Septic Arthritis

Author(s): Kehinde Sunmboye and John L. Klein

Consider the diagnosis in any patient who has fever with joint pain and swelling, particularly if only one large joint is involved.

Septic arthritis is typically mono-articular but can be poly-articular (15% of cases).
The knee is the joint most commonly involved, followed by the elbow, shoulder and hip.
Staphylococcus aureus is the causative organism in 50% of cases of native joint infection; other causative organisms include streptococci, gonococci and Gram-negative bacilli.
Prosthetic joint infection is caused by a wider range of pathogens.

Priorities ⬆ ⬇

Your clinical assessment should address the following points:

Does the patient have arthritis or periarticular inflammation (bursitis, tendinitis or cellulitis)? Painful limitation of movement of the joint suggests arthritis. Causes of acute mono- or oligo-arthritis are given in Table 28.1 (p. 183).
Is the patient at risk of septic arthritis? Septic arthritis usually follows an overt or occult bacteraemia (e.g. from infective endocarditis, pneumonia or IV drug use) in a patient at risk because of rheumatoid arthritis, the presence of a prosthetic joint, or immunosuppression (including anti-TNF therapy).
Could this be a crystal arthritis (gout or pseudogout; Chapter 97): is there a history of previous similar attacks of arthritis?
Could this be a reactive arthritis: is there an associated rash, diarrhoea, urethritis or uveitis?
Could this be gonococcal arthritis (Table 98.1)?

Aspirate the joint (Chapter 124) and send synovial fluid for cell count (in an EDTA tube; normal cell count is <180/mm³, most mononuclear); Gram stain; culture; and microscopy under polarized light for crystals. Other investigations needed urgently are given in Table 98.2.

If you are not familiar with joint aspiration, ask the help of a rheumatologist or orthopaedic surgeon.
Both crystal and septic arthritis give rise to a purulent effusion, although the white cell count is usually higher in septic arthritis (50,000–200,000/mm³), with a polymorphonuclear cell count of >90%.
Bloodstaining of the effusion is common in pseudogout but rare in sepsis.

Further Management ⬆ ⬇

Outline

Organisms on Gram Stain of Synovial Fluid, or High Probability of Septic Arthritis
No Organisms on Gram Stain of Synovial Fluid and Low Probability of Septic Arthritis

Organisms on Gram Stain of Synovial Fluid, or High Probability of Septic Arthritis

Start antibiotic therapy IV (Table 98.3).

Intra-articular administration is not needed.
The antibiotic regimen may need modification in the light of blood and synovial fluid culture results: discuss this with a microbiologist.
Antibiotic therapy for non-gonococcal septic arthritis usually needs to be given for 2–4 weeks, initially IV, but may be switched to an appropriate oral agent in uncomplicated cases.
Gonococcal arthritis may be cured with just 1–2 weeks of therapy.

If septic arthritis is confirmed, seek advice on further management from a rheumatologist or orthopaedic surgeon.

Daily aspiration of the joint until an effusion no longer re-accumulates is an acceptable approach where access to the joint is easy (e.g. the knee).
Other larger joints (e.g. hip or shoulder) may be more effectively drained by arthroscopic washout.
While the infection is resolving, the joint should be immobilized using a splint or cast.
Physiotherapy should be started early.
Give an NSAID for pain relief (e.g. indomethacin or diclofenac).
In patients with gonococcal arthritis, a sexual health screen of the patient and his/her sexual partners should be offered.

No Organisms on Gram Stain of Synovial Fluid and Low Probability of Septic Arthritis

Consider the other causes of acute arthritis (Table 28.1).

Pseudogout is the commonest cause of acute mono-or oligo-arthritis in the elderly.
Hold off antibiotic therapy (pending the results of blood and synovial fluid culture for definite exclusion of infection).
Treat with an NSAID, covered with a proton-pump inhibitor in the elderly or patients with previous peptic ulceration).
If gout is confirmed (also check plasma urate) and fails to respond to an NSAID, use colchicine. Allopurinol should not be started until the acute attack has completely resolved.

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Information ⬇

Priorities ⬆ ⬇

Further Management ⬆ ⬇

Further Reading ⬆