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Introduction
  • Overview
    • inflammation of the synovium and a common cause of hip pain in pediatric patients that must be differentiated from septic arthritis of the hip
      • treatment is usually anti-inflammatories and supportive measures 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
    • location
      • can affect any major joint but most commonly affects the hip joint
    • risk factors
      • 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
  • 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
Presentation
  • History
    • 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 the affected extremity
      • usually improves during 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 toxic appearance
    • motion
      • mild to moderate restriction of hip abduction 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 factors to RULE OUT septic arthritis
    • 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 the affected side
      • most important factor to RULE OUT septic arthritis
    • ESR > 40mm/h
  • Invasive studies
    • synovial fluid aspiration
      • septic arthritis if synovial WBC is >50,000
Differential
  • Transient synovitis is a diagnosis of exclusion
    •  Table - Differential diagnosis of Hip Pain in Children
Treatment
  • 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 and NSAIDs
      • modalities
        • treat the 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 the 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
        • fluoroscopic guided aspiration
    • irrigation and debridement of hip
      • indications
        • confirmed septic arthritis following aspiration 
          • 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
        • suspected septic hip
      • outcomes
        • treatment of infection with I&D is time sensitive
        • a prolonged infection will affect cartilage survival
Complications
  • Legg-Calvé-Perthes 
    • incidence
      • 0-10%
  • Recurrence
    • incidence
      • 4-26%
 

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