Osteomyelitis is an infection of the bone. Osteomyelitis can occur in infants, children, and adults. Different types of bacteria typically affect age groups differently. In children, osteomyelitis most commonly occurs at the ends of the long bones of the arms and legs, affecting the hips, knees, shoulders, and wrists. In adults, it is more common in the bones of the spine (vertebrae) or in the pelvis.