Osteomyelitis

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Localised osteomyelitis plus sequestrum (Image sourced from Bristol Biomed Image Archive with permission)
  • Mainly due to haematogenous spread in young animals
  • Often as an extension from suppurative arthritis
  • Usually isolated: Actinomyces pyogenes, Salmonella, E.coli, Klebsiella, Streptococci
  • Metaphyses and epiphyses mostly affected
  • Most infections are exacerbated by host response
  • Pathogenesis:
    • Prostaglandin and cytokines stimulate osteoclastic bone resorption
    • Blood vessel occlusion and tissue necrosis -> lack of removal of agent and cartilage -> cartilage thickening + persistance of infection
  • Affected area may be surrounded by fibrous inflammatory tissue
  • Metaphyseal abscesses may develop
  • Sequestra may also develop -> surrounded by granulation tissue
    • Isolated from osteoclastic resorption
    • May persist for long time
    • Obstruct repair


  • Vertebral osteomyelitis
    • Lesions may affect the spinal cord
    • Usually due to Actinomyces pyogenes
    • Suppurative inflammation may cause fracture of vertebral body -> dorsal displacement -> damage to spinal cord
    • May form encapsulated abscess protruding into spinal canal -> spinal cord compression
  • Actinomycosis
    • = Lumpy jaw in cattle
    • Caused by Actinomyces bovis
      • Gram positive, branching, filamentous
      • Obligatory parasite of mucous membranes of oropharynx
      • Surface tissue is usually injured for infection to occur
      • Osteomyelitis of mandible -> destruction of bone -> replacement by fibrous tissue with pyogranulomatous nodules cotaining 'club colonies' of bacteria
      • Suppurative osteomyelitis
      • Fistulous tracts may discharge onto skin and into oral cavity
      • Excessive periosteal bone formation
      • Greatly enlarged mandible