Patent ID: 8100946
Filing Date: 2012-01-24
Classification: A61B

Abstract:
1. A polyaxial bone anchor for rigidly attaching a rod to a bone, the bone anchor comprising: an anchor head comprising a longitudinal bore having a top opening and a bottom opening, a channel transverse to the longitudinal bore for receiving the rod, and a central axis extending through the anchor head, the anchor head including an inner spherical surface formed in a lower portion; an anchor member for attaching to the bone, the anchor member consisting of a first end, a second end, a first portion for engaging a bone including the first end, and a second portion positioned adjacent to, adjoining and extending from the first portion to the second end wherein the second portion is generally spherical and substantially devoid of any projections; a bushing received within the longitudinal bore formed in the lower portion of the anchor head, the bushing including a top end, a bottom end, an exterior spherical surface for interacting with the inner spherical surface formed in the anchor head, an internal space defining an inner spherical surface for mating with the spherical head portion of the anchor member and a slot extending from the top end to the bottom end and from the exterior spherical surface to the inner spherical surface, the slot rendering the bushing radially expandable for receiving the head portion of the anchor member and radially compressible for applying a force to the head portion of the anchor member, the bottom end of the bushing extending beyond the bottom opening formed in the anchor head, the inner spherical surface of the bushing has a spherical centerpoint and the exterior spherical surface of the bushing has a spherical centerpoint, the spherical centerpoint of the inner spherical surface being vertically displaced toward the bottom end relative to the spherical centerpoint of the exterior spherical surface; a sleeve slidably received within the longitudinal bore formed in the anchor head, at least a portion of the sleeve located between the rod and the top end of the bushing; and a fastener removably mountable to the anchor head, the anchor member operable between an unlocked position and a locked position, in the unlocked position the rod and the anchor member are moveable with respect to the anchor head and in the locked position, the fastener applies a downward force to the rod, which applies a downward force to the sleeve, which applies a downward force to the bushing causing the bushing to radially compress against the head portion of the anchor member to thereby secure a position of the anchor member with respect to the anchor head and a position of the rod with respect to the anchor head.