Septic Arthritis
Septic arthritis is an orthopaedic emergency caused by infection within a joint, most commonly due to bacteria
Disclaimer on choice of guideline
Information in this article is based on a combination of the 2006 British guideline for the hot swollen joint and the more recent 2023 SANJO guideline.
The British guideline is now considerably outdated, while an updated British Society for Rheumatology guideline remains in development. Therefore, contemporary SANJO recommendations have been used to supplement areas where the older UK guidance may no longer reflect current practice.
Causes
Mechanisms of Infection
Septic arthritis usually results from 3 main mechanisms: [Ref]
- Haematogenous spread from systemic infection (as the highly vascularised joint synovium lacks a basement membrane)
- Direct inoculation (direct introduction of organisms into the joint)
- Contiguous spread from adjacent infection
Causative Organisms
Septic arthritis is most commonly caused by a bacterial infection: [Ref]
- Staphylococcus aureus – most common overall
- Streptococcal species
- Haemophilus influenzae
Important organism associations: [Ref]
| Context | Associated organism |
|---|---|
| Sexually active adolescents and young adults (with non-traumatic septic arthritis) | Neisseria gonorrhoeae |
| Puncture wound / traumatic / IVDU-associated septic arthritis | Pseudomonas aeruginosa |
| Sickle cell disease | Salmonella species |
| Children <5 y/o | In <2-3 y/o: Kingella kingae
In neonates: GBS, Staphylococcus aureus, Neisseria gonorrhoeae, Gram-negative bacilli |
Risk Factors
Septic arthritis is more common in children [Ref]
- Peak incidence: 2-3 y/o
- More common in males
- Risk factors
- Neonates
- Haemophilia (esp. with haemarthroses)
- Immunocompromised (e.g. sickle cell disease)
Risk factors in adults: [Ref]
- >80 y/o
- Immunocompromised (e.g. diabetes mellitus)
- IVDU
- Pre-existing joint disease (e.g. RA, OA)
- Recent joint trauma (e.g. traumatic injury, joint surgery, intra-articular injections)
- Prosthetic joints
- Concurrent systemic or local infection (e.g. bacteraemia, osteomyelitis, or soft tissue infection)
Clinical Features
| Onset | Acute onset |
| Joint involvement | Monoarticular
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| Local features |
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| Systemic features |
In children, systemic features may include irritability, poor feeding and reduced activity Systemic features may be absent in septic arthritis, esp. in older or immunocompromised patients. |
In those who are sexually active, gonococcal septic arthritis may present as disseminated gonococcal infection, which may present in 2 classic patterns:
- Arthritis-dermatitis syndrome – triad of
- Migratory polyarthritis
- Tenosynovitis
- Dermatitis (typically a small number of petechial or pustular lesions on the distal limbs)
- Purulent gonococcal arthritis (typically acute monoarthritis)
Investigation and Diagnosis
| Investigation | Description | Findings in septic arthritis |
|---|---|---|
| Joint aspiration for synovial fluid analysis | Investigation of choice to confirm septic arthritis and guide treatment
Synovial fluid should be sent for:
Whenever possible, joint aspiration should be performed before starting antibiotics. |
A synovial WBC count >50,000 cells/µL is suggestive but not diagnostic of septic arthritis. A lower WBC count, -ve Gram stain or -ve culture does not exclude septic arthritis, particularly after prior antibiotics or in immunocompromised patients. |
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| Imaging |
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In acute septic arthritis, X-ray is often normal or may only show non-specific findings like joint effusion and soft-tissue swelling. Radiographic changes are usually only seen in established, prolonged or inadequately treated infection (e.g. joint space narrowing, erosions, subchondral bone destruction). |
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Septic Arthritis vs Transient Synovitis
Septic arthritis and transient synovitis are important differential diagnoses to consider in a child with an acute limp.
| Feature | Septic arthritis of the hip | Transient synovitis |
|---|---|---|
| Underlying cause | Infection of the joint (usually bacterial) | Sterile inflammation of the hip synovium |
| Typical age group | <3 y/o | 3-9 y/o (uncommon in <3 y/o) |
| Onset | Usually acute and progresses rapidly | Acute / subacute, often preceded by a recent viral illness (but not necessarily) |
| Local features |
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| Systemic features |
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Kocher’s criteria
The Kocher criteria are used in a child presenting with an acutely painful or irritable hip to estimate the likelihood of septic arthritis of the hip rather than transient synovitis.
| Criterion | Threshold |
|---|---|
| Fever | >38.5°C |
| Weight-bearing | Unable to bear weight |
| Serum WBC count | >12 × 10⁹/L |
| ESR | >40 mm/hour |
Interpretation: The greater the number of criteria present, the greater the probability of septic arthritis of the hip
- 1 out of 4: 3%
- 2 out of 4: 40%
- 3 out of 4: 93%
- 4 out of 4: 99%
Important: The Kocher criteria apply specifically to differentiating paediatric septic arthritis of the hip from transient synovitis. They are not validated as a general diagnostic score for adult septic arthritis or septic arthritis affecting other joints.
Management
Approach:
- Initial management: empirical antibiotics (after diagnostic joint aspiration)
- Definitive management: serial aspiration or surgery
If the patient is septic / unstable → sepsis and resuscitation
Referral criteria in children:
- ALL <3 y/o children with an acute limp (as septic arthritis is more common in this age group, compared to transient synovitis)
- Acute limp + fever + other clinical features (e.g. redness, swelling, unable to bear weight)
Antibiotic Therapy
Choice of initial empirical antibiotics:
- 1st line: flucloxacillin
- Alternative:
- If penicillin allergic: clindamycin
- If MRSA suspected: vancomycin / teicoplanin
- If gonococcal arthritis / Gram -ve infection suspected: cefotaxime / ceftriaxone
Duration of treatment: 4-6 weeks (typically 2 weeks of antibiotics, followed by 4 weeks of oral antibiotics)
Once synovial-fluid culture and sensitivity results are available, adjust antibiotic therapy accordingly.
Important: Whenever possible, obtain microbiological samples (i.e. diagnostic joint aspiration and blood cultures) before starting antibiotics, as prior antibiotics may reduce the culture yield.
Exception: if the patient is in sepsis or septic shock, then empirical antibiotics should be started immediately as per sepsis protocol.
Definitive Management
Septic arthritis requires urgent orthopaedic assessment to consider:
- Arthroscopic washout and debridement – generally preferred for a large joint septic arthritis
- Open surgical washout – may be necessary for advanced infection, extensive adhesions, cartilage / bone involvement
- Serial joint aspiration – may be considered when surgery is not appropriate or while awaiting surgery
Selected points regarding definitive management:
- Septic arthritis of the hip often requires urgent open debridement
- Tuberculosis arthritis should be managed medically with anti-TB therapy in the early active phase and avoid surgical interventions
- Paediatric septic arthritis is often managed conservatively with antibiotic therapy and serial joint aspirations, where surgery is often reserved for failed conservative management
Do NOT give intra-articular corticosteroid injections if septic arthritis is suspected or confirmed, as local immunosuppression may worsen or mask the infection.