This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Surgery
Earliest site of bone involvement in acute hematogenous osteomyelitis in children is: 
Select and explain. 
A. Metaphysis, B. Diaphysis, C. Epiphysis, D. Point of entry of the nutrient aery
A: Metaphysis
Answer: A: Metaphysis 
Explanation: In acute hematogenous osteomyelitis in children, the metaphysis is commonly involved. The end vessels of the nutrient aery empty into much larger sinusoidal veins, causing a slow and turbulent flow of blood at this junction. These conditions predispose bacteria to migrate through adjacent gaps in the endothelium. Also, low oxygen tension in this region may compromise phagocytic activity of white blood cells. Thrombosis caused by infection results in a region of avascular necrosis that may lead to abscess formation. Must know: Staphylococcus aureus, Streptococcus, and Haemophilus influenzae are the most common causes of acute hematogenous osteomyelitis in children. The most common causes of septic ahritis are Neisseria gonorrhoeae, S. aureus, and group A Streptococcus. Ref: Wilson S.C., Skinner H.B. (2006). Chapter 8. Ohopedic Infections. In H.B. Skinner (Ed), CURRENT Diagnosis & Treatment in Ohopedics, 4e.