Objective To explore patient, clinician and decision-maker perceptions on a clinical trial evaluating the effectiveness of total hip arthroplasty (THA) compared with exercise to inform the trial protocol. Design This is an exploratory qualitative case study using a constructivist paradigm. Setting and participants Participants were enrolled into three key stakeholder groups: patients eligible for THA, clinicians, and decision makers. Focus group interviews were conducted in undisturbed conference rooms at two hospitals in Denmark, according to group status using semi-structured interview guides. Analysis Interviews were recorded, transcribed verbatim and thematic analysed using an inductive approach. Results We conducted 4 focus group interviews with 14 patients, 1 focus group interview with 4 clinicians (2 orthopaedic surgeons and 2 physiotherapists) and 1 focus group interview with 4 decision-makers. Two main themes were generated. 'Treatment expectations and beliefs impact management choices' covered three supporting codes: Treatment without surgery is unlikely to lead to recovery; Clinician authority impacts the management narrative; The 'surgery vs exercise' debate. 'Factors influencing clinical trial integrity and feasibility' highlighted three supporting codes: Who is considered eligible for surgery?; Facilitators and barriers for surgery and exercise in a clinical trial context; Improvements in hip pain and hip function are the most important outcomes. Conclusions Based on key stakeholder treatment expectations and beliefs, we implemented three main strategies to improve the methodological rigorousness of our trial protocol. First, we added an observational study investigating the generalisability to address a potential low enrolment rate. Second, we developed an enrolment procedure using generic guidance and balanced narrative conveyed by an independent clinician to facilitate communication of clinical equipoise. Third, we adopted change in hip pain and function as the primary outcome. These findings highlight the value of patient and public involvement in the development of trial protocols to reduce bias in comparative clinical trials evaluating surgical and non-surgical management. Trial registration number NCT04070027 (pre-results).