FFinalistSouthampton · 2027
Child health
AKT · Child health/Growth, GI & MSK

Septic arthritis (paediatric)

Staph aureus (commonest); Strep, Kingella, gonococcus (adolescents)

Overview

Bacterial infection of a joint — an orthopaedic EMERGENCY, because pus destroys cartilage within hours. In children the hip/knee are common, and the discrimination from transient synovitis is the high-yield task.

Recognise

  • Hot, swollen, exquisitely tender joint held still; refuses to move/weight-bear
  • Fever, systemically unwell
  • Pseudoparalysis of the limb in infants

Red flags

  • Any febrile, unwell child refusing to use a limb/joint → emergency; delay risks permanent joint destruction

Differentials & how to tell them apart

Transient synovitis (irritable hip)WELL child, afebrile, will weight-bear, normal CRP/WCC — Kocher-low
Osteomyelitismetaphyseal bone tenderness; may coexist
Reactive arthritissterile, follows GI/GU infection
Juvenile idiopathic arthritis (JIA)chronic >6 weeks, not acutely septic

Investigations

Kocher criteria (fever >38.5°C, non-weight-bearing, ESR/CRP↑, WCC↑). URGENT joint aspiration (Gram stain, culture, WCC) before antibiotics; blood cultures, FBC/CRP; USS for effusion.

Management

Urgent joint aspiration → IV antibiotics + surgical washout

  1. 1Emergency orthopaedic referral. Aspirate the joint (before antibiotics where possible), then IV empirical antibiotics covering S. aureus.Gate: Do not give antibiotics before aspiration unless the child is septic — it obscures the culture
  2. 2Surgical washout; targeted antibiotics on culture; prolonged course; physiotherapy.
IV empirical antibiotics (e.g. flucloxacillin) — after aspiration; cover S. aureus per local/age guideline
Surgical washout — drainage/lavage of the joint

Key points

Kocher criteria stratify septic arthritis vs transient synovitis. Consider Kingella in infants and disseminated gonococcus in sexually active adolescents.

Monitor & prognosis

CRP/clinical response; joint function; complete the antibiotic course.

Good if treated within hours; delay → cartilage destruction and growth disturbance.

Source: NICE CKS; BOA/BSCOS; Kocher criteria