25th February 2025

Septic arthritis

Overview of septic arthritis

This is an emergency, requiring rapid management to prevent joint destruction and with a mortality of 22%.

It describes bacterial infection in the joint, usually through haematogenous spread but sometimes local infection. 

In developed countries, incidence is 10 times higher with joint disease or prosthetic joints. Other risk factors include IV drug use, immunosuppression (immunodeficiency, alcoholism, diabetes, CKD, age >80), recent surgery and skin infection. 

A large majority of cases are caused by Staphylococcus aureus (including MRSA [methicillin-resistant Staphylococcus aureus]) and Streptococcus species, but Gram-negative bacilli can be causative in IVDU or immunosuppression and Salmonella in sickle cell disease. Neisseria gonorrhoea will be discussed.

Signs and symptoms of septic arthritis

Septic arthritis should be considered in any acutely painful, hot, swollen or immobile joint. Most people are febrile and unwell, but in the elderly or immunosuppressed, it may be insidious. The knee is most commonly infected (>50%), alongside the wrist, ankles and hips. In 20% it affects more than 1 joint, with higher mortality.  

Investigations in septic arthritis

Joint aspiration should be attempted before antibiotic treatment, though one must not delay this. Aspirate should be sent for Gram stain, cell count/differential, microscopy and culture. Bloods usually show leukocytosis. Blood cultures should be sent, and potentially wound/sputum/throat swabs and urine culture.

Management of septic arthritis

The joint must be aspirated to dryness to remove infection and relieve pressure. Surgical involvement may be needed, particularly with prosthetic joints. Empiric antibiotic therapy should be started immediately. This is often 2 weeks of IV flucloxacillin QDS (four times daily) ± IV gentamicin, followed by an oral switch. Rest is advised initially, with early physiotherapy.