Developmental pathogenesis of acute osteomyelitis

(A) In newborns, infection often spreads from the metaphysis to adjacent joints via transphyseal vessels that are present at birth. Purulence commonly spreads along the periosteum or ruptures through the cortex into soft tissue or adjacent joint spaces.
(B and C) In older infants and children, transphyseal capillaries are no longer present. Infection in older children is generally confined to the metaphysis, and the thicker cortex and denser periosteum limit spread to soft tissues. Involvement of adjacent joints is less common.