Transient synovitis

Transient synovitis is characterized by nonspecific inflammation and hypertrophy of the synovial membrane of the hip joint and is a common cause of acute, nontraumatic hip pain and/or limp in children. Transient synovitis is self-limited and is associated with recent viral infection. Clinical features include antalgic gait, groin pain, and limited painful hip motion. Transient synovitis is a clinical diagnosis supported by diagnostic tests to rule out septic arthritis and other common causes of hip pain in children. Treatment is supportive and consists of rest and NSAIDs. Symptoms typically improve within 24 hours and resolve within 2 weeks.

• Common cause of acute, nontraumatic hip pain and/or limp in children ^[1][2]
• Peak incidence: 3–8 years of age ^[1]
• Sex: ♂ > ♀ (2:1) ^[1]

Epidemiological data refers to the US, unless otherwise specified.

• Exact cause is unknown. ^[1]
• Associated with recent viral upper respiratory infection and gastroenteritis ^[1][2]

Nonspecific inflammation and hypertrophy of the synovial membrane

• Onset of symptoms over 3–5 days ^[1]
• Well-appearing; possible low-grade fever ^[1]
• Unilateral groin pain that may radiate to the medial thigh, buttock, and/or knee ^{[2] [1]}
• Examination findings ^{[1] [2]}
  • Antalgic gait and/or refusal to bear weight
  • Hip usually flexed, abducted, and externally rotated
  • Limited range of motion with pain at the limit of the range of motion of the hip

Diagnosis is clinical. Diagnostic testing is indicated to rule out alternative diagnoses, particularly septic arthritis. ^[1][2]

• Laboratory studies
  • Indication: to assess for evidence of infection
  • Findings: CBC, ESR, CRP, and serum procalcitonin are typically normal.
• Imaging ^[3]
  • X-ray (e.g., anterior-posterior pelvis and bilateral frog-leg lateral views)
    • Indications: to assess for bony causes of pain and/or limp, sacroiliac joint evaluation
    • Findings are usually normal.
  • Ultrasound of the hip (including POCUS)
    • Indications: to assess for effusions or for imaging-guided hip aspiration
    • Findings: joint effusion
  • MRI: rarely performed as an initial study
    • Indications: to assess for infection, tumor, or diagnostic uncertainty
    • Findings: joint effusion ^[2]
• Arthrocentesis with synovial fluid analysis
  • Obtain urgently in all patients with suspected infection, e.g.: ^[1]
    • Clinical features of septic arthritis (e.g., non-weight bearing, pain throughout range of motion, ill-appearing)
    • Elevated ESR, CRP, white blood cell count, and/or procalcitonin (see “Diagnosis of septic arthritis”)
  • For findings suggesting infection, see “Interpretation of synovial fluid analysis.”

The Kocher criteria for septic arthritis can help assess the probability of septic arthritis vs. transient synovitis based on symptoms and laboratory findings. Arthrocentesis with synovial fluid analysis facilitates definitive diagnosis. ^[1]

• Other common causes of hip pain in children, e.g.,
  • Septic arthritis
  • Legg-Calvé-Perthes disease
• Lyme arthritis ^[4]
• Trauma

The differential diagnoses listed here are not exhaustive.

• Reassure patients and caregivers that transient synovitis is benign and self-limited.
• Outpatient, conservative management is usually appropriate. ^[1]
  • Rest
  • NSAIDs as needed for pain relief (for dosages, see “Nonopioid oral analgesia in children”)
• Consider hospital admission for 24-hour observation if the diagnosis is unclear. ^[1]

• Symptoms generally improve within 24 hours and resolve within 2 weeks. ^[1][5]
• Recurs in approx. 20% of affected children ^[5]