• Abnormal development of the meniscus leads to a hypertrophic and discoid shaped meniscus
    • discoid meniscus is larger than usual
    • also referred to as "popping knee syndrome"
  • Epidemiology
    • incidence
      • present in 3-5% of population
    • location
      • usually lateral meniscus involved
      • 25% bilateral
Watanabe Classification
Type I  • Incomplete

Type II  • Complete

Type III  • Wrisberg (lack of posterior meniscotibial attachment to tibia
  • Symptoms
    • pain, clicking, mechanical locking 
    • often becomes symptomatic in adolescence
  • Physical exam
    • mechanical symptoms most pronounced in extension
  • Radiographs
    • recommended views
      • AP and lateral of knee
    • findings    
      • widened joint space due to widened cartilage space (up to 11mm)
      • squaring of lateral condyle with cupping of lateral tibial plateau
      • hypoplastic lateral intercondylar spine
  • MRI
    • indications
      • study of choice for suspected symptomatic meniscal pathology
    • findings
      • diagnosis can be made with 3 or more 5mm sagittal images with meniscal continuity  ("bow-tie sign")
      • sagittal MRI will show abnormally thick and flat meniscus 
      • coronal MRI will show thick and flat meniscal tissue extending across entire lateral compartment 
  • Nonoperative
    • observation
      • indications
        • asymptomatic discoid meniscus without tears  
  • Operative
    • partial meniscectomy and saucerization    
      • indications
        • pain and mechanical symptoms
        • meniscal tear or meniscal detachment
      • technique
        • obtain anatomic looking meniscus with debridement 
        • repair meniscus if detached (Wrisberg variant)

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Questions (2)

(OBQ07.129) An 11-year-old soccer player presents with a 6 month history of snapping and discomfort along the lateral joint line of the knee. Examination shows a 10 degree loss of active extension. An AP radiographs is shown in Figure A. Sequential sagittal MRI images of the lateral compartment of the knee are shown in Figure B. What is the most appropriate course of action? Review Topic


Physical therapy with a focus on concentric knee strengthening




Non-weightbearing for 6 weeks




Arthroscopic saucerization of the lateral meniscus and/or meniscal repair




Open lateral meniscectomy




Arthroscopic microfracture treatment of the defect on the lateral femoral condyle



Select Answer to see Preferred Response


The history, radiographs, and MRI are consistent with a diagnosis of discoid lateral meniscus. Surgery for discoid menisci is indicated for persistent pain or motion loss in order to prevent further meniscal damage.

The classification system most widely used for discoid meniscus is that of Watanabe et al (Illustration A), who described three types of discoid lateral menisci based on arthroscopic appearance. In this classification, discoid menisci with normal peripheral attachments are either type I (complete) or type II (incomplete). Type III discoid menisci, the so-called Wrisberg ligament type, are described as lacking posterior capsular attachments with the exception of the posterior meniscofemoral ligament, thus producing the classic “snapping knee” syndrome. Complete meniscectomy of discoid lateral meniscus is avoided due to the development of early degenerative changes. Most authors now recommend repair of a detached posterior or peripheral attachment, with saucerization of the discoid morphology depending on the underlying meniscal shape and presence of a meniscal tear. Klingele et al found that 28.1% of patients in their series of discoid menisci had peripheral rim instability, and instability was more common in patients with a complete discoid morphology and in younger patients.

A. Complete discoid lateral meniscus (Type I); B. Incomplete discoid; C. Wrisberg variant which lacks capsular attachments (Type III) and may be either complete or incomplete.

Incorrect Responses:
1. Strengthening in physical therapy will not address the mechanical symptoms or the lack of extension.
2. Non-weightbearing will not lead to healing of a unstable or torn discoid meniscus.
4. Open lateral meniscectomy is largely historical and should be avoided due to the development of early degenerative changes.
5. No chondral lesion is seen.


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Question COMMENTS (6)

(OBQ05.166) An 8-year-old boy was playing at school and took a direct blow to his knee causing pain and swelling. His pediatrician ordered an MRI which is shown in Figure A. The patient was referred to your office for a consultation. He denies any past history of pain, clicking, or locking. His knee exam is unremarkable. Radiographs of the knee in your office are normal. What course of action will you recommend? Review Topic


Surgical debridement and repair




Ligamentous reconstruction




Casting in 45 degrees of flexion




Knee immobilizer and non weight bearing for 6 weeks







Select Answer to see Preferred Response


The clinical presentation and MRI are consistent with an asymptomatic lateral discoid meniscus without evidence of tear. No intervention is indicated for asymptomatic discoid menisci. When these are symptomatic, surgical saucerization and possible repair are indicated. Klingele et al reviewed a series of 112 surgically treated patients and found that 28% were unstable, and 69% had an associated meniscus tear. Ogut et al reported their follow-up on 11 surgically treated discoid mensici, and had 82% excellent results and 18% good results. Davidson et al reported their results in 32 children who underwent partial, complete or no excision of the discoid meniscus, with 16 excellent, 10 good, 6 fair and 4 poor results.

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