The Hallym Aging Study (HAS) is a prospective cohort study investigating the health of elderly community residents in Chunchun, a city about 120 km east of Seoul, Korea. This ongoing study commenced in 2004 with follow-up examinations scheduled every 3 years. Its methods have been described elsewhere in detail. Briefly, eligibility criteria included an age of more than 50 years. Using Korean National Census data for 2000, 200 of 1,408 census tracts were sampled according to residential area. Study subjects were selected so that those over 65 years old represented about 70% of the study cohort.
Nine hundred and eighteen subjects were surveyed in the first triennial examination. This cross-sectional study involved 702 subjects from the second triennial examination (64 subjects died, 49 moved, and 103 declined to participate or could not be contacted since the first examination). Of the 702 participants, 129 subjects declined knee radiographs and 69 subjects were excluded due to poor knee radiograph quality(n = 4), total knee replacement surgery(n = 3) or missing films due to clerical error(n = 62). The remaining 504 subjects were analyzed for this study. The ethics committee of Hallym University approved the study protocol. Written informed consent was obtained from all the study participants.
Demographic information was collected using a standard questionnaire. Knee pain was assessed by asking, "Have you had pain, aching, or stiffness lasting at least a month in your knee? All subjects also completed the WOMAC and the SF-12 questionnaire for evaluating the pain, self-reported functional status and QoL.
Physical performance test
Physical performance of lower extremity was tested using the Health ABC battery, as reported previously, with modifications. Briefly, standing balance, a 6-m usual walk, and five repeated chair stands were tested. To test standing balance, the subjects were asked to attempt to keep their feet in side-by-side, semi-tandem, and tandem positions for 10 seconds each. The subjects were given a score of 0 if they could hold a side-by-side standing position for 10 seconds but were unable to hold a semi-tandem position for 10 seconds, a score of 1 if they could hold a semi-tandem position for 10 seconds but were unable to hold a full tandem position for more than 2 seconds, a score of 2 if they could stand in the full tandem position for 3 to 9 seconds, and a score of 3 if they could stand in the full tandem position for 10 seconds. For the 6-m usual walk test, a 6-m walk at the subject's normal pace was timed twice, and the time of the faster of the two walks was used for scoring. For repeated chair stands, the subjects were asked to fold their arms across their chests and to stand up and sit down five times as quickly as possible, and the length of time required was measured. For repeated chair stands and 6-m usual walks, we created quartiles based on the performance of the study subjects, with quartile 0 representing the worst and quartile 3 representing the best performance.
Radiographic evaluations consisted of weight-bearing anteroposterior, 14 × 17-inch, semi-flexed knee radiographs. A Plexiglas frame (SYNARC, San Francisco, CA, USA) was used to standardize knee positions, according to the manufacturer's recommendations. Each knee was graded using the Kellgren-Lawrence (K-L) grade. Radiographic knee OA was defined as being present if the subject had a radiographic grade in the tibiofemoral joint of ≥K-L grade 2. All radiographs were read twice by one reader, an academically based rheumatologist (HAK). The reproducibility of intra-reader assessments was high (for OA versus no OA, = 0.89). Films allocated different K-L grades at the two readings were adjudicated by consensus between the original reader and a second reader(DJH).
Because a sizable majority of subjects marked 0 for WOMAC subscales, they were categorized into quartiles 0-3 with quartile 3 representing the worst scores. To compare the pain, stiffness and function as measured with WOMAC between subjects with and without radiographic OA( K-L grade 0 or 1), we performed logistic regression analysis to estimate odd ratios and the associated 95% confidence interval (CI) for belonging to the worst quartile after adjustment of age, BMI and sex. Male and female OA subjects were compared after adjustment of age, BMI and OA severity. In addition, sex-specific quartiles were created and analyzed.
Mean scores for SF-12 items were analyzed using general linear models (GLM) to control for factors influencing SF-12 scores. The mean scores were compared between subjects with OA and subjects without OA entering age, BMI and sex as covariates. In addition, sex-specific comparisons were made between subjects with and without OA entering age and BMI as covariates. Comparison between male and female OA subjects were made entering age, BMI and OA severity defined as K-L grade as covariates.
The proportion of subjects belonging to each category of physical performance test was compared between subjects with and without radiographic OA using Chi-square test. The risks for belonging to the worst scores (0 and 1 were combined due to small subject size) and the worst quartile were compared for standing balance test and for 6-m usual walk and chair stands tests, respectively, using logistic regression analysis in OA subjects. Data were analyzed using SPSS software (version 15.0; SPSS Inc., Chicago, IL). P < 0.05 (two-tailed) was considered statistically significant.