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

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.