Ultrasounds outperform magnetic resonance imaging in quantifying meniscal extrusion in patients with knee osteoarthritis

Purpose: The aim of this study was to quantify meniscal extrusion through ultrasound (US) evaluation in supine and standing positions and to compare the results with those documented through magnetic resonance (MR) imaging in patients affected by knee osteoarthritis (OA). Methods: Sixty patients (38 men, 22 women, mean age 60.8 +/- 9.7 years) with knee OA were enrolled and underwent a 1.5 T MR evaluation and an US examination of the symptomatic OA knee for the evaluation of the medial and lateral meniscus extrusion both in the supine clinostatic position (clino-US) with the knee fully extended and in the standing weight-bearing orthostatic position (ortho-US). For the three imaging evaluations (MR, clino-US and ortho-US), both semi-quantitative and quantitative measurements were performed. Results: The quantitative analysis documented higher values of medial meniscal extrusion at the ortho-US evaluation (5.2 +/- 2.3 mm) compared to MR (4.2 +/- 2.2, p < 0.0005) and clino-US (4.5 +/- 2.3, p < 0.0005) and of the lateral meniscus at the ortho-US evaluation (4.3 +/- 1.8) compared to MR (3.3 +/- 1.6, p < 0.0005) and clino-US (3.8 +/- 1.6, p < 0.0005). The semi-quantitative analysis confirmed the same trend for both menisci. Higher extrusion values were documented in women and more advanced OA, as well as in older patients with higher body mass index, the latter being underestimated the most by the MR approach. Conclusion: US outperforms MR imaging in quantifying meniscal extrusion in patients with knee OA. Moreover, the highest values of meniscal extrusion have been documented using US in standing position compared to the supine position, underlining the importance of the weight-bearing assessment of meniscal extrusion in knee OA patients. Level of EvidenceII.