Before Islamic experts brought a semblance of reason to the practice of not allowing sick people to die on the operation table, the realm of medicine in the Medieval period was mostly a blood-soaked shambles led by military doctors who were used to cutting away at wounds during the heat of battle. Combine this lack of experience with excruciatingly primitive tools, all-encompassing superstition, and virtually no knowledge of mental health, and a rather grim picture is painted for the Medieval who might find themselves unfortunate enough to develop a sore arse or a nervous twitch. Imagine visiting your local GP complaining of night spasms, being diagnosed with demonic possession, and thusly having a pole driven through your skull, and you get the picture of what was going on. Let's have a look at two of the most prominent forms of "surgery" during the Medieval period.
Blood-letting was an exercise designed to aid people in bad humour. No, we're not talking about snotty politicos with social media accounts. Humours in the Medieval times referred to what was believed to be their four cardinal bodily fluids, the innards which made a person healthy, namely phlegm, yellow bile, black bile, and blood. When someone would complain of bodily ailment, they would be faced with a few options including a change in diet, but more often than not, the "doctor" would prescribe a draining of "bad humours." In order to drain these ailing humours, an incision would have to be made on one of the patient's body parts in order to drain the bad blood inside of them, thus restoring balance to the all-important four humours. One of the reasons blood-letting was used this was due to the Medieval belief that each body part held veins connected to a specific internal organ, so by draining the blood from this body part, the insides would become detoxified. Of course, this was horseshit, and many patients would bleed to death due to a bumbling doctor, sometimes a barber, slicing away and tapping a vein dry.
Thankfully, we have Web MD for misdiagnosis these days and are happy enough to ignore major health issues until they claim us much later on down the line. We've come a long way, and further we shall go.