Background Pain and disability related to osteoarthritis (OA) may generally be considered to be chronic, but it is known that its course can be very different between patients.

Objectives In this study, it is investigated whether there is a difference in development of pain and physical functioning during follow-up between two OA cohorts: Osteoarthritis Initiative (OAI) and Cohort Hip& Cohort knee study (CHECK).

Methods For the current study, longitudinal data of three years follow-up of the CHECK study and OA Initiative were used. The CHECK study is a Dutch prospective 10-year follow-up study, initiated by the Dutch Arthritis Association, to study progression of OA in participants with early symptomatic OA of knee or hip. Individuals were eligible if they had pain of knee or hip, were aged 45-65 years, and had not yet consulted their physician for these symptoms. In the same time in the U.S. an observational 4-year follow-up study was started to create a public archive of data, biological samples and joint images to study the natural history of, and risk factors for, the onset and progression of knee OA. The WOMAC was utilized to measure pain during activities (range 0-20) and physical functioning (range 0-68). For comparison with CHECK a subgroup of the incidence OAI cohort was selected which was comparable with the CHECK cohort: participants with age 45-65 years, frequent or infrequent knee symptoms and no surgery in either knee. Generalized estimating equations were used to account for correlations within individuals (GEE) and the interaction term (OAcohort* time) was also investigated within the model.

Results For this study, the data of 688 CHECK participants with knee pain at baseline were analyzed, mean age 56 years, BMI 25 kg/m² and 79% were female. The subgroup of OAI Incidence cohort with infrequent or frequent knee pain consisted of 1417 participants, with a mean age of 56, BMI of 28 and 64% female. The CHECK cohort reported at baseline more pain and more problems in physical functioning compared to the subgroup of OAI Incidence cohort (p<0.001). A final longitudinal regression model with pain as outcome and adjusted for BMI shows that pain is 3 points lower (better health) of people in the subgroup of OAI Incidence, and improves in both cohorts after 1 year of follow-up with 0.2 points, after 2 years with 0.3 points, after 3 years with 0.3 points. In a final model with function as outcome and adjusted for BMI, this outcome is 10.2 points higher (worse health) in CHECK cohort and improves in both cohorts after 1 year of follow-up with 0.6 points, after 2 years with 0.8, after 3 years with 0.7 points. These results were not influenced by the characteristics of both cohorts (interaction term (OAcohort* time) was not statistically significant in both outcomes).

Conclusions In the total group, participants of the OAI Incidence subgroup and the CHECK participants with knee pain, there is a gradually improvement over time in pain and physical functioning, despite baseline values on pain and physical functioning. In the early phase of OA there is overall a slight improvement in the complaints. Though, a difference at start between the two cohorts, completely parallel development of pain and function over 3 years.

Disclosure of Interest None Declared