Clinical presentation
Septic arthritis in a child is an orthopaedic emergency. The hip and knee are the most commonly affected large joints. Typical features include:
- Acute pain and refusal to use the limb
- Limp or inability to bear weight
- Fever or systemic illness
- Painful restriction of passive joint movement
- Irritability in infants; pseudoparalysis may be the presenting feature
The absence of fever does not exclude infection, particularly in young infants or partially treated infection.
Initial assessment
- Keep the child fasting if operative treatment may be required
- Examine the child for a source of infection and for adjacent osteomyelitis
- Obtain full blood count, CRP and ESR
- Obtain blood cultures if febrile
- Plain radiographs are useful to exclude other pathology and may show joint-space widening or late bony changes
- Ultrasound is sensitive for a hip effusion and can guide aspiration, but cannot distinguish a sterile from an infected effusion
- MRI is useful when adjacent osteomyelitis, pyomyositis or an occult collection is suspected
Kocher criteria for the painful paediatric hip
The original predictors are:
- Temperature >38.5 °C
- Inability to bear weight
- ESR >40 mm/h
- Serum WBC >12,000/mm³
CRP >2 mg/dL (20 mg/L) is commonly added as a modified predictor.
The criteria help estimate the likelihood of septic arthritis in a child with an irritable hip, but they are not diagnostic and should not be applied indiscriminately to other joints.
Joint aspiration
Hip aspiration should be performed promptly when septic arthritis is suspected. Send fluid for:
- Cell count and differential
- Gram stain
- Culture and sensitivities
A synovial WBC >50,000/mm³ with a high polymorphonuclear percentage strongly supports infection, although lower counts do not exclude it.
Whenever the child is clinically stable, obtain blood and joint cultures before starting antibiotics. Do not delay resuscitation or treatment in a septic child.
Organisms
- Staphylococcus aureus is the commonest organism overall
- Kingella kingae is important in young children
- Organisms vary with age, immunisation status and comorbidity
Treatment
The principles are:
- Urgent drainage of the infected joint
- Thorough irrigation and debridement
- Obtain adequate microbiological specimens
- Preserve joint stability and articular cartilage
- Start empiric intravenous antibiotics after cultures are obtained, then tailor treatment to sensitivities
- Monitor clinical improvement and serial CRP
For septic arthritis of the hip, urgent surgical drainage is standard treatment. Other accessible joints may be managed by arthroscopic or open washout depending on age, joint and local expertise.
Complications
Delayed diagnosis or inadequate treatment may result in:
- Articular cartilage destruction
- Chondrolysis
- Osteonecrosis of the femoral head
- Growth disturbance
- Hip instability or dislocation in infants
- Secondary osteoarthritis
- Sepsis
Poorer prognosis is associated with very young age, associated osteomyelitis and delay in treatment.