What is the meniscal root?
- The meniscal root is a small portion of the meniscus that attaches and anchors the anterior and posterior horns of the meniscus to the intercondylar fossa or eminence of the tibia.
- Its usually the posterior root of the meniscus that is torn and medial more than lateral meniscus.
Where is it? It is the component of the meniscus between its tibial attachment and the point on the tibial margin where cartilage ends. Rough guide is where the bone of the tibial plateau elevates ( green arrow below)
Image Above: Red arrows demonstrate the medial meniscus posterior root. It commences just lateral to the apex of the medial tibial plateau ( yellow arrow). Green arrow and dashed green line demonstrate where cartilage of medial tibial plateau ceases which is another marker for the beginning of the meniscal root.
Image above: Coronal scans, posterior to anterior. Yellow arrow in B and C demonstrates attachment of medial meniscus root to tibia anterior to PCL ( green arrow) tibial attachment. Note in Image B blue arrow demonstrates posterior root attachment of lateral meniscus.
Sagittal Images above: Yellow arrow demonstrates medial meniscus posterior horn and meniscal root ( yellow arrow). Note how meniscal root extends to the level of the PCL lying anterior to PCL ( green arrow).
Why are these tears important? A tear of the meniscal root results in significant dysfunction of the meniscus because
- The meniscal root anchors the meniscus and prevents its being extruded.
- This enables the meniscus to generate hoop stress which transfers load from the femur to the tibia without damage to underlying cartilage.
- The effect of a meniscal root tear is equivalent to having a total meniscectomy in terms of function and increases risk of damage to cartilage.
What do these tears look like?
- Tears are best seen on the coronal images and then confirmed on the sagittal scans
- The root of the posterior horn medial meniscus attaches immediately anterior to the PCL. If its absent indicates a tear. On the sagittal scan you should see the posterior horn on every sagittal image until the PCL. If you dont see in front of the PCL, there is a tear.
- There should be no fluid between the PCL and the meniscal root on the coronal scans.
Image Above: Image D yellow arrow PCL attachment. As you move anteriorly ( Image D>A), there is no normal meniscus in front of the PCL ( see normal images at beginning of post). Red Arrow posterior horn “Axe Murderer” Tear
Above same patient as coronal images: Images B, C and D demonstrate torn posterior horn and root. Note in Image D yellow arrow demonstrates no normal meniscal root in front of PCL ( refer to normal images earlier part of post).
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