Root Tear

In the case of a meniscus, a root tear extends from the anterior or posterior root attachment to the central tibial plateau.⁶

Root Tear: Injury

Tears of the meniscal root, or root ligament attachment, are typically radial-type tears that can involve both the posterior or anterior roots. Because the meniscal root is the anchor point for the meniscus, a complete tear of the meniscal root will result in shifting or displacement of the horn and/or body; on imaging one may see the meniscal body displaced into the femorotibial gutter. Posterior root tears are more common than anterior root tears. Lateral meniscus posterior root tears are often seen in conjunction with ACL tears.

Root Tear: Pearls

Root tears are a pitfall by virtue of the fact that they are easily missed because they are so close to the inner aspect of the meniscal root
Best seen in the coronal plane with thin sections
A root tear can be simulated by enlargement of the anterolateral meniscosynovial recess with associated anterolateral meniscal hypoplasia
Enlarged anterolateral root meniscosynovial recesses can simulate meniscal cysts⁵

Root Tear: Pathology

Root tears can result from numerous sources, but are typically chronic.⁴

Root Tear: MRI

T2 or PD SPIR (coronal) weighted sequences are prefered.

With the posterior root, medial root tears can be visualized more easily than lateral root tears.

Medial posterior root tears display:¹

On sagittal images: shortening or absence of the root (“ghosting”)
On coronal T2 images: vertical fluid cleft

Posterior root radial tears:

On lateral meniscus, may be a similar appearance to radial tears in other locations

Root tears in general:

Sagittal imaging could result in meniscal ghost sign⁶
Coronal images may have truncation sign²
Coronal plane may feature meniscal extrusion of posterior horn and body²

Root Tear: Associations

In the lateral meniscus, ACL tears display association with root tears of the posterior horn.⁶

Root Tear: Treatment

Meniscal root tears tend to be unstable given the lack of anchor mechanism for the root and body remnants. If features of instability are present, surgical intervention may be warranted; it may either be repaired or addressed through meniscectomy.⁵

Root Tear: References

De Smet AA. How I diagnose meniscal tears on knee MRI. AJR Am J Roentgenol. 2012;199 (3): 481-99.
Choi SH, Bae S, Ji SK et-al. The MRI findings of meniscal root tear of the medial meniscus: emphasis on coronal, sagittal and axial images. Knee Surg Sports Traumatol Arthrosc. 2012;20 (10): 2098-2103.
Pagnani M, Cooper D, Warren R. Arthroscopy: The Journal of Arthroscopic & Related Surgery. 1991;7 (3)
Papalia R, Vasta S, Franceschi F et-al. Meniscal root tears: from basic science to ultimate surgery. Br. Med. Bull. 2013;106 (1): 91-115.
Pomeranz SJ. Gamuts & Pearls in MRI & Orthopedics. Ohio, The Merten Company, 1997.
Weerakkody Y., et-al. Meniscal Root Tear: Radiopaedia (sourced 10Jan2018): https://radiopaedia.org/articles/meniscal-root-tear

Root Tear: Example

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On coronal images, a root tear will appear similar to a radial tear elsewhere in the meniscus, with a "gap" present at the root. Sagittal images demonstrate "ghost meniscus" where the meniscus will be invisible scrolling through the images where the tear occurs. For a root tear, the meniscus will disappear 1-2 slices prior to visualizing the cruciate ligaments.

Image 1 (arrow) shows a vertical linear signal at the medial posterior root indicating a radial root tear. This is similar in appearance to other radial tears, but just happens to be located at the root. Consecutive sagittal proton density fat suppressed images (images 2-5) demonstrate root tear of the medial meniscus. The arrow in image 4 delineates the space where the meniscal root should be, however it is not present ("ghost meniscus"). On image 5, the PCL is visible, with no indication of root substance in the adjacent space.