An orthopedic assembly comprising: a) a plate member (50, 150) having an upper surface and a lower surface, and an aperture extending through the upper surface and the lower surface; b) an anchor received within the aperture, the anchor comprising a head portion, a neck portion and a shank portion that form a unitary body, wherein at least a portion of the shank portion includes inner threads; and c) a locking mechanism received within the anchor, the locking mechanism comprising a head and a shaft having outer threads, wherein the outer threads of the locking mechanism engage the inner threads of the shank portion, d) wherein the locking mechanism expands the head portion of the anchor as the locking member is downwardly inserted into the locking mechanism, thereby securing the anchor to the plate member, and wherein e) the head portion of the anchor comprises a four resilient flexible quadrants, f) each of the quadrants including an inner relief formed along an inner surface thereof providing a region in which the head portion of the locking mechanism is designed to contact and nest within the anchor, g) so that when the head of the locking mechanism is inserted into the anchor, the head of the locking mechanism causes outward expansion of the head portion of the anchor as the locking member is downwardly inserted into the locking mechanism, thereby securing the anchor to the plate member; h) and then upon further downward insertion of the locking mechanism once the head of the locking mechanism is nested and positioned within the inner reliefs, the resilient quadrants of the head portion of the anchor retract radially inward to tighten and capture the locking mechanism within the anchor. a) a plate member (50, 150) having an upper surface and a lower surface, and an aperture extending through the upper surface and the lower surface; b) an anchor received within the aperture, the anchor comprising a head portion, a neck portion and a shank portion that form a unitary body, wherein at least a portion of the shank portion includes inner threads; and c) a locking mechanism received within the anchor, the locking mechanism comprising a head and a shaft having outer threads, wherein the outer threads of the locking mechanism engage the inner threads of the shank portion, d) wherein the locking mechanism expands the head portion of the anchor as the locking member is downwardly inserted into the locking mechanism, thereby securing the anchor to the plate member, and wherein e) the head portion of the anchor comprises a four resilient flexible quadrants, f) each of the quadrants including an inner relief formed along an inner surface thereof providing a region in which the head portion of the locking mechanism is designed to contact and nest within the anchor, g) so that when the head of the locking mechanism is inserted into the anchor, the head of the locking mechanism causes outward expansion of the head portion of the anchor as the locking member is downwardly inserted into the locking mechanism, thereby securing the anchor to the plate member; h) and then upon further downward insertion of the locking mechanism once the head of the locking mechanism is nested and positioned within the inner reliefs, the resilient quadrants of the head portion of the anchor retract radially inward to tighten and capture the locking mechanism within the anchor.