Bone anchor closure pivot-splay control flange form guide and advancement structure
Open implant closure structures include a helically wound guide and advancement flange form having pivot-splay accommodating and splay control surfaces with opposing load flanks in initial non-parallel relation.
1. A spinal fixation structure comprising:
a closure flange form extending helically about a central axis of a closure;
a closure load flank of the closure flange form, the closure load flank sloping in a direction radially outwards from a root surface towards an outer crest surface, the closure load flank in a non-parallel relationship with a receiver load flank of a receiver flange form extending helically along an inner surface of a set of upright arms of a receiver; and
a closure splay control ramp disclosed adjacent the closure load flank, the closure splay control ramp configured to engage a receiver splay control ramp of the receiver flange form, the engagement of the closure flange form and the receiver flange form generating a controlled pivot-splay during rotational mating of the closure within the receiver, the controlled pivot-splay generating an outward pivot having a center of rotation disposed within each of the upright arms and reducing torque of the closure during loading of the closure into the receiver, the controlled pivot-splay arresting the outward pivot of the set of upright arms when the closure is it a locking engagement with the receiver.