Print Friendly, PDF & Email

Septic Arthritis


Definition of septic arthritis

  • Infection of the joint space.
  • Can rapidly destroy a joint over hours to days, so a high index of suspicion is required.


Presentation of septic arthritis

  • Single hot, red, swollen, agonisingly painful joint
    • Often held immobile
  • In older people and RA, picture sometimes less obvious, so have a low index of suspicion
  • 20% of septic arthritis affects more than one joint
  • May be systemically septic


Causes of septic arthritis

  • There may or may not be a history of trauma to the joint
  • Frequent pathogens:
    • Staph aureus
    • Streptococci
    • Neisseria gonorrhoeae
      • Suspect in young, sexually active adults, but actually not very common
    • Haemophilus (in kids, but rare due to vaccination)
    • The elderly and people with chronically inflamed joints (e.g. RA) are prone to infection with unusual organisms.
  • Lyme disease (Borellia burgdorferi) can cause an inflammatory arthritis
    • Look for the typical 6cm bullseye lesion of erythema migrans.



Investigations in septic arthritis

  • Bloods
    • WBC raised unless highly immunosuppressed
    • High CRP and ESR
      • Note both can be normal, particularly in immunosuppressed
  • Blood cultures often also positive
  • Aspirate joint
    • Send the fluid for URGENT microscopy and culture, including culture techniques for gonococci and anaerobes – the fluid is often frankly purulent though. Check for crystals as well.
      • Gram stain positive in only 50%
      • Synovial fluid growth positive in 90%
      • MUST be done prior to starting antibiotics
  • Swabs from skin wounds and the throat, sputum and urine can all be collected for culture and might indicate the source/organism responsible.
  • X-ray as a baseline investigation


Treatment of septic arthritis

  • Empirical antibiotic treatment
    • Depends on local guidelines but if no risk factors for atypical organisms then use flucloxacillin 2g qds IV
    • Vancomycin IV if risk of MRSA
    • Elderly/frail/recurrent UTIs/recent abdominal surgery (risk of gram neg): 2nd or 3rd gen cephalosporin e.g. cefuroxime
    • Change antibiotics if organism later found to be resistant
  • Often need prolonged antibiotic course
    • Minimum 6 weeks (usually 2/52 IV then 4/52 PO)
  • Refer all infected prosthetic joints to orthopaedics
  • Septic joints should be as pirated to dryness & may need arthroscopic washout
    • Prosthetic joints often need removal
  • In all cases, early physio should be given once the infection is under control, to prevent joint stiffness and muscle wasting.


Prognosis in septic arthritis

  • Case fatality of 11%
  • Worse if complicated by osteomyelitis
  • Secondary osteoarthritis can occur


Click here for medical student OSCE and PACES questions about Septic Arthritis

Common Septic Arthritis exam questions for medical students, finals, OSCEs and MRCP PACES

Click here to download free teaching notes on Septic Arthritis

Perfect revision for medical students, finals, OSCEs and MRCP PACES