Knee osteoarthritis (OA) is a degenerative disease which produces pain and exhibits damage to cartilage, bone marrow and the development of synovitis. Biomarkers are needed to aid patient stratification for developing improved treatment strategies. We have investigated how type II collagen degradation products (CTX2), which are generated during OA, relate to MRI features of knee damage and patient reported pain. CTX2 was strongly related to synovitis and cartilage damage whereas reported pain was more strongly related to depression and BMI. CTX is thus complementary to pain scores as a marker of OA severity.