Paeds Elective iSAWE 15

Question

A 7 year old girl has a painless clunk in her knee with loss of full extension.

Paeds Elective iSAWE 15, coronal MRI of the knee
Coronal MRI of the knee. Image by Hellerhoff, Wikimedia Commons, CC BY-SA 3.0.
  1. What does the MRI show?
  2. Describe the classification.
  3. Outline management.

Answer

MRI

  • Thickened lateral meniscus covering most of the lateral tibial plateau
  • Discoid lateral meniscus
  • Continuity of the meniscus across three or more consecutive 5 mm sagittal slices (bow tie sign)
  • Bilateral in up to 20%

Watanabe classification

TypeDescription
IComplete, covers the whole plateau, stable
IIIncomplete, stable
IIIWrisberg variant, no posterior tibial attachment, unstable
  • Ahn classification describes the direction of meniscal shift on MRI

Management

  • Asymptomatic discoid menisci are observed
  • Arthroscopic saucerisation for symptomatic tears, leaving a 6 to 8 mm rim
  • Repair the peripheral rim if unstable
  • Avoid total meniscectomy, which leads to early lateral compartment arthritis
  • Osteochondritis dissecans of the lateral femoral condyle can coexist

Related pages

Author Contributions

Orthofracs team

Reviewed by Professor Phong Tran, Head of Orthopaedic Surgery, Western Health. Last updated 10 October 2026.