What is the recommended imaging protocol for a patient presenting with knee swelling and pain?

Recommended Imaging Protocol for Knee Swelling and Pain

For patients presenting with knee swelling and pain, radiography (X-ray) should be the initial imaging study, followed by MRI if radiographs are normal or show only joint effusion but clinical suspicion for internal derangement remains high. 1, 2

Initial Imaging Approach

Radiography (First-Line)

• Required views:

  • Anteroposterior (AP) view
  • Lateral view
  • Tangential patellar view (skyline/sunrise)
  • Weight-bearing views when possible 1

• Benefits:

  • Quick and cost-effective 3
  • Identifies fractures, osteoarthritis, osteochondral defects, and effusions
  • Helps narrow differential diagnosis and guide subsequent imaging

MRI (Second-Line)

• Indications for MRI:

  • Normal radiographs with persistent symptoms
  • Radiographs showing only joint effusion
  • Suspected internal derangement (meniscal or ligamentous injury)
  • Clinical instability 1, 2

• Benefits:

  • Near 100% sensitivity for fracture detection
  • Excellent for evaluating:
    • Meniscal tears
    • Ligament injuries
    • Bone marrow edema/contusions
    • Cartilage damage
    • Synovitis
    • Soft tissue pathology 1, 2

Special Considerations

CT Scanning

• Indications:

  • Suspected radiographically occult fractures
  • Evaluation of patellofemoral anatomy in chronic subluxation
  • Assessment of trochlear morphology
  • When MRI is contraindicated 1, 2

• Benefits:

  • Superior sensitivity (80-100%) compared to radiographs
  • Excellent visualization of fracture comminution and articular surface involvement 2

Ultrasound

• Indications:
  • Confirmation of suspected effusion
  • Guidance for aspiration
  • Evaluation of popliteal cysts
  • Assessment of medial plicae
  • Monitoring of iliotibial band syndrome 1

Imaging Algorithm Based on Clinical Presentation

1. All patients with knee swelling and pain:

   • Begin with radiographs (AP, lateral, and tangential patellar views)

2. If radiographs are normal or show only effusion:

   • MRI without contrast is recommended as the next step if symptoms persist

3. If radiographs show osteoarthritis or chondrocalcinosis:

   • MRI generally not needed unless symptoms are disproportionate to radiographic findings

4. If radiographs show osteochondritis dissecans, loose bodies, or history of cartilage/meniscal repair:

   • MRI is indicated for further evaluation
   • CT may be considered if MRI is contraindicated or to better visualize bony details

5. If radiographs show signs of prior knee injury:

   • MRI to evaluate for associated soft tissue injuries

Common Pitfalls to Avoid

• Premature MRI: Approximately 20% of patients with chronic knee pain have MRI performed without recent radiographs, which is unnecessary and costly 1

• Overlooking referred pain: Consider hip or lumbar spine radiographs if knee radiographs are unremarkable and clinical suspicion for referred pain exists 1

• Relying solely on radiographs for soft tissue injuries: Radiographs have limited sensitivity for meniscal and ligamentous injuries

• Unnecessary radiation exposure: CT should be reserved for specific indications due to higher radiation exposure compared to radiographs 2

• Overreliance on imaging: Recent evidence suggests that X-ray-based diagnosis of knee osteoarthritis may lead patients to believe surgery is more necessary compared to clinical diagnosis 4

By following this evidence-based imaging protocol, clinicians can efficiently diagnose the cause of knee swelling and pain while avoiding unnecessary tests, reducing costs, and minimizing radiation exposure.