Pathophysiology
Clinical meaning
Osteomyelitis is an infection of the bone that can involve the cortex, medullary canal, and periosteum. The most common causative organism is Staphylococcus aureus, which accounts for approximately 70-80% of all cases. The infection reaches bone through three primary routes: hematogenous spread (bloodstream seeding from a distant infection site, most common in children and older adults), contiguous spread (direct extension from an adjacent soft tissue infection such as a diabetic foot ulcer or surgical wound), and direct inoculation (penetrating trauma, open fracture, or surgical contamination). Once bacteria reach the bone, they adhere to the bone matrix using surface adhesion molecules and produce biofilm, a protective polysaccharide layer that shields the organisms from both the immune system and antibiotics. The inflammatory response triggers vascular congestion, thrombosis of local blood vessels, and subsequent ischemia of the surrounding bone tissue. As the infection progresses, pus accumulates within the rigid bony structure, increasing intramedullary pressure and further compromising blood flow. Devitalized bone separates from living tissue and forms a sequestrum -- a segment of dead, infected bone that acts as a persistent reservoir for...