Quantitative evaluation of the characteristic of infrapatellar fat pad Fat Content and Unsaturation Index by using hydrogen proton MR spectroscopy

Abstract

Objective: To investigate the characteristics of fat content and component in IFP using hydrogen proton MR spectroscopy (¹H-MRS), and to explore the correlation with the severity of OA, Hoffa-synovitis, and knee pain.

Materials and methods: 80 volunteers were enrolled. Subjects were grouped based on Kellgren-Lawrence (K-L) grading. Fat fraction (FF) and unsaturation index (UI) of IFP were measured using ¹H-MRS. Hoffa-synovitis was evaluated based on the MRI Osteoarthritis Knee Score system (MOAKS). Knee pain was assessed by a self-administered Western Ontario and McMaster Osteoarthritis Index (WOMAC) questionnaire. One-way ANOVA or Kruskal-Wallis test and Spearman's correlation tests were applied for statistical analysis.

Results: After matching BMI, waistline, and K-L grade, a total of 64 knees were included and divided into 23 normal, 25 mild OA, and 16 advanced OA. The mean values were 76.79% ± 7.24%, 70.35% ± 7.42%, and 58.29% ± 10.32% for FF in the healthy controls, mild OA, and advanced OA group, and 6.36 ± 1.19%, 6.08 ± 1.35%, and 5.69 ± 1.78% for UI, respectively, the statistical difference was found for FF (p < 0.01). A good negative correlation was observed between the FF and the severity of OA, Hoffa-synovitis (r = -0.625, -0.758, respectively, p < 0.0001), and a weak inverse correlation with knee pain.

Conclusion: FF alteration in IFP is associated with the severity of OA, Hoffa synovitis, and knee pain, and has the potential to be a new quantitative imaging biomarker in knee OA.

Keywords: Fat content; Infrapatellar fat pad; Knee osteoarthritis; MRS; Unsaturation index.