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 US ) and the prevalence of medial meniscus posterior root tear detected on magnetic resonance imaging (MMPRT MRI ). We recruited 127 patients (135 knees; 90 females; mean age: 64.4 ± 8.7 years old; mean BMI: 25.5 ± 3.4 kg/m 2 ) 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 US was measured with patients in the supine position. Based on fat-suppressed T2-weighted images, MMPRT MRI 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 US 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 US 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 US 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 US 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 US was associated with a higher MMPRT MRI prevalence.