Polyaxial pedicle screw

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, a lower portion of the housing including a plurality of deflectable tabs arranged around a perimeter of the housing, 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;
• a spacer positionable in the bore of the housing, the spacer movable in the bore of the housing between a first position and a second position, the spacer being closer to the lower end of the housing in the first position and closer to the upper end of the housing in the second position;
• a bone screw including a head portion and a shank, extending from the head portion, the head portion of the bone screw positionable in a cavity of the spacer with the shank extending from the lower end of the housing;
• a collar positionable circumferentially exterior of the plurality of deflectable tabs to inhibit outward radial deflection of the plurality of tabs;
• and
• a resilient spring means biasing the spacer toward the first position into engagement with the head portion of the bone screw;
• wherein the head portion of the bone screw is insertable into the bore of the housing from the lower end of the housing by deflecting the plurality of tabs radially outward, but is not removable from the housing when the collar is positioned circumferentially exterior of the plurality of deflectable tabs.

A method of assembling a polyaxial bone anchor comprising:

• providing 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;
• inserting a retainer into the bore of the housing from the lower end of the housing by passing the retainer through the lower opening, the retainer having an outermost diameter greater than a diameter of the lower opening, the retainer including a plurality of alternating tabs and slots formed therein providing the retainer with sufficient flexibility to be urged through the lower opening from the lower end of the housing by radially compressing the retainer;
• inserting a head portion of a bone screw into a cavity of the retainer from the lower end of the housing by moving the retainer toward the upper end of the housing allowing the plurality of tabs to splay radially outward to accommodate passage of the head portion of the bone screw into the cavity of the retainer;
• and
• urging the retainer, with the head portion of the bone screw positioned in the cavity of the retainer, back toward the lower end of the housing to retain the head portion of the bone screw in the cavity of the retainer;
• wherein the retainer is biased toward the lower end of the housing by a biasing spring means.