Introduction

Transient synovitis (a.k.a. Irritable Hip) is the most common cause of hip pain in children aged 3-8.  It can be difficult to differentiate from the much more serious septic arthritis, and as such, transient synovitis should be a diagnosis of exclusion.

Other causes of hip pain in children include viral arthritis (common), juvenile arthritis (rare),

It is caused by inflammation of the synovium of the hip.

The condition is self limiting and usually resolves within a few days.

Epidemiology

  • Most common cause of hip pain in children aged 3-8
  • Can occur between ages of about 1-10
  • M:F – 2:1

Pathology

  • Non specific inflammation of the synovial lining of the hip – often 1-2 weeks after an upper respiratory tract infection (URTI)

Presentation

  • Child reluctant to weight bear, complaining of hip pain
  • Often still able to walk with difficulty (unlike septic arthritis where they often cannot walk at all)
  • Usually 1-2 weeks after a viral URTI
  • Otherwise, afebrile and systemically well
  • Pain often worse first thing in the morning – usually improves throughout the day
  • Child often sits or lies in position with least pressure on the hip – flexion, abduction and external rotation

Examination

  • Reduction in ROM of hip, particularly internal rotation
  • Often still able to weight bear with encouragement
  • More severe limitation of movement suggest septic arthritis

Investigations

  • X-ray – request AP, lateral and frog leg views
    • Usually normal
    • May show some joint space widening
    • Should always be performed
  • Bloods – including FBC and CRP – to rule out a septic arthritis
  • USS – not routinely performed – can show a fusion (more likely septic arthritis) or synovial inflammation (suggest synovitis as most likely diagnosis)
  • MRI – not routinely performed – can show osteomyelitis or myositis

Differentials

  • Viral Arthritis
    • Most similar to synovitis and also a benign course. Other viral symptoms (e.g. a rash or URTI symptoms) usually still ongoing at time of presentation
  • Slipped Capital Femoral Epiphysis (SCFE)
    • Usually older children (mean age around 12)
    • Can be acute or chronic
    • Associated with obesity
  • Septic Arthritis
    • Child often unwell
    • Signs of sepsis
    • Bloods suggestive of infection (raised WCC and CRP)
  • Perthes Disease
    • Usually younger children (age 4-8)

Management

  • Firstly – make sure you are confident it is not septic arthritis!
    • No fevers
    • Weight bearing
    • Systemically well
    • Inflammatory markers (WCC and CRP) are not raised
  • NSAIDs – e.g. ibuprofen 15mg/Kg TDS
  • Symptoms usually resolve in less than a week

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