Is an MRI with or without contrast (Magnetic Resonance Imaging) preferred for evaluating a knee injury?

MRI Without IV Contrast is Preferred for Knee Injury Evaluation

MRI without IV contrast is the preferred imaging modality for evaluating knee injuries as it provides superior contrast resolution and multiplanar imaging capability for accurately assessing soft tissue injuries, bone marrow contusions, and occult fractures. 1

Initial Imaging Approach

• Plain radiographs should be obtained first to rule out fractures before proceeding to advanced imaging 2, 1
• For patients with acute knee trauma, radiographs are indicated when any Ottawa knee rule criteria are present, including:
  • Age >55 years
  • Focal tenderness at patella or fibular head
  • Inability to bear weight for 4 steps immediately after injury
  • Inability to flex knee to 90 degrees 3
• A minimum of two radiographic views (anteroposterior and lateral) should be obtained, with additional patellofemoral view for suspected patellar fractures or subluxation 2

When to Use MRI Without Contrast

• MRI without contrast should be the next imaging study after negative radiographs when internal derangement is suspected 2, 1
• MRI without contrast is highly accurate for evaluating:
  • Meniscal tears (accuracy of 87.5% for medial meniscus and 90% for lateral meniscus) 4
  • Ligamentous injuries (accuracy of 90% for ACL and 95% for PCL) 4
  • Bone marrow contusions and occult fractures 2, 1
  • Articular cartilage damage 1

Why MRI Without Contrast is Superior to MRI With Contrast

• The American College of Radiology recommends avoiding MRI with contrast for routine meniscal or ligamentous injuries as it provides no additional diagnostic value over non-contrast MRI 1
• MRI without contrast accurately depicts joint effusions and synovitis 1
• MRI of the knee should be examined in three orthogonal imaging planes with both T2-weighted fluid-sensitive and T1-weighted images 5

Special Considerations

• For tibial plateau fractures identified on radiographs, MRI without contrast is the next best imaging modality to evaluate for additional radiographically occult fractures and internal derangements 2
• In cases of significant trauma or suspected knee dislocation, vascular assessment may be necessary due to risk of popliteal artery injury 1
• CT is primarily useful for evaluating complex fractures, especially tibial plateau fractures, but is not routinely used as the initial imaging study for knee trauma 2, 1

Clinical Pearls and Pitfalls

• Be aware that meniscal tears are often incidental findings in older patients and may not correlate with symptoms 1
• MRI can alter treatment decisions in approximately 21% of knee injury cases, particularly for meniscal and chondral pathology 6
• MRI has high sensitivity (98.1%) for detecting ACL injuries, making it an excellent screening tool before proceeding to therapeutic arthroscopy 7
• The basic MRI protocol should include evaluation of ligamentous structures, cartilage, bony structures, bone marrow, soft tissues, bursae, and alignment 5

When Other Imaging Modalities Are Indicated

• MR arthrography is not routinely used for initial evaluation of acute knee trauma or suspected meniscal/ligamentous injuries 1
• CT arthrography may be considered as an alternative to MRI in specific cases where menisci and articular cartilage need evaluation but MRI is contraindicated 1
• For suspected knee dislocation, MRA may be performed simultaneously with MRI for evaluation of internal derangement and vascular injuries 2