Helical guide and advancement flange with radially loaded lip
View Patent ↗A spinal fixation device combines an open-headed anchor member, such as a bone screw or a hook, with a closure member to thereby clamp a spinal fixation rod to the anchor member. The anchor member has spaced apart arms forming a rod receiving channel. The arms have arm extensions or tabs connected to main portions of the arms by weakened regions to enable the tabs to be broken-off or separated after the rod is clamped. The closure member and inner surfaces of the arms and tabs have helical anti-splay guide and advancement interlocking flanges formed thereon which cooperate to prevent splaying the arms and extensions as the closure member is advanced into the rod receiving channel. The flanges have anti-splay contours which can be formed on load flanks or stab flanks of the flanges. The load flanks can be oriented in such a manner as to aid in the anti-splay characteristics of the flanges or to control the proportioning of axial stresses between the flanges.
1. A flange structure for guiding and advancing an inner member into an outer member having spaced arms along an axis in response to relative rotation between said inner member and said outer member about said axis and comprising:
(a) an inner flange helically wound about and along said inner member;
(b) a discontinuous outer flange helically wound about and along an opening in said outer member;
(c) one of said inner and outer flanges being a lipped flange and having a lip projecting axially therefrom and extending therealong, said lip having an axial peak and a curvate surface;
(d) the other of said flanges being a grooved flange and having a groove formed axially into said grooved flange and extending therealong, said groove having an axial trough and a curvate surface; and
(e) said lipped flange and said grooved flange being configured in such a manner so as to radially interlock to resist radial splaying of the outer member arms relative to the inner member and so as to enable rotary joining of portions of said lip and said groove in response to said inner member being rotated relative to said outer member and being helically advanced into said outer member.
2. A structure as set forth in claim 1 wherein:
(a) said arms including main portions and extended portions connected to said main portions by weakened regions, said outer flange extending longitudinally along said arm inner surfaces.