Galen was a pretty accomplished medical researcher, and Roman-era medical implements were quite sophisticated, and were well-established by the time of the dark ages. By the late dark ages, we also saw a lot of modern medical techniques coming in from the Middle East.
There's this stereotype of people being filthy, ignorant, and dumb, but it's not really true. And for many of the bad practices from then do persist in poorer parts of the world today affecting likely around a billion people (and some, like homeopathy, even in wealthy parts).
Note that I'm not weighing in on the overall debate about where modern medicine is relative to the dark ages. We've made a lot of progress. I'm just refuting the stereotype of the dark ages.