Mortise view : To obtain a better view of the ankle mortise, the patient's leg must be internally rotated just enough so that the lateral malleolus (which is normally posterior to the medial malleolus), is on the same horizontal plane as the medial malleolus, and a line drawn through both malleoli would be parallel to the tabletop.
Usually this only requires approximately 10 - 20 degrees of internal rotation. In other words, when viewing the mortise view, the tibia and fibula must be viewed without superimposition on each other. This mortise view represents a true AP projection of the ankle mortise and also provides a good visualization of the talar dome (to rule-out osteochondral talar dome fractures).