Osteomyelitis in Horses: Etiology, Pathogenesis, and Diagnosis Tuskegee University

Osteomyelitis can be caused by trauma in horses of any age or may have a hematogenous origin in foals. Diagnosis of this disease is based on clinical signs, radiographic changes, and laboratory values of protein and inflammatory cells, especially neutrophils. Clinical signs of inflammation may include edema, joint effusion, fever, and pain. Lameness is a variable clinical sign depending on the structures involved in the infection. Radiographic changes are usually diagnostic, but the use of advanced imaging modalities, if available, may also be of significant value. Osteomyelitis is a bone infection involving the cortical bone and the marrow cavity, whereas osteitis involves only the cortical bone. Osteomyelitis can affect membranous or long bones. It typically involves only one bone; however, multiple bones can be simultaneously affected, especially in foals. Osteomyelitis of the appendicular skeleton is relatively common in horses of all ages but occurs more frequently in foals. Hematogenous osteomyelitis occurs as a result of bacteremia with spread to bones and joints and is most common in foals. The infection may be predisposed by trauma, neonatal infections (e.g., omphalophlebitis), or other infections that result in bacteremia. Osteomyelitis after trauma occurs when the infection reaches the bone by direct contamination of open fractures or penetrating wounds or by indirect insult to structures (e.g., tendon sheath, joint, bursae). This type of osteomyelitis may have draining tracts and occurs more CE 760 Vol. 23, No. 8 August 2001 n Omphalophlebitis, gastroenteritis, and pneumonia are the common sources of bacteria for hematogenous spread of bacteria, resulting in osteomyelitis in foals. n Radiographic changes of soft tissue swelling, bone lysis, periosteal new bone formation, and sequestra are indicative of