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Updated: Jun 13 2021

Transient Synovitis of Hip


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  • summary
    • Transient Synovitis of Hip is inflammation of the synovium and a common cause of hip pain in pediatric patients that must be differentiated from septic arthritis of the hip.
    • Diagnosis is one of exclusion and can be suspected in a patient with hip pain with low CRP and near normal synovial WBC count.
    • Treatment is usually anti-inflammatories and observation given self-limiting nature.
  • Epidemiology
    • Incidence
      • most common cause of hip pain in the pediatric population
      • 3% of children between 3-10yo
      • recurrence rate is as high as 20%
    • Demographics
      • most common in children aged 4-8 years old
      • male-to-female ratio is 2:1
    • Anatomic location
      • can affect any major joint but most commonly affects the hip joint
    • Risk factors
      • the exact cause of transient synovitis is largely unknown, however, may be related to
        • viral infection (upper respiratory)
        • bacterial infection (poststreptococcal toxic synovitis)
        • trauma
        • higher interferon concentration
        • allergic reaction
  • Etiology
    • Pathophysiology
      • pathoanatomy
        • non-specific inflammation and hypertrophy of the synovial lining/membrane
  • Presentation
    • History
      • recent upper respiratory infection or trauma
    • Symptoms
      • mild or absent fever
      • acute or insidious onset of groin/thigh pain
        • refusal to bear weight on the affected extremity
        • usually improves during the day (child can walk with a limp later in the day)
      • muscle spasms
    • Physical exam
      • inspection
        • hip presents in flexion, abduction, and external rotation (position with least amount of intracapsular pressure)
        • usually does not have a toxic appearance
      • motion
        • mild to moderate restriction of hip internal rotation is the most sensitive range-of-motion restriction
        • a painless arc of motion is more likely synovitis rather than septic arthritis
      • neurovascular
        • toe-walking, cavus foot, or clawing of the toes may suggest a neurological cause of limp
      • provocative tests
        • log-rolling leg can detect involuntary muscle guarding
        • non-tender motion of lumbar spine and ipsilateral knee
  • Imaging
    • Radiographs
      • recommended views
        • AP, lateral or frog leg hip views
      • optional radiographs
        • spine films
      • findings
        • usually normal
    • Ultrasonography
      • indications
        • history and physical examination suspicious for septic arthritis
      • findings
        • accurate for detecting intracapsular fluid/effusion
        • may show synovial membrane thickening
      • sensitivity/specificity
        • difficult to distinguish transient synovitis from septic arthritis, but infection less likely if effusion absent
    • MRI
      • indications
        • suspicion for myositis or osteomyelitis
        • significantly elevated lab values
  • Studies
    • Serum labs
      • WBC may be slightly elevated
      • CRP < 20 mg/l
        • most important factor to RULE OUT septic arthritis
      • ESR usually less than 20 mm/h
    • Invasive studies
      • synovial fluid aspiration if concern for septic arthritis based on clinical judgment or Kocher criteria
        • assume it is septic arthritis if synovial WBC is >50,000
  • Differential
    • Hip septic arthritis 
    • Osteomyelitis
    • SCFE
  • Treatment
    • Nonoperative
      • NSAIDS and close observation
        • indications
          • low clinical suspicion of septic arthritis
        • modalities
          • treat the patient with IV or PO NSAIDS and observe over 24 hours
          • minimize walking for 24 hours
          • consider traction to enforce rest
        • outcomes
          • if symptoms improve with NSAIDS, more likely to be transient synovitis
          • symptom resolution in under 1 week from the date of presentation
  • Complications
    • Recurrence ~ 20%
    • Legg-Calve-Perthes
      • reported as 0-10% incidence however his is controversial as most series show no long term sequelae
  • Prognosis
    • Natural history of disease
      • usually benign
      • marked improvement, usually in 24-48 hours
      • complete resolution of symptoms will usually occur in 1-2 weeks
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