Background/Purpose: Currently, no established marker effectively stratifies knee osteoarthritis (OA) patients into subgroups. The infrapatellar fat pad (IPFP) has been proposed as a potential key player in this disease. However, findings on whether its morphology can forecast disease symptoms, joint structural changes, and the need for knee replacement (KR) are sparse and conflicting. This longitudinal study aimed to identify the most effective prognostic markers by comparing various IPFP morphological features with these outcomes.

Methods: This longitudinal study analyzed 1075 target knees (Kellgreen-Lawrence≥2) from the Osteoarthritis Initiative (OAI) progression cohort. Structural changes include the joint space width (JSW), as well as the cartilage volume, bone marrow lesions (BML), joint effusion volumes, the IPFP global volume and maximal area, and signal (hyper and hypo) intensities volume and area assessed using quantitative and automated magnetic resonance imaging systems. Symptoms were evaluated using the WOMAC total and pain scores. Data on KR was obtained from the OAI database. Longitudinal data was collected at baseline and 12-, 24-, 48- and 96-months post-inclusion. A mixed model for repeated measures (MMRM) and ANCOVA were used to analyze associations with IPFP morphologies.

Results: The baseline characteristics were mild to moderate knee OA. Over time, disease symptoms (WOMAC) decreased along with JSW, cartilage volume, IPFP global and hypointense signal volumes, and maximal and hypointense signal areas (all p£0.001). Joint effusion and hyperintense signal volume and area increased (both p£0.001).

Associations were found between the IPFP morphologies at inclusion and changes over time with JSW (hyperintense volume, 96 months, b: -4.69, p=0.01), medial cartilage volume (hypo- and hyperintense volumes, 48, 96 months, b: -0.13 to -1.08, p£0.04), BML volume (global volume, 48 months, b: 0.07, p£0.05; hyperintense area, 12 months, b: -5.35 to -8.77, p£0.04), and effusion volume (hypo- and hyperintense volumes, 48, 96 months, b: 3.36, -24.80, p£0.05).

Over time changes in IPFP volume correlated with changes in knee structure JSW (global, hypo- and hyperintense, 48, 96 months, b: -44.54 to 37.50, p£0.05), cartilage volume (global, hypo- and hyperintense, 48, 96 months, b:1.55 to 19.70, p£0.05), BML (global, hypointense, 12, 24 months, b: -3.06 to -3.31, p£0.04) and joint effusion (hyperintense, 12 to 96 months, b: 33.92 to 80.05, p£0.02). IPFP area changes were associated with changes in BML (hypo- and hyperintense, 24 to 96 months, b: -23.37 to 29.72, p£0.05) and effusion volume (hypo- and hyperintense, 12, 48 and 96 months, b: -92.63 to -1.23, p£0.04).

At inclusion, smaller IPFP sizes (below median) were associated with cumulative KR at 96 months (global and hypointense volumes, b: -0.11 to -0.14, p≤0.04; and maximum area, b: -5.32; p< 0.05).

Conclusion: This study provides, for the first time, novel information about the comparative value of IPFP morphologies (volume and area) as predictors of OA disease structural changes and KR occurrence, providing a new approach to stratify knee OA patients.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/a-longitudinal-study-of-infrapatellar-fat-pad-morphologies-as-predictive-markersin-knee-osteoarthritis/