Healthcare today is mainly knowledge-based and the diffusion of medical knowledge is imperative for proper treatment of patients. Our study of the industry explored barriers to knowledge flow using a Cultural Historical Activity Theory framework. Our work was exploratory and qualitative in nature, and consisted of three phases: in-depth interviews to explore medical knowledge flow barriers resulting in a model; a case study using a survey approach to test and modify the model; and a Delphi study to validate the generalizability of the model. We concluded that knowledge flow experienced five barriers: knowledge source, knowledge receiver, knowledge transfer, knowledge flow context, and the organizational context. Furthermore, these were correlated.