Relationship between Kellgren–Lawrence grading (KL), joint space width (JSW) and biochemical markers. Pyridinoline (Pyr) level is expressed as nmol/mmol creatinine. There were significant relationships between joint space width (P = 0.003), pyridinoline (P = 0.034) and TIMP-1 (P = 0.017) determined with the Kruskal–Wallis test. Bars indicate maximum and minimum values within the observation range. P values are shown in each panel; N.S. indicates not significant. CRP, C-reactive protein; MMP, matrix metalloproteinase; TIMP, tissue inhibitor of metalloproteinases.