The persistent uncertainty that defines and at the same time constraints the ability to address effectively medical problems offers important insights into the broader framework of analysis of technological change. This paper sets out to explore the process of hybridization, that is, the embodiment of multiple competing operational principles within a single medical device. The history of the development of the hybrid artificial disk presented here illustrates vividly the dualism between medical science as area of scientific research, e.g. what disease is, and as practical knowledge, e.g. how disease can be cured.