Advocates for patient involvement argue that seeking the active contribution of patients and families in the coordination of care can help mitigate system complexity, and lead to improvements in quality. However, sociological and organisational research has identified barriers to involving patients in care planning, not least the power of, and boundaries between, multiple professional groups. This study draws on literature from Science and Technology Studies (STS) to explore the patients' role in coordinating care across professional-practice boundaries in complex care systems. Findings are drawn from a two-year ethnographic study (including 69 qualitative interviews) of hospital discharge following hip-fracture care and describe the changing role of the patient as they move out of hospital into community settings. Findings describe how 'the patient' plays a relatively passive role as boundary object while recovering from surgery within hospital, where inter-professional coordination was prescribed by evidence-based guidelines, leaving little space for patient voice. As discharge planning begins, patient involvement is both encouraged and contested by different professional groups, with varying levels of commitment to include patient subjectivities in care. As patients move into home and community settings, they, their families and carers play an increasingly active role in coordination, often in light of perceived gaps in coordination between care providers. This paper argues that whilst the need for patient and carer involvement is becoming increasingly evident, such involvement plays into, and is mediated through, existing relations between professional and practice groups. Patient and carer involvement is therefore not straightforward and should be considered across the health and care systems in order to meaningfully improve care quality.