Bone screw fixation assembly, bone screw therefor and method of fixation

A fixation device, comprising:

• (a) a cylindrical shank having first and second end portions;
• (b) first thread means formed in said first end portion extending toward but terminating short of said second end portion;
• (c) a head mounted to said second end portion, said head having an upper surface being uninterrupted and arcuate, and a side rim extending from said upper surface;
• and,
• (d) second thread means formed about said side rim.

A bone screw insertion assembly, comprising:

• (a) a longitudinally extending member having a central aperture therethrough defining an inner wall with spaced first and second end portions;
• (b) first thread means formed in said inner wall at said first end portion;
• (c) a bone screw having a head with second thread means formed exteriorly thereabout and an upper surface being arcuate and uninterrupted, said second thread means in threaded engagement with said first thread means so that said bone screw is operably associated with said member and extends therefrom;
• (d) rod means received within said aperture and having a first end portion engaged with and conforming to said bone screw upper surface for applying a force thereto so that movement of said first thread means relative to said second thread means is prevented;
• and,
• (e) means operably associated with said member for selectively locking said rod means in engagement with said bone screw.

The method of securing a bone screw, comprising:

• (a) providing a tubular screw holder having a central aperture therethrough defining an inner wall with a first set of threads formed therein at a first end portion thereof;
• (b) providing a bone screw having a head which has an upper surface being arcuate and uninterrupted and a second set of threads formed about the head;
• (c) threadedly engaging the first and second sets of threads so that the bone screw is attached to the holder and extends therefrom;
• (d) positioning a rod means in the aperture so that an end of the rod means engages the bone screw upper surface and presses the first and second sets of threads together so that movement of the sets of threads relative to each other is prevented;
• and,
• (e) locking the rod means.