Discoid meniscus

Discoid meniscus is a rare human

anatomic variant that usually affects the lateral meniscus of the knee. Usually a person with this anomaly has no complaints; however, it may present as pain, swelling, or a snapping sound heard from the affected knee. Strong suggestive findings on magnetic resonance imaging

includes a thickened meniscal body seen on more than two contiguous sagittal slices.

Description

The Watanabe classification of discoid lateral meniscus is: (A) Incomplete, (B) Complete, and (C) Wrisberg-ligament variant^[1]

Normally, the

orthopedic classification of discoid menisci includes: complete, incomplete or Wrisberg-ligament types as depicted here. Coverage of the lateral tibial plateau determines the designation of complete or incomplete. The Wrisberg-ligament type has an abnormal posterior attachment by attaching to part of the posterior cruciate ligament

.

Symptoms

Symptom is usually pain in the knee. And when the knee is bent or stretched it makes the sound of bouncing bones.

Diagnosis

The transverse diameter of a normal meniscus is approximately 10 to 11 mm; therefore a normal meniscus body will be visible on only 2 slices of a MR with 4-5-mm sagittal slices. A discoid meniscus should be considered if more than two contiguous body segments are present. However, this method may lead to a false negative when evaluating people with the Wrisberg variant of discoid meniscus since it maintains a narrow crescent shape. Coronal and radial images of the meniscus are useful to demonstrate the extension of the aberrant meniscus into the joint as seen here. On coronal images, it is diagnosed when the horizontal measurement between the free margin and the periphery of the body is more than 1.4 cm.^[2] Rarely, X-ray may show lateral joint space widening, squaring of the lateral condyle, cupping of the lateral tibial plateau and hypoplasia of the lateral tibial spine that suggest discoid meniscus.

Treatment

In a patient complaining of acute onset knee pain, an

MRI would be necessary to visualize the discoid meniscus. If the patient is asymptomatic and does not complain of significant locking sensation in the knee or pain, treatment is conservative and consists of stretching and strengthening exercises for the quadriceps and hamstring muscles. “In cases where there is significant disability, surgical excision may be needed. When the discoid meniscus is severely damaged, total excision of the meniscus may be necessary. In most cases where the meniscus is still generally intact, a partial excision to preserve the cushioning function may be sufficient.”^[3]^{[medical citation needed}

]

References

^ Neuschwander DC, Dres D, Finney TP:"Lateral meniscal variant with absence of the posterior coronary ligament". Journal of Bone and Joint Surgery American, 1992;74: 1186-1190.
^ Weissleder, et al.:"Primer of Diagnostic Imaging", Mosby editions, 2003
^ "Orthoseek | Orthopedic Topics | Discoid Meniscus".

External links

Discoid Meniscus in eMedicine

[1] Neuschwander DC, Dres D, Finney TP:"Lateral meniscal variant with absence of the posterior coronary ligament". Journal of Bone and Joint Surgery American, 1992;74: 1186-1190.

[2] Weissleder, et al.:"Primer of Diagnostic Imaging", Mosby editions, 2003

[3] "Orthoseek | Orthopedic Topics | Discoid Meniscus".

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