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Infection

Acute osteomyelitis - pathophysiology

Haematogenous seeding, vascular anatomy, progression and treatment principles.

10 questions 1 source pages

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10 questions
Q1Describe the pathophysiology of acute osteomyelitis.▸
  • Haematological spread; bacteria adhere and proliferate in the metaphyseal region
  • Pus formation, drains along Haversian and Volkmann canals, then breaks out as a subperiosteal abscess
  • High intraosseous pressure + poor blood supply due to elevated periosteum -> bone ischaemia (vessel thrombosis) -> sequestrum
  • Subperiosteal new bone -> involucrum; pus breaks through involucrum -> cloaca
Q2Why do bacteria proliferate in the metaphyseal region?▸
  • Hairpin turn with sluggish flow
  • Low oxygen tension
  • Acidic environment
Q3What is a sequestrum?▸
  • Devitalised bone resulting from high intraosseous pressure and poor blood supply due to the elevated periosteum
  • Caused by bone ischaemia (blood vessel thrombosis)
Q4What is an involucrum?▸
  • Subperiosteal new bone formation
Q5What is a cloaca?▸
  • Pus breaking through the involucrum
Q6Which patients with acute osteomyelitis develop septic arthritis?▸
  • Neonate <1.5 years old with a patent transphyseal artery
  • Infection in the 4 intra-articular epiphyses: proximal humerus, hip, radial head, distal fibula
Q7What are the common pathogens of acute osteomyelitis by age group?▸
  • Most common in all ages: Staph aureus
  • Neonates: Group B strep, Haemophilus influenzae
  • 1-16 years: Strep pyogenes, Haemophilus influenzae
  • Infants: also gram-negative rods; consider MRSA
Q8What is the presentation and investigation of acute osteomyelitis?▸
  • PMHx, recent injury, failure to thrive, refusal to walk, other source of infection
  • Bloods: WBC, CRP, ESR and cultures
  • X-ray: periosteal reaction at 1 week, lytic lesion at 2 weeks (metaphyseal rarefaction)
  • MRI: early diagnosis and drainable abscess; bone scan: Indium/Technetium + gallium
  • +/- image-guided aspiration
Q9What are the indications for surgery in acute osteomyelitis?▸
  • No systemic response to antibiotics for 48hrs (fever not settling, CRP not dropping)
  • Drainable abscess
Q10What are the complications of acute osteomyelitis?▸
  • Chronic osteomyelitis (5%)
  • LLD: over- or under-growth, arthritis, pathological fracture
  • 30% have concomitant septic arthritis (shoulder, elbow, hip, ankle can all spread via transphyseal vessels)
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