Evaluating the efficacy of complex interventions such as multimodal, impairment-based physical therapy treatments in randomized controlled trials is essential to inform practice and compare relative benefits of available treatment options. Studies of physical therapy interventions using highly standardized intervention protocols, although methodologically rigorous, do not necessarily reflect "real-world" clinical practice, and in many cases results have been disappointing. Development of a complex intervention that includes multiple treatment modalities and individualized treatment technique selection requires a systematic approach to designing all aspects of the intervention based on theory, evidence, and practical constraints. This perspective article outlines the development of the rationale and structure of a multimodal physical therapy program for painful hip osteoarthritis to be assessed in a clinical trial. The resulting intervention protocol comprises a semi-structured program of exercises and manual therapy, advice, physical activity, and optional prescription of a gait aid that is standardized, yet can be individualized according to physical assessment and radiographic findings. The program is evidence based and reflects contemporary physical therapist practice, while also being reproducible and reportable. This perspective article aims to encourage physical therapy researchers involved in evaluation of complex interventions to better document their own intervention development, as well as the outcomes, thus generating a body of knowledge about the development processes and protocols that is generalizable to the real-world complexity of providing physical therapy to individual patients.