In haematogenous osteomyelitis of long bones in children, which vascular anatomical feature predisposes the metaphysis to bacterial seeding?

• A High arterial pressure at the metaphyseal arterioles
• B Metaphyseal sinusoids are lined by activated macrophages
• C Sluggish blood flow in metaphyseal sinusoids with lack of phagocytic cells ✓
• D Diaphyseal periosteum is thicker and more resistant to infection

Explanation

The metaphysis is predisposed because the terminal capillary loops make sharp U-turns, creating sluggish, turbulent blood flow in the sinusoidal vascular spaces. These sinusoids lack phagocytic lining cells, allowing bacteria to settle and multiply after bacteraemic episodes. The vascular loops also lack nutrient foramen equivalents, making this a relative ischaemic zone. This is why Staphylococcus aureus septicaemia (most common cause) seeds the metaphysis of growing bones in children, particularly the distal femur and proximal tibia.

Reference: Maheshwari Essential Orthopaedics, 6th ed.

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