Polyaxial pedicle screw with increased angulation

A polyaxial bone anchor, comprising:

• a housing having an upper end, a lower end and a bore extending through the housing from the upper end to the lower end, the bore opening out at the lower end at a lower opening, the housing including a channel configured for receiving an elongate stabilization member therethrough which extends from a first side surface of the housing to a second side surface of the housing opposite the first side surface transverse to the bore;
• and
• a bone screw including a head and a shank extending from the head, the head of the bone screw positionable in the housing with the shank extending from the lower end of the housing;
• wherein the lower opening of the bore defines an angulation limit of the bone screw for each azimuthal angle around a longitudinal axis of the bore;
• wherein the angulation limit has a maximum value in a high-angulation direction;
• wherein the angulation limit is generally constant over an azimuthal range of at least 50 degrees centered about the high-angulation direction;
• and
• wherein for a low-angulation direction opposite the high-angulation direction, the angulation limit is less than the maximum value.

A method of assembling a polyaxial bone anchor, the method comprising:

• providing an upper housing having a bore extending vertically therethrough, the upper housing including a plurality of plastically deformable tabs circumferentially around a lower end of the upper housing, each tab having a portion that extends radially outward beyond a radial extent of the bore and a portion that extends radially inside the bore;
• providing a lower housing having a lip proximate an upper end of the lower housing;
• placing the lower housing beneath the upper housing so that the lip is radially adjacent the tabs;
• inserting a mandrel downward through the bore in the upper housing;
• forcing the tabs radially outward with the mandrel, each tab on the upper housing plastically deforming radially outward and engaging the lip on the lower housing;
• and
• withdrawing the mandrel from the upper housing.