The impact of an illness perception conversation on open-label placebo response in knee osteoarthritis: A randomised controlled trial

Objective

To compare the effect of an illness perception conversation (IPC), relative to a research participation conversation (RPC), on 2-week changes in knee pain in patients with knee osteoarthritis.

Method

This was a randomised single-blind trial. Patients were randomised to two matched conversations. An IP conversation concerning the participant’s knee pain-related illness perception (IP) or an RPC concerning the participant’s motivation for participating in research. Both conversations were followed by an open-label intraarticular saline injection in the most symptomatic knee. The primary outcome was change in knee pain from baseline to 2 weeks follow-up on a 100 mm visual analogue scale (VAS). Key secondary outcomes included the Knee injury and Osteoarthritis Outcome Score (KOOS) subscales: Activities of daily living (ADL) and Quality of life (QoL). Main analyses were based on the intention-to-treat population using repeated measures mixed effects linear models.

Results

103 patients were randomised to the IPC group (n = 52) and the RPC group (n = 51). VAS knee pain scores changed statistically significantly from baseline to end of treatment in both groups, −13.7 (standard error [SE]: 3.2) in the IPC group and −13.0 (SE: 3.1) in the RPC group with an adjusted between-group difference of −0.7 (95% CI: −8.3 to 6.9; P = 0.85). Likewise, no group differences were seen in KOOS ADL and KOOS QoL.

Conclusion

A conversation concerning knee pain-related IP did not augment the pain-relieving effect of an open-label placebo injection when compared to a similar control conversation concerning motivations for participating in research.

Trial registration

NCT05225480.