Abstract: A washer for use with a bone screw having a shank and a head defining a maximum diameter, includes a body having a bottom face for engaging the surface of a bone and an opening therethrough sized to receive the shank of a bone screw extending therethrough. The washer includes a cavity in communication with the opening at the bottom face and configured to receive the head of the bone screw when the shank extends through the opening at said bottom face. The washer includes a plurality of flaps distributed around the opening of the cavity that are bendable from a first configuration in which the flaps define an opening sized to receive the head of the bone screw, to a second configuration in which the flaps define an opening smaller than the maximum diameter of the head of the bone screw.