Septic arthritis is destruction of a joint from an infection such as staphyloccocus, streptococcus, or salmonella inside the joint. Septic arthritis in children after a closed bone fracture is rare.
With a closed fracture, there is no disruption of skin or other soft tissues. In other words, there was no obvious or known way for the bacteria that caused the infection to enter the body.
In some cases (usually adults), septic arthritis develops after the person has had an infection somewhere else in the body. For example, pneumonia, urinary tract infection, or an infected IV in a hospitalized patient is the source of the bacteria. In children, strep throat, measles, tonsillitis, or upper respiratory infections are more likely to cause bacteria that can move through the blood system to a joint.
When there is no history of any of those potential problems or causes surgeons look for a different mechanism causing the infection. Some theories put forth include bacteria from a hematoma (pocket of blood caused by the fracture) might have entered the joint. Or perhaps there was an unknown lung, kidney, or bladder infection.
Like your daughter, the infection typically develops days to months after the original injury. Symptoms of persistent pain, fever, and erythema (redness of the skin) bring the children back to the surgeon for further follow-up.
Without knowing exactly what brought the infection on, the important thing is to identify the bacteria and take an antibiotic specific to that organism. Many bacteria have become resistant to antibiotics so it’s important to find the right one and avoid taking too many antibiotics.
It sounds like your daughter received the proper care needed and is well on her way to recovery. If there are any other suspicious symptoms that crop up, don’t hesitate to call the physician treating her. Early intervention is the key to a successful outcome in cases like this.