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Femoral Head Necrosis, Proximal Femoral Degeneration, Bacterial Chondronecrosis
Enterococcal spondylitis (ES), also referred to as bacterial chondronecrosis or femoral head necrosis, is a severe degenerative bone disease affecting commercial broiler chickens worldwide. ES is caused by infection of the free thoracic vertebra (FTV) with pathogenic strains of Enterococcus cecorum. Chickens with existing skeletal disorders, such as osteochondrosis dissecans (OCD) lesions in the FTV are more vulnerable to developing ES. OCD lesions occur usually on the growth plates of long bones, particularly the proximal growth plate of the femur and tibiotarsus, but other bones may also be affected.
Chickens affected by ES show varying degrees of lameness, often along with swollen, inflammed hocks and a characteristic posture known as hock-sitting. The onset of hock-sitting and posterior paresis/paralysis correlates with the development of advanced vertebral osteomyelitis lesions.
ES was first reported in 1972. In 2002, the organism Enterococcus cecorum was isolated from osteomyelitis lesions during an outbreak of lameness in broilers in Scotland and the Netherlands.