Abstract
ObjectivesMedial 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.MethodsNine 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.ResultsThe 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%).ConclusionsThe 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.
Highlights
The term meniscal extrusion is often used when the peripheral border of the meniscus is substantially located outside the knee joint margin
The Kellgren and Lawrence (KL) grading system is most commonly used for assessing severity of osteoarthritic disease in the whole knee joint, and we made no specific discrimination for the medial compartment
The intra-reader intraclass correlation coefficient (ICC) for the primary reader was 0.91, and the inter-reader ICC was 0.73
Summary
The term meniscal extrusion is often used when the peripheral border of the meniscus is substantially located outside the knee joint margin. Certain semi-quantitative magnetic resonance imaging (MRI) OA scoring systems use 2 mm as the recommended starting point to denote the presence of meniscal body extrusion. The Boston-Leeds Osteoarthritis Knee Score (BLOKS) uses a four-point scale (0, < 2; 1, 2–2.9 mm; 2: 3–4.9 mm; 3, > 5 mm extruded) [21,22,23]. The MRI Osteoarthritis Knee Score (MOAKS) uses the same classification for medial and lateral extrusion [24]. Originally from Gale et al in 1999, medial meniscal body extrusion of 3 mm or more was suggested to be Bpathologic^ [3, 5, 27] and is probably the most widely acknowledged cut-off for research purposes. There is a lack of evidence of what may be regarded as Bpathologic.^
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