Distribution of osteoarthritis in a Norwegian population-based cohort: associations to risk factor profiles and health-related quality of life.

The objective of the study was to examine the hand-, knee- and hip osteoarthritis (OA) distribution, risk factor profiles and health-related quality of life (HRQoL) in a population-based OA cohort. Persons with self-reported OA responded to questionnaires and attended a clinical examination (N = 606). We analyzed cross-sectional associations to risk factor profiles and HRQoL dimensions (Short Form 36) in four mutually exclusive groups based on fulfillment of The American College of Rheumatology criteria: no OA (NOA), monoarticular upper extremity (hand) OA (MOAupper-ex.), monoarticular lower extremity (hip or knee) OA (MOAlower-ex.) and polyarticular OA (POA). Multivariate regression analyses and correspondence analysis were performed. The distribution of NOA, MOAupper-ex. MOAlower-ex. and POA was 21.1, 25.4, 22.4 and 31.0%, respectively. Compared to NOA, minor differences were found in risk factor profile in MOAupper-ex., whereas POA was significantly associated with sociodemographic, metabolic and mechanical features. The correspondence analysis identified different risk factor profiles between the four OA phenotypes, but the differences were not statistically significant (p = 0.13). Regarding HRQoL, neither OA groups were associated with poorer mental functioning. MOAlower-ex. and POA were associated with, among other things, poorer physical functioning (β = -6.2, 95% CI -11.2 to -1.2 and β = -12.5, 95% CI -17.4 to -7.9, respectively) and more pain (β = -5.4, 95% CI -10.4 to -0.3 and β = -10.5, 95% CI -15.3 to -5.8, respectively). In this cohort of persons with self-reported OA, POA was the most prevalent phenotype and was associated with an unfortunate risk factor profile and several diminished HRQoL dimensions. POA needs further attention in research and clinical care.