In acute haematogenous osteomyelitis of childhood, which is the most common metaphyseal site affected and why?

• A Proximal femoral metaphysis, because it is the only intra-articular metaphysis making it vulnerable to septic arthritis
• B Distal tibial metaphysis, because the periosteum is tightly adherent and prevents subperiosteal abscess
• C Distal femoral metaphysis, because it has the slowest blood flow and largest capillary sinusoids in the metaphysis, promoting bacterial seeding ✓
• D Proximal humeral metaphysis, because it has the highest perfusion pressure in the upper limb

Explanation

The distal femoral metaphysis is the most common site of haematogenous osteomyelitis in children. The metaphysis is preferentially affected because nutrient arterioles form sharp hairpin loops at the growth plate, creating turbulent, sluggish flow in wide sinusoidal capillaries. This reduces phagocytic efficiency and bacterial clearance, allowing organisms to lodge and proliferate. The proximal femoral, proximal humeral, and proximal radial metaphyses are intra-articular (important for septic arthritis spread), but the distal femur is still the most common overall site.

Reference: Maheshwari Essential Orthopaedics, 6th ed.

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