps you can take:

• Don't smoke. It will weaken your immune system.
• Keep your immunisations up to date. Your GP can advise you about this.
• Eat a healthy diet, as this will boost your immune system.
• Take regular exercise, as this also boosts your immune system.
• Wash your hands regularly with soap and hot water, particularly after going to the toilet, before and after preparing food, and after being in crowded places.

Poor circulation

If you have poor circulation, avoid activities that could make it worse and make lifestyle changes that will improve your circulation, such as the following:

Stop smoking (if you smoke)

Smoking cigarettes can clog up your arteries and increase your blood pressure, both of which are bad for your circulation.

Eat a healthy diet

High-fat foods can cause a build-up of fatty plaques in your arteries, and being overweight can lead to high blood pressure. To improve your circulation, a low-fat, high-fibre diet is recommended, including plenty of fresh fruit and vegetables (at least five portions a day) and wholegrains.

Take regular exercise

Regular exercise will lower your blood pressure and make your heart and blood circulatory system more efficient.

For most people, 30 minutes of moderate to vigorous exercise a day, at least five times a week, is recommended. However, if you're in a poor state of health, it may be necessary for you to start an exercise plan gradually. Your GP will be able to advise you about the most suitable level of exercise for you.

Drink alcohol in moderation

Drinking too much alcohol will raise your cholesterol level and increase your blood pressure. Stick to the recommended daily amounts of alcohol.

The recommended daily level of alcohol consumption is three to four units of alcohol for men, and two to three units for women. A unit of alcohol is about half a pint of normal strength lager, a small glass of wine, or a pub measure (25ml) of spirits.

Carek, P.J., Dickerson, L.M., Sack, J.I. (2001). Diagnosis and management of osteomyelitis. American Family Physician, 63(12), 2413-20.

Ferguson L.P., Beattie, T.F.(2002). Lesson of the week: Osteomyelitis in the well looking afebrile child. BMJ  2002;324:1380-1381, doi: 10.1136/bmj.324.7350.1380

Kapoor, A. et a; (2007). Magnetic Resonance Imaging for Diagnosing Foot Osteomyelitis: A Meta-analysis. Arch Intern Med. 2007;167(2):125-132.

Lew, D.P., Waldvogel, F.A.  (1997). Osteomyelitis. The New England Journal of Medicine, 336(14), 999-1007.

Lew, D.P., Waldvogel, F.A. (2004). Osteomyelitis. The Lancet, 364(9431), 369-79.

NICE (2006). Single mini-incision hip replacement

The symptoms of osteomyelitis will depend on whether you or your child has developed acute, sub-acute or chronic osteomyelitis.

Acute osteomyelitis

Symptoms of acute osteomyelitis include:

• fever (although it is not always present, or may be mild in children),
• pain, swelling, tenderness, redness and/or heat in an affected area of bone, and
• there may be some loss of movement in the affected body part.

Sub-acute and chronic osteomyelitis

Symptoms of sub-acute and chronic osteomyelitis usually develop after an initial wound or injury to the bone or tissue.

Symptoms of sub-acute and chronic osteomyelitis include:

• localised bone pain,
• redness and swelling of the affected body part,
• drainage of pus or fluid from the affected body part,
• the affected body part may appear deformed and unusual looking, and
• instability or loss of movement in the affected body part.

In some cases, chronic osteomyelitis may not cause any obvious symptoms, or the symptoms may be the result of an injury rather than infection.

The lack of readily identifiable symptoms is a problem when osteomyelitis develops inside the hip, spine or pelvis.

Acute osteomyelitis

Acute osteomyelitis can usually be successfully treated using antibiotics and antifungal medicines. Most adults will require a four to six-week course of daily antibiotics or intravenous (into a vein) antifungal injections.

Depending on your general state of health, you may need to stay in hospital during this time. Alternatively, it may be possible for you to receive these injections as an outpatient, or be trained to give yourself the injections at home.

Infections that are caused by drug-resistant bacteria, such as MHRA, may require a longer course of treatment using a combination of different antibiotics.

Children will also require an initial course of intravenous antibiotics or antifungal medicines. However, it may be possible to switch to antibiotics or antifungal tablets (oral antibiotics or antifungals) if a child responds well to treatment.

Sub-acute osteomyelitis

The recommended treatment for sub-acute osteomyelitis will depend on the severity of the infection and whether there is any associated bone damage.

It should be possible to treat mild cases of sub-actue osteomyelitis, which have no associated bone damage, in the same way as acute osteomyelitis. More severe cases, with bone damage, will need to be treated in the same way as chronic osteomyelitis.

Chronic osteomyelitis

People with chronic osteomyelitis will usually require a combination of antibiotics or antifungal medication and surgery to repair any bone damage. A surgeon may need to make an incision near the site of the infection to drain away any pus.

In cases of extensive bone damage, it will be necessary to surgically remove any diseased bone and tissue. This procedure is known as debridement.

Debridement can often leave an empty space in the bone (or tissue) so surgeons may take healthy bone or tissue from elsewhere in your body and graft it into place.

The grafted bone or tissue should start to grow new blood vessels, which will help restore the blood supply to the bone.

In cases where an orthopaedic implant, such as an artificial hip, has led to osteomyelitis, it may be necessary to remove the implant, clean out the infection, and replace it with a new implant.

Learn about the medicines used to treat or manage this condition - preparations, benefits and side-effects are all covered.

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Medicine guides: Osteomyelitis