Discoid Meniscus

Question 1

definition

Answer 1

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”

Question 2

Epidemiology

Answer 2

• incidence
  
  • present in 3-5% of population
• location
  
  • usually lateral meniscus involved
  • 25% bilateral

Question 3

Classification

Answer 3

• Watanabe
  
  • Wrisberg Ligament type:
    
    • Lateral meniscotibial ligaments are absent
  • Complete type:
    
    • Discoid meniscus covers tibial plateau
    • Lateral ligaments are in tact, therefore stable
  • Incomplete type:
    
    • Similar to complete, covers less of the plateau

Question 4

Presentation

Answer 4

• often presents as a “snapping knee”
• Usually presents around age 8
• Snapping, shift of tibial plateau
• Visible/palpable mass, prominent anterolaterally with flexion, reduces with extension

May become associated with osteochondritis dissicans

• Symptoms
  
  • pain, clicking, mechanical locking
  • often becomes symptomatic in adolescence
• Physical exam
  
  • mechanical symptoms most pronounced in extension

Question 5

Imaging

Answer 5

• Radiographs
  
  • recommended views
    
    • AP and lateral of knee
  • findings
    
    • widened joint 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

Question 6

Treatment

Answer 6

• 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)