Patent ID: 7837716

Claim:
A bone screw apparatus for securing a spinal implant rod to a patient's vertebra; said apparatus comprising: a) a bone screw shank adapted to be implanted into the vertebra; b) a head secured to the shank during usage and having a pair of spaced and upstanding arms forming a channel therebetween with said channel being sized and shaped to receive the rod; c) each of the arms having an inner surface with a discontinuous and aligned helically wound first threadform on each of the arm's inner surfaces; said first threadform having a lower surface nearest said shank and an upper surface; said head having an axis of rotation; said first threadform lower surface having a vertical cross section with a first angle of inclination relative to a radius perpendicular to said axis in a range from 30° to 70° and said first threadform upper surface having a vertical cross section with a second angle of inclination relative to a radius perpendicular to said axis that is always less than said first angle and is within a range of between 1° and 45° with respect to said axis; said first threadform lower surface having a first outer edge and said first threadform upper surface having a second outer edge spaced from said first outer edge; said first threadform having a third surface connecting said first and second outer edges; said third surface joining the lower surface first outer edge and the upper surface second outer edge such that the first outer edge is substantially spaced below the second outer edge; both of said first threadform lower and upper surfaces being sloped in the same direction and said first threadform lower and upper surfaces being sloped both radially outwardly and upwardly relative to said axis, wherein a third angle defined by the upper and third surfaces is less than 90°; and d) a closure sized and shaped to close said channel after placement of the rod in the channel; said closure including a cylindrical body and a generally continuous helically wound threadform thereon that wraps on an outer surface of the body about said axis; said second threadform being sized and shaped to thread into and snugly mate with said first threadform upon joining and rotation of said closure between said arms; said closure including removal structure to provide for removal of the closure after inserting between the arms.