Tanamas et al. Arthritis Research & Therapy 2010, 12:R58 http://arthritis-research.com/content/12/2/R58 Open Access RESEARCH ARTICLE BioMed Central © 2010 Stephanie K Tanamas et al.; licensee BioMed Central Ltd. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and repro- duction in any medium, provided the original work is properly cited. Research article The association between subchondral bone cysts and tibial cartilage volume and risk of joint replacement in people with knee osteoarthritis: a longitudinal study Stephanie K Tanamas 1 , Anita E Wluka 1 , Jean-Pierre Pelletier 2 , Johanne Martel-Pelletier 2 , François Abram 3 , Yuanyuan Wang 1 and Flavia M Cicuttini* 1 Abstract Introduction: To examine the natural history of subchondral bone cysts and to determine whether knee cartilage loss and risk of joint replacement is higher in knees with cysts, compared with those with bone marrow lesions (BMLs) only or those with neither BMLs nor cysts. Methods: The symptomatic knee in 132 subjects with knee osteoarthritis (OA) was imaged by using magnetic resonance imaging at baseline and 2 years later. Tibial cartilage volume, subchondral bone cysts, and BMLs were measured by using validated methods. Knee arthroplasty over a 4-year period was ascertained. Results: Bone cysts were present in 47.7% of subjects, 98.1% of whom also had BMLs. Over a 2-year period, 23.9% of subjects had cysts progress, 13.0% developed new cysts, and 11.4% had cysts regress. Bone cysts at baseline were associated with lower medial and lateral tibial cartilage volume compared with those with BMLs only or those with neither (P for trend 0.004 and <0.001, respectively). Annual medial cartilage volume loss was greatest in those with bone cysts compared with those with BMLs only or those with neither (9.3%, 6.3%, and 2.6%, respectively; P for trend, <0.001). As the severity of bone abnormality in the medial compartment increased from no BMLs or cysts present, to BMLs only, to subchondral bone cysts present, the risk of knee replacement was increased (odds ratio, 1.99; 95% confidence interval (CI), 1.01 to 3.90; P = 0.05). Conclusions: When cysts are present, cartilage loss and risk of knee replacement are higher than if only BMLs are present, suggesting that cysts identify those most likely to benefit from prevention of disease progression. As cysts can regress, they may also provide therapeutic targets in knee OA. Introduction Subchondral bone cyst formation is often encountered in osteoarthritis (OA) of the knee, particularly in advanced OA [1]. Visualised by using magnetic resonance imaging (MRI), subchondral bone cysts occur where the overlying cartilage has largely been eroded [2]. Two main theories are proposed about cyst formation: the synovial breach theory [3,4] and the bony contusion theory [1,5]. Subchondral bone cysts are present in ~50% of subjects with knee OA [6,7] and in 13.6% of healthy volunteers [8]. Studies of subchondral bone cysts have predominantly been descriptive, relating to the prevalence of subchon- dral bone cysts in OA [2,7,9,10]. Two recent studies that examined the relationship between subchondral bone cysts and knee pain found conflicting evidence [11,12]. A cross-sectional study of 143 subjects with knee OA reported no association between cysts and knee pain [12]. In contrast, a prospective study, which is part of an ongoing Genetics, Osteoarthritis, and Progression Study, of 205 subjects with knee OA found a trend for an associ- * Correspondence: Flavia.Cicuttini@med.monash.edu.au 1 Department of Epidemiology and Preventive Medicine, School of Public Health and Preventive Medicine, Monash University, Alfred Hospital, Commercial Rd, Melbourne 3004, Victoria, Australia Full list of author information is available at the end of the article