Volume and Quantitative Dynamic Contrast-Enhanced MR Blood Perfusion Parameters of the Infrapatellar Fat Pad and Their Relationship with Edema and Effusion in Patellofemoral Pain

Purpose: Patellofemoral pain (PFP) is a common knee condition and possible precursor of knee osteoarthritis. Inflammation or increased volume of the infrapatellar fat pad (IPFP) may induce knee pain. The aim of the study was to compare quantitative dynamic contrast-enhanced (DCE)-magnetic resonance imaging (MRI) parameters as a surrogate measure of inflammation, and volume of the IPFP between patients with PFP and controls and between patients with or without IPFP edema or joint effusion.

Methods and Materials: PFP patients and healthy control subjects were included and underwent 3-T MRI comprising non–fat-saturated three-dimensional fast-spoiled gradient-echo and DCE-MRI. Image registration was applied to correct for motion. The IPFP was delineated on the fast spoiled gradient echo sequence using Horos software. Volume was calculated and quantitative perfusion parameters (K^trans, K_ep, V_e, and V_p) were extracted by fitting the extended Tofts pharmacokinetic model. Differences in volume and DCE-MRI parameters between patients and controls were tested by regression analyses with adjustment for these confounders: sex, age, body mass index, and sports participation. IPFP edema and effusion were analyzed identically.

Results: A total of 43 controls and 35 PFP patients were included. Mean IPFP volume was 26.04 mL in controls and 27.52 mL in patients. In controls, mean K^trans was 25.62 min⁻¹and K_ep was 161.58 min⁻¹; in patients this was 24.49 min⁻¹ and 193.47 min⁻¹, respectively. None of the differences in volume, perfusion parameters, and IPFP edema were significantly different between groups. Knees with effusion showed a higher perfusion of the IPFP in patients.

Conclusion: The IPFP has been implied as source of knee pain, but its blood perfusion, as a surrogate measure of inflammation, and volume do not seem to play a role in PFP. Patients’ knees with effusion showed a higher perfusion, indicating inflammation.

Fig. 1 Overlay of the K^trans map of a patient with patellofemoral pain on the non-FS fast spoiled gradient echo sequence with the infrapatellar fat pad delineated.

Fig. 2 Mean K^trans (min⁻¹) in relation to infrapatellar fat pad (IPFP) edema and effusion in patients with patellofemoral pain and control subjects. Perfusion parameters were multiplied by 1,000.

Table 1 Mean, standard deviation, and mean difference of the volume and the volume of interest mean for K^trans, K_ep, V_e, and V_p in patients and controls[a]

	Mean patients (N = 35)	Mean controls (N = 44)	Mean difference (95% CI)	Adjusted p value
Volume, mL	27.52 (5.37)	26.04 (4.18)	1.48 (− 0.66 to 3.62)	0.12
Ktrans, min−1	24.49 (25.66)	25.62 (28.64)	− 1.12 (− 13.47 to 11.21)	0.98
Kep, min−1	193.47 (104.23)	161.58 (78.58)	31.88 (− 9.07 to 72.84)	0.48
Ve	149.67 (61.39)	171.04 (64.51)	− 21.37 (− 49.85 to 7.11)	0.29
Vp	1.57 (5.81)	0.46 (0.52)	1.10 (− 0.65 to 2.85)	0.10

Abbreviations: K_ep, rate constant from extracellular extravascular space back into the vascular system; K^trans, volume transfer constant; V_e, fractional volume of the extravascular extracellular space; V_p, fractional plasma volume.

^a Perfusion parameters were multiplied by 1,000.

Publication History

Article published online:
17 December 2020