What is the appropriate workup for a 6-year-old with severe right knee and calf pain without trauma?

Workup for a 6-Year-Old with Severe Right Knee and Calf Pain Without Trauma

The initial workup for a 6-year-old with severe right knee and calf pain without trauma should include radiographs of the knee, laboratory studies to evaluate for infection or inflammation, and consideration of MRI if radiographs are negative but symptoms persist, as these steps are essential to rule out limb- and life-threatening conditions. 1, 2

Initial Assessment

History

• Pain characteristics: onset, duration, severity, location (knee vs. calf), aggravating/alleviating factors
• Associated symptoms: fever, night pain, weight loss, swelling, redness, warmth
• Functional limitations: ability to bear weight, walk, or perform daily activities
• Recent illnesses or infections
• Family history of rheumatologic conditions

Physical Examination

• Vital signs (especially temperature to evaluate for infection)

• Observation for:

  • Swelling, erythema, warmth
  • Limb alignment and deformity
  • Gait pattern if able to walk

• Palpation:

  • Joint line tenderness
  • Effusion (using the bulge sign or ballottement test)
  • Calf tenderness or masses

• Range of motion assessment:

  • Active and passive knee flexion/extension
  • Hip examination (crucial as hip pathology can present as knee pain)

Diagnostic Studies

First-Line Imaging

• Knee radiographs (AP and lateral views) are indicated as the initial imaging study since the patient has focal tenderness and severe pain 3
• Consider including hip radiographs to rule out referred pain from hip pathology 3, 1

Laboratory Studies

• Complete blood count (CBC) with differential
• Erythrocyte sedimentation rate (ESR)
• C-reactive protein (CRP)
• Consider blood cultures if fever or signs of infection are present

Second-Line Imaging

• MRI without contrast is recommended if:

  • Radiographs are negative but symptoms persist
  • There is suspicion of occult fracture, internal derangement, or soft tissue injury 3, 4
  • Clinical concern for infection, malignancy, or inflammatory condition

• Ultrasound may be useful to:

  • Identify effusion prior to aspiration if infection is suspected 3
  • Evaluate for Baker's cyst or other soft tissue pathology 4

Differential Diagnosis to Consider

Emergent Conditions (Require Immediate Attention)

• Septic arthritis
• Osteomyelitis
• Malignancy (bone tumors, leukemia)
• Slipped capital femoral epiphysis (hip pathology presenting as knee pain)

Non-Emergent Conditions

• Juvenile idiopathic arthritis
• Reactive arthritis
• Osteochondritis dissecans
• Growth plate injury
• Discoid meniscus 5
• Popliteal cyst (Baker's cyst)
• Growing pains (diagnosis of exclusion)

Management Algorithm

1. If signs of infection present (fever, significant swelling, erythema, warmth):

   • Urgent orthopedic consultation
   • Joint aspiration if effusion present
   • Blood cultures and empiric antibiotics if septic arthritis suspected

2. If radiographs show abnormality:

   • Refer to pediatric orthopedics for management based on findings

3. If radiographs negative but symptoms severe or persistent:

   • MRI without contrast
   • Pain management with acetaminophen as first-line medication 4
   • Activity modification and relative rest 4

4. If hip pathology suspected:

   • Include hip examination and imaging in workup
   • Urgent referral if slipped capital femoral epiphysis suspected

Common Pitfalls to Avoid

• Failing to examine the hip in a child with knee pain - hip pathology commonly presents with referred knee pain 1, 2
• Attributing pain to "growing pains" without adequate evaluation to rule out serious conditions
• Overlooking systemic symptoms that might indicate malignancy or infection
• Delaying imaging in a child with severe pain, as timely diagnosis is critical for conditions like septic arthritis or malignancy
• Focusing only on the knee when calf pain is present - consider vascular conditions or compartment syndrome

Remember that in children, severe knee and calf pain without trauma requires thorough evaluation to rule out serious conditions before attributing to more benign causes.