ISSUE: NOVEMBER 2013 | VOLUME: 11
Madrid—The presence of metabolic syndrome and its components is associated with an increased risk for severe osteoarthritis (OA) of the knee, leading in many cases to joint replacement, according to new research. However, this connection was not true of hip OA. The association with knee OA was found independent of obesity (body mass index [BMI]).
According to senior investigator Anita Wluka, MBBS, FRACP, associate professor, Department of Epidemiology and Preventive Medicine, Monash University, Melbourne, Australia, the findings, from a population-based cohort study presented at the 2013 annual meeting of the European League Against Rheumatism, suggest that knee and hip OA have different pathogeneses, although at this point the reasons are speculative.
“Other authors have found an association between the metabolic syndrome and OA,” she told attendees. “This study shows that OA and the metabolic syndrome do not simply coexist, but that the metabolic syndrome is one of the pathways to knee OA, but not hip OA, suggesting a different pathogenesis for these two different diseases. Managing the metabolic syndrome may reduce the burden of knee OA.”
The study population included 20,300 community dwellers enrolled in the Melbourne Collaborative Cohort Study. There were 660 participants who went on to knee replacement for severe knee OA and 562 with severe hip OA who went on to hip replacement surgery. All participants had various combinations of risk factors associated with the metabolic syndrome for several years. These included dyslipidemia, hypertension, impaired fasting glucose and central obesity (waist circumference >94 cm in men and >80 cm in women).
Participants with severe knee OA leading to joint replacement had higher percentages of metabolic syndrome components compared with those with severe hip OA leading to joint replacement (i.e., central obesity plus two or more of the following factors: hypertension, hypertriglyceridemia, dyslipidemia and hyperglycemia).
In a multifactorial analysis adjusted for age, sex, birth country, education and BMI, central obesity and hypertension significantly increased the risk for severe knee OA (central obesity hazard ratio [HR], 1.51; 95% confidence interval [CI], 1.20-1.91; hypertension HR, 1.25; 95% CI, 1.05-1.50).
Independent of BMI, a nonlinear increase was observed between the number of metabolic syndrome risk factors and the cumulative risk for severe knee OA. Interestingly, these associations were not significant for risk for severe hip OA.
Dr. Wluka noted that the association between OA and the metabolic syndrome and its components has been written about previously. Chinese researchers recently speculated on the potential mechanisms by which hypertension, hyperlipidemia, hypoglycemia and obesity contribute to osteoarthritic changes (Nat Rev Rheumatol 2012;8:729-737).
U.S. researchers cite the growing supportive evidence for OA as a metabolic disorder that is initiated and promoted by an interplay of lipid, metabolic and humoral mediators (Metab Syndr Relat Disord 2010;8:295-305).
Roy D. Altman, MD, professor of medicine in the Department of Rheumatology at the University of California, Los Angeles, stated that population-based studies are an excellent method for exposing potential associations. However, he noted that in this study, associations are not confirmed because of the nature of the data, in that it is retrospective and many variables are not captured and collected.
“Only those undergoing total hip replacement and total knee replacement are included in the analysis, separating those with moderate to severe knee OA or hip OA who are not undergoing joint replacement,” he said. “It is unclear how those not going to surgery distort the control group, as we do not know the size of this cohort. Also important is that it is unclear how the cohort with OA not going to surgery compares with those having the surgery.”
The take-away message from the study, he said, is the need to “recognize and address the components of metabolic syndrome as part of the management of … those with knee OA.”
—Alice Goodman