Equis ISSN 2398-2977

Joint: septic arthritis - foal

Synonym(s): Joint ill

Contributor(s): Steve Adair, Patrick Colahan, Kate Hepworth-Warren, Prof Derek Knottenbelt, Graham Munroe, Vetstream Ltd, Chris Whitton


  • Cause: usually hematogenous infection of joint(s) secondary to bacteremia or sepsis, direct entry via wound, local spread.
  • Signs: reluctance to stand, severe lameness, joint(s) swelling, heat and pain.
  • Diagnosis: synovial fluid analysis, microbiology, hematology, radiography, culture and sensitivity of synovial fluid.
  • Treatment: antibiotics, joint lavage, anti-inflammatories, regional limb perfusion, surgical debridement.
  • Prognosis: guarded to poor.



  • Hematogenous spread from generalized bacteremia.
  • Direct entry of micro-organisms via a wound is possible, but uncommon in foals.
  • Local spread, eg from a physeal infection or adjacent perisynovial infection.
  • Common organisms isolated from foals:
  • Anaerobic infection is less common, egClostridiumspp   Clostridia spp  .
  • Fungal infections are rare.
  • Mixed infections do occur.
  • The bacteria isolated from synovial fluid is not always the same as that isolated from a blood culture.

Predisposing factors




  • Persistent or transient bacteremia allows for hematogenous spread of bacteria to bones and joints.
  • In foals, unlike adult horses, transphyseal blood vessels exist which allow for the settling of bacteria into joints.
  • Presence of bacteria stimulates inflammatory response   →   infiltration of polymorphonuclear cells and release of proteolytic enyzmes and inflammatory cytokines into joint.
  • Dynamics of fluid resorption and production within the joint are altered, leading to distention of joint.
  • Blood flow and nutrition to the synovium and subchondral bone are interrupted, beginning cycle of cartilage destruction.
  • Fibrin clots can trap bacteria and limit mobility of the joint, further decreasing nutrition available for healthy cartilage.
  • Proteinases   →   erode articular cartilage   →   loss of biomechanical strength   →   fissuring   →   increased forces on subchondral bone.
  • Septic process may erode cartilage and involve subchondral bone   →   septic osteomyelitis   Stifle: septic arthritis (foal) - pathology      Stifle: osteoarthritis 08 (subchondral cartilage) - pathology  .
  • Multifocal disease often present.
  • 4 classified types - based on clinical signs, history, radiography, bacterial culture results +/- post mortem findings:
    • S type: septic synovitis; no bone involvement; any joint.
    • E type: joint infection + adjacent epiphysis; femorotibial/femoropatella/tarsocrural joints.
    • P type: infected adjacent metaphyseal growth plate; distal radius/tibia/metacarpus, etc.
    • T type: infection small tarsal/carpal bones +/- other joints.
  • Clinically difficult to distinguish.
  • S and E type most common in young foals.


  • Septic arthritis can develop at any time.
  • Radiographic changes may lag behind clinical signs.


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Further Reading


Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Hepworth-Warren K L et al (2015) Bacterial isolates, antimicrobial susceptibility patters, and factors associated with infection and outcome in foals with septic arthritis: 83 cases (1998-2013). JAVMA 246 (7), 785-793 PubMed.
  • Annear M J, Furr M O & White N A (2011) Septic arthritis in foals. Equine Vet Educ 23 (8), 422 VetMedResource.
  • Roberts B L, Reimer J M, Woodie J B & Reed S M (2010) Septic arthritis of the first and second cervical vertebral articulations with vertebral osteomyelitis in a foal caused by SalmonellaEquine Vet Educ 22 (7), 328-333 VetMedResource.
  • Paradis M R (2010) Septic arthritis in the foal: What is the best imaging modality? Equine Vet Educ 22 (7), 334-335 VetMedResource.
  • Vos N J & Ducharme N G (2008) Analysis of factors influencing prognosis in foals with septic arthritis. Irish Vet J 61 (2), 102-106 PubMed.
  • Booth T M et al (2001) Treatment of sepsis in the small tarsal joints of 11 horses with gentamicin-impregnated polymethylmethacrylate beads. Vet Rec 148, 376-380 PubMed.
  • Stoneham S J (1997) Septic arthritis in the foal: practical considerations on diagnosis and treatment. Equine Vet J (1), 25-29 VetMedResource.
  • Schneider R K, Bramlage L R, Mecklenbury L M et al (1992) Open drainage, intra-articular and systemic antibiotics in the treatment of septic arthritis/tenosynovitis in horses. Equine Vet J 24 (6), 443-449 PubMed.
  • Madison J B, Sommer M & Spencer P A (1991) Relations amoung synovial membrane histopathological findings, synovial fluid cytologic findings, and bacterial culture results in horses with suspected infectious arthritis - 64 cases (1979-1987). JAVMA 198 (9), 1655-1661 PubMed.

Other sources of information

  • Weisbrode S E (2007) Bone and Joints. In: Pathologic Basis of Veterinary Disease. 4th edn. Eds: McGavin M D & Zachary J F. Mosby Elsevier, USA. pp 1096-1097.
  • Ducharme N G (2004) Advances in the Treatment of Bone and Joint Infections in Foals.  In: Proc 13th Annual Scientific Meeting ECVS. Eds: Schramme M, Tremaine H, Walmsley J, Bellinger C & Houlton J. ECVS, Zurich. pp 181-184.
  • Bertone A L (2003) Infectious Arthritis. In: Diagnosis and Management of Lameness in the Horse. Eds: Ross M W & Dyson S J. Saunders, USA. pp 598-606.
  • Wilson W D, Vatistas N J, Pascoe Jr et al (1994) Septic Arthritis in Foals - Bacterial Isolates and Antimicrobial Susceptibility. In: Equine Infectious diseases VII - Proc 7th International Conference, Tokyo, Japan. Ed: Polwright W. R & W Publications Ltd, UK. 0-9516604-9-7-962203061.