Septic Arthritis
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Septic arthritis is an infection within a joint space. it can affect both native and prosthetic joints. It is typically acute, although in some cases in chronic.

In acute cases it can lead to sepsis and death (mortality: 10-20%). Prompt diagnosis and management are important to reduce disk of mortality and to reduce long-term disability.

It typically presents as a single warm, red painful joint, typically with pain whenever the joint is moved. Any warm, red, painful joint should be considered septic arthritis until proven otherwise.

  • An exception to this rule may be in a patient with previously known gout in the affected joint, whom is systemically well, may be treated for gout with tight safetynetting

The common cause is staphylococcus aureus, but in adults, many cases are causes by gonorrhoea, especially in the elderly or immunosuppressed

    • Nearly always bacterial, but in rare cases can be viral or fungal

Any joint that is hot, red and tender is a septic joint until proven otherwise! You must aspirate these joints! Septic arthritis can rapidly cause irreversible joint damage. Patients often (but not always) have systemic fever, and raised inflammatory markers (ESR and CRP).

Treatment is by surgical joint washout in combination with IV antibiotics. Cases involving prosthetic joint may need joint replacement.


  • Most cases are staphylococcus aureus. Streptococcus also causes a proportion of cases
  • Gonorrhoea accounts for 3 cases per 100 000 people per year
  • The risk is relatively high for joint replacement
    • About 2% risk for primary infection at the time of joint replacement procedure
    • As high as 20% in joint revision procedures
    • Prosthetic joints can be infected at any other time – as for native joints


  • Diabetes mellitus
  • Increasing age
  • Previous joint damage – e.g. rheumatoid arthritis, gout
  • Joint surgery
  • Prosthetic joint
  • Cellulitis – particularly if overlying a prosthetic joint
  • Immunodeficiency – particularly HIV
  • IV drug use
  • Hx of STI


  • Single hot, red painful joint
    • Polyarthritis is uncommon
    • Most commonly affects the hip and knee (about 30% of cases) but can affect any joint
    • Patients typically unwilling¬†to move the joint due to severe pain
    • In children:¬†limp, refusal to weight bear
    • On examination
      • Joint exquisitely tender to move
      • Effusion
      • Red, swollen joint
  • Fever +/- rigors
  • If bacteraemia is present
    • Vomiting
    • Hypotension
  • Gonoccoal disease
    • Often associated with multiple skin lesions
    • Multiple joints often affected (not always)
  • Prosthetic joints
    • More likely to be a chronic, low-grade infection
    • Gradually increasing pain over weeks or months
    • Often no fevers, no joint swelling or redness

Differentials diagnosis

In children

In adults

  • Gout
    • The most likely differential diagnosis
    • Typically gout presents without fevers, or signs of sepsis but otherwise the appearance and examination of gout and septic arthritis can be strikingly similar
  • Rheumatoid arthritis
  • Reactive arthritis
    • Typically multiple joints affected, in a symmetrical pattern
  • Viral arthritis
    • Typicallyy multiple joints and symmetrical
    • Causes include parvovirus, rubella, Hep C and HIV
  • Lyme disease
  • Infective endocarditis
    • Septic arthritis is a complication of IE



Diagnosis is typically on the basis of blood tests (raised FBC and CRP) and positive joint aspiration culture. However there are many other supportive investigations, which may detect septic arthritis where these first line investigations have failed.


  • FBC
  • CRP
  • Both are typically raised

Joint aspiration for synovial fluid

  • Is the diagnostic gold standard test, but can’t always be obtained – especially from smaller joints
  • MC+S
    • White cell count (if raised, is suggestive but not diagnostic of septic arthritis)
    • Culture
    • Gram staining
  • Take BEFORE giving antibiotics – unless septic and acutely unwell
  • Be wary of aspiration in prosthetic joint
    • Should¬†ONLY¬†be performed by a specialist
    • High risk of causing septic arthritis if not already present
  • In cases of a large effusion, aspiration of the joint can also provide an analgesic effect

Blood cultures

  • Take at least 2 samples fro different sites
  • Take BEFORE giving antibiotics – unless septic and acutely unwell

Gonococcal testing

  • Consider swabs of rectum, throat, vagina, or urine sample (men) for gonococcal PCR (NAAT) +/- culture
  • Only if gonococcal disease is suspected as the cause

Other investigations

  • Consider testing for Lyme disease and causes of immunosuppression



  • Often not useful – especially int he first few days of infection
  • May show osteomyelitis (typically in chronic cases)
  • May show fat pad swelling as a sign of joint inflammation


  • Can show joint effusion – which is a non-specific sign

CT and MRI

  • Can see abscess and joint effusion

Radionuclide bone scan

  • Show areas of high cell turnover – which indicates an inflammatory process
  • Non-specific
  • Useful chronic cases where the cause of joint pain is unclear


Typically involves a combination of surgical washout of the joint and IV antibiotics. Some cases may be suitable for antibiotics alone.

  • Start antibiotics empirically before the result of cultures are known. A typical regimen might include:
    • Flucloxacillin 2g IV QID¬†(child: 50mg/Kg, max 2g QID)
    • MRSA – Vancomycin
    • Penicillin allergy – Cefazolin 2g IV TDS¬†(child 50mg/Kg IV TDS, max 2g)¬†OR¬†Clindamycin 600mg IV TDS¬†(child 15mg/Kg, max 600mg IV TDS)
  • For streptococcus or gram negative organisms
    • Ceftriaxone 2g IV OD¬†(child 50mg/Kg IV OD, max 2g)
  • Typically antibiotics are required IV for 2-3 weeks before switching to oral therapy

Joint splinting

  • Recommended for first few days
    • Knees in extension
    • Wrist in neutral or slight extension
    • Elbow at 90 degrees
  • Once pain settles – early mobilisation will help promote healing and reduce contractures


  • Mortality of septic arthritis is 10-20%
  • Risk factors associated with an increased risk of death include:
    • Age >65
    • Shoulder, elbow or multiple joints affected
  • Typically, patients have reduced function of the affected joint for life
  • 30% of patients will end up with severe disability – including severely reduced joint function, amputation or prosthetic joint


  • Septic arthritis – eTG
  • Septic Arthritis –
  • Murtagh‚Äôs General Practice. 6th Ed. (2015) John Murtagh, Jill Rosenblatt
  • Oxford Handbook of General Practice. 3rd Ed. (2010) Simon, C., Everitt, H., van Drop, F.
  • Beers, MH., Porter RS., Jones, TV., Kaplan JL., Berkwits, M. The Merck Manual of Diagnosis and Therapy

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Dr Tom Leach

Dr Tom Leach MBChB DCH EMCert(ACEM) FRACGP currently works as a GP and an Emergency Department CMO in Australia. He is also a Clinical Associate Lecturer at the Australian National University, and is studying for a Masters of Sports Medicine at the University of Queensland. After graduating from his medical degree at the University of Manchester in 2011, Tom completed his Foundation Training at Bolton Royal Hospital, before moving to Australia in 2013. He started almostadoctor whilst a third year medical student in 2009. Read full bio

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