[4] In his document about Fistula in ano, John of Arderne sets out not only his operative procedures but also his code of conduct for the ideal medical practitioner.
He saw active military service in the Hundred Years' War in the army of Henry of Grosmont, Duke of Lancaster, and John of Gaunt.
He fought also at the Siege of Algeciras (1342-1344), one of the first European battles in which gunpowder was used; the injuries he saw there informed his medical writings for three decades.
He developed several treatments for knights, most notably for an infliction called "Fistula In Ano", a condition where a large, painful lump appears between the base of the spine and the anus, caused by long amounts of time sitting on a horse.
In technical terms, the Fistula in Ano, without any regard to the strict definition of the word, is understood to be an abscess, running upon, or into the Intestinum Rectum; though an abscess in this part, when once ruptured, does generally, if neglected, grow callous in its cavity and edges, and become at last what is properly called a fistula.