Meniscal extrusion

Measured from the outer meniscal edge to proxiaml tibial margin
More than 3 mm is abnormal
Considered as normal in anterior horn of the LM

Reference:
Michael G. Fox. MR Imaging of the Meniscus: Review, Current Trends, and Clinical Implications. RCNA Volume 45, Issue 6, Pages 931-1068 (November 2007)