Infectious arthritis is most frequently associated with bacterial agents such as staphylococci, streptococci, and coliforms. Causes include hematogenous spread; direct inoculation, including via surgery; or extension from adjacent tissues. Synovial membranes in degenerated joints have increased permeability, predisposing these joints to becoming infected.
Other agents involved in infectious arthritis include fungi (blastomycosis, coccidioidomycosis), rickettsiae (Rocky Mountain spotted fever, ehrlichiosis), spirochetes (borreliosis), mycoplasmas, viruses, and protozoa (leishmaniosis).
Clinical signs of septic arthritis include lameness, swelling, pain in affected joints, and systemic signs of fever, malaise, anorexia, and stiffness; however, not all of these signs are always present.
Radiography can reveal joint effusion and adjacent soft tissue swelling in early septic arthritis cases, and degenerative joint disease (DJD) in chronic conditions. Arthrocentesis reveals increased levels of WBCs, especially neutrophils (> 3,000/mcL). Bacteria might be visible. The synovial fluid can be grossly purulent.
Bacterial culture and antimicrobial susceptibility testing can confirm a diagnosis of septic arthritis; however,in up to 50% of septic arthritis cases, culture can be negative (1, 2). Serological testing is used for nonbacterial agents.
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Treatment of septic arthritis includes appropriate oral antimicrobials for at least 4–6 weeks (generally 6 weeks) and analgesics. Initially, broad-spectrum antimicrobials such as beta-lactams (eg, amoxicillin–clavulanic acid at 22 mg/kg, PO, every 8–12 hours for 6 weeks, unless culture and susceptibility test results suggest that a change to another antimicrobial is warranted [3]) or cephalosporins can be prescribed before the results of culture and susceptibility testing are received. This treatment can be continued for a total of 6 weeks or switched to another antimicrobial on the basis of the susceptibility test results.
If clinical signs of septic arthritis are severe (pain, swelling, heat, etc), antimicrobials and analgesics (opioids) may be administered intravenously while the patient is in the hospital, and switched to oral administration after clinical signs have improved and the patient has been discharged. Joint lavage and surgical debridement are not necessary in most cases but might be required in severe cases. In cases of multiresistant bacteria, local delivery of antimicrobials via antimicrobial-impregnated pearls or collagen sponges might be necessary.
Key Points
Septic arthritis in dogs and cats is caused by bacterial infection of the joint, typically via direct inoculation (trauma, surgery, penetrating wounds), hematogenous spread, or extension from nearby infections. Common pathogens include Staphylococcus spp, Streptococcus spp, and E coli.
Affected animals usually present with acute onset of joint pain, swelling, heat, lameness, and decreased range of motion. Systemic signs such as fever and lethargy can also be present, especially in dogs.
Diagnosis is based on arthrocentesis, with joint fluid showing high neutrophil counts, and positive bacterial culture.
Treatment includes systemic antimicrobials and analgesics. Joint lavage and sometimes surgical drainage or debridement are reserved for more severe cases. Early intervention is critical to prevent joint destruction.
For More Information
Septic arthritis: diagnosis, management and prognosis. Vet Ireland J. 2018;8(3):175-179.
Innes J. Septic arthritis. In: Griffon D, Hamaide A, eds. Complications in Small Animal Surgery. John Wiley & Sons; 2016:34-38.
Phillips TF, Bleyaert HF. Retrospective evaluation of 103 cases of septic arthritis in dogs. Vet Rec. 2022;190(5):e938.
Weir M. Septic arthritis in dogs. VCA Animal Hospitals; 2023.
Boldan M. Septic arthritis in dogs. PetMD. 2022.
Also see pet owner content regarding septic arthritis in dogs and cats.
References
Mielke B, Comerford E, English K, Meeson R. Spontaneous septic arthritis of canine elbows: twenty-one cases. Vet Comp Orthop Traumatol. 2018;31(6):488-493. doi:10.1055/s-0038-1668108
Clements DN, Owen MR, Mosley JR, Carmichael S, Taylor DJ, Bennett D. Retrospective study of bacterial infective arthritis in 31 dogs. J Small Anim Pract. 2005;46(4):171-176. doi:10.1111/j.1748-5827.2005.tb00307.x
Greene C, Calpin J. Antimicrobial drug formulary. In: Greene CE, ed. Infectious Diseases of the Dog and Cat. 4th ed. Elsevier/Saunders; 2012:1207-1320.
