The dynamics of knowledge use in the context of care is complex and particularly challenging when knowledge is shared across boundaries in collaborative healthcare. The process is reliant on contextual features that support perceptions of shared information, and usually occurs within a complex structure of medical practice shaped by a wide range of factors, including local work patterns, organizational contexts, and patients' circumstances that vary across settings. Consequently, designing computational systems to support contextual knowledge sharing among clinicians working across boundaries remains a challenge. In particular, very few mechanisms exist for representing the notion of practice for computational design. This paper presents an approach for formalising and representing medical practice for cross-boundary knowledge sharing in healthcare. The approach is based on the practice theoretic paradigm, and draws upon a view of context as an interaction problem, representing practice as a context parameter for the design of cross-boundary collaborative healthcare systems.