Constrained Motion Bone Screw Assembly

摘要

A bone screw assembly includes an anchor portion and a head portion, such as a rod-receiving portion, movably mounted to the anchor portion to allow for controlled angulation between the anchor portion and the head portion. The anchor portion is pivotable in one or more selected directions about an axis relative to the head portion. A restriction member, which may be a rod seat, prevents the anchor portion from pivoting in one or more different directions about another axis relative to the head portion and/or a spinal fixation element received in the head portion. The restriction member may be inserted in the head portion to control direction that the anchor portion pivots relative to the head portion. The restriction member may also serve as a compression member and/or rod seat for seating a spinal rod coupled to the bone screw assembly.

主权项

1. A bone anchor assembly comprising:
a bone anchor having a proximal head and a distal shaft configured to engage bone, the distal shaft having a central longitudinal axis, the proximal head having two opposed flat side surfaces oriented parallel to the longitudinal axis of the distal shaft and two curved surfaces each interposed between the flat side surfaces, a receiving member have a proximal end and a distal end, the proximal end having two spaced apart upright arm defining a recess for receiving a spinal rod therebetween, the distal end having a bore therethrough, the bore having a proximal opening at the recess and a distal opening sized to allow insertion of the proximal head of the bone anchor therethrough, a retaining member positioned within a groove in the bore of the distal end of the receiving member, the retaining member retaining the proximal head of the bone anchor within the bore, a compression member positioned within the receiver member proximal to the proximal head of the bone anchor, and a closure mechanism engageable with inner surfaces of the arms of the receiving member to secure a spinal rod within the recess, wherein the bone anchor is rotatable about a rotation axis that intersects the flat side surfaces and is oriented perpendicular to the flat side surfaces, the bone anchor being prevented from rotation about an axis oriented perpendicular to the rotation axis and perpendicular to the longitudinal axis of the bone anchor.