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Joint: septic arthritis - adult





  • 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 from PubMed and VetMedResource.
  • Milner P I et al (2014) Factors associated with survival to hospital discharge following endoscopic treatment for synovial sepsis in 214 horses. Equine Vet J 46 (6), 701-705 PubMed
  • Clegg P (2006) Conditions of the equine tarsal joints. UK Vet 11 (7), 6-12 Wiley.
  • Hewes C A et al (2005) Septic arthritis and granulomatous synovitis caused by infection with Mycobacterium avium complex in a horse. JAVMA 226 (12), 2035-2038 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.
  • Bertone A L (1999) Update on infectious arthritis in horses. Equine Vet Educ 11 (3), 143-152 VetMedResource.
  • Lapointe J M et al (1992) Septic arthritis in 15 Standardbred racehorses after intra-articular injection. Equine Vet J 24, 430-434 PubMed.
  • Moore R M et al (1992) Antimicrobial susceptibility of bacterial isolates from 233 horses with musculoskeletal infection during 1979-1989. Equine Vet J 24, 450-456 PubMed.
  • Schneider R K et al (1992) A retrospective study of 192 horses affected with septic arthritis-tenosynovitis. Equine Vet J 24, 436-442 PubMed.
  • Schneider R K et al (1992) Open drainage, intra-articular and systemic antibiotics in the treatment of septic arthritis-tenosynovitis in horses. Equine Vet J 24, 443-449 PubMed.
  • Tulamo R-M et al (1989) Sequential clinical and synovial fluid changes associated with acute infectious arthritis in the horse. Equine Vet J 21, 325-331 PubMed.
  • Tulamo R-M et al (1989) The influence of corticosteroids on sequential clinical and synovial fluid parameters in joints with acute infectious arthritis in the horse. Equine Vet J 21, 332-337 PubMed.
  • Byars T D et al (1984) Non-erosive polysynovitis in a horse. Equine Vet J 16, 141-143 PubMed.

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, USA. pp 598-606.

Related Images


Acupuncture: channel (meridian) systems


Anesthesia: analgesia - overview

Anesthesia: epidural

Bladder: cystorrhaphy

Blood: leukocytes

Blood: microbiology

Blood: neutrophils

Bone: osteitis - septic

Bone: osteochondrosis

Bone: scintigraphy

Carpal joint: disease - overview

Carpus: chip removal

Carpus: fracture - comminuted



Chondroitin sulfate

Clostridia spp

Coxofemoral joint: disease - overview

Detomidine hydrochloride

Digital sheath: tenosynovitis

Dimethyl sulfoxide

DIP joint: disease - overview

Distal phalanx: fractures

Elbow: osteoarthritis

Enterobacter / Aerobacter spp

Escherichia coli

Fluid therapy: overview

Flunixin meglumine

Foot: subsolar abscess/infection

Forelimb: joint anesthesia


Hindlimb: joint anesthesia

Joint: arthroscopy - overview

Joint: immune-mediated polysynovitis

Joint: septic arthritis - foal

Joint: synovial pathobiology

MC / MT 2 and 4: fracture repair

MC / MT 4: removal

MCP / MTP joint: chronic proliferative synovitis

MCP / MTP joint: disease - overview

MCP/MTP joint: luxation

Musculoskeletal: fracture

Musculoskeletal: gait evaluation

Musculoskeletal: manipulative tests

Musculoskeletal: osteoarthritis (joint disease)

Musculoskeletal: physical examination - adult

Navicular bursa: injection

Pelvis: fracture


Plasma: fibrinogen

Proximal sesamoid: fracture

Pseudomonas spp

Radiography: contrast media

Skin grafting overview

Skin grafting techniques

Sodium hyaluronate


Staphylococcus aureus

Staphylococcus spp

Stifle: femoropatellar osteochondrosis

Streptococcus spp

Sulfadoxine with Trimethoprim

Synovial fluid: cell count

Synovial fluid: collection

Synovial fluid: cytology

Synovial fluid: microbiology

Synovial fluid: mucin clot test

Synovial fluid: protein

Tarsus: tarsocrural synovitis (bog spavin)

Therapeutics: antimicrobials

Therapeutics: beta-lactam antibacterials

Therapeutics: nitrofurans - nitroimidazoles - quinolones


Ulna: fracture repair

Ultrasonography: musculoskeletal


Wound: drainage

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