Bone anchor receiver with extension portions having controlled splay allowance helically wound flange forms

Abstract

Open implant closure structures include a helically wound guide and advancement flange form having splay control surfaces. Multi-start closures and closures with inner set screws have splay control contours for interlocking with cooperating flange forms of bone anchor receivers. Flange form heights, thicknesses and other geometry, such as splay control ramp angle may be varied.

What is claimed and desired to be secured by Letters Patent is as follows: 
     
         1 . A spinal fixation structure comprising:
 a receiver having a set of arms, each of the set of arms having an inner surface;   a channel defined by the set of arms;   a closure rotationally receivable into the channel;   a closure flange extending continuously and helically about the closure, the closure flange having a closure load flank and a closure splay control ramp; and   a receiver flange extending discontinuously and helically along the inner surface of each of the set of arms, the receiver flange form having a receiver load flank and a receiver splay control ramp, the closure flange and the receiver flange allowing an outward splay of the set of arms as a torque between the closure and the set of arms increases during loading of the closure load flank and the receiver load flank, the receiver splay control ramp mutually engaging the closure splay control ramp in a locking relationship, the locking relationship constraining the outward splay of the set of arms.