0.85). 31 of 44 peptide markers, resulting from ECM proteins such as COL1A1, COL3A1, and novel detection of COL6A1 and COL6A3 in bone, with significantly elevated abundance in our full OA cohort, indicate disease progression. Spatial maps of these markers revealed distinct tissue damage and disease pathologies in the subchondral bone that are related to protein structural changes in the ECM, changes that may precede overlying cartilage loss in OA.]]>