Septic arthritis

• Septic arthritis refers to an infection in a joint - this is a medical emergency
• The infection can rapidly destroy the joint and cause systemic illness. Septic arthritis has a mortality of around 10%.
• Infection may occurs in a native joint or prosthetic joint (most commonly)

  More likely to occur in revision surgery than in the initial joint replacement
• Septic arthritis usually only affects a single joint, often a knee. It presents with a rapid onset of:

  • A hot, red, swollen and painful joint
  • Stiffness and reduced range of motion
  • Systemic symptoms, such as fever, lethargy and sepsis
• Staphylococcus aureus is the most common causative organism.
• Other bacteria:

  • Neisseria gonorrhoea (gonococcus) in sexually active individuals 
  • Group A Streptococcus (most commonly Streptococcus pyogenes)
  • Haemophilus influenza
  • Escherichia coli (E. coli)
• The key differential diagnoses of a single warm swollen joint are:

  • Gout (joint fluid shows urate crystals that are negatively birefringent of polarised light)
  • Pseudogout (joint fluid shows rod-shaped calcium pyrophosphate crystals that are positively birefringent)
  • Reactive arthritis (typically triggered by urethritis or gastroenteritis and associated with conjunctivitis)
  • Haemarthrosis (bleeding into the joint, usually after trauma)
• Management:

  • Joint aspiration before starting antibiotics
  • Empirical IV antibiotics until sensitivities are known, usually 4-6 weeks
  • Flucloxacillin usually first line (clindamycin if penicillin allergy)
  • Ceftriaxone for Neisseria gonorrhoea
• Sometimes irrigation and washout in theatre is needed
• Joint aspiration is performed before starting antibiotics. The sample is sent for gram staining, crystal microscopy, culture and antibiotic sensitivities. The joint fluid may be purulent (full of pus).