Transient Synovitis

Overview

Transient synovitis describes self-limiting inflammation of the synovium of the hip joint. It is one of the most common causes of hip pain in children aged 3-8 years. It is a diagnosis of exclusion and the most important differential diagnosis to exclude is septic arthritis.

Transient synovitis is rare in children <3 years old and septic arthritis is more common.

Pathophysiology

The exact cause of transient synovitis is unknown. It is thought to be due to temporary inflammation secondary to a viral upper respiratory tract or gastrointestinal infection as many children with transient synovitis have a preceding viral infection days to weeks before the onset of symptoms.

Epidemiology

• Transient synovitis affects children aged 3-8 years old
• Transient synovitis is rare in children <3 years old and septic arthritis is more common
• Children >9 years old with painful/restricted hip movements may have slipped upper femoral epiphysis

Risk Factors

• Aged 3-8 years old
• Male sex
• History of recent viral infections in the days to weeks before the onset of symptoms

Presentation

Children present with mild-moderate hip pain that gradually improves:

• Pain is not usually severe but there may be a limp or preference not to weight bear
• There may be a preceding history of a viral upper respiratory tract or gastrointestinal infection
• Children are usually afebrile, but a low-grade fever (<38.5°C) may be present
  • A high-grade fever should raise suspicion of septic arthritis
• There is no or mild restriction of hip movements
• Children appear well

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

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

Septic arthritis

• Pain is more severe and children often cannot walk
• Any motion of the hip is painful, even small movements
• Children generally appear unwell and have a high fever
• One or more of the Kocher criteria are met
• Always keep a low threshold of suspicion for septic arthritis, transient synovitis is rare in <3 year olds and septic arthritis is more common

Management

Overview

Transient synovitis is self-limiting and rest and simple analgesia with paracetamol and/or NSAIDs should be used.

Monitoring

• In general, patients are followed up if the limp is still ongoing at 7 days. If pain persists at this point, further evaluation may be necessary to rule out other conditions.

Patient Advice

• Patients should take their child to the emergency department if any features of septic arthritis are present or if symptoms worsen such as:
  • Developing fever
  • Pain that is worsening despite being given analgesia
  • Redness/swelling of any part of the leg
  • Stops walking or the limp worsens
  • If the child becomes more unwell (e.g. reduced appetite, drowsy etc.)

Prognosis

• Transient synovitis starts to improve after around 3 days and usually resolves after around 2 weeks