Osteomyelitis in adult intravenous drug abusers most commonly affects which bones?

• A. Vertebral spine
• B. Femur
• C. Skull
• D. Pelvis

Answer: (A)

The key idea is that in adults, osteomyelitis from bloodstream infection tends to seed the spine, especially in intravenous drug users. Bacteria that enter the blood often travel through the valveless Batson venous plexus, which links pelvic and abdominal veins to the vertebral bodies. This venous pathway makes the vertebral endplates and adjacent marrow particularly susceptible to establishment of infection after bacteremia. Staphylococcus aureus is a common culprit in IV drug users, so the spine becomes the usual site of hematogenous osteomyelitis in this group. While other bones can be involved, the vertebral column is the most frequently affected in this scenario.