Infectious arthritis is most frequently associated with bacterial agents such as staphylococci, streptococci, and coliforms. Causes include hematogenous spread or penetrating trauma, including surgery. Other agents producing a septic arthritis include rickettsia (Rocky Mountain spotted fever, ehrlichiosis) and spirochetes (borreliosis).
Clinical signs of septic arthritis include lameness, swelling, pain of affected joint(s), and systemic signs of fever, malaise, anorexia, and stiffness. Radiography may reveal joint effusion in early cases and degenerative joint disease in chronic conditions. Arthrocentesis reveals increased levels of WBCs, especially neutrophils. The synovial fluid may be grossly purulent. Bacterial culture and antimicrobial sensitivity testing may confirm the diagnosis. Serologic testing is used for nonbacterial agents. Treatment is with appropriate IV and oral antibiotics, joint lavage, and surgical debridement in severe cases.