Bottom-loading bone anchor assemblies

摘要

Bone anchor assemblies are disclosed herein and include bone anchors, receiver members, and closure mechanisms. In one embodiment, a receiver member can be configured to seat a portion of a bone anchor and to receive a spinal fixation element, such as a rod. In an exemplary embodiment, the receiver member is bottom-loading and can include a seat having an opening that can be selectively increased and decreased in size so as to allow a bone anchor to be bottom-loaded. A force can be applied to the receiver member to increase a size of the opening, allowing a portion of the anchor to pass through the opening and into the seat. A closure element can be coupled to the receiver member and can apply a force to decrease a size of the seat and a size of the opening, angularly fixing the receiver member relative to the bone anchor.

主权项

1. A bone anchor assembly, comprising:
a bone anchor having a proximal head and a distal threaded portion; and a receiver member having a proximal portion with opposed arms configured to receive a spinal fixation rod therebetween, the opposed arms of the receiver member defining a U-shaped recess having opposed planar surfaces for seating spinal fixation rods of differing diameters, the opposed planar surfaces extending at an oblique angle relative to a longitudinal axis of the receiver member, the receiver member having a distal portion having a polyaxial seat formed therein and configured to polyaxially seat the proximal head of the bone anchor, and the opposed arms having interior receiver threads, the receiver threads having a major diameter that increases in a distal-to-proximal direction when the opposed arms are parallel to each other, the receiver member having opposed relief slots formed therein, each slot having a first portion that extends parallel to the longitudinal axis of the receiver member and a second portion that is substantially perpendicular to the first portion; wherein the opposed arms are configured to move toward one another to cause a size of the polyaxial seat to increase and to cause the second portions of the slots to form a crescent shape, and the opposed arms are configured to move away from one another to cause the size of the polyaxial seat to decrease.