Causes of Osteomyelitis
Many cases of osteomyelitis develop because of a bacteria known as staphylococcus and usually live on the skin or in the nose of individuals who are healthy. These germs can enter a bone in a number of ways, including:

Contamination which is direct
This happens when an individual has a bone that is broken so severely that a part of it might be sticking thru the skin. Direct contamination can also occur because of surgeries to replace joints or repair bones that are broken.

Thru the blood stream
Bacteria from other areas of the body – for instance, pneumonia or a urinary tract infection – may travel thru the blood system to a spot in a bone that is weak. In children, osteomyelitis is more commonly found in softer areas, known as growth plates, at either end of the long bones of the legs and arms.

Nearby infection
Severe wounds from punctures can carry bacteria very deep inside the body. If such an injury gets infected, the bacteria can migrate into any nearby bone.