Patent ID: 7951172

Claim:
A bone anchor assembly, comprising: a bone anchor having a proximal head and a distal shaft extending along a longitudinal axis configured to engage bone; a receiving member for receiving a spinal fixation element and for engaging the proximal head of the bone anchor; and a restriction member inserted in the receiving member for allowing the bone anchor to pivot relative to the receiving member about a first axis of the proximal head in at least a first direction and for restricting the bone anchor from pivoting about a second axis in a second direction, the restriction member comprising: a cap for seating the proximal head within a cavity of the receiving member; and first and second protrusions extending from opposite ends of the cap and beyond a bottom surface of the cap along the first axis forming an open-ended passage collinear with the second axis, between the first and second protrusions, allowing the bone anchor to pivot relative to the receiving member about the first axis of the proximal head in at least a first direction and restricting the bone anchor from pivoting about a second axis in a second direction; wherein the cap includes a seat formed in a first surface of the cap for receiving the spinal fixation element, and wherein the seat has a U-shaped profile in cross-section.