Bacterial Osteomyelitis: Pathogenesis and clinical findings
Authors: Mehul Gupta Reviewers: Stephen Vaughan* Yan Yu* * MD at time of publication
Iatrogenic:
Penetrating medical procedure introduces bacteria directly to bone
Systemic immune reaction
Macrophages, neutrophils and dendritic cells are activated by recognizing
bacterial pathogen associated molecular patterns (PAMPs)
Trauma:
Penetrating injury or open fracture introduces bacteria directly to bone
Hematogenous:
Blood carries bacteria from distant site of infection to bone
Contiguous:
Neighboring site of infection seeds bacteria directly to bone
Bacterial Osteomyelitis
Innate Immune cells and local mast cells release vasoactive cytokines
Capillaries dilate to ↑blood flow to affected area and become more permeable to allow for exit of immune cells and plasma contents
Localized Immune response
Poorly understood mechanismsàinnate immune systems unable to clear the bacteria in some individualsàchronic infection
Immune cells produce pyrogenic intermediates (i.e. PGE2, IL-6, and IL-1)
Pyrogenic intermediates travel through the
bloodstream to the hypothalamus and alters the body’s thermal setpoint
Fever
Immune cells produce inflammatory cytokines (i.e. TNFα and IL6)
Systemic inflammatory cytokines result in the production of Non-specific acute- phase reactants
High Serum CRP and ESR
Warmth Erythema
Progressive blood vessel occlusion by immune cellular and bacterial debris causing infarct and necrosis of bone
More permeable capillaries allow plasma to leak into surrounding periosteal tissue
More permeable capillaries allow macrophages and neutrophils to exit the capillaries at the site of infection
Immune cells phagocytize bacteria, producing an of opaque off-white fluid
Pus
Immune cells sequester necrotic bone tissue into a regional abscess within medullary bone
Sequestrum seen as localized opacity on CT or late X-ray imaging
↑ Osteoclast activity to remove damaged medullary bone and ↑ Osteoblast activity to reform new bone
Osteoclasts and osteoblasts remodel and deposit new bone in area surrounding necrotic tissue
Swelling
↑ Periosteal fluid applies ↑ pressure to surrounding nerve endings
Bone Pain manifesting as refusal to use limb
New layer of bone formed
Positive Bone Scan in area of infection
Abbreviations:
• IL – Interleukin
• PGE2 – Prostaglandin E2
• TNFα – Tumor necrosis factor alpha
Involucrum / Periosteal Reaction: seen as regional luminance surrounding sequestrum on CT or late X-ray imaging
Legend:
Pathophysiology
Mechanism
Sign/Symptom/Lab Finding
Complications
Published May 21, 2021 on www.thecalgaryguide.com