Just to clear up a point about 'medieval' pteruges, I cannot speak to the effectiveness of pteruges when they were used on the classical era, but later Medieval or renaissance portrayals of flaps are likely to be a sort of artistic trope used when portraying classical figures (mythical or Historical) or biblical/angelic figures. Thus they are often seen on altarpieces or tapestries depicting ancient events and not in contemporary portraits, illustrations or funerary effigies. Eventually life immitated art and they were incorporated into parade armour 'ala antiqua.'

Thus, pteruges were not used as protection during the high and later middle ages and early modern period in Western Europe.