Discoid meniscus - Phoenix Diagnostic Clinic

– 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

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

Questions:
• 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
capsule
– Discoid meniscus:
• lower collagen concentration=degenerated meniscus
• loss of normal orientation
Clinical impact: 38-88% tears in discoid meniscus
Treatment: partial meniscetomy

Clinical impact: 38-88% tears in discoid meniscus Treatment: partial meniscetomy

Discoid meniscus varieties and classification
Watanabe and Takeda. 1974.

Type	Physiology/ pathology	Clincal symptoms
Complete	Complete cover of tibial plateau	Pain/meniscal degenration/tear
Incomplete	Farther across tibial plateau	Pain/meniscal degeneration/tear
Wrisberg	Lack of posterior attachment	Hipermobility and luxation into the joint

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:

Type	MR findings	Treatment
No shift	No separation between meniscus and capsule	Central meniscectomy
Shift Antero-central	Meniscocapsular separation and displacement	Subtotal meniscectomy and repair
Postero-lateral
Central

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

Anomalous insertion of the medial meniscus (AIMM) (Click to enlarge!)

August 26, 2009

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Information belongs to Phoenix Diagnostic Clinic, Bucharest

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