Spinal stabilization system including bottom loading wide angulation polyaxial rod anchor assemblies

A method of assembling a polyaxial anchor assembly, comprising:

• a. providing a bone anchor having a first end, a second end, a longitudinal axis extending through the first and second ends, and a neck positioned on the longitudinal axis between the first end and the second end, the first end comprising a spherical shaped head and a recess formed within the head;
• b. providing a receiver having a first receiver end, a second receiver end, and a receiver axis extending through the first and second receiver ends, the first receiver end comprising a socket cavity, a socket aperture, a socket cavity slot extending from the socket cavity in a transverse direction relative to the receiver axis, and an interference element extending over a portion of the socket aperture opposite the socket cavity slot;
• c. inserting a first portion of the head into the socket cavity while the bone anchor is oriented at a first angular orientation relative to the receiver axis such that the recess is engaged with the interference element and the neck is at least partially inserted within the socket cavity slot;
• d. advancing the first portion of the head further into the socket cavity by at least rotating the bone anchor to a second angular orientation relative to the receiver axis in a first rotation direction while the recess is engaged with the interference element, wherein the angle between the longitudinal axis and the receiver axis in the second angular orientation is greater than the angle between the longitudinal axis and the receiver axis in the first angular orientation;
• e. advancing a second portion of the head into the socket cavity by at least rotating the bone anchor in a second rotation direction different from the first rotation direction such that the second portion of the head clears the interference element and enters the socket cavity, fully capturing the head within the socket cavity;
• and
• f. rotating the bone anchor with respect to the socket cavity about the head in the second rotation direction such that the neck disengages from the socket cavity slot.

A polyaxial spinal anchor assembly comprising:

• a. a bone anchor having:
• i. a first end and a second end, the first end comprising a head comprising a first keyed contour in at least one plane;
• and
• ii. a neck extending from the head toward the second end, the neck having a diameter less than a diameter of the head;
• and
• b. a receiver having:
• i. a base having a first end, a second end, an outer surface, and an inner surface defining a volume configured to receive and articulate the head;
• ii. a first opening having a second keyed contour configured to engage and disengage with the head of the bone anchor;
• and
• iii. a second opening extending from the first opening and the volume, wherein the second opening is generally perpendicular to the first opening and configured to engage and disengage with the neck of the bone anchor, and wherein the first and second openings permit insertion of the head into the volume upon at least rotation of the first keyed contour with respect to the second keyed contour in a first rotation direction and subsequent rotation of the first keyed contour with respect to the second keyed contour in a second rotation direction different from the first rotation direction before the head is fully captured and pivotable within the volume.