Infra-patellar fat pad morphology and MRI signal distribution in advanced radiographic knee OA – Data from the OAI

Abstract

s / Osteoarthritis and Cartilage 23 (2015) A82eA416 A219 349 INFRA-PATELLAR FAT PAD MORPHOLOGY AND MRI SIGNAL DISTRIBUTION IN ADVANCED RADIOGRAPHIC KNEE OA e DATA FROM THE OAI F. Eckstein yz, J. Diepold y, A. Ruhdorfer y, T. Dannhauer yz, W. Wirth yz, A. Guermazi xk. y Paracelsus Med. Univ., Salzburg & Nuremberg, Austria; zChondrometrics GmbH, Ainring, Germany; xBoston Univ. Sch. of Med., Boston, MA, USA; kBoston Imaging Core Lab, Boston, MA, USA Purpose: Recent studies suggest that obesity-related risk of knee OA is not fully explained by mechanical challenge, i.e. increased body weight. Yet, adipokines (e.g. leptin) secreted from fat tissue appear to cause lowgrade inflammation, and to contribute to the release of metallo-proteinases and growth factors, which are known to promote cartilage loss and osteophyte formation. The infra-patellar fat pad (IPFP) is unique in representing intra-articular adipose tissue, and is a source of intraarticular leptin. Only few studies, however, have studied the role of the IPFP in human knee OA. Here we explore whether quantitative imaging measures of IPFP size and MRI signal differ between painful knees with and without advanced radiographic knee OA in the same person, and between OA and healthy reference knees. Methods: The sample was drawn from the Osteoarthritis Initiative (OAI) cohort and fulfilled the following criteria: OARSI medial JSN in one knee, no-JSN in the contra-lateral knee, BMI>25, frequent knee pain in both knees. The 28 participants who displayed OARSI JSN grades 2 or 3 in one (and grade 0 in the other) knee were matched 1:1 with subjects from the OAI healthy reference cohort without knee pain radiographic signs, or risk factors of incident knee OA, based on the same sex and similar body height. A sagittal fat-suppressed IM-weighted TSE sequence was used for segmentation of the entire IPFP (J.D.), volumetric 3D analysis of its morphology and signal, and for semi-quantitative evaluation of MOAKS synovitis scores (A.G.). Paired t-tests were used to compare JSN with contra-lateral non-JSN knees, and with matched reference knees. Results: The 28 JSN participants (21 medial JSN grade 2 and 7 grade 3; 21 women, 7 men) were 165±11 cm tall (age 61±10y; weight 87±14 kg, BMI 32.2±4.4). The matched healthy reference subjects were of similar height (165±10cm), but younger (54±6y) and less heavy (70±13 kg; BMI 26±2.7). No significant differences in IPFP volume, surface areas, or thickness were observed between JSN and no-JSN knees. Compared with healthy reference knees, JSN knees displayed a 10% larger IPFP anterior surface area (p<0.01), but a slightly lower thickness, and no significant difference in IPFP volume (Table 1). JSN knees displayed a significantly greater mean MRI signal intensity (SI) and greater MRI SI heterogeneity (i.e. standard deviation [SD]) than the no-JSN knees; further JSN knees displayed a substantially and significantly greater SD SI than healthy reference knees (Table 1: (b) 1⁄4 p<0.01; (c) 1⁄4 p<0.001)).