How did they treat broken bones in medieval times?

Answer 1

Medieval people had certain medicines, some of which were effective in treating wounds. Today we would regard them as home remedies. But the most effective thing they had was a healthy immune system. The problem was not just one of the middle ages, as antibiotics were not really effective until the introduction of penicillin in World War II. People died of infected blisters and pimples within the memory of people who are alive today.

Since I wrote this answer about four months back, I have come across references to use of primitive antibiotics in the Middle Ages. One was used on festering wounds, and this was a blue mold growing on bread, thought to be a form of penicillin. Another may be sphagnum, which has been used for centuries as a dressing on wounds. There may have been others, including hops which has antibacterial properties. We know hops were cultivated in 736 AD, but we have no record that they were used in beer until 1079; they might have been used to treat sleeping problems, but they are certainly used for as an antibiotic, and so they could have been. There are a couple links below.

Answer 2

Medicine was really not very good and there were few, if any, surgeons. Most people died of their wounds because they became infected or the bleeding couldn't be stopped. The doctors of the time were not allowed by the Church to look at a human body and this actually was followed all the way into the 1800's. Medical schools had to steal bodies to learn about the internal organs. In the Middle Ages there was a great deal of superstition involved in medicine so things like bleeding, leeches, and drinking urine were used. Herbal medicines were also used and going into a hospital was a guarantee of death.