Abstract
OBJECTIVE: To compare illness perception (IP), pain, functional level and health-related quality of life (HR-QoL) between patients with musculoskeletal pain who participate versus those who do not participate in clinical research projects. METHODS: Data were collected between 1 January 2019 and 31 December 2021 in patients visiting the Outpatient Osteoarthritis Clinic at Frederiksberg Hospital, Copenhagen, as part of either clinical research or regular treatment. Questionnaires were collected at baseline and after 10-18 months. Major outcome measure was the change from baseline to follow-up in the Brief Pain Inventory - Short Form (BPI-SF) item 'Average pain'. Secondary outcome measures included The Brief Illness Perception Questionnaire (B-IPQ), measured only at baseline, the EuroQol (EQ-5D-3L), the Health Assessment Questionnaire Disability Index and PainDETECT. RESULTS: 1495 patients were included with 358 (24%) categorised as research participants (exposed) and 1137 (76%) being non-participants (unexposed). The baseline B-IPQ item scores were generally more favourable in the exposed group with statistically significant standardised differences (SD) of 0.2-0.3. Similarly, an SD of 0.3 on the EQ-5D-3L score indicated a better HR-QoL in the exposed group. At follow-up, 24% in the exposed group and 27% in the unexposed group, completed the questionnaires. The mean BPI-sf Average pain between-group difference was: -0.01 points (95% CI: -0.6 to 0.6). Similar clinically irrelevant differences were seen in the other outcomes. CONCLUSIONS: Among musculoskeletal pain patients, research participants report more positive IP and better HR-QoL than non-participants. No additional effect of research participation was found in any outcome over time. TRIAL REGISTRATION NUMBER: NCT03785561.