Septic arthritis

Question 1

What is it?

Answer 1

Septic arthritis is where an infection occurs within a joint. This could be in a native joint, meaning the persons own joint, or in a joint replacement. Infection in a joint is an emergency as the infection can quickly begin to destroy the joint and cause systemic illness. Septic arthritis has a mortality of around 10%.

It 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.

Question 2

Presentation

Answer 2

Hot, red, swollen and painful joint
Stiffness and reduced range of motion
Systemic symptoms such as fever, lethargy and sepsis

Question 3

Common Bacteria

Answer 3

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)

Question 4

Differentials?

Answer 4

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

Question 5

Management

Answer 5

Aspirate the joint prior to antibiotics and 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.