(Fig 1-B.28) Indirect signs of root tears -1

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MM Extrusion:

• MM extrusion refers to the displacement of the midbody segment of the medial meniscus by 3 mm or more beyond the tibial plateau cartilage, as visualized on a coronal image.
• It's significantly more likely to occur in knees with a posterior root tear, but can also be seen in cases of large radial meniscus tears, osteoarthritis, and lower extremity malalignment (e.g., knee varus).

Posterior Shiny-Corner Sign:

• This sign involves subcortical bone marrow edema-like signal intensity deep to the root anchor in the posteromedial tibial plateau, with a sensitivity of approximately 62%.
• It's a useful diagnostic tool, especially when performing an early-phase MRI examination following the onset of a medial meniscus posterior root tear (MMPRT).

Subchondral Insufficiency (Stress) Fracture:

• These fractures typically occur at the mid-medial femoral condyle and can appear as a curvilinear subchondral infraction line or a hemispheric subchondral sclerotic focus.
• There are two key components: a) A hypointense line in the subarticular marrow, often irregular or discontinuous, parallel to the subchondral bone plate. b) An area of low signal intensity immediately below, creating a thickened subchondral bone plate appearance. This includes a combination of fracture with callus, granulation tissue, and secondary osteonecrosis between the fracture line and the articular surface.

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