To analyse the relation of joint damage on evolution of pain and physical functioning in two different cohorts of early phase of osteoarthritis (OA): Osteoarthritis Initiative (OAI) and Cohort Hip & Cohort Knee study (CHECK).
Longitudinal data of 4-5 years follow-up (= medium term) of CHECK study and OAI were used. The Western Ontario and McMaster Universities of Osteoarthritis Index (WOMAC) was used to measure pain and physical functioning. For comparison with CHECK a subgroup of the OAI Incidence cohort was selected, Generalised estimating equations were used and all models were adjusted for gender, Body Mass Index, age, amount of working hours, racial background and hip pain at baseline. Finally, an interaction term was added to assess a possible differential effect of radiological progression on evolution of pain and function in the two cohorts.
At baseline, CHECK had less radiographic OA (K&L ≥2) compared with the OAI Incidence subgroup, but at follow-up CHECK had more radiographic change (51% vs 15% ≥1 K&L point increase; p<0.001). Over 4 years of follow-up, evolution of pain and physical functioning remained fairly stable in both cohorts, however, at different levels, OAI participants had less pain and less problems with physical functioning compared to CHECK participants. Both cohorts showed the same negative effect of rapid radiological change (K&L change of 2 points) on pain and physical function.
In participants with 'early symptomatic OA' rapid radiological change (change of ≥2 grades of K&L in 4 or 5 years) is related to worsening of pain and function.