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