Rack Torture is a form of torture used during the middle ages. It involves a victim being tied down on a wood board while his hands were manacled to a roller at the top of the board and his ankles manacled to another  roller at the bottom.  An implementer of this said torture would very slowly turn a handle on the side of the board, and at each turn, the limbs would be pulled more. This pulling would continue until the felon's limbs were dislocated and they were in terrible pain.  

For criminals accused of a greater crime, instead of their arms simply being dislocated, they would be ripped out of their sockets. This is one of the longest and most uncomfortable form of tortures, and was widely used during the middle ages.