What diagnostic tests should be run on a 14-year-old female presenting with knee pain?

Diagnostic Tests for a 14-Year-Old Female with Knee Pain

Plain radiographs (X-rays) should be the initial imaging test for a 14-year-old female presenting with knee pain, including anteroposterior, lateral, and patellofemoral views. 1

Initial Diagnostic Approach

First-Line Imaging

• Plain radiographs (X-rays) should include:
  • Anteroposterior (AP) view
  • Lateral view (with knee at 25-30 degrees flexion)
  • Patellofemoral (tangential patellar) view 2, 1

When to Order Advanced Imaging

If radiographs are normal or show only joint effusion but clinical symptoms persist, proceed to:

• MRI without contrast: This is the preferred second-line imaging for adolescents with persistent knee pain 2, 1
  • MRI is superior for evaluating:
    • Soft tissue injuries (menisci, ligaments)
    • Bone marrow edema
    • Osteochondritis dissecans (OCD) lesions
    • Cartilage abnormalities
    • Synovitis

Common Causes of Knee Pain in Adolescent Females

When evaluating a 14-year-old female with knee pain, consider these common conditions:

1. Patellofemoral pain syndrome (most common cause in adolescent females) 3, 4

   • MRI may show patellar tracking abnormalities

2. Patellar subluxation/dislocation 1, 3

   • MRI can identify bone marrow edema in classic locations

3. Osteochondritis dissecans 2, 5

   • May require MRI for diagnosis as radiographs are often initially normal

4. Apophysitis (Osgood-Schlatter or Sinding-Larsen-Johansson syndrome) 4

   • Often visible on radiographs

5. Referred pain from hip pathology 2, 3

   • Consider hip radiographs if knee imaging is normal but symptoms persist

Special Considerations

• Avoid premature MRI ordering: Approximately 20% of patients with chronic knee pain have MRIs without recent radiographs, which is unnecessary 2

• Clinical decision rules: Consider the patient's ability to bear weight and take four steps, which could reduce unnecessary radiographs by up to 53% without missing fractures 1

• Ultrasound: May be useful in specific situations to evaluate:

  • Joint effusion
  • Popliteal cysts
  • Medial plicae
  • Tendinopathy 2

• CT scans: Generally not indicated as initial imaging for adolescent knee pain unless complex fracture evaluation is needed 1, 6

Red Flags Requiring Urgent Evaluation

• Inability to bear weight
• Significant joint effusion
• Fever with knee pain (possible septic arthritis)
• Gross deformity
• History of significant trauma 1, 7

Clinical Pearls

• Teenage girls are more likely to have patellar tracking problems such as patellar subluxation and patellofemoral pain syndrome 3
• Osteochondritis dissecans lesions may not be visible on initial radiographs but will be apparent on MRI 5
• Always consider referred pain from hip pathology, such as slipped capital femoral epiphysis, which can present as knee pain in adolescents 3

By following this systematic approach to diagnostic testing, you can efficiently identify the cause of knee pain in a 14-year-old female while avoiding unnecessary imaging studies.