Modular screw assembly

A modular screw assembly for use in stabilizing a spinal column, comprising:

• a fastener which couples to a screw head of a bone anchor;
• a screw head coupler;
• a retaining ring;
• and
• a friction ring,
• wherein
• the fastener houses the screw head coupler, the retaining ring, and the friction ring,
• translation of the fastener past the screw head results in the retaining ring elastically deforming and then snapping around the screw head, wherein the retaining ring comprises a split ring having a gap on a perimeter and further comprises inwardly protruding ribs angularly disposed around the retaining ring to grip the screw head of the bone anchor after the retaining ring snaps around the screw head, and
• the inwardly protruding ribs extend along a direction of the translation.

A system for stabilizing a spinal column, comprising:

• at least one modular screw assembly;
• at least one bone anchor;
• a connecting rod;
• and
• at least one set screw,
• wherein
• the at least one modular screw assembly has a fastener which couples to a screw head of the at least one bone anchor, a screw head coupler, a retaining ring, and a friction ring,
• after securing the at least one modular screw assembly by snapping the retaining ring around the screw head, the connecting rod is fastened to the modular screw assembly by the at least one set screw, and
• the friction ring mates to an outer wall of the retaining ring such that, upon translation of the fastener past the screw head, the retaining ring slides along an inner surface of the friction ring resulting in the retaining ring elastically deforming and then snapping around the screw head.