Locking compression members for use with bone anchor assemblies and methods

摘要

Various exemplary methods and devices are provided for fixing bone anchors to bone. In general, the methods and devices can allow for a bone anchor to be fixed to a bone at a desired angle to a surface of the bone. In an exemplary embodiment, a bone anchor assembly is provided that includes a bone anchor configured to engage bone, a receiver member for seating a head of the bone anchor, and a compression member for securing the bone anchor at fixed angle with respect to the receiver member when the compression member is seated within the receiver member. Corresponding engagement features of the compression member and the receiver member can be engaged in a secured configuration to inhibit or prevent removal of the compression cap from the receiver member and optionally to substantially prevent longitudinal and/or rotational movement of the compression member with respect to the receiver member.

主权项

1. A bone screw assembly, comprising:
a screw having a proximal head portion and a distal shank portion; a receiver member having a polyaxial seat formed therein and configured to polyaxially seat the head portion of the screw; a compression cap disposed within the receiver member and having a distal end configured to engage the head portion of the screw, the compression cap including opposed projections extending radially therefrom configured to mate with complementary recesses formed in the receiver member such that the compression cap is retained within the receiver member and exerts a frictional force on the head portion of the screw sufficient to prevent free movement of the screw relative to the receiver member while still allowing a user to polyaxially move the receiver member relative to the screw, wherein at least one dimension of the recesses is slightly larger than a corresponding dimension of the projections to allow for some adjustment of the compression cap when the projections are seated in the recesses, and the receiver member further includes ramped shoulders disposed proximal to the recesses, the ramped shoulders being angled such that an inner diameter of the receiver member decreases in a proximal to distal direction and such that the ramped shoulders engage and deform the projections as the compression cap is advanced distally into the receiver member; wherein the compression cap further includes a lip disposed proximal to the projections and configured to engage the ramped shoulders of the receiver member when the projections are seated within the recesses.