Background: Extended scope physiotherapists (ESP) are increasingly supplementing orthopaedic surgeons (OS) in diagnosing patients with musculoskeletal disorders. Studies have reported satisfactory diagnostic and treatment agreement between ESPs and OSs, but methodological study quality is generally low, and only few studies have evaluated inter-professional collaboration. Our aims were: 1) to evaluate agreement on diagnosis and treatment plan between ESPs and OSs examining patients with shoulder disorders, 2) to explore and evaluate their inter-professional collaboration. Methods: 1)In an orthopaedic outpatient shoulder clinic, 69 patients were examined independently twice on the same day by an ESP and an OS in random order. Primary and secondary diagnoses (nine categories) and treatment plan (five categories, combinations allowed) were registered by each professional and compared. Percentage of agreement and kappa-values were calculated.2)Two semi-structured focus-group interviews were performed with ESPs and OSs, respectively. Interviews were based on the theoretical concept of Relational Coordination, encompassing seven dimensions of communication and relationship among professionals. A thematic analysis was conducted. Results: 1)Agreement on primary diagnosis was 62% (95% CI: [50; 73]). ESPs and OSs agreed on the combination of diagnoses in 79% (95% CI: [70; 89]) of the cases. Partial diagnostic agreement (one professional’s primary diagnosis was also registered as either primary or secondary diagnosis by the other) was 96% (95% CI: [91; 100]). Across treatment categories, agreement varied between 68% (95% CI: [57; 79]) and 100%. In 43% (95% CI: [31; 54]) of the cases, ESP and OS had full concordance between treatment categories chosen, while they agreed on at least one recommendation in 96% (95% CI: [91; 100]).2)Positive statements of all dimensions of relational coordination were found. Three themes especially important in the inter-professional collaboration emerged: Close communication, equal and respectful relationship and professional skills. Conclusions: In the majority of cases, the ESP and OS registered the same or partly the same diagnosis and treatment plan. Indications of a high relational coordination implying a good inter-professional collaboration were found. Our results support that ESPs and OSs can share the task of examining selected patients with shoulder disorders in an orthopaedic clinic. Trial registration: ClinicalTrials.gov Identifier: NCT03343951. Registered 10 November 2017