Validity of radiograph-based infrapatellar fat pad opacity grading for assessing knee synovitis: Correlation with contrast-enhanced mri

Seong Jong Yun, Youngsik Lim, Wook Jin, Yong Sung Park, Sun Hwa Lee, Kyung Nam Ryu

Research output: Contribution to journalArticlepeer-review

5 Scopus citations


OBJECTIVE. The purpose of this study was to determine the validity of infrapatellar fat pad (IPFP) opacity grading based on lateral knee radiography for assessing knee synovitis using correlation with contrast-enhanced (CE) MRI. MATERIALS AND METHODS. Retrospective reviews of radiographs and CE knee MR images from 79 patients were independently performed by two radiologists. They evaluated IPFP opacity alteration (IPFPCR) and joint effusion grades on lateral knee conventional radiographs, IPFP signal intensity alteration (IPFPMR) and joint effusion grades on CE MR images, and synovitis (SYNMR) grade in nine divided regions, three compartments (parapatellar, periligamentous, perimeniscal), and the whole knee on CE MR images. Correlations between radiographic grades and MRI assessments were evaluated using Spearman correlation tests, and the correlation coefficients (ρ) were compared. Interobserver agreement was evaluated using weighted kappa values. RESULTS. The IPFPCR grade was very highly correlated with the IPFPMR grade (ρ = 0.906, p < 0.001) and highly correlated with SYNMR grades from four regions (suprapatellar, infrapatellar, intercondylar, lateral parapatellar recess), the parapatellar compartment, and the whole knee (ρ = 0.614-0.740, all p < 0.001). The IPFPCR grade was moderately correlated with the SYNMR grades of the remaining five regions and two compartments (ρ = 0.457- 0.547, all p < 0.001). The differences between correlation coefficients for SYNMR grades and the IPFPCR and IPFPMR grades were not statistically significant (p = 0.290-1.0). Interobserver reliabilities were excellent or good for IPFPCR, IPFPMR, and SYNMR grades (κ = 0.661-1.000). CONCLUSION. IPFPCR grade assessment enables valid evaluation and reporting of knee synovitis, especially in the parapatellar compartment and the whole knee.

Original languageEnglish
Pages (from-to)1321-1330
Number of pages10
JournalAmerican Journal of Roentgenology
Issue number6
StatePublished - Dec 2017

Bibliographical note

Publisher Copyright:
© 2017 American Roentgen Ray Society.


  • Infrapatellar fat pad
  • Knee synovitis
  • MRI
  • Radiograph
  • Scoring


Dive into the research topics of 'Validity of radiograph-based infrapatellar fat pad opacity grading for assessing knee synovitis: Correlation with contrast-enhanced mri'. Together they form a unique fingerprint.

Cite this