Etiology

• Osteomyelitis is a challenging condition across all species and has been defined as inflammation and infection of the bone and bone marrow.
• In young animals, Salmonella spp Salmonella spp particularly the cattle adapted, Salmonella dublin Salmonellosis is often associated with clinical disease.
• In older animals Trueperella pyogenes Trueperella pyogenes is the most common isolate, often in combination with anaerobes such as Fusobacterium necrophorum Fusobacterium necrophorum.
• Osteomyelitis in neonates may also occur secondary to fractures of the metacarpus or metatarsus, through inappropriate use of calving chains Dystocia Calving aids: correct use.
• Actinomycosis (lumpy jaw) Actinomycosis is a specific type of osteomyelitis affecting the mandible +/- maxilla of cattle.

Predisposing factors

General

• Post-traumatic or post-surgical bacterial inoculation of wounds.

Specific

• Hematogenous osteomyelitis secondary to failure of passive transfer or concurrent co-morbidities, eg septicemia Neonatal septicemia and meningitis or septic omphalitis Omphalophlebitis and omphaloarteritis in neonatal animals.

Pathophysiology

• Hematogenous spread of bacteria may disrupt the blood supply to bone tissue through the occlusion of small vessels and reduced blood flow. This will exacerbate bone necrosis and facilitate the localized spread of infection.
• The metaphysis of long bones contains sparse mononuclear phagocytes and sluggish blood flow in the metaphyseal sinusoids which favor bacterial proliferation.
• Epiphyseal growth plate perfusion occurs via small vessels which form a closed capillary plexus which favor the deposition of pyogenic bacteria.
• Young animals are predisposed to hematogenous osteomyelitis due to the presence of metaphyseal vascular anastomoses which reduce blood flow and promote bacterial seeding.
• Hematogenous osteomyelitis in cattle can be defined as physeal or epiphyseal in origin:
  • Physeal osteomyelitis usually originates at or near the growth plates and is most common in the distal extremities of the metacarpus, metatarsus radius or ulnar bones.
  • Epiphyseal osteomyelitis originates at or near the junction of the subchondral bone and the immature epiphyseal joint cartilage and is most common in the distal femoral condyle, patella and distal radius.

Timecourse

• Clinical signs in acute cases of osteomyelitis develop rapidly over a short number of days, whilst chronic disease can be defined as being present for several weeks with radiographic findings consistent with bone sequestra, draining sinus tracts and changes in bone architecture.

Epidemiology

• Hematogenous osteomyelitis is more frequently encountered than post traumatic osteomyelitis in cattle, with disease more commonly seen in young animals.