Intra- and inter-observer reliability of quantitative analysis of the infra-patellar fat pad and comparison between fat- and non-fat-suppressed imaging—Data from the osteoarthritis initiative

Abstract

The infra-patellar fat pad (IPFP), as intra-articular adipose tissue represents a potential source of pro-inflammatory cytokines and its size has been suggested to be associated with osteoarthritis (OA) of the knee. This study examines inter- and intra-observer reliability of fat-suppressed (fs) and non-fat-suppressed (nfs) MR imaging for determination of IPFP morphological measurements as novel biomarkers. The IPFP of nine right knees of healthy Osteoarthritis Initiative participants was segmented by five readers, using fs and nfs baseline sagittal MRIs. The intra-observer reliability was determined from baseline and 1-year follow-up images. All segmentations were quality controlled (QC) by an expert reader. Reliability was expressed as root mean square coefficient of variation (RMS CV%). After QC, the inter-observer reliability for fs (nfs) imaging was 2.0% (1.1%) for IPFP volume, 2.1%/2.5% (1.6%/1.8%) for anterior/posterior surface areas, 1.8% (1.8%) for depth, and 2.1% (2.4%) for maximum sagittal area. The intra-observer reliability was 3.1% (5.0%) for volume, 2.3%/2.8% (2.5%/2.9%) for anterior/posterior surfaces, 1.9% (3.5%) for depth, and 3.3% (4.5%) for maximum sagittal area. IPFP volume from nfs images was systematically greater (+7.3%) than from fs images, but highly correlated (r = 0.98). The results suggest that quantitative measurements of IPFP morphology can be performed with satisfactory reliability when expert QC is implemented. The IPFP is more clearly depicted in nfs images, and there is a small systematic off-set versus analysis from fs images. However, the high linear relationship between fs and nfs imaging suggests that fs images can be used to analyze IPFP morphology, when nfs images are not available.

Responsiveness of Infrapatellar Fat Pad Volume Change to Body Weight Loss or Gain: Data from the Osteoarthritis Initiative

“…As the OAI acquired axial thigh MR images, this provided us with the opportunity to measure SCF CSA change, co-occurring with longitudinal change in body weight, as a benchmark to evaluate the responsiveness of IPFP morphology. The reliability of the measurement technologies used for this purpose has been reported previously Steidle-Kloc et al, 2016]. A methodological strength of the current study was that the IPFP was measured volumetrically (3-D) in addition to analyzing the IPFP area in a single 2-D slice as done in previous studies [Han et al, 2014;Pan et al, 2015;Teichtahl et al, 2015], because volumetric measures provide more information about IPFP morphology but also because the 3-D measures IPFP volume and depth showed statistically significant decreases in women with weight loss while no significant changes were observed in the 2-D slice with the largest IPFP area.…”

“…Morphological parameters of the IPFP were computed from the segmentations using custom software and included its 3-D volume, its anterior surface area (facing the ligamentum patellae), its posterior surface area (facing the knee joint), depth (mean thickness) and maximum sagittal slice area (the slice with the greatest IPFP area). The intra-and interreader reliability of the method has been published before [Steidle-Kloc et al, 2016].…”

“…All slices clearly depicting the IPFP (∼15) were manually segmented while border slices showing severe partial volume effects were not included. All segmentations were quality controlled and used for the quantitative analysis as described previously [Steidle-Kloc et al, 2016]. Pathological alterations (e.g., visible recesses, clefts) or vessels that were located in the periphery of the IPFP were excluded from segmentation [Saddik et al, 2004;Diepold et al, 2015;Steidle-Kloc et al, 2016;Roemer et al, 2016].…”

“…All segmentations were quality controlled and used for the quantitative analysis as described previously [Steidle-Kloc et al, 2016]. Pathological alterations (e.g., visible recesses, clefts) or vessels that were located in the periphery of the IPFP were excluded from segmentation [Saddik et al, 2004;Diepold et al, 2015;Steidle-Kloc et al, 2016;Roemer et al, 2016]. Morphological parameters of the IPFP were computed from the segmentations using custom software and included its 3-D volume, its anterior surface area (facing the ligamentum patellae), its posterior surface area (facing the knee joint), depth (mean thickness) and maximum sagittal slice area (the slice with the greatest IPFP area).…”

“…The purpose of this observational, longitudinal study was therefore to investigate the responsiveness of intraarticular adipose tissue (IPFP volume) to body weight loss and gain in women and to quantitatively compare this potentially "dynamic" response to that of thigh SCF anatomical cross-sectional area (CSA) using state-of-the-art imaging and image analysis methodology Ruhdorfer et al, 2015;Steidle-Kloc et al, 2016]. …”