Change in serum COMP concentration due to ambulatory load is not related to knee OA Status

The aim of this study was to test the hypothesis that a change in serum cartilage oligomeric matrix protein (COMP) concentration is related to joint load during a 30‐min walking exercise in patients with medial compartment knee osteoarthritis (OA) and in age‐matched control subjects. Blood samples were drawn from 42 patients with medial compartment knee OA and from 41 healthy age‐matched control subjects immediately before, immediately after, and 0.5, 1.5, 3.5, and 5.5 h after a 30‐min walking exercise on a level outdoor walking track at self‐selected normal speed. Serum COMP concentrations were determined using a commercial ELISA. Basic time–distance gait variables were recorded using an activity monitor. Joint loads were measured using gait analysis. Serum COMP concentrations increased immediately after the walking exercise (+6.3% and +5.6%; p < 0.001) and decreased over 5.5 h after the exercise (−11.1% and −14.6%; p < 0.040 and p = 0.001) in patients and control subjects, respectively. The magnitude of increase in COMP concentration did not differ between groups (p = 0.902) and did not correlate with any variables describing ambulatory loads at the joints of the lower extremity. These results, taken together with a previous study of a younger healthy population, suggest the possibility that the influence of ambulatory loads on cartilage turnover is dependent on age.