Discoid meniscus

Discoid menisci are those that have a body that is too wide, usually affecting the lateral meniscus. They are incidentally found in 3-5% of knee MRI examinations.

Discoid menisci condition is congenital, frequently bilateral (up to 50%) and has been reported in twins, although no genetic locus has been identified 2. There is no gender predilection, although it may have a higher incidence in Japan 2.

Although frequently asymptomatic, it is prone to cystic degeneration with subsequent tears. Clinical presentation is therefore with pain, locking or a 'clunk'.

Classification

Classification is based on the degree of peripheral attachments to the tibia plateau, and the shape of the meniscus itself:

  • complete vs. incomplete
  • stable vs. unstable
    • stable: normal peripheral attachments with an intact posterior meniscofemoral ligament
    • unstable (also known as a Wrisberg variant): lack or tear of a posterior meniscocapsular (in particular meniscopopliteal) ligaments with an attachment only from the meniscofemoral ligament of Wrisberg 4.
  • anterior or posterior mega horn
Plain radiograph

Radiographs may well suggest the diagnosis with the widening of the lateral joint space and cupping of the lateral tibial plateau, which is normally flat or even slightly convex. Additionally, there may be associated hypoplasia of the lateral tibial spine.

MRI

A discoid meniscus is seen as an abnormally wide body. Usually, the body of the lateral meniscus is only seen on two adjacent sagittal slices. A discoid meniscus can be diagnosed if it is seen on three or more standard sagittal images (the opposite of the absent bow tie sign).

It is also evident on coronal images.

Ideally, the meniscus is preserved with conservative management. If this is unsuccessful, then partial or total resection may be carried out. This invariably leads to some advanced degenerative change.

Complications
  • meniscal tears
  • early bony degenerative change
  • into substance degeneration

Lower limb anatomy
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Article Information

rID: 1226
Section: Anatomy
Tags: knee, variant
Synonyms or Alternate Spellings:
  • Discoid menisci

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