Greater Medial Meniscus Extrusion Seen on Ultrasonography Indicates the Risk of Posterior Root Tear in Non-radiographic Knee Osteoarthritis Population

Purpose: To elucidate the association between medial meniscus extrusion measured on ultrasonography (MMEUS) and the prevalence of medial meniscus posterior root tear detected on magnetic resonance imaging (MMPRTMRI). Methods: We recruited 127 patients (135 knees) 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. MMEUS was measured with patients in the supine position. Based on T2*-weighted images, MMPRTMRI was defined as the presence of “Ghost meniscus sign” and “Creft/truncation sign”, indicating an abnormal high signal intensity of a disrupted posterior root. MMEUS 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 MMEUS to predict MMPRT+.Results: The prevalence of MMPRT+ was 31.3% (25/80 knees) and 29.1% (16/55 knees) in the non-ROA and ROA groups. The MMEUS 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 MMEUS 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.Conclusions: In early non-radiographic KOA stages, a greater MMEUS was associated with a higher MMPRTMRI prevalence.Level of evidence: III, Cross-sectional cohort study