Rheumatol Int (2012) 32:1009–1014 DOI 10.1007/s00296-010-1716-7 123 ORIGINAL ARTICLE Moderate loading of the human osteoarthritic knee joint leads to lowering of intraarticular cartilage oligomeric matrix protein Ida C. Helmark · Marie C. H. Petersen · Helle E. Christensen · Michael Kjaer · Henning Langberg Received: 18 May 2010 / Accepted: 30 December 2010 / Published online: 19 January 2011  Springer-Verlag 2011 Abstract The non-pharmacological treatment of osteoar- thritis (OA) includes exercise therapy; however, little is known about the speciWc eVect of exercise on the joint per se. The purpose of the present study was to investigate the direct eVects of a load-bearing exercise upon cartilage in a single, human osteoarthritic joint determined by biochemical markers of cartilage turnover and inXammation in the syno- vial Xuid (SF), serum and urine. Eleven subjects with OA of the knee(s), but with no other joint- or inXammatory disor- ders, volunteered for the study and had samples of blood, urine and synovial Xuid drawn both at baseline and follow- ing 30-min one-legged knee-extension exercise. Workload: 60% of 1 RM (Repetition Maximum). Determination of car- tilage oligomeric matrix protein (COMP), aggrecan, C-ter- minal collagen II peptide (CTX-II) and interleukin (IL)-6 were performed in synovial Xuid (SF), serum and urine. A signiWcant decrease was found in SF concentration of COMP following exercise, whereas aggrecan, CTX-II and IL-6 remained unchanged. No diVerences in any of the tested markers were found in serum and urine between base- line and post-exercise. Thirty minutes of mechanical loading of a single knee joint in human subjects with knee OA resulted in a reduced COMP concentration in SF. Keywords Osteoarthritis · Exercise · Biological markers · Cartilage Introduction Osteoarthritis (OA) is a chronic, destructive joint condition that involves a large and increasing part of the population worldwide [1]. The beneWcial eVects of exercise on the well-being of patients with OA are well documented [2–5], and evidence indicates that the type of exercise (aerobic vs. resistance) is not critical [5], presumably due to an eVect on other tissues than the cartilage itself. Quadriceps strength and knee proprioception are reduced in patients with knee OA compared to healthy age-matched controls [6, 7], and the improvement of function with exercise in these patients can very likely be ascribed to better stability and pain con- trol. Alternatively, the positive eVect of exercise could be exerted directly upon the cartilage. Exercise has been shown to cause rise in circulating cartilage markers like cartilage oligomeric matrix protein (COMP), aggrecan and CTX-II (C-terminal telopeptide of collagen II) all of which have been proposed as possible candidates for diagnosing and monitoring patients with OA [8–11] since they origi- nate from the extracellular matrix of cartilage. The initial processes leading to loss of cartilage in OA are not well understood, though it has been recognized for some time that a low-grade inXammation is present in OA [12, 13], presumably an eVect of as well as a reason for the patholog- ical Wndings. Interleukin-6 (IL-6) is an anti-inXammatory cytokine known to increase in serum, muscle and peritendi- nous tissue following exercise [14, 15], but to what extent it is also released from the knee joint in relation to exercise is at present unknown. Even though a major concern is whether weight-bearing exercise in patients with OA of the I. C. Helmark (&) · M. C. H. Petersen · M. Kjaer · H. Langberg Institute of Sports Medicine, Department of Orthopaedic Surgery, Bispebjerg Hospital and Center for Healthy Aging, Faculty of Health Sciences, University of Copenhagen, Bispebjerg Bakke 23, 2400 Copenhagen, Denmark e-mail: ida_caroe@dadlnet.dk H. E. Christensen Department of Radiology, Bispebjerg Hospital, Copenhagen, Denmark