Association between quantitatively measured infrapatellar fat pad high signal intensity alteration and MRI-assessed progression of knee osteoarthritis

Objective: To describe the cross-sectional and longitudinal associations between quantitative measures of infrapatellar fat pad (IPFP) signal intensity alteration and knee structural abnormalities in patients with symptomatic knee OA.

Methods: 261 participants (mean age 63.0 ± 7.2 years) with symptomatic knee OA were selected from a randomized controlled trial with a follow up of 2 years. IPFP signal intensity alterations at baseline were quantitatively measured on T2-weighted fat-saturated MRI using MATLAB. These quantitative measures included the standard deviation [sDev (IPFP)] of whole IPFP signal intensity, the upper quartile value [UQ (H)] of high signal intensity, the ratio of volume of high signal intensity alteration to volume of whole IPFP [Percentage (H)] and Clustering factor (H) representing the clustering effect of high signal intensity. Cartilage volume and defects, and BMLs were assessed using validated measures.

Results: Higher baseline sDev (IPFP), UQ (H) and Clustering factor (H) were associated with greater loss of tibial cartilage volume and larger increases in tibiofemoral cartilage defects over 2 years. Patients with high and medium tertiles of Clustering factor (H) had greater loss of cartilage volume per annum compared with those with low tertile (4.9% and 4.6% vs 3.3% p.a.). Baseline Percentage (H) and Clustering factor (H) were positively and significantly associated with increases in tibiofemoral BMLs over 2 years. Cross-sectional associations between IPFP measures and knee structures were similar but more consistent.

Conclusion: Quantitative measures of increased signal intensity in the IPFP were associated with knee structural abnormalities in tibiofemoral compartment, suggesting that these measurements could be used as an additional entry criteria in order to enrich for 'faster progressors' in studies of knee OA.