Scrutinizing the cut-off for “pathological” meniscal body extrusion on knee MRI

Research output: Contribution to journalArticle


Objectives: Medial meniscal body extrusion ≥ 3 mm on MRI is often considered “pathologic.” The aims of this study were to (1) assess the adequacy of 3 mm as cut-off for “pathological” extrusion and (2) find an optimal cut-off for meniscal extrusion cross-sectionally associated with radiographic knee osteoarthritis, bone marrow lesions (BMLs), and cartilage damage. Methods: Nine hundred fifty-eight persons, aged 50–90 years from Framingham, MA, USA, had readable 1.5 T MRI scans of the right knee for meniscal body extrusion (measured in mm). BMLs and cartilage damage were read using the whole organ magnetic resonance imaging score (WORMS). Knee X-rays were read according to the Kellgren and Lawrence (KL) scale. We evaluated the performance of the 3-mm cut-off with respect to the three outcomes and estimated a new cut-off maximizing the sum of sensitivity and specificity. Results: The study persons had mean age of 62.2 years, 57.0% were women and the mean body mass index was 28.5 kg/m2. Knees with radiographic osteoarthritis, BMLs, and cartilage damage had overall more meniscal extrusion than knees without. The 3-mm cut-off had moderate sensitivity and low specificity for all three outcomes (sensitivity between 0.68 [95% CI 0.63–0.73] and 0.81 [0.73–0.87], specificity between 0.49 [0.45–0.52] and 0.54 [0.49–0.58]). Using 4 mm maximized the sum of sensitivity and specificity and improved the percentage of correctly classified subjects (from between 54 and 61% to between 64 and 79%). Conclusions: The 4-mm cut-off may be used as an alternative cut-off for denoting pathological meniscal extrusion. Key Points: • Medial meniscal body extrusion is strongly associated with osteoarthritis. • The 3-mm cut-off for medial meniscal body extrusion has high sensitivity but low specificity with respect to bone marrow lesions, cartilage damage, and radiographic osteoarthritis. • The 4-mm cut-off maximizes the sensitivity and specificity with respect to all three osteoarthritis features.


External organisations
  • Boston University
  • Friedrich-Alexander University Erlangen-Nürnberg
Research areas and keywords

Subject classification (UKÄ) – MANDATORY

  • Radiology, Nuclear Medicine and Medical Imaging
  • Orthopedics


  • Cartilage, Knee joint, Magnetic resonance imaging, Meniscus, Osteoarthritis
Original languageEnglish
Pages (from-to)2616-2623
JournalEuropean Radiology
Issue number5
Early online date2019 Jan 10
Publication statusPublished - 2019
Publication categoryResearch