LONGITUDINAL SENSITIVITY TO CHANGE AND PROGNOSTIC VALIDITY OF AUTOMATICALLY MEASURED EFFUSION SYNOVITIS VOLUME (ESV)

Albeit not specific to inflammation only, effusion-synovitis (ES) - assessed using non-contrast enhanced MRI - is used as a proxy of synovial activation in knee OA. ES is defined as hyperintensity within the synovial cavity, and is commonly graded using established scoring systems, based on the amount of capsular distension. Quantitative approaches to measure the amount of ES volume (ESV) have been proposed and permit quantitative, precise, and longitudinal evaluation of ES using a continuous measure. We have previously developed a fully automated AI-based technology for measuring ESV and demonstrated criterion validity vs. manual segmentation. The FNIH1 Biomarker Consortium Study is ideally suited to evaluate ESV as a baseline or longitudinal predictor of progression.

To test the longitudinal sensitivity to change of ESV in progressor vs. non-progressor knees, and to test its baseline, follow-up (FU), and longitudinal prognostic validity.

The analyses were performed in the FNIH-1 Biomarker Consortium Cohort: 194 knees exhibited combined radiographic and pain progression at 2, 3, or 4 years [Y] FU [ComP], 103 radiographic only [RoP], 103 pain progression only [PoP], and 200 neither type [NoP]. Fully automated segmentation of peripatellar ESV was carried out on baseline, Y1, and Y2 axial reformats of DESS MRI. An AI-based convolutional neural network (CNN) model was trained with 77 manually segmented knees. We evaluated the rate (µl and %) and sensitivity to change (SRM) of ESV in the four groups. The strength of the association was examined using odds ratios (ORs), and the effect size of the between (progressor) group differences by the Cohen's d.

The ESV increased by 38% over 2Y in ComP (SRM: 0.46), by 18% in RoP (0.19), and by 9% in PoP (0.15). In contrast, it diminished by 11% in NoP (-0.20) (Table 1). Between ComP and NoPs, the ESV differed by 1013 µl at baseline, by 3010 µl at Y1, and by 4417 µl at Y2. The ORs for the ESV in ComP vs. NPs were 1.15 (95% CI 0.94, 1.40) at baseline, 1.64 (95% CI 1.33, 2.03) at Y1, and 1.96 (95% CI 1.60, 2.39) at Y2 (Table 1). Fig. 1 shows the Cohen's d values throughout groups, time points, or observation periods.

The ESV - determined from non-contrast enhanced DESS MRI - was sensitive to longitudinal change (an increase) in knees with OA disease progression. The current results should be confirmed using standard clinical MRI sequences (IW TSE FS) and in other cohorts, ideally in direct comparison with contrast enhanced MRI. Yet, the current analysis is promising in that the ESV yielded strong prognostic validity and differentiated well between knees with different types of progression, as well as between (combined) progressors vs. non-progressors.