Reliability and Convergent Construct Validity of Quantitative Ultrasound for Synovitis, Meniscal Extrusion, and Osteophyte in Knee Osteoarthritis With MRI.

AIMS To determine: 1) inter-rater reliability of quantitative measurements of ultrasound-detected synovitis, meniscal extrusion, and osteophytes; and 2) construct (convergent) validity via correlations and absolute agreements between ultrasound- and gold-standard magnetic resonance imaging (MRI)-outcomes in knee osteoarthritis. METHODS Dynamic ultrasound images for supra-patellar synovitis, meniscal extrusion, and osteophytes were acquired and quantified by a physician operator, musculoskeletal ultrasonographer, and medical student independently. On the same day, 3T MRI images were acquired. Effusion-synovitis, meniscal extrusion, and osteophytes were quantified on sagittal or coronal proton-density-weighted fat-suppressed noncontrast TSE sequences, respectively. Intra-class correlation coefficients (ICCs), Pearson's correlations (r), and Bland-Altman plots were used to analyze inter-rater reliability, and correlations, and agreements between the two imaging modalities. RESULTS Eighty-nine participants [48 females (53.9%)] with mean (standard deviation) age of 61.5 ± 6.9 years were included. The inter-rater reliability was excellent for osteophytes (ICC range = 0.90-0.96), meniscal extrusion (ICC range = 0.90-0.93), and synovitis (ICC range = 0.86-0.88). The correlations between ultrasound pathologies and their MRI counterparts were very strong (ICC range = 0.85-0.98) except for lateral meniscal extrusion [0.66 (95% CI, 0.52-0.76)]. Bland-Altman plots showed 0.01, 0.05, 0.10, 0.53, and 0.60 mm larger size in ultrasound medial tibial and medial femoral osteophytes, medial meniscal extrusions, synovitis, and lateral meniscal extrusions with 95% limits of agreements [±0.39, ±0.44, ±0.85, ±0.70, and ±0.90 (SDs)] than MRI measures, respectively. The lines of equality were within 95% CI of the mean differences (bias) only for medial osteophytes and medial meniscal extrusion. CONCLUSION The quantitative assessment of synovitis, meniscal extrusion, and osteophytes generally showed excellent inter-rater reliability and strong correlations with MRI-based measurements. Absolute agreement was strong for medial tibiofemoral pathologies.