Background While population studies usually consider undifferentiated osteoarthritis (OA), cohort and other studies of OA typically focus on OA characterized by a primary joint involved, most frequently the knee, hip or hand. Relatively little attention has been paid to the involvement of other joints.

Objectives To investigate the extent of multi-joint involvement in a representative sample of the population with OA.

Methods Analysis of data from the Survey on Living with Chronic Diseases in Canada, Arthritis Component. This was based on a nationally representative sample of people aged 20 or older reporting arthritis as a long term health problem, diagnosed by a health professional, in the parent Canadian Community Health Survey, 2008. Respondents were asked about their type of arthritis, extent of pain on a 0–10 scale, and the extent to which arthritis affected their life (not at all; a little; moderately; quite a bit; extremely). Participants were also asked to indicate which joints were painful. The joints asked about were the right and left hands, wrists, elbows, shoulders, hips, knees, ankles, feet, back and neck. Data on other reported chronic health conditions (heart disease, respiratory, high blood pressure, migraines, mood disorders, bowel disorder/ulcers, stroke, cancer, and diabetes) and body mass index (BMI) were obtained from the parent survey. Analysis was restricted to people reporting OA (n=1749).

Results The mean age of the sample was 65 years, with 44% aged less than 65; 74% were women. Ninety-three percent reported joint pain in the previous month. The mean “average” pain score was 5.2/10 with very little variation by age and gender. Overall, 92% reported that their arthritis affected their life at least a little, with 24% reporting quite a bit or worse, similarly with little variation by age and gender. The most frequently reported joint sites (e.g. one or both knees) were the knee (58%), hands (49%), back (47%), and hips (42%). Overall the sample was characterized by multi-joint involvement: only 10% reported only one troublesome joint, and 17% only one site. The mean number of painful joints was 5.6 (ranging from 1 to 18: median 5), and the mean number of joint sites was 3.9 (median 3). Women reported more joints than men (mean 5.9 vs 4.8) but there was no significant trend by age. There was no significant trend in number of joints by BMI, although the number of co-occurring conditions was higher in people with more painful joints; 25% of those with only 1–2 joints had a 2 or more co-occurring conditions, compared to 43% of those with 5 or more joints.

Conclusions Although the most frequently reported painful joints were the knee, hip or hand, few people reporting OA in this representative population-based sample had joint symptoms in that joint alone, suggesting that studies that focus only on a primary joint may be missing the point. The lack of association of mean number of joints with obesity was surprising given a postulated metabolic contribution to OA. The association with co-occurring conditions needs further investigation. A reappraisal of our understanding of OA appears to be warranted given that multi-joint involvement appeared to be the rule not the exception.

Disclosure of Interest None declared