MRI KNEE TUTORIAL

Introduction

This tutorial provides a comprehensive guide on evaluating an MRI examination of the knee, following the approach used by Dr. Omar Awana, an associate professor of radiology. Understanding the distinct compartments of the knee and the evaluation patterns for various structures will enhance your ability to interpret knee MRIs effectively.

Step 1: Review the Sagittal T2 Fat Saturation Images

• Begin with the sagittal T2 fat-saturated images.
• Assess the bone marrow for edema and hyperintensity:
  • Identify the three compartments:
    • Medial femoral and tibial compartment
    • Lateral femoral compartment
    • Patellofemoral compartment
• Look for signs of:
  • Marrow edema (T2 hyperintensity) indicating contusions or degenerative changes.
  • A normal MRI should show no edema or hyperintensity in the marrow.

Step 2: Examine the Coronal Images

• Evaluate the medial and lateral compartments again in the coronal view.
• Assess the articular cartilage:
  • Look for gray intermediate signals between the cortex and cartilage.
  • Check for cartilage defects or hyperintensities indicating potential injuries (partial or full-thickness defects).
• Confirm normal cartilage appearance in both medial and lateral compartments.

Step 3: Analyze the Axial Images

• Focus on the patellofemoral compartment using axial images.
• Assess the patella:
  • Check for contour defects in the patellar cartilage.
  • Look for signs of degeneration or minimal partial thickness defects (e.g., T2 hyperintensity).
• Evaluate the supporting structures such as the medial and lateral patellar retinacula.

Step 4: Assess the Bone Marrow with T1-Weighted Images

• Review T1-weighted images to further evaluate the marrow.
• Confirm normal fatty marrow appearance:
  • Hyperintense marrow should appear brighter than underlying muscle.
  • Look for signs of marrow replacement processes or abnormalities.

Step 5: Evaluate the Menisci

• Start with the medial meniscus:
  • Confirm that the posterior horn is double the size of the anterior horn.
  • Look for any signal within the meniscus that approaches the articular surface on at least two consecutive sequences.
• Move to the lateral meniscus:
  • Check that both horns are equal in size.
  • Assess for similar signs of tears or displacement.
• Look for any signs of a discoid meniscus if the meniscus appears larger than usual.

Step 6: Check the Cruciate Ligaments

• Focus on the anterior cruciate ligament (ACL) and posterior cruciate ligament (PCL):
  • Ensure they are intact and exhibit normal hypo-intense signals.
  • Confirm the ACL runs from the lateral femoral condyle to the medial tibial spine, and the PCL runs from the medial intercondylar notch to the tibia.

Step 7: Review the Extensor Mechanism

• Evaluate the quadriceps tendon:
  • Look for normal striations indicating healthy tendons.
• Assess the patellar tendon:
  • Identify any signs of tendinopathy or patellar tendonitis.

Step 8: Examine Lateral Support Structures

• Assess the medial collateral ligament (MCL):
  • Check for integrity and signs of sprain (grade 1 to 3).
• Review lateral structures:
  • Examine the iliotibial band, fibular collateral ligament, biceps femoris tendon, and popliteus tendon.

Step 9: Final Assessment of Soft Tissues and Muscles

• Look for any signs of effusions, cysts, or abnormalities in the soft tissues.
• Evaluate muscle bulk and check for any signs of edema or atrophy.
• Pay attention to the presence of the Baker's cyst and any related fluid collections.

Conclusion

This step-by-step approach to evaluating knee MRI images focuses on identifying important anatomical structures and potential abnormalities. By following these steps, you can systematically assess an MRI of the knee, ensuring thoroughness and accuracy in your evaluations. Consider using this guide as a reference for future MRIs, and continually practice to enhance your interpretation skills.