The Contribution of Age and Obesity to the Number of Painful Joint Sites in Individuals Reporting Osteoarthritis

A Population-Based Study

Elizabeth M. Badley; Jessica M. Wilfong; Calvin Yip; Dov B. Millstone; Anthony V. Perruccio


Rheumatology. 2020;59(11):3350-3357. 

In This Article


Study Design and Setting

Data were obtained from the 2009 Survey on Living with Chronic Diseases in Canada –Arthritis Component (SLCDC-A). The purpose of this survey was to provide information on the impact of arthritis on individuals and their families, and to assess clinical and self-management strategies. This survey was conducted by Statistics Canada in collaboration with the Public Health Agency of Canada (PHAC) as an extension to the 2008 Canadian Community Health Survey (CCHS).[33] The CCHS is an annual cross-sectional survey to collect data on the health of the population. The CCHS uses a complex cluster design to generate a nationally representative sample of the household population, estimated to cover ~98% of the Canadian population. Details of the methodology of the 2008 CCHS are provided elsewhere.[34] The sample for the arthritis component of the 2009 SLCDC-A was drawn from respondents aged ≥20 years responding affirmatively to an arthritis question in the 2008 CCHS. The question asked 'Do you have arthritis, excluding fibromyalgia?' as part of a series of questions about long-term health conditions diagnosed by a health professional that had lasted or were expected to last for 6 months or longer. Figure 1 outlines the sampling strategy for the SLCDC-A. Trained personnel administered the survey via structured telephone interviews (English and French) in February and March of 2009. A total of 4565 respondents with arthritis consented to participate and to share their linked data with partnering organizations (PHAC, Health Canada and provincial governments): 78.4% participation rate. Figure 1 also indicates how the sample for the current study was selected. Respondents to the SLCDC-A who confirmed that they had arthritis were asked what kind of arthritis they had: our analyses were restricted to respondents reporting having OA and no other kind of arthritis. Questions were then asked about whether they had ever experienced joint symptoms of pain, aching or stiffness related to their arthritis and at what age they first started experiencing these symptoms. Joint symptom duration was calculated as the difference between the age at which participants reported they first experienced joint symptoms and their age at the time of the survey, and was grouped into year quartiles (0–5, 6–10, 11–19 and 20+ years) for descriptive analyses. Respondents were further asked to indicate which joints had been painful in the past month. The joints were right and left shoulder, elbow, wrist, hand/fingers/thumb, hip, knee, ankle, foot/toes, neck, back and other. Individual joints were grouped into sites (i.e. one or both knees) for a total of 11 sites including the neck and back. Analyses were limited to respondents with OA who reported pain in the past month in at least one specified joint site for a final sample size of 1614. The SLCDC-A was linked to the more comprehensive data set of the CCHS, enabling us to include key variables in our analyses as indicated in Figure 1.

Figure 1.

Flow chart of the sample selection from the CCHS 2008 for the SLCDC-A 2009
aThe 2009 SLCDC included two questionnaires: one questionnaire for arthritis and one questionnaire for hypertension. To reduce response burden, every respondent sampled could receive only one questionnaire even if they reported both chronic conditions in the CCHS 2008. The sample allocation by questionnaire was done proportionally to the size of the number of 2008 CCHS respondent for each condition and weighting adjustments were made to account for individuals with arthritis and hypertension not selected for the arthritis questionnaire.

Age was categorized as 20–44, 45–54, 55–64, 65–74 and 75+ years. We calculated BMI [weight (kg)/height (m2)] using self-reported height and weight, excluding pregnant women. For descriptive analyses, BMI was categorized as under/normal weight (≤24.9 kg/m2), overweight (25–29.9 kg/m2) and obese (≥30 kg/m2). The highest level of education achieved was dichotomized as less than secondary school and completed secondary school or more. Smoking status was dichotomized as current or former smoker and never smoker. Respondents were asked to indicate the presence of health professional diagnosed long-term health conditions as indicated above. The conditions included were high blood pressure, mood disorder, diabetes, migraine, cancer, lung disease (asthma, chronic obstructive pulmonary disease), heart disease, stomach illness (ulcers, bowel disorder) and stroke. For descriptive analyses, the number of comorbidities was grouped as 1, 2 and 3+.

Statistical Analysis

Descriptive statistics were generated for the population overall and by grouping of painful joint sites (1, 2–3 and 4+ sites). Differences between groups were assessed using Chi-squared tests. Zero-truncated negative binomial regression models were used to evaluate the adjusted associations between number of painful joint sites and study variables, allowing the calculation of rate ratios (RRs) for a continuous count of number of painful joint sites, starting with one.[35] A consolidated set of weights provided by Statistics Canada that took into account sampling and response issues for the parent CCHS as well as the SLCDC-A were used to derive descriptive estimates representative of the population in Canada, with bootstrapping to estimate statistical significance taking into account potential clustering in the sample.

This study is based on analyses of previously de-identified data collected by Statistics Canada and accessed through their Research Data Centre (Toronto). The data were made available for this study through a formally reviewed research proposal to Statistics Canada, and in view of this our Institutional Review Board waived the requirement for institutional ethics approval.

Supplementary Analyses

As MJOA has been variously defined in the literature as being ≥2 or ≥3 joint sites,[8] we carried out sensitivity analyses using ordinal logistic regression with categories of joint count site grouping the number of painful joint sites as 1, 2–3 and 4+, and 1–2, 3–4 and 5+. We further replicated our analyses excluding cases with only one joint site to eliminate the possibility that our findings had been affected by trauma-related single-joint OA.[36]

To establish generalizability of our findings to clinical populations, we carried out a parallel analysis using data from 843 patients scheduled for primary knee or hip joint replacement surgery for OA who completed a questionnaire within the 3-week period prior to their scheduled surgery.[37] Variables parallel to those in the SLCDC-A were extracted from the data set: age, sex, highest level of education, BMI (based on measured height and weight), smoking status and a comorbidity count derived from the sum of yes responses to a list of 20 health conditions similar to those in the SLCDC-A. The number of painful joint sites was ascertained from a homunculus diagram asking which joints (neck, back, right and left shoulder, elbow, wrist, hand, hip, knee, ankle and foot) were 'painful, stiff or swollen on most days of the past month'. Unfortunately, no information was available for duration of joint symptoms. Further details of this study are given in the Supplementary materials, available at Rheumatology online.