Transient synovitis

Alternate Names

• Irritable hip
• Transient coxitis
• Coxitis fugax

Definition

• Transient synovitis (TS) is an acute, non-specific, self-limited inflammatory process affecting the joint synovium. Transient synovitis of the hip is a common cause of hip pain in the pediatric patient population.

Etiology

• The exact etiology of TS is unknown. Proposed risk factors include:
  1. Preceding upper respiratory tract infection
  2. Preceding trauma
  3. Preceding bacterial infection
  4. Post-streptococcal toxic synovitis

Inflamed hip joint

Epidemiology

• TS of the hip most frequently occurs in children ages 3 to 10 years old. The average annual incidence of TS and the total lifetime risk are estimated to be at 0.2% and 3%, respectively.
• The incidence rate in males is twice that of females, and about 1% to 4% of the time a patient may demonstrate bilateral involvement.

Signs and symptoms

• Acute unilateral limb disuse ranging from nonspecific hip pain or subtle limp to a refusal to bear weight.
• Child or infant becoming increasingly agitated or crying more often than at baseline.
• The patient may present with the hip in the flexed, abducted, and externally rotated position as this relaxes the hip joint capsule to decrease intra-articular pressure.
• May be febrile at presentation.

Diagnosis

• TS remains a diagnosis of exclusion.
• Synovial WBC counts: (5,644 - 15,388) in Transient synovitis while (105,432 - 260,214) in Septic arthritis.
• Inflammatory markers slightly raised in TS.
  1. ESR range for SA patients was 44 - 64 mm/hr
  2. ESR range for TS patients was 21 - 33 mm/hr
• If the aspirate has a positive gram stain, more than 90% polymorphonuclear cells, or a glucose less than 40 mg/dL or markedly different from the serum glucose, the patient is more likely to have septic arthritis and not transient synovitis.
• Although plain films may be normal for months after the onset of symptoms, the medial joint space is typically slightly wider in the affected hip indicating the presence of fluid. One-half to two-thirds of patients with transient synovitis may have an accentuated pericapsular shadow.
• Ultrasound is extremely accurate for detecting an intracapsular effusion. Ultrasound-guided hip aspiration not only relieves pain and limitation of movement but often provides a rapid distinction from septic arthritis. Ultrasound-guided hip aspiration should be done in all individuals in whom ultrasonography has exhibited evidence of an effusion, and any of the following predictive criteria are present:
  1. Temperature greater than 99.5 F
  2. ESR greater than or equal to 20 mm/hr
  3. Severe hip pain and spasm with movement
• The Kocher criteria remain a helpful set of clinical risk factors differentiating SA(septic arthritis) and TS in pediatric patients presenting with hip pain.  The criteria include the increasing diagnostic probability in favor of the former, yielding a 99.6% probability favoring SA as a diagnosis when all four criteria are met:
  1. WBC > 12,000 cells per microliter of serum
  2. Inability or refusal to bear weight
  3. Febrile (> 101.3 degrees Fahrenheit or 38.5 degrees celsius)
  4. ESR > 40 mm/hr When none of the above risk factors are present upon presentation, the probability of the patient having SA of the hip drops below 0.2%.  

Management

• It involves supportive care and rest from activity. NSAIDS can be used for pain control. Other modalities include the application of heat and/or massage modalities.
• Symptoms generally improve after 24 to 48 hours. Complete resolution of symptoms often takes up to 1 to 2 weeks in up to 75% of patients. The remainder may have less severe symptoms for several weeks.
• If significant symptoms persist for seven to 10 days after the initial presentation, consider other diagnoses. Patients with symptoms for more than a month have been found to have a different pathology.

Differential diagnosis

• Osteomyelitis
• Septic arthritis
• Primary or metastatic lesions
• Legg–Calvé–Perthes disease (LCPD)
• Slipped capital femoral epiphysis (SCFE)

Prognosis

• In total, TS of the hip recurs in up to 20% to 25% of patients. The patient should be educated regarding the increased risk of recurrence in the setting of a previously documented diagnosis of TS.

Complications

• The major complication associated with TS is a recurrence of symptoms.

References

• Christine C. Whitelaw; Matthew Varacallo. Transient synovitis [Updated June 29,2021]. In StatPearls[Internet]. Available at: https://www.ncbi.nlm.nih.gov/books/NBK459181/

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