Metabolic syndrome and knee osteoarthritis
Obesity is a well-known risk factor for OA (8, 25).
Abdominal obesity might affect knee OA development
by the combined metabolic effects of adipose tissue
and mechanical stress of body weight. In our study,
hypertension, in addition to abdominal obesity, was
significantly associated with an increased risk of knee
OA. The association was valid even after adjusting for
abdominal obesity. Moreover, this relationship was
also present in men. Zhang et al. reported that multiple
genes or the proinflammatory cytokine interleukin-6
plays an important role in the association between
hypertension and knee OA (26). Yoshimura et al. also
clarified that hypertension was significantly associated
with the occurrence of knee OA and vice versa (23,
27). Other metabolic syndrome components, apart
from abdominal obesity and hypertension, showed
a significant association with the development of
knee OA in several analysis models. However, after
adjusting for all compounding factors in model 2, the
effects were insignificant. Nevertheless, caution is
needed in determining the individual effect of each
component based solely on the results of the current
study, because every metabolic component interacts
with, and usually coexists with, other components.
Considering the dose-response relationship for meta-
bolic syndrome components, each factor has an effect
on the development of knee OA with some interactions
and accumulative effects.
Strengths and limitations
The present study has several strengths. First, not only
did it investigate the association between the presence
of metabolic syndrome and development of knee OA,
but it also evaluated the dose-response relationship by
considering the number of metabolic syndrome com-
ponents. Moreover, this study assessed the individual
effect of each metabolic syndrome component. These
analyses revealed that some components may be more
associated with the development of knee OA than other
components. Secondly, the current study evaluated
knee OA in an objective manner, using radiographic
images. In addition, it divided the disease into knee OA
and severe knee OA, based on the KL grading system.
Therefore, it was possible to make a more detailed ana-
lysis. Thirdly, participants were divided and analysed
by sex, and substantial differences were confirmed
between the 2 groups. Fourthly, the current study was
based on a nationwide representative large-sample
survey. Thus it was possible to reduce selection bias
and the results are applicable to the general population.
The current study also has some limitations. First,
it was a cross-sectional study, and thus could not
establish a causal relationship between metabolic
syndrome and knee OA. Secondly, various risk factors
469
that may affect the development of knee OA were ad-
justed for, but there could be more factors affecting the
development of OA that need to be adjusted. Thirdly,
there were many fewer men with OA than women with
OA, which will have reduced the statistical power to
investigate associations in men.
Conclusion
Overall, the results of this study showed that the
presence of metabolic syndrome was associated with
increased risk of knee OA and severe knee OA in
women. The risk of knee OA in women increased
as the number of metabolic syndrome components
increased. However, these findings were not definite
in men. Hypertension and abdominal obesity were
significantly associated with the development of knee
OA and severe knee OA in women. In men, abdominal
obesity and hypertension significantly increased the
risk of knee OA, but only abdominal obesity increased
the risk of severe knee OA. Further studies are needed
to determine the exact mechanism by which metabolic
syndrome affects the development of knee OA.
ACKNOWLEDGEMENTS
This study was supported by a grant (2017–661) from the
Asan Institute for Life Sciences, Asan Medical Center, Seoul,
South Korea.
All procedures performed in studies involving human
participants were in accordance with the ethical standards of
the institutional and/or national research committee and with
the 1964 Declaration of Helsinki and its later amendments or
comparable ethical standards.
The authors have no conflicts of interests to declare.
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J Rehabil Med 51, 2019