Osteomyelitis is an inflammation of bone caused by an infecting organism. Staphylococcus aureus is the most common cause. Acute hematogenous osteomyelitis usually involves the metaphysis of long bones in children. Diagnosis is based on clinical features like localized tenderness and lab tests showing elevated inflammatory markers. Plain X-rays may initially only show soft tissue swelling and osteopenia before lytic bone changes appear in subacute or chronic cases.