Medical implant fastener with nested set screw and method

A nested fastener and set screw assembly for operably securing a rod within a bone screw head, the head having an opening, the assembly comprising:

• a) a fastener having a first end, a second end and an abutment shoulder disposed near the second end, the fastener adapted to be interferingly positioned within the bone screw head opening when in an installed configuration, the fastener having a centrally located through bore extending from the first end to the second end and a helical thread partially defining the through bore;
• b) a break-off head connected to and coaxial with the fastener, the break-off head operably breaking from the fastener at a preselected torque;
• c) a threaded set screw rotatably mateable with the helical thread of the fastener and receivable into the bore at the first end, the abutment shoulder interferingly prohibiting advancement of the set screw out of the second end;
• and
• d) an interference structure disposed on the set screw shaped and positioned to provide compressive force along a central axis of the set screw when in a setting configuration wherein the interference structure is in frictional engagement with the rod.

A nested fastener and set screw combination for securing a structural element within a receiver of a medical implant, the receiver having an opening, the combination comprising:

• a) a fastener adapted to be interferingly positioned within the opening of the receiver so as to close the opening when in an installed configuration, the fastener having an inner guide and advancement structure defining a bore extending therethrough;
• b) a set screw having an outer guide and advancement structure rotatingly mateable with the inner guide and advancement structure for loading and receiving the set screw in the bore of the fastener;
• and
• c) a curved, substantially convex interference structure projecting from a base of the set screw shaped and positioned to provide compressive force along a central axis of the set screw when in a setting configuration wherein the interference structure is in frictional engagement with the structural element.