IVIM-DWI and virtual MR elastography of the infrapatellar fat pad in early knee osteoarthritis: Associations with cartilage lesions and patient-reported outcomes.

OBJECTIVE: To characterize quantitative imaging features of the infrapatellar fat pad (IPFP) using intravoxel incoherent motion diffusion-weighted imaging (IVIM-DWI) and DWI-derived virtual magnetic resonance elastography (vMRE) in adults with knee pain and to evaluate their associations with cartilage lesions and patient-reported outcomes. METHODS: Adults with early knee osteoarthritis (EKOA; n = 55) and individuals without EKOA (n = 38) were prospectively enrolled. International Knee Documentation Committee (IKDC) scores were recorded. Between-group comparisons were adjusted for age and BMI. Within the EKOA group, multivariable linear regression and exploratory parallel path analysis were performed. RESULTS: After adjustment, the EKOA group had higher D and lower μdiff than the non-EKOA group (adjusted P = 0.022 and 0.002, respectively), whereas D*, f, and IPFP volume did not differ significantly. Within the EKOA group, higher D was independently associated with lower IKDC scores (B = - 24.45; 95 % CI, -37.57 to - 11.33; P < 0.001), whereas higher μdiff was associated with higher IKDC scores (B = 4.06; 95 % CI, 2.49-5.63; P < 0.001). Exploratory path analysis identified a significant μdiff-related indirect association and a significant total indirect association through D and μdiff, while the D-related indirect association and direct association were not significant. CONCLUSION: IVIM-DWI and DWI-derived vMRE identified quantitative differences in IPFP D and μdiff between the groups. These cross-sectional findings support further longitudinal validation of quantitative IPFP MRI parameters as candidate imaging biomarkers for EKOA.