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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