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

 

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