Abstract
The development of interventions in healthcare often lacks a robust theoretical basis, which may contribute to suboptimal engagement and effectiveness. This paper provides insights into and practical guidance on the development of complex interventions in healthcare, using the example of a digital self-management tool for children with Perthes' disease, called the Non-Surgical Treatment of Perthes' (NON-STOP) app. We applied the Medical Research Council framework, used psychological theory, and integrated stakeholder engagement to develop the intervention. The lessons learned and considerations for the developments of other complex interventions provide practical actions for clinicians and researchers in orthopaedics.