Fig. 2

Concentrations of (A) phosphatidylcholine (PC) species and (B, C) ether phosphatidylcholine (PC O) species in serum. ESI-MS/MS quantification of serum samples from controls (n = 31, blue) and early stage OA (eOA, n = 29, yellow) and late stage OA (lOA, n = 29, grey) patients. Ether species were assigned based on the assumption that the PCs contained only fatty acids with an even number of carbon atoms. Data are presented as box plots with median, interquartile range, and outliers. The solid polylines connect the medians to support the visual impression. Statistically significant differences were determined by Wilcoxon´s rank sum test and are indicated by the FDR-adjusted p-values: * < 0.05. Precise concentrations, serum/SF ratios, and statistical results are listed in Supplementary Table S2