Conclusion
It is methodologically feasible to conduct a fully powered RCT to compare the clinical and cost-effectiveness of the OPTimisE treatment protocol against usual physiotherapy treatment. However, both intervention and usual care groups showed similar improvements over time, questioning the importance of a future comparative main trial. Future research might now consider comparing whether diagnosis, reassurance and comprehensive self-help advice is non-inferior to usual physiotherapy care in terms of cost-effectiveness. Any future trial would need to be adapted to simplify patient identification, shorten outcome questionnaires and include incentivisation, use online data collection by default, add monthly SMS text message outcomes, include minimum data collection by telephone, and incorporate language translation.