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 can be associated with longstanding open skin ulcers that penetrate deep into the bone or with a traumatic injury that penetrates down to the bone. Bones are usually well protected and don't become infected easily.
Bone infection can occur if:
- there is trauma to the bone, or 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 bloodstream
- there is poor circulation (as seen in diabetes)
An infection can spread into the bone in many ways. It can enter during bone surgery or through a broken bone that protrudes through the skin. 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.
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) through this route.
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 bloodstream and are carried to the artificial hip or knee.
People who take illicit drugs by injection and people on kidney dialysis are at higher risk for developing osteomyelitis due to the higher risk of bloodstream infections in these groups.
The bacteria responsible for tuberculosis can also infect the bones in a rare condition called Pott's disease.