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Phoenix Diagnostic Clinic

Discoid meniscus


Morphologic anomaly described in 1889
– Broad and disc-like appearance rather than semilunar
– Frequent in Asian population 20%; less frequent in whites 0.5%
– 15-35 years; men > women
– More frequent laterally versus medially
Key information:

– MR appearance
– Different structure from the normal meniscus
– Different classification of discoid meniscus

MR diagnosis
Discoid meniscus
– An asymptomatic discoid meniscus does not need surgery
– Patients in MR: symptomatic – surgery

• Is discoid? Lateral or medial?
• Tear or not? Peripheral or not?
• Fixed or mobile meniscus?

MR advantages:
• Visualization of the entire meniscus (difficult to assess during arthroscopy)
• Visualization of horizontal and inferior tears that can be missed by arthroscopy

MR criteria of diagnosis
– normal transverse diameter of lateral meniscus 11-12 mm

Diagnosis criteria:

– 2 adjacent sagittal images (5 mm) that displays equal or nearly equal meniscal heights
– 3 adjacent sagittal images (5 mm) that displays continuity between anterior and posterior horn
– abnormal shape on coronal images (height)


Slice 3 mm

DM structure and clinical impact
– The number and the orientation of the collagen fibers
are responsible for tears and degeneration
Atay OA et al. Am J Sports Med 2007;35:475
– Normal meniscus:
• dense collagen fibers centrally circular oriented
• at the outer surface radially oriented fibers – anchor to joint
– Discoid meniscus:
• lower collagen concentration=degenerated meniscus
• loss of normal orientation
Clinical impact: 38-88% tears in discoid meniscus
Treatment: partial meniscetomy
DM structure and clinical impact
Clinical impact: 38-88% tears in discoid meniscus  Treatment: partial meniscetomy

Discoid meniscus varieties and classification
Watanabe and Takeda. 1974.

CompleteComplete cover
of tibial plateau
IncompleteFarther across
tibial plateau
WrisbergLack of posterior
Hipermobility and
luxation into the
Hall FM. Arthrography of the discoid lateral meniscus.AJR 1977; 168: 75

New classification
Ahn JH et al. “A novel classification of DLM……”. Am J Sports Med; May 13: 2009
– Preoperative exclusively based MRI classification
– More information for surgeons regarding the arthroscopy procedure
– Ikeuchi‘s grading scale and Lysholm‘s scores:
TypeMR findingsTreatment
No shiftNo separation between
meniscus and capsule
Central meniscectomy
separation and displacement
Subtotal meniscectomy and repair

Swift meniscocapsular separation

Other meniscal anomalies

– Hypoplasia of the anterior horn
– Complete absence of meniscus

Anomalous insertion of the medial meniscus (AIMM)

• Insertion of the MM into the ACL (12%)
• Close connection with the presence of discoid MM
• All patients with AIMM have infrapatellar plica
• Problems in differentials: anterior horn tear, ACL tear
Click to enlarge!
Anomalous insertion of the medial meniscus (AIMM)  (Click to enlarge!)

August 26, 2009

Phoenix Diagnostic Clinic, Bucharest

This site is primarily intended for use by qualified medical or sport professionals.
If you are a consumer, you should evaluate the information together with your physician or other qualified healthcare professional.
The information provided here is for educational and informational purposes only and should not be considered as a medical advice.
As medical and sport science is permanently changing, we (authors and publishers) use our best efforts to provide accurate information, but we can not warrant that the information in this article and web site is accurate, complete or up-to-date.
This article reflects the opinions and judgments of it's author and may be further updated.
If you have questions regarding this article, please contact the author.
Information belongs to Phoenix Diagnostic Clinic, Bucharest

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