Osteoarticular Infection

Paediatric Acute Osteomyelitis

Epidemiology

  • Boys > Girls
  • <10 years old
  • Neonatal infections are more aggressive with higher complications.
  • Acute osteomyelitis is the most common presenting form.

Aetiology

  • Usually acute haematogenous spread:
    • Direct inoculation (trauma, varicella, or other bacteraemia).
  • Infection originates in metaphysis:
    • Metaphyseal vessels are end arteries, with slow capillary blood flow allowing bacterial seeding.
    • Localised infection activates osteoclasts, causing necrosis and purulent exudate.
    • Subperiosteal abscess forms, spreading toward the diaphysis, leading to sequestrum formation.
    • Periosteum attempts to wall off necrotic bone (involucrum), progressing to chronic osteomyelitis if untreated.

Risk Factors

  • Local trauma.
  • Immunocompromise (diabetes, renal disease, chemotherapy/steroids, rheumatoid conditions).
  • Most cases occur in otherwise healthy children.

Pathogens

  • Staphylococcus aureus: Most common across all age groups.
  • MRSA: Higher virulence, multifocal osteomyelitis, abscess formation.
  • Special Situations:
    • Sickle Cell: Salmonella.
    • Shoe Puncture: Pseudomonas.
    • Neonates: Group B Streptococcus.
    • Infants: Group A Streptococcus, Haemophilus (if unvaccinated).
    • Varicella: Streptococcus.

Clinical Evaluation

  • History: Trauma, immunisations, systemic symptoms, pain, fever.
  • Examination: Pain site, cardiac assessment, septic arthritis, weight-bearing status.

Investigations

  1. Bloods:
    • CRP rises after 6 hours.
    • ESR rises after 3 days.
    • WCC: Variable elevation.
    • Blood cultures: ~30% yield (collect from 3 sites during temperature spikes).
  2. Imaging:
    • X-ray: Changes visible after 7–14 days.
    • Bone Scan: 90% sensitivity for multifocal osteomyelitis.
    • MRI: High sensitivity, lower specificity; good for surgical planning and subperiosteal abscess diagnosis.
  3. Aspiration:
    • Gold standard diagnostic test.
    • Aspirate fluid for microbiology and histology.

Management Principles

  • Establish diagnosis and rule out underlying causes.
  • Start antibiotics empirically after aspiration or earlier in toxic children.
  • Antibiotics are sufficient in most cases if:
    • Early diagnosis (<3 days).
    • No periosteal abscess.
    • Standard pathogens.
    • Clinical improvement within 72 hours.

Surgical Indications

  • Subperiosteal abscess or frank pus on aspiration.
  • Failure to improve with antibiotics.
  • Chronic osteomyelitis with sequestrum.

Surgical Technique

  • Drain abscess, debride necrotic tissue, and decompress bone to prevent further damage.
  • Avoid violating other compartments unnecessarily.

Subacute Osteomyelitis

Features

  • Subtle presentation (e.g., limp, pain).
  • Normal inflammatory markers.
  • Positive imaging (bone scan, X-ray, MRI).

Brodie’s Abscess

  • Aetiology: Low virulence pathogen and fit host.
  • Features: Lytic area with a sclerotic rim.
  • Management:
    • Biopsy to rule out bone tumours.
    • Similar treatment to acute osteomyelitis.

Septic Arthritis

Epidemiology

  • More common than osteomyelitis in children.
  • 75% of cases occur in children under 5 years old.

Aetiology

  • Haematogenous seeding, contiguous spread, or direct inoculation.
  • Large joints (hip > knee) are most commonly affected.

Pathophysiology

  • Proteolytic enzymes degrade hyaline cartilage within 8 hours.
  • Secondary effects: AVN, physeal growth arrest.

Diagnosis

  • Kocher’s Criteria:

    1. Temperature >38.5°C.
    2. ESR >40 mm/hr.
    3. Non-weight-bearing.
    4. WCC >12,000/mm³.
    • Presence of 3–4 criteria is 93–99% predictive of septic arthritis.

Management

  • Withhold antibiotics until aspiration.
  • Perform arthrotomy, irrigate, and leave the joint open or with a drain.

Special Situations

Neonates

  • Immature immune response increases susceptibility.
  • Pathogens: Group B Streptococcus, Staphylococcus aureus.
  • Management: Early aspiration and surgical drainage.

Sickle Cell Disease

  • Increased risk of osteomyelitis due to infarcts and slow blood flow.
  • Pathogens: Salmonella, but Staphylococcus aureus remains most common.

Tuberculosis

  • Skeletal TB accounts for ~3% of cases in children (spine > hip/knee > long bones).
  • Diagnosis via biopsy and acid-fast bacilli staining.
  • Management includes surgical drainage and multi-drug therapy.

Lyme Disease

  • Pathogen: Borrelia burgdorferi.
  • Features: Arthritis with bulls-eye rash and cardiac arrhythmias.
  • Treatment with antibiotics.

Gonococcal Arthritis

  • Neisseria gonorrhoeae (adolescents, child abuse cases, perinatal transmission).
  • Management: Use specialized culture media (e.g., chocolate agar).

Chronic Recurrent Multifocal Osteomyelitis (CRMO)

  • Epidemiology: Girls > Boys.
  • Features: Waxing and waning bone pain, low-grade fever.
  • Management: Exclude malignancy; treat with NSAIDs or biopsy if necessary.
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