Patent ID: 8425607

Claim:
An implantable medical device, comprising: an implant member having an upper surface configured to interface with a bone structure, a lower surface configured to interface with a bone structure, and a side surface extending from the upper surface to the lower surface, the implant member also having an angled aperture extending through the side surface, the aperture having an axis and having an inner surface with a semicircular channel formed in the inner surface, the channel being disposed in a plane substantially normal to the axis and disposed at a depth within the angled aperture where the plane intersects with the inner surface along a partial circumferential line and not a complete circumferential line, the semicircular channel being formed by first and second sidewalls and end boundary walls, the end boundary walls forming ends of the channel and being disposed on substantially opposing sides of the aperture; and a semicircular locking ring disposed in the semi-circular channel and being sized to extend about to the end boundary walls of the channel, the locking ring having an upper surface and a lower surface, the upper surface being disposed to face the first side wall of the channel and the lower surface being disposed to face the second sidewall of the channel, wherein the end boundary walls are configured to limit rotation of the locking ring in the semicircular channel, the locking ring being configured to cooperate with the implant member to prevent back-out of an anchor member in the aperture.