Transient Monoarticular Synovitis
Transient Monoarticular Synovitis (Toxic Synovitis)
Definition
Transient synovitis is a self-limiting inflammatory condition of the hip joint, primarily affecting children aged 3-10 years. It is the most common cause of acute hip pain in children and is characterized by temporary inflammation of the synovial membrane.
Epidemiology
- Age Distribution:
- Peak incidence: 4-8 years
- Rare before age 2 and after age 12
- Gender Distribution:
- Male predominance (2:1 ratio)
- Higher incidence in active children
- Seasonal Variation:
- More common in winter/spring
- Often follows upper respiratory infection
Pathophysiology
- Proposed Mechanisms:
- Post-viral inflammatory response
- Immune-mediated synovial reaction
- Transient synovial hyperemia
- Associated Factors:
- Recent viral infection (2-3 weeks prior)
- Upper respiratory tract infections
- Minor trauma
Clinical Presentation
Symptoms
- Primary Symptoms:
- Acute onset hip pain
- Limping or refusal to bear weight
- Pain may refer to knee/thigh
- Morning stiffness
- Associated Features:
- Low-grade fever (<38.5°C)
- Recent illness history
- Preserved hip motion
- Good general condition
Physical Examination
- Hip Examination:
- Limited internal rotation
- Pain on passive movement
- Antalgic gait
- Preserved but painful ROM
- Key Signs:
- No visible swelling
- No warmth or erythema
- Mild muscle spasm
- FABER test often positive
Diagnostic Approach
Laboratory Studies
- Basic Workup:
- Complete blood count (CBC)
- ESR (<20mm/hr typically)
- CRP (<1.0 mg/dL typically)
- Blood culture if febrile
- Kocher Criteria:
- Non-weight bearing
- ESR >40mm/hr
- Fever >38.5°C
- WBC >12,000/μL
Imaging Studies
- Ultrasound:
- First-line imaging
- Shows effusion
- Measures joint space
- Dynamic assessment
- X-ray:
- AP and frog-leg lateral views
- Rules out bony pathology
- May show joint space widening
- Advanced Imaging:
- MRI if diagnosis unclear
- Used to exclude osteomyelitis
- Helpful in atypical cases
Treatment & Management
Conservative Management
- Initial Treatment:
- Rest and activity modification
- NSAIDs (ibuprofen preferred)
- Weight bearing as tolerated
- Observation for symptoms
- Home Care:
- Limited bed rest (24-48 hours)
- Regular pain assessment
- Temperature monitoring
- Activity modifications
Monitoring
- Follow-up Schedule:
- 24-48 hour reassessment
- Weekly until resolution
- Monitor for red flags
- Return Precautions:
- Worsening pain
- High fever development
- Non-weight bearing >1 week
- New symptoms
Differential Diagnosis
Critical Differentials
- Must Rule Out:
- Septic arthritis (emergency)
- Osteomyelitis
- Legg-Calvé-Perthes disease
- Slipped capital femoral epiphysis
- Other Considerations:
- Juvenile idiopathic arthritis
- Trauma/fracture
- Rheumatic fever
- Neoplasm
Red Flag Symptoms
- Concerning Features:
- High fever (>38.5°C)
- Severe pain
- Complete immobility
- Systemic symptoms
- Indications for Emergency Referral:
- Multiple Kocher criteria
- Toxic appearance
- Marked restriction of all movements
- Failed conservative treatment
Prognosis & Follow-up
Expected Course
- Natural History:
- Self-limiting condition
- Resolution within 7-10 days
- No long-term sequelae
- Recurrence in 15% cases
- Recovery Phases:
- Acute phase (2-4 days)
- Recovery phase (3-7 days)
- Return to activities (7-14 days)
Follow-up Care
- Monitoring Points:
- Resolution of symptoms
- Return of normal gait
- Pain-free range of motion
- Activity tolerance
- Long-term Considerations:
- No residual disability
- Monitor for recurrence
- Parent education
- Activity guidelines
