Causes and Risk Factors
Bacteria (primarily S. aureus, including MRSA; also streptococci, Gram-negatives, anaerobes) invade via bloodstream, contiguous spread, or direct entry, thriving in ischemic or traumatized bone where biofilms form and antibiotics falter. Pathophysiology involves microbial adhesion to bone matrix, pus accumulation raising intramedullary pressure, cortical erosion, and sequestra (dead bone) formation.
Risk factors: Diabetes (neuropathy, vascular disease), peripheral artery disease, IV drug use, trauma/open fractures, orthopedic implants, immunosuppression (HIV, chemotherapy), sickle cell disease, and chronic wounds. Incidence rises with age and male sex, at ~21.8 per 100,000 person-years.