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Inflammatory features of infrapatellar fat pad in rheumatoid arthritis versus osteoarthritis reveal mostly qualitative differences
  1. Anja Jacoba de Jong,
  2. Inge R. Klein-Wieringa,
  3. Joanneke C Kwekkeboom,
  4. René E.M. Toes,
  5. Margreet Kloppenburg,
  6. Andreea Ioan-Facsinay
  1. Department of Rheumatology, Leiden University Medical Center, Leiden, The Netherlands
  1. Correspondence to Andreea Ioan-Facsinay, Rheumatology, C1-R, Albinusdreef, 2333 ZA, Leiden, The Netherlands; a.ioan{at}

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Rheumatoid arthritis (RA) and osteoarthritis (OA) are characterised by joint destruction. In both diseases, inflammation is implicated; however, RA is generally associated with more inflammation in synovium1 and synovial fluid (SF)2–4 compared with OA. The infrapatellar fat pad (IFP), an adipose tissue located in the knee joint, has been proposed to contribute to disease progression in OA. Although IFP of OA has been extensively characterised and identified as a source of inflammation in the joint,5–7 only scarce information is available on IFP in patients with RA. Therefore, our aim was to get a first insight into the possible contribution of IFP to the inflammatory processes in the RA joint.

To this end, we compared leftover IFP and synovium from patients with RA (n=20: 80% women, mean (SD) age 64 (10.7) years, median (range) body mass index (BMI) 26.9 (18) kg/m2) and patients with primary knee OA (n=51: 62% women, mean (SD) age 66 (8.9) years, median (range) BMI 28.9 (15) kg/m2); all were undergoing knee joint replacement surgery. The study was approved by the local medical ethical committee. Fat-conditioned medium (FCM) and adipocyte-conditioned medium (ACM) were generated as previously described.5 Adipokines and cytokines were measured in FCM …

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  • Contributors AJJ and IKW contributed to the acquisition, analysis and interpretation of the data and drafting and revision of the manuscript. JCK carried out the acquisition of the data. REMT and MK contributed to the conception and design of the study and analysis and interpretation of the data. AIF contributed to the conception and design of the study, analysis and interpretation of the data and drafting and revising of the article. All authors contributed to revising of the article for important intellectual content and approved the final version.

  • Competing interests None declared.

  • Patient consent Detail has been removed from this case description to ensure anonymity. The editors and reviewers have seen the detailed information available and are satisfied that the information backs up the case the authors are making.

  • Ethics approval Local medical ethical committee.

  • Provenance and peer review Not commissioned; externally peer reviewed.

  • Correction notice This article has been corrected since it published Online First. The median level of IL6 in FCM of OA patients in table 1 has been corrected to 10.1ng/ml.