Bacterial osteomyelitis and arthritis are significant causes of lameness in broilers and turkeys. They are most often a consequence of hematogenous bacterial spread from enteric or respiratory disease but can develop from direct extension from surrounding infected tissues.
Staphylococcus aureus and Escherichia coli are frequently responsible for bacterial infections in the bones and joints of chickens, turkeys, and other birds. Other sporadic causes of osteomyelitis and/or arthritis in poultry include coagulase-negative Staphylococcus spp, Pasteurella multocida, Ornithobacterium rhinotracheale, Trueperella (Arcanobacterium) pyogenes, Enterococcus spp, Streptococcus spp, Salmonella spp, Streptobacillus moniliformis, and Aspergillus spp. Mycoplasma synoviae and M meleagridis can cause arthritis in chickens and turkeys, respectively.
Lesions are most common in the femoral head and proximal tibiotarsus. Other locations, such as the metatarsus, distal femur and tibiotarsus, vertebrae, radius, and ulna, occur less commonly. In the proximal femur, the condition is referred to as femoral head necrosis, which is reported to be the most common cause of lameness in broiler chickens. Affected broilers are often >22 days old. Infection of bones, joints, and periarticular tissues with E coli, Staphylococcus aureus, or S hyicus is referred to as turkey osteomyelitis complex (TOC) or green-liver osteomyelitis complex. Green discoloration of the liver is often associated with TOC and is mostly observed at the processing plant but is rare in birds that die or are euthanized in the field. The green discoloration of the liver is used to identify carcasses that require closer examination at slaughter. Enterococcus cecorum is a commensal enteric bacterium that can cause epidemics of osteomyelitis, arthritis, and spondylitis in broilers and broiler breeders. Enterococcal spondylitis is a defined clinical syndrome with infection of the free thoracic and adjacent vertebrae, resulting in chronic osteomyelitis and spinal cord compression. Clinical signs of symmetrical leg paresis and paralysis often develop in broilers 5–8 weeks of age. Flock mortality varies from 5%–15%. The pathogenesis is not completely understood, but genetically related virulent strains of E cecorum and the presence of osteochondrosis dissecans lesions in the free thoracic vertebrae predisposes to development of enterococcal spondylitis.
Osteomyelitis and arthritis are detected on gross examination by examination of articular surfaces and bone physes. Detection of subtle lesions requires histopathology. Affected joints are often swollen with fibrinous or caseous exudate. Bones have areas of lysis and/or replacement by caseous exudate, most often within the physeal region.
Response to treatment with antibiotics currently approved for use in poultry is often poor for bacterial bone and joint infections. Antibiotics may be used to control the bacteremia contributing to new cases. When individual birds are of high value, longterm antibiotic therapy may improve some less severe cases. Prevention depends on adequate control and treatment of respiratory and enteric diseases that can lead to bacteremia.
Osteopetrosis in chickens is due to infection with specific strains of avian leukosis/sarcoma virus. Growth and differentiation of osteoblasts is altered by the virus, resulting in diaphyseal and/or metaphyseal, periosteal, and circumferential accumulation of woven and lamellar bone. Osteopetrosis is bilaterally symmetrical and involves the long bones, especially the tibiotarsus and tarsometatarsus. Birds 8–12 weeks of age are most commonly affected. Lymphoid leukosis often occurs concurrently in chickens with osteopetrosis. Avian osteopetrosis differs from mammalian osteopetrosis, in which a defect in osteoclast function results in abnormal bone resorption and accumulation of primary spongiosa in the marrow cavity.
Reactive (AA type) amyloidosis develops secondary to chronic inflammation. Systemic amyloidosis with deposition of amyloid predominantly in the joints (amyloid arthropathy) has been observed following infection with Enterococcus faecalis or Mycoplasma synoviae. Clinical cases are seen only occasionally, and most frequently affect the hock joint. Brown layer chickens are particularly susceptible. Turkeys, broilers, guinea fowl, and other birds can also develop amyloid arthropathy. Some cases have been attributed to contamination of a previously sterile vaccine diluent with E faecalis during administration (eg, Marek's disease vaccine in day-old chicks). Joints may be enlarged by yellow-orange material in the articular space. No treatment exists for amyloidosis.