• Hip pain due to inflammation of the synovium of the hip
  • Epidemiology
    • incidence
      • most common cause of hip pain in the pediatric population
    • demographics
      • most common in children aged 4-8 years old
      • male-to-female ratio is 2:1
    • risk factors
      • exact cause of transient synovitis is largely unknown, however may be related to
        • viral infection
        • bacterial infection (poststreptococcal toxic synovitis 
        • trauma
        • higher interferon concentration
        • allergic reaction
  • Pathophysiology
    • pathoanatomy
      • non-specific inflammation and hypertrophy of the synovial lining/membrane
  • Prognosis
    • natural history of disease
      • usually benign
      • marked improvement, usually in 24-48 hours
      • complete resolution of symptoms will usually occur in <1 week
  • History
    • key questions
      • site of pain
        • groin vs. hip 
      • timing (intermittent vs constant)
      • lack of mechanical symptoms (locking, catching, giving way)
      • associated limp
      • constitutional symptoms 
      • recent infection or trauma
  • Symptoms
    • mild or absent fever
    • acute or insidious onset of groin/thigh pain
      • pain is typically worse on awakening
      • refusal to bear weight on affected extremity
      • usually improves during day (child can walk with a limp later in the day)
    • very commonly associated with a preceeding infection
    • muscle spasms
  • Physical exam
    • inspection
      • hip presents in flexion, abduction, and external rotation (position with least amount of intracapsular pressure)
      • usually does not have toxic appearance
    • motion
      • mild to moderate restriction of hip abduction is the most sensitive range-of-motion restriction 
      • log-rolling leg can detect involuntary muscle guarding
        • painless arc of motion is more likely synovitis rather than septic arthritis
      • non-tender motion of lumbar spine and ipsilateral knee
    • neurovascular
      • toe-walking, cavus foot, or clawing of the toes may suggest neurological cause of  limp
  • Radiographs
    • recommended views
      • AP, lateral or frog leg hip views
    • findings
      • usually normal
      • may show medial joint space widening  
  • Ultrasonography
    • indications
      • history and physical examination suspicious for septic arthritis
    • findings
      • accurate for detecting intracapsular fluid/effusion
      • may show synovial membrane thickening
      • difficult to distinguish transient synovitis from septic arthritis, but infection less likely if effusion absent
  • MRI
    • indications
      • suspicion for myositis or osteomyelitis
    • findings
      • can differentiate transient synovitis from septic arthritis
      • usually not necessary to make diagnosis of toxic synovitis.  Only required to rule out other conditions when necessary
  • Lab values
    • WBC may be slightly elevated
    • CRP < 20 mg/l 
    • ESR usually less than 20 mm/h
  • Kocher criteria for septic arthritis (3 out of 4 = 93% chance of septic arthritis)
    • fever > 38.5 C
    • WBC > 12,000 mm3
    • non-weightbearing on affected side
    • ESR > 40mm/h
  • Most important factors to RULE OUT septic arthritis
    • patient weight-bearing on limb
    • CRP< 20 mg/l
  • Transient synovitis is a diagnosis of exclusion
    •  Table - Differential diagnosis of Hip Pain in Children
  • Nonoperative
    • NSAIDS and close observation
      • indications
        • low clinical suspicion of septic arthritis
          • patient is afebrile for the past 24 hours with mild symptoms
          • improved ambulation
      • modalities
        • treat patient with IV or PO NSAIDS and observe over 24 hours
        • early weight-bearing with physiotherapy
      • outcomes
        • if symptoms improve with NSAIDS, more likely to be transient synovitis
        • symptom resolution in under 1 week from date of presentation
  • Operative
    • joint aspiration, then initiation of IV antibiotics
      • indications
        • high clinical suspicion for septic arthritis
        • worsening hip pain despite treatment with NSAIDs
      • modalities
        • ultrasound guided aspiration
        • MR guided aspiration
      • outcomes
        • aspirate suggestive of infection
          • WBC count > 50,000, though septic arthritis is still the most common diagnosis in children with synovial WBC count of 25,000 to 75,000
          • positive gram stain
    • irrigation and debridement of hip
      • indications
        • documented infection
        • suspected septic hip
      • outcomes
        • treatment of infection with I&D is time sensitive
        • prolonged infection will affect cartilage survival
  • Legg-Calvé-Perthes (1-3%)
  • Coxa magna
  • Hip dysplasia

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