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Meniscal extrusion increases with age: Decade-specific magnetic resonance imaging reference values.

Riccardo Compagnoni1,2, Rossella Ravaglia3, Matteo Parmigiani2,3

  • 1Department of Biomedical, Surgical and Dental Sciences Università degli Studi di Milano Milan Italy.

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|July 14, 2026
PubMed
Summary

Medial meniscal extrusion index (MEI) increases with age in healthy knees, with values rising significantly in older adults. These decade-specific reference values aid in interpreting MRI findings, especially for medial meniscal extrusion.

Keywords:
agingknee MRImeniscal extrusionmeniscal extrusion indexnormative values

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Area of Science:

  • Orthopedic imaging
  • Radiology
  • Biomedical engineering

Background:

  • The medial meniscal extrusion index (MEI) is an MRI-based measurement used to assess meniscal health.
  • Establishing normative values for MEI across different age groups is crucial for accurate interpretation of knee MRI scans.
  • Previous studies have not fully characterized decade-specific MEI values in adults without significant knee pathology.

Purpose of the Study:

  • To establish decade-specific magnetic resonance imaging (MRI)-based reference values for the medial meniscal extrusion index (MEI) in adults without significant structural knee pathology.
  • To assess the association between age and sex with MEI.
  • To test the hypothesis that MEI increases with age without significant sex differences in healthy knees.

Main Methods:

  • Retrospective screening of 500 knee MRI examinations from adults aged 20-69 without significant osteoarthritis or meniscal tears.
  • Measurement of MEI on coronal MRI images.
  • Linear regression analysis to assess the association between age, sex, and MEI.
  • Reporting of decade-specific MEI reference values (mean, SD, mean + 1 SD, mean + 2 SD).

Main Results:

  • MEI showed a positive association with age (p < 0.001), with no significant age × sex interaction.
  • Mean MEI increased from 0.041 in the 20-29 decade to 0.122 in the 60-69 decade.
  • The mean + 1 SD threshold approached or exceeded a 20% MEI cut-off in individuals aged 50-69.

Conclusions:

  • Medial meniscal extrusion index (MEI) progressively increases with age in individuals with structurally normal knees on MRI.
  • No meaningful sex-related differences were observed in MEI.
  • Decade-specific MEI reference intervals can aid in the age-adjusted interpretation of isolated medial meniscal extrusion on MRI, particularly in older adults.