Medical knowledge was restricted by European universities. Although we have no real records of why this happened, it is fairly easy to guess that the university professors, who had renewed access to ancient texts, wanted to promote European science over Islamic, which was also available at the time. As a result, they took the stand that Aristotelian science was correct and anything that disagreed with it was wrong.
There were two great problems with this. The first was that by insisting on conformity to Aristotelian science, they prevented any progress going beyond Aristotelian science. The second was that the Islamic science, being dynamic, encouraged research and observation of empirical results, and so was superior. This situation ended when the Church stepped in by issuing the Condemnations of 1277. These made teaching the idea that Aristotle was always right a heresy, which effectively freed science from the strictures imposed by the universities.
Unfortunately for all, the thinkers European Renaissance, in their conscious attempt to resurrect the culture of ancient Rome, threw out much of the new science that had been developed in the Middle Ages. It took until the 19th century for Europe to recover to the point that physicians performed such simple tasks as washing their hands before operations, which had been standard practice in the Middle Ages.