INTRODUCTION Perceived diagnostic uncertainty can leave adolescents confused about their condition and impede their ability to understand ″what′s wrong with me″. Our aim is to develop credible explanations (trustworthy and understandable explanation of the condition) for adolescents suffering from chronic non-traumatic knee pain. METHODS This multiple-method study integrated findings from a systematic literature search of qualitative studies, an Argumentative Delphi with international experts (n=16) and think-aloud sessions with adolescents (n=7). Experts provided feedback with arguments on how to communicate credible explanations to meet adolescents′ needs. We analyzed feedback using thematic analysis before tailoring explanations to end-users. RESULTS We screened 3.239 titles/abstracts and included 16 papers which explored diagnostic uncertainty from adolescents′ and parents′ perspectives. Five themes emerged: (1) Understanding causes and contributors to the pain experience, (2) Feeling stigmatized for having an invisible condition, (3) Having a name for pain, (4) Controllability of pain, and (5) Worried about something being missed. The Argumentative Delphi revealed the following themes: (1) Multidimensional perspective, (2) Tailored to adolescents, (3) Validation and reassurance, and (4) Careful wording. Merging findings from the systematic search and the Delphi revealed three essential domains to address in credible explanations: ″What is non-traumatic knee pain and what does it mean?″, ″What is causing my knee pain?″ and ″How do I manage my knee pain?″. CONCLUSIONS Six credible explanations for the six most common diagnoses of chronic non-traumatic knee pain were developed. We identified three domains to consider when tailoring credible explanations to adolescents experiencing non-traumatic knee pain.

MSH has received support from non-industrial professional, private, and scientific bodies (reimbursement of travel costs and speaker fees) for lectures on pain, and he receives book royalties from Gyldendal, Munksgaard Denmark, FADL, and Muusmann publications. Otherwise, none of the authors declare conflicts of interest.

This work is funded by the TrygFonden ID: 118547.

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Ethics Committee of North Denmark Region. This study was exempt from a full ethical approval by The North Denmark Region Committee on Health Research Ethics due to the non-interventional nature of the study and the data that was collected. Signed informed consent was obtained from all participants.

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