John Arderne was a fourteenth century surgeon with the enviable title, Father of Proctology. Arderne specialized in the surgical treatment of anal fistula (fistula in ano), a "condition where a large, painful lump appears between the base of the spine and the anus" (Wikipedia), which he was able to excise in a dramatic, dangerous, and surprisingly successful procedure. A manuscript describing Arderne's method -- with pictures! -- is featured in the Glasgow Special Collections Library:
The instruments depicted [above], from left to right, are: the 'sequere me' ('follow me') a flexible probe, so called because it was the guide to be followed by other instruments; a syringe; the 'Acus rostrata' or snouted needle, a grooved director along which the scalpel was passed; the 'fraenum Caesaris' or strong thread, a ligature that constricted the rectal side of the fistula; the 'tendiculum', which was used to keep the ligature taut whilst the fistula was being divided; another syringe. The 'cochlear' (or shield) is shown at the top; this was probably held by the surgeon's mate and was used to protect the rectum during the operation. At the bottom is another snouted needle accompanied by a razor like scalpel.
The various stages of the operation are shown [here], starting with the position Arderne recommended that a patient should be secured exposing the fistula (top right). The basic premise of the operation was to cleanly divide the fistula by means of a scalpel inserted along the snouted needle.
Arderne's method of operation certainly worked, but it was probably his simple and clean application of sponge pressure to arrest immediate haemorrhage, followed by conservative care of the wound (avoiding cauterising and powerful purgatives) that ensured his relatively high success rate.
The work goes on to discuss various complicated cases that Arderne dealt with, including that of a man from Northampton. Apparently he suffered from three fistula holes in his left buttock and three in his testicle. Arderne says he cured these by cutting through all the holes in the same operation. Since the fistula were deep, the poor man lost so much blood that he swooned; Arderne managed to stem the haemorrhaging with a sponge and made his patient sit in a chair until the blood flow ceased. After taking meat and drink, the man went to bed, slept soundly, and was healed within 14 weeks. In another case, Arderne claims that his patient made such a dramatic recovery that he was able ride some forty days after his operation.