Causes
A bone infection is usually caused by bacteria, but sometimes other organisms such as a fungus may be the cause. The most common bacterial cause of osteomyelitis is Staphylococcus aureus. Other bacterial causes include Streptococcus group A and group B, H. influenzae, coliforms and Pseudomonas aeruginosa, all of which are usually associated with adjacent chronic open ulcers that penetrate deep to bone or with an open traumatic injury to the bone. Bones are usually well protected and don't become infected easily.
Bone infection can occur if:
- a bone has been broken and is protruding through the skin
- there is an adjacent infection of surrounding soft tissue that spreads to the bone underneath
- it is carried to the bone via the blood stream
Children may develop bone infections in their arms and legs from an infection carried from another part of the body through the blood. Adults tend to develop infections in the bones of their spine (spinal vertebrae).
If you've had orthopedic surgery, such as hip replacement or knee replacement, where a piece of metal was attached to a bone, an infection can develop. The infection may occur early after surgery if bacteria from the surface of the skin contaminated the artificial hip or knee. The infection may occur years later if bacteria enter the blood stream and are carried to the artificial hip or knee.
People who take illegal drugs by injection and people on kidney dialysis are at higher risk for developing osteomyelitis in the vertebrae due to the higher risk of blood stream infections in these groups.
The bacteria responsible for tuberculosis can also infect the bones in a condition called Pott's disease.
An infection can spread through a break in the bone in many ways. It can enter during bone surgery or through a broken bone. It can also spread from an infected artificial joint, such as a knee joint, into the surrounding bone. Any contaminated object that pierces the bone, such as a piece of metal from a car accident, can cause an infection.
Infection in soft tissue, such as muscles or organs, can develop in an area that has been injured or has poor blood circulation. Once the infection appears, it can then spread to the nearby bone.