Osteomyelitis is most commonly caused by which route of infection in adults?

• A. Direct invasion from adjacent tissue
• B. Lymphatic spread
• C. Environmental spores inhalation
• D. Hematogenous spread of bacteria

Answer: (D)

The main concept is that osteomyelitis usually starts when bacteria travel through the bloodstream and seed the bone. Bacteria circulating in blood can lodge in the bone’s capillary networks, especially in areas with slower flow such as the metaphyses of long bones and the vertebral endplates. Once bacteria settle there, the body’s inflammatory response causes local destruction, pus formation, and often bone changes like sequestrum or involucrum. This hematogenous seeding explains why infection of bone is often linked to a prior or concurrent bacteremia from various sources (skin, urinary tract, dental infections, IV catheters, etc.), and why the bloodstream route is considered the typical route initiating osteomyelitis in adults. Direct invasion from a nearby infected area or direct inoculation from trauma or surgery can occur, but the bloodstream route best accounts for the common pattern of disease in adults.