Journal of Rehabilitation Medicine 51-6 | Página 71

Metabolic syndrome and knee osteoarthritis
between metabolic syndrome and development of OA
has not been fully studied. Some studies have linked
OA to metabolic syndrome, on the basis that OA is
not only a mechanical disease, but also a metabolic
disease (12, 13).
Therefore, the aim of the current study was to in-
vestigate the association of metabolic syndrome with
the development of knee OA, based on a nationwide
survey. In addition, the study attempted to identify
the relationship between the number of metabolic
syndrome components and development of knee OA.
PATIENTS AND METHODS
Data sources and study population
The data used in this study were obtained from the fifth Korea
National Health and Nutrition Examination Survey (KNHA-
NES). This was conducted from 2010 to 2012 by the Korea
Centers for Disease Control and Prevention. The KNHANES is
a nationwide, representative survey. Participants were selected
using a multi-stage clustered and stratified random-sampling
method. The sampling method considered the residential area,
sex, and age group based on the National Census Data. The fifth
KNHANES was conducted in 25,534 subjects (11,616 men,
13,918 women), and 10,152 subjects were 50 years of age or
older. From this pool of subjects, those who had complete data
on components of metabolic syndrome, plain knee radiographs,
height, body weight, level of physical activity (PA), smoking,
alcohol consumption, and educational status were selected. All
subjects provided informed consent. This study was approved
by the institutional review board (IRB) of our hospital (IRB
No. 2016-1354).
Exposures
Metabolic syndrome was diagnosed using the criteria of the
National Cholesterol Education Program Adult Treatment Pa-
nel III (14). Subjects with 3 or more of the following criteria
were considered as having metabolic syndrome: high blood
pressure (≥ 130/85 mmHg) or use of antihypertensive medica-
tion; fasting glucose ≥ 100 mg/dl or undergoing treatment for
diabetes; abdominal obesity (waist circumference ≥ 90 cm in
men and ≥ 80 cm in women); and fasting triglyceride ≥ 150 mg/
dl or high-density lipoprotein cholesterol (HDL-C) < 40 mg/dl
in men and < 50 mg/dl in women (15).
The cut-off values applied for the criterion of abdominal
obesity in Korean adults were proposed by The Korean Society
for the Study of Obesity (16). The criterion for hyperglycaemia
was adopted from the American Diabetes Association guide-
lines (17).
Outcomes
Knee OA was assessed using radiographs. Plain anterior-pos-
terior and lateral radiographs of the knee were taken routinely
on a representative sample of KNHANES participants using
DigiRAD-PG (Sitec Medical Co., Seoul, South Korea). Knee
radiographs were taken according to a standard protocol, with
the film centred 1 cm below the patellar apex for both the
anterior-posterior and lateral views. Two radiologists performed
the evaluation individually, using the Kellgren-Lawrence (KL)
465
grading system. Participants with KL grade 2 or greater were
defined as having knee OA, and participants with KL grade 3
or greater were defined as having severe knee OA (18). If the
radiologists assigned different KL grades in the same case,
another radiologist provided an opinion to achieve consensus.
The weighted kappa coefficient for inter-rater reliability was
0.6522, indicating moderate reliability.
Covariates
In the initial survey, body weight, height, and waist circumfe-
rence were measured using standard protocols. Body mass index
(BMI) was calculated (kg/m 2 ). Obesity was defined as BMI ≥ 25
kg/m 2 , in accordance with the criteria of the Asia-Pacific region.
For the assessment of other possible contributing factors, age,
education, alcohol consumption, smoking, obesity, and range
of PA were included in the analysis. Participants were divided
into 4 age groups: 50–59, 60–69, 70–79 and ≥ 80 years. The
level of education was classified as elementary school graduate
or below, middle-school graduate, high-school graduate, or
college graduate or above. Smoking status was categorized as
current smoker or non- or ex-smoker. Alcohol consumption
was divided into those drinking twice a week or more and
those drinking less than twice a week. The Korean version of
the International Physical Activity Questionnaire-Short Form,
which includes questions regarding the frequency, duration,
and intensity of recent PA, was used to assess the participants
(19). PA was defined as follows: vigorous PA, vigorous activity
of at least 20 min on 3 days or more in a week; moderate PA,
moderate-intensity activity of at least 30 min on 5 days or more
in a week; walking, more than 30 min of walking on 5 days or
more in a week; strength and flexibility exercises, strength and
flexibility exercises on 2 days or more in a week.
Statistical analysis
Univariate and multivariate logistic regression analyses were
performed to identify associations between metabolic syndrome
and knee OA or severe knee OA. To accommodate the effect
of covariates, Model 1 was adjusted for age group, which has
the most definite effect on development of OA. Model 2 was
adjusted for additional environmental factors; age group, edu-
cation, smoking, alcohol consumption, and PA. In addition,
the relationship between the number of metabolic syndrome
components and development of knee OA, and the effect of
each component, adjusted by 5 metabolic components, on the
development of knee OA were analysed, in the same manner.
The results were presented as means with 95% confidence in-
tervals (95% CI). The odds ratios (OR) were calculated with the
corresponding p-values < 0.05. Sampling weights were applied
to each participant’s data to represent the Korean population
without biased estimates. All statistical analyses were applied
using SAS, version 9.4 (SAS Institute, Cary, NC, USA).
RESULTS
Clinical characteristics of the subjects
A total of 8,491 subjects (3,684 men and 4,807 women)
were included, and 1,661 subjects were excluded among
the subjects who were 50 years of age or older. The
overall prevalence of knee OA was 35.2% (n = 2,991).
Among subjects with knee OA, 59.8% (n = 1,790) had
J Rehabil Med 51, 2019