Giovanni Dosi´s technological paradigm theory was developed in part to correct the then dominant practise to focus on either "demand pull" when explaining technical change. In Doi´s view, demand can act as a "focusing device" for the supply side to select among the available technological paradigms for development. In this article, we study a specific case, the technological evolution of a surgical implant (an artificial disc in the spinal column), to analyse this selection dynamics. We conclude Dosi´s theory can be extended by adding some technological signals interacting with demand forces in this pre-market selection process, which help to explain the historical supply side choices in the evolution of the artificial disc.Peer reviewed