Background Digital tools are becoming more and more common in healthcare. Their potential to improve treatment, monitoring, and coaching in physiotherapy has been recognized. Yet studies report that the adoption of digital health tools in ambulatory physiotherapy is rather low and that their potential is underexploited. Objective This paper aims to investigate how digital health tools in general, and the mobile health tool physitrackTM (hereafter the app) more particularly, are used in outpatient physiotherapy clinics and also to identify what facilitates or hinders the app’s use. Methods The paper is part of a larger study and adopts an ethnographic approach. It is based on observational and interview data collected at two outpatient clinics. Results We reveal how physiotherapists and patients use the app in physiotherapy and identify 16 interdependent factors, on the macro-, meso-, and micro-level, that either facilitate or hinder its use. Conclusions We argue that a single factor’s facilitating or hindering impact cannot be grasped in isolation but needs to be investigated as one piece of a dynamic interplay. Further qualitative research is required, especially to shed more light on the app’s compatibility with physiotherapy practice and use in therapist-patient interactions.