Equis ISSN 2398-2977

Joint: septic arthritis - adult

Contributor(s): Patrick Colahan, Graham Munroe, Prof Jonathon Naylor, Chris Whitton




  • Several possible routes of infection.
  • Traumatic:
    • Injury to limb near synovial structures   Elbow: septic arthritis - wound    →   bacteria enter joint.
    • Approximately 25% of cases in one survey in the USA but more common in UK (36%).
  • Hematogenous:
    • Septicemia or transient bacteremia   →   bacteria deposited in synovial membrane or vessels of physis. Rare in adult   Joint: septic arthritis - foal  .
  • Iatrogenic:
    • Diagnostic, surgical or therapeutic joint injection   →   bacteria introduced to joint. 25% post-intra-articular injection and 12% post-surgery in USA survey; less in UK.
  • Common isolates are:
  • Anaerobic infection is less common (<10%), egClostridiumspp   Clostridia spp  .
  • Fungal infections are rare.
  • Mixed infections do occur.

Predisposing factors

  • Penetration of joint.


  • Wounds - most common etiology in population as a whole.
  • Injection of joint, eg corticosteroids, polysulfated glycosaminoglycans, hyaluronic acid, local anesthetic.
  • Use of polysulfated glycosaminoglycans and corticosteroids intra-articularly.
  • Surgery, arthroscopy.


  • Bacteria deposited into synovial cavity   →   inflammatory response   →   fibrin clots form, sequestrate bacteria (inaccessible to antibiotics) AND articular cartilage damage.
  • Rate of blood flow through hairpin shaped vessels of synovial membrane and subchondral bone is slowed, allowing deposition of bacteria and then colonization.
  • Presence of bacteria   →   typical inflammatory response   →   vasodilatation, chemotaxis of white blood cells and release of inflammatory mediators.
  • Arrival of other cells and inflammatory cascade   →   release of lysosomal enzymes and activation of neutral metalloproteinases and other proteinases, eg collagenase, gelatinase, stromolysin, plasmin.
  • Fibrin clots   →   trap bacteria   →   :
    OrSequestered from synovial fluid and therefore difficult for body to remove.
  • 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.


  • Acute - may be within 24 h.
  • Onset of early clinical signs usually within 2 days from time of intra-articular injection.
  • Onset of signs may be delayed if steroids injected or horse is on systemic NSAIDs.


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Further Reading


Refereed papers

  • Recent references fromPubMedandVetMedResource.
  • Milner P Iet al(2014)Factors associated with survival to hospital discharge following endoscopic treatment for synovial sepsis in 214 horses.Equine Vet J46(6), 701-705PubMed
  • Clegg P (2006)Conditions of the equine tarsal joints.UK Vet11(7), 6-12Wiley.
  • Hewes C Aet al(2005)Septic arthritis and granulomatous synovitis caused by infection withMycobacterium aviumcomplex in a horse.JAVMA226(12), 2035-2038PubMed.
  • Booth T Met al(2001)Treatment of sepsis in the small tarsal joints of 11 horses with gentamicin-impregnated polymethylmethacrylate beads.Vet Rec148, 376-380PubMed.
  • Bertone A L (1999)Update on infectious arthritis in horses.Equine Vet Educ11(3), 143-152VetMedResource.
  • Lapointe J Met al(1992)Septic arthritis in 15 Standardbred racehorses after intra-articular injection.Equine Vet J24, 430-434PubMed.
  • Moore R Met al(1992)Antimicrobial susceptibility of bacterial isolates from 233 horses with musculoskeletal infection during 1979-1989.Equine Vet J24, 450-456PubMed.
  • Schneider R Ket al(1992)A retrospective study of 192 horses affected with septic arthritis-tenosynovitis.Equine Vet J24, 436-442PubMed.
  • Schneider R Ket al(1992)Open drainage, intra-articular and systemic antibiotics in the treatment of septic arthritis-tenosynovitis in horses.Equine Vet J24, 443-449PubMed.
  • Tulamo R-Met al(1989)Sequential clinical and synovial fluid changes associated with acute infectious arthritis in the horse.Equine Vet J21, 325-331PubMed.
  • Tulamo R-Met al(1989)The influence of corticosteroids on sequential clinical and synovial fluid parameters in joints with acute infectious arthritis in the horse.Equine Vet J21, 332-337PubMed.
  • Byars T Det al(1984)Non-erosive polysynovitis in a horse.Equine Vet J16, 141-143PubMed.

Other sources of information

  • Bertone A L (2003)Infectious Arthritis. In:Diagnosis and Management of Lameness in the Horse. Eds: Ross M W & Dyson S J. Saunders, Missouri. pp 598-606.