A line that extends from the first metatarsophalangeal joint, over the navicular tubercle, to the apex of the medial malleolus. Changes in the angle formed by this line before and during weightbearing can be used to determine excessive pro nation of the foot. If the angle formed by Feiss’ line is in the range of 30 to 90 degrees while the foot is weight bearing, it may be considered hyperpronated.