Quantitative DCE-MRI Demonstrates Increased Blood Perfusion in Hoffa’s Fat Pad Signal Abnormalities in Knee Osteoarthritis

Purpose: Infrapatellar fat pad (IPFP) fat-suppressed T2 (T2FS)-hyperintense regions on magnetic resonance imaging (MRI) are an important imaging feature of knee osteoarthritis (OA) and are thought to represent inflammation. These regions are also common in non-OA subjects and may not always be linked to inflammation. Our aim was to evaluate quantitative blood perfusion parameters, as surrogate measure of inflammation, within T2FS-hyperintense regions in knee OA patients with patellofemoral pain (PFP) (supposed OA precursor) and control subjects.

Methods and Materials: A total of 43 healthy controls, 35 patients with PFP, and 22 patients with knee OA were included. All underwent MRI including T2 mapping and dynamic contrast-enhanced (DCE)-MRI. Image registration was used to correct for motion. If present, hyperintense T2 regions in the IPFP were delineated on T2 maps using Horos software (Horosproject.org). A second region was drawn in an adjacent area without T2 signal intensity alteration ([Fig. 1]). Quantitative perfusion parameters (K^trans, V_e, and V_p) were extracted by fitting the extended Tofts pharmacokinetic model where K_trans represents the inflow, V_e the extravascular extracellular space, and V_p the vascular fraction of the region. A paired Wilcoxon signed rank test was used to compare regions with and without T2 regions within subjects for each subgroup.

Results: T2FS-hyperintense IPFP regions were present in 16 of 22 (73%) OA patients, 13 of 35 (37%) PFP patients, and 14 of 43 (33%) controls. DCE-MRI perfusion parameters were significantly different between regions with and without a T2FS-hyperintense signal in OA patients, demonstrating higher K^trans compared with normal IFPF tissue (0.039 min⁻¹ versus 0.025 min⁻¹; p = 0.017) and higher V_e (0.157 versus 0.119; p = 0.010). For PFP patients and controls, no significant differences were found ([Fig. 2]).

Conclusion: IPFP T2FS-hyperintense regions are associated with higher perfusion in knee OA patients in contrast to identically appearing regions in PFP patients and controls, pointing toward an inflammatory pathogenesis in OA only.

Fig. 1 Two regions of interest were drawn in the infrapatellar fat pad, one within the fat-suppressed T2-hyperintense region and the second in an adjacent area without T2 hyperintensity.

Fig. 2 Delineated T2-hyperintense region within the infrapatellar fat pad on the T2 map (left) and corresponding K^trans map (values in min⁻¹) (right) in patient with patellofemoral pain (upper row) and patient with osteoarthritis (lower row). Higher values of K^trans are depicted in red.

Publication History

Article published online:
17 December 2020