Septic Arthritis

Septic arthritis refers to infection inside a joint. This can occur at any age, but is most common in children under 4 years. Infection in a joint is an emergency, as the infection can quickly begin to destroy the joint and cause serious systemic illness. Septic arthritis has a mortality around 10%. Therefore, early recognition and management is essential.

Septic arthritis is a common and important complication of joint replacement. It occurs in around 1% of straight forward hip or knee replacements. This percentage is higher in revision surgery.



Septic arthritis usually only affects a single joint. This is often a knee or hip. It presents with a rapid onset of:

  • Hot, red, swollen and painful joint
  • Refusing to weight bear
  • Stiffness and reduced range of motion
  • Systemic symptoms such as fever, lethargy and sepsis

Septic arthritis can be subtle in young children, so always consider it as a differential when a child is presenting with joint problems.


Common Bacteria

Staphylococcus aureus is the most common causative organism.

Other bacteria:

  • Neisseria gonorrhoea (gonococcus) in sexually active teenagers
  • Group A streptococcus (Streptococcus pyogenes)
  • Haemophilus influenza
  • Escherichia coli (E. coli)


Differential Diagnosis

  • Transient sinovitis
  • Perthes disease
  • Slipped upper femoral epiphysis
  • Juvenile idiopathic arthritis



Have a low threshold for treating a patient for septic arthritis until it has been excluded with examination of the joint fluid. Be particularly cautious with immunosuppressed patients.

Patients with suspected septic arthritis require admission to hospital and involvement of the orthopaedic team.

The joint should be aspirated prior to giving antibiotics where possible. Send the sample for gram staining, crystal microscopy, culture and antibiotic sensitivities. The joint fluid may be purulent (full of pus). The gram stain will come back quite quickly and may give a clue about the organism. The full culture will take longer.

Empirical IV antibiotics should be given until the microbial sensitivities are known. Antibiotics are usually continued for 3 to 6 weeks in total when septic arthritis is confirmed. The choice of antibiotic depends on the local guidelines.

Patients may require surgical drainage and washout of the joint to clear the infection in severe cases.


Last updated January 2020
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