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

OBJECTIVE

To investigate the characteristics of fat content and component in IFP using hydrogen proton MR spectroscopy (H-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 H-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.