Septic Arthritis in Children

Overview

Septic arthritis describes the infection of a joint resulting in inflammation which can lead to disseminated infection and sepsis and/or irreversible joint damage and long-term joint problems.

The most common cause of septic arthritis in all age groups is Staphylococcus aureus.

The most commonly affected joints are the hip, knee, and ankle.

Presentation

Overview

Septic arthritis may be difficult to identify in children, therefore, a low threshold of suspicion should be kept. Features include:

• Joint pain that can be worsened by movement
• Joint swelling, warmth, erythema
• Limp/inability to weight bear
  • The child may refuse to sit, stand, or walk
• Fever and features of systemic upset such as lethargy, irritability
• In infants, the only sign may be ‘pseudoparalysis’ – an inability to move the body due to pain
• Some children may maximally abduct, flex, and externally rotate the hip to maximise the space for infected synovial fluid to relieve pain

Referral and Investigations

Referral

Arrange an urgent specialist assessment if any of the following apply:

• Is suspected of being maltreated
• Is <3 years old:
  • Transient synovitis is rare in this age group and septic arthritis is more common
• Has a fever and/or red flags such as:
  • Red flags for trauma/infection:
    • Unable to weight bear or painful limitation in range of motion – suggests trauma or infection
    • Severe pain, anxiety, and agitation after trauma – suggest neurovascular compromise or compartment syndrome
  • Red flags for malignancy:
    • Pain waking the child at night – suggests malignancy
    • Palpable mass – suggests malignancy
  • Red flags for malignancy or inflammation:
    • Redness/stiffness/swelling of the joint or limb – suggests infection or inflammatory joint disease
    • Constitutional symptoms (fever, weight loss, night sweats, fatigue, anorexia) – suggest malignancy, infection, or inflammation
    • Limp stiffness that is worse in the morning – suggests inflammatory joint disease

Investigations

Investigations include:

• Joint aspiration and synovial fluid microscopy, culture, and sensitivities:
  • Ideally before giving antibiotics but do not delay treatment
  • The synovial fluid may appear turbid, have raised white cells, or may have a positive gram stain
• Blood culture:
  • Ideally before giving antibiotics but do not delay treatment
  • May identify causative pathogen
• Full blood count (FBC) and differential:
  • May show leukocytosis, suggesting infection
• Erythrocyte sedimentation rate (ESR) or C-reactive protein (CRP):
  • Non-specific markers of inflammation, may be elevated
• X-ray of the affected bone/joint:
  • May show soft tissue swelling or features of erosion

Kocher criteria

The Kocher criteria are used in the diagnosis of septic arthritis and predict is likelihood. It is also helpful in differentiating septic arthritis from transient synovitis. One point is given if any of the following apply:

• Non-weight bearing
• Fever >38.5 °C
• Raised ESR
• Raised white cell count

The scores and the likelihood of septic arthritis are as follows:

Differential Diagnoses

Transient synovitis

• Children appear well and the pain and limitation in hip movements are mild
• None of the Kocher criteria is met
• The fever is low-grade (<38.5 °C)

Management

Overview

If a prosthetic joint is involved, refer to orthopaedics immediately.

Treatment involves immediate needle aspiration and blood cultures (ideally before giving antibiotics, but do not delay treatment), then giving IV antibiotics according to local hospital policy. The BNF states that:

• Flucloxacillin is first-line
• Clindamycin is first-line for those who are penicillin-allergic

For patients who are unresponsive to treatment, there may be an underlying abscess forming or osteomyelitis and surgery may be necessary.

Complications

• Joint destruction
• Osteomyelitis
• Sepsis