Knee MRI (Approach to MSK MRI Series)

Introduction

This tutorial provides a systematic approach to reading knee MRI scans, as outlined in Dr. Walter Mak's video. It focuses on the key sequences to review, the relevant anatomy, and basic pathologies to recognize. This guide is particularly useful for radiology residents and healthcare professionals looking to enhance their skills in musculoskeletal imaging.

Step 1: Familiarize with Routine Sequences

Understanding the common MRI sequences is crucial for effective analysis. The main sequences to know include:

• Coronal Proton Density (PD)
• Axial T2 Fat Saturated
• Sagittal PD and PD Fat Saturated

Practical Tips

• Always have multiple planes displayed simultaneously. This helps in cross-referencing structures across different views and increases diagnostic confidence.

Step 2: Systematic Approach to Knee Structures

When reviewing a knee MRI, focus on six categories:

1. Menisci
2. Cruciate ligaments
3. Collateral ligaments
4. Extension mechanism
5. Articular cartilage
6. Miscellaneous findings

Practical Tips

• Use a checklist to ensure you address each category systematically.

Step 3: Assess Menisci

Menisci act as shock absorbers in the knee. Key points to consider:

• Use sagittal views to examine anterior and posterior horns.
• Use coronal views for assessing the body of the meniscus.
• Look at the axial sequence for a clear view of the anterior and posterior horns.

Diagnosing Meniscal Tears

• Identify linear surface signals extending to articular surfaces on two images, or note abnormal morphology on one image.
• Distinguish between:
  • Parallel tears (longitudinal)
  • Perpendicular tears (radial)

Common Pitfalls

• Mistaking normal signals (e.g., from the popliteus tendon) for tears.

Step 4: Evaluate Cruciate Ligaments

Assess the Anterior Cruciate Ligament (ACL) and Posterior Cruciate Ligament (PCL):

• Use sagittal views for alignment; look for normal orientation relative to the intercondylar notch.
• The axial view is ideal for assessing femoral attachments.

Key Observations

• Increased signal in the ACL is normal; however, loss of its normal contour may indicate a tear.
• For PCL, homogeneous low signal across all sequences indicates normal integrity.

Step 5: Review Collateral Ligaments

Start with the medial side:

• Assess the Medial Collateral Ligament (MCL) using coronal and axial views.
• Look for signs of sprains (thickening, heterogeneity) or tears (defects).

Lateral Side Assessment

• Identify the Lateral Collateral Ligament (LCL) and associated structures (iliotibial band, biceps femoris).

Step 6: Analyze the Extension Mechanism

Examine the quadriceps and patellar tendons:

• Look for striated appearances indicating normal structure.
• Identify any thickening or defects.

Practical Tips

• Use sagittal images to assess the patellar tendon and check for artifacts that may confuse the analysis.

Step 7: Assess Articular Cartilage

Cartilage evaluation is vital for diagnosing joint pathologies. Follow these steps:

• Use sagittal and coronal views to assess the cartilage quality and thickness.
• Apply the Outerbridge classification system to categorize cartilage damage:
  • Grade 1: Mild softening
  • Grade 2: Moderate thinning
  • Grade 3: Severe thinning with defects
  • Grade 4: Full-thickness loss with subchondral changes

Important Note

Understand the normal appearance of cartilage varies and includes a gradient effect.

Step 8: Miscellaneous Findings

Finally, scan for any incidental or systemic findings:

• Look for Baker’s cysts by assessing the interface between muscle and joint structures.
• Identify any bone marrow edema or lesions that may require further investigation.

Conclusion

This systematic approach to knee MRI reading emphasizes the importance of knowing the anatomy, understanding the sequences, and being vigilant for both normal and abnormal findings. Regular practice and familiarization with normal MRI appearances will enhance your diagnostic skills. Consider reviewing additional resources or training to further refine your expertise in musculoskeletal imaging.