The present invention refers to osteomodulin (OMD) protein or fragment of osteomodulin (OMD) protein for use in the prognosis and/or diagnosis of osteoarthritis and/or subchondral bone sclerosis of mammals, preferably human individuals. The present invention further refers to a method for prognosis and/or diagnosis of osteoarthritis and/or subchondral bone sclerosis, comprising the following steps: i) measuring osteomodulin (OMD) protein or a fragment or fragments of osteomodulin (OMD) protein in samples of body fluids of mammalian individuals, preferably human serum samples; ii) judging that decreased levels of osteomodulin (OMD) protein or of said fragment(s) compared to levels in body fluids, preferably serum, of healthy individuals indicate onset of osteoarthritis and/or subchondral bone sclerosis. The present invention also provides an immunological binding partner specifically binding to osteomodulin (OMD) protein or fragment of osteomodulin (OMD) protein for use in the prognosis and/or diagnosis of osteoarthritis and/or subchondral bone sclerosis of mammals, preferably human individuals and a kit comprising said immunological binding partner.