Journal of Medical Internet Research - International Scientific Journal for Medical Research, Information and Communication on the Internet #Preprint #PeerReviewMe: Warning: This is a unreviewed preprint. Readers are warned that the document has not been peer-reviewed by expert/patient reviewers or an academic editor, may contain misleading claims, and is likely to undergo changes before final publication, if accepted, or may have been rejected/withdrawn. Readers with interest and expertise are encouraged to sign up as peer-reviewer, if the paper is within an open peer-review period. Please cite this preprint only for review purposes or for grant applications and CVs (if you are the author). Background: Modern healthcare focuses on Shared Decision Making (SDM) because of its positive effects on patient satisfaction, therapy compliance, and outcomes. Patients’ knowledge about their illness and available treatment options, gained through medical education, is one of the key drivers for SDM. Current patient education relies heavily on medical consultation and is known to be ineffective. Objective: To determine whether providing patients with information in a subdivided, categorized, and interactive manner via an educational app for smartphone or tablet may increase the knowledge of their illness. Methods: A surgeon blinded randomized controlled trial was conducted with 213 patients who were referred to one of the six Dutch hospitals by their general practitioner owing to knee complaints that were indicative of knee osteoarthritis (OA). An interactive app that, in addition to standard care, actively sends informative and pertinent content to patients about their illness on a daily basis by means of push notifications in the week prior to their consultation. The primary outcome was the level of perceived and actual knowledge that patients had about their knee complaints and the relevant treatment options after the intervention. Results: In total 122 patients were enrolled in the control group and 91 in the intervention group. After the intervention, the level of actual knowledge (measured on a 0-36 scale) was 52% higher in the app group (26.4 versus 17.4, P < 0.001). Moreover, within the app group, the level of perceived knowledge (measured on a 0-25 scale) increased by 22% during the week within the app group (from 13.5 to 16.5, P < 0.001), compared to no gain in the control group. Conclusions: Actively offering patients information in a subdivided (per day), categorized (per theme), and interactive (video and quiz questions) manner significantly increases their levels of knowledge (both perceived and actual), compared to standard care educational practices. Clinical Trial: The trial was approved by the regional Medical Ethical Board (Maxima Medisch Centrum, Eindhoven, The Netherlands), reference number N16.130.