Patent ID: 7736380

Claim:
An anchor device for securing to a bone a plate having an upper surface and a lower surface and apertures extending from the upper surface to the lower surface, the apertures having inside concave edge walls spaced apart a given inner diameter and having an upper surface opening and a lower surface opening, each having a diameter smaller than the inner diameter, comprising: a screw including a head portion and a threaded shank with a distal tip and a central longitudinal axis, the head portion having a central opening exposed at the proximal end of the screw and an annular wall around the central opening, the annular wall having an inner and an outer surface, the outer surface having a relaxed outer diameter substantially equal to the inner diameter of the aperture, and the annular wall having a plurality of slots that separate the annular wall into a plurality of petals, wherein the inner surface of the annular wall includes a plurality of shallow recesses and a plurality of deep recesses, wherein at least one of the petals has an inner surface of the annular wall having at least two of the shallow recesses, the screw further including an internal surface of defined shape originating in the central opening for engagement by a matingly-configured screw driving tool for driving the screw into the bone; and a locking disc rotatably disposed within the central opening and having a periphery of defining a plurality of extending protrusions, the locking disc rotatable between a first rotational position and second rotational position; wherein the shallow recesses, the deep recesses, and the protrusions are configured so that when the locking disc is in the first rotational position, the protrusions are disposed in the deep recesses in the inner surface of the annular wall with a clearance permitting the petals to flex inwardly to insert the screw head into the aperture past the upper surface opening, and when the locking disc is rotated to the second rotational position two of the protrusions are disposed in and engage with a corresponding two of the shallow recesses formed on the inner surface of at least one of the petals to establish a corresponding two engagements when the petal substantially is at its free relaxed state to prevent the petal from flexing inwardly, whereby the head is selectively captured within the concave edge walls of the plate aperture.