Lateral Meniscus

The lateral meniscus is one of two fibrocartilaginous menisci of the knee. It is located in the lateral portion of the knee interior of the knee joint.

Lateral Meniscus: Anatomy

The lateral meniscus is seen as a symmetric bow tie in the sagittal plane on at least one or two sections before it divides into two asymmetric triangles near the midline. It may have a relatively steep concavity in the posterior horn, simulating a bucket handle tear. Its capsular attachments are much looser than those on the medial side, and in the sagittal projection the posterior body and anterior body are symmetric, unlike the medial meniscus.¹

The anterior horn of the lateral meniscus is quite variable in its height and overall length. Hypoplasia of this horn is not uncommon, and volume averaging of the anterolateral meniscal recess, synovial interdigitation at its interface with the anterolateral horn and the interface with the transverse ligament of Winslow may create the false impression of a horizontal meniscal tear. Anterolateral horizontal tears are rare as isolated lesions. Agenesis of a meniscus is most common in the posterolateral horn and body. The lateral meniscus is C-shaped and therefore has a tighter radius of curvature than the medial meniscus.¹

Lateral Meniscus: Pearls

• Tight C-shape
• Posterior and anterior horn body regions are symmetric in size
• Abuts the popliteus tendon posteriorly with superior and inferior fascicles forming the roof and floor of the popliteus hiatus
• Separated from and loosely attached to the lateral collateral ligament
• The anterior horn may be hypoplastic, demonstrate interdigitation with the anterior capsule, may be short in height or extremely thin; but meniscal agenesis is more common in the posterolateral horn
• Discoid meniscus and meniscal cyst more common laterally¹

Lateral Meniscus: References

1. Pomeranz SJ. Gamuts & Pearls in MRI & Orthopedics. Ohio, The Merten Company, 1997.

Lateral Meniscus: Example

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This is a 20-year-old college athlete who plays soccer, competing for a national championship in his senior year. He has anterolateral knee pain. You are shown two coronal PD SPIR images (image 1 and image 2), a sagittal T2 SPIR or fat-suppression image (image 3), and a sagittal T1 (image 4). How would you describe this tear (arrows)? Would you let him play?

Image 1 - Coronal PD SPIR                                    Image 2 - Coronal PD SPIR 

Image 3 - Sagittal T2 SPIR                                    Image 4 - Sagittal T1

The tear is a horizontal cleavage tear (yellow arrows) involving the anterior horn of the lateral meniscus. While most horizontal or cleavage tears are chronic and degenerative in older adults, they do occur traumatically. The tear (higher signal) is like the turkey on a sandwich with the meniscus (lower signal) sitting on either side like the pieces of bread.

Because there is no clear articular surface communication on any of the sequences, one might describe this as a “closed” traumatic tear, predominantly horizontal, of at least 2 cm in length. One should carefully point out that the tear has precipitated active inflammation which manifests as swelling just anterior to the meniscal pathology, sagittal image 3 and 4 (anterior oblique green arrow).

Initial reaction to a tear that is so conspicuous in a young patient is to sit the patient down. However, given the fact that this patient is a senior in college, his college career is coming to an end, there is an important game coming forth, and the risk of splitting this meniscus into two or exacerbating the horizontal tear is very low in the absence of discoid meniscus, this patient was allowed to play. However, he did receive a steroid injection to diminish his pain. Another medication that is used in performance athletes, especially professional athletes in situations such as this, is Toradol. Finally, “closed” cleavage tears, as suggested above, are particularly common in discoid meniscus. These are usually symptomatic.

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