Routes of infection
Your bones are usually resistant to infection. Bone can become infected when:
- a pre-existing infection in the blood spreads to a bone
- there is an injury, such as a bone fracture, or a complication from a surgical procedure
- there is a pre-existing health condition, such as diabetes, which means the bone does not get a steady blood supply, so infection-fighting white blood cells cannot reach the site of injury
Blood infections that spread to the bone are more common in children than adults. This may be because children’s bones are still developing, which makes them more vulnerable to this type of blood-borne infection than adult bones, which are fully grown.
In addition, a child's immune system (the body’s natural defence against infection and illness) is still developing, so it is less effective than an adult’s at fighting off infection.
When a bone becomes infected
When an infection develops inside a bone, the immune system will attempt to stop it by sending infection-fighting white blood cells known as neutrophils to the source of the infection.
The neutrophils will try to kill the bacterial or fungal cells that are causing the infection, but sometimes they are unable to do so. If the infection is not treated, a collection of dead neutrophils 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 cause the bone to die. Dead bone with no blood supply must be removed if infection is to be cleared.
Risk factors
There are several risk factors that can make people more vulnerable to developing osteomyelitis. They include:
- weakened immune system
- poor circulation
- diabetes and foot injury
- injury and trauma
- orthopaedic surgery
- intravenous drug use
These risk factors are described below.
Weakened immune system
If your immune system is weakened, it is more likely that an infection that develops in one part of your body will spread to a bone. Your immune system may become weakened for any of the following reasons:
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 and foot injury
People with diabetes are particularly vulnerable to osteomyelitis because they are at risk of developing foot injuries.
Increased levels of glucose in the blood can cause nerve damage. This means that people with poorly controlled diabetes may begin to lose sensation in their feet so small cuts or injuries to the feet go unnoticed. Due to poor circulation, a serious infection can quickly develop in the feet before spreading to the bone.
See the Live Well section about Foot care and diabetes for more information and advice.
Injury and trauma
If you break a bone or have a serious puncture injury that exposes deep tissue to germs, there is a chance you will develop osteomyelitis. This risk is increased if you also have a weakened immune system and/or poor circulation. Any broken bone with a loss of skin cover needs emergency surgery to clean the wound, get rid of dead tissue and stabilise the fracture.
Orthopaedic surgery
If you have orthopaedic surgery (surgery that involves the bones or joints) or you have had metalwork implanted, there is a small chance you may develop osteomyelitis. The risk is less than 1%.
Intravenous drug misuse
People who regularly inject themselves with illegal drugs such as heroin or methamphetamine (crystal meth) have an increased risk of developing osteomyelitis. This is because many people who misuse drugs do not use properly sterilised needles, which significantly increases the risk of introducing bacteria into their bloodstream.
