Greater medial meniscus extrusion seen on ultrasonography indicates the risk of MRI-detected complete medial meniscus posterior root tear in a Japanese population with knee pain.

To elucidate the association between medial meniscus extrusion measured on ultrasonography (MME) and the prevalence of medial meniscus posterior root tear detected on magnetic resonance imaging (MMPRT). We recruited 127 patients (135 knees; 90 females; mean age: 64.4 ± 8.7 years old; mean BMI: 25.5 ± 3.4 kg/m) in this cross-sectional study. All participants had medial knee pain without a knee trauma or surgery history. Knee osteoarthritis (KOA) severity was evaluated using Kellgren-Lawrence grade (KLG) scores. Patients with KLG scores 0-1 and ≥ 2 were classified in non-radiographic (non-ROA) and radiographic KOA (ROA) groups, respectively. MME was measured with patients in the supine position. Based on fat-suppressed T2-weighted images, MMPRT was defined as the presence of "Ghost meniscus sign" and "Cleft/truncation sign", indicating an abnormal high signal intensity of a completely disrupted posterior root. MME was compared between MMPRT+ and MMPRT- patients using a non-paired t-test. Receiver operating characteristic (ROC) curves were used to determine the optimal cut-off MME to predict MMPRT+. The prevalence of MMPRT+ was 31.3% (25/80 knees) and 29.1% (16/55 knees) in the non-ROA and ROA groups. The MME of MMPRT+ patients were significantly greater than that of MMPRT- patients in both the non-ROA (5.9 ± 1.4 mm vs. 4.4 ± 1.0 mm, P < 0.001) and ROA (7.8 ± 1.3 mm vs. 6.3 ± 1.3 mm, P < 0.001) groups. ROC curves demonstrated that 5-mm and 7-mm MME were the optimal cut-off values in non-ROA (adjusted odds ratio: 6.280; area under the curve [AUC]: 0.809; P < 0.001) and ROA (adjusted odds ratio: 15.003; AUC: 0.797; P = 0.001) groups. In both early non-radiographic and established radiographic KOA stages, a greater MME was associated with a higher MMPRT prevalence.