Top and bottom loadable bone screw assembly with direct pivotal engagement between shank head and receiver

A spinal screw assembly for securing a fixation rod to patient bone via a closure, the spinal screw assembly comprising:

• a screw having a longitudinal axis, a head portion including a first thread form on an outer surface thereof, and a threaded shaft portion extending distally from the head portion for attachment to the bone;
• a body member having a lower portion defining a bottom opening, an upper portion defining an open first channel for receiving the fixation rod, and an axial bore having a width centered around a longitudinal axis, the axial bore communicating with a bottom of the body member through the bottom opening and extending upwardly through the open first channel to a top of the body member, the axial bore including a narrowed width adjacent the bottom opening defining an interior seating surface, the bottom opening having a second thread form threadably mateable with the first thread form, the axial bore being sized to permit downward passage of the screw threaded shaft portion therethrough while preventing the screw head portion from exiting the body member through the bottom opening by engagement with the interior seating surface;
• and
• a bushing member disposed within the axial bore and engageable with the screw head portion so as to at least partially inhibit the screw head portion from moving upward within the axial bore prior to the insertion and securement of the fixation rod via the closure.

A spinal screw assembly for securing a fixation rod to a bone via a closure, the spinal screw assembly comprising:

• a screw having a longitudinal axis, a screw head, and an integral anchor portion extending downward from the screw head for fixation to the bone, the screw head having an upper curvilinear surface, a lower curvilinear surface adjacent the anchor portion, and an outer surface between the upper curvilinear surface and the lower curvilinear surface, the outer surface having a first helically wound structure formed therein;
• a body member having a base, a pair of upright arms extending upward from the base to define an open channel for receiving the fixation rod, and an axial bore centered around a longitudinal axis, the axial bore communicating with the open channel and with a bottom of the body member through a lower opening, the axial bore further including a supporting surface defined by a narrowed width for the axial bore disposed about the lower opening, the lower opening extending below the supporting surface and having a second helically wound structure formed therein and mateable with the screw head first helically wound structure, the supporting structure preventing the screw head from exiting the body member through the lower opening;
• and
• a bushing positionable within the body member and having a concave bottom surface engageable with the upper curvilinear surface of the screw head,
• wherein the screw head outer surface is in pivotal engagement with the axial bore supporting surface when the screw is disposed within the body member axial bore, with the anchor portion extending downward through the lower opening, so as to allow variable angular movement of the screw relative to the body member when assembled with the first and second helically wound structures dis-engaged and prior to the assembly being locked via the closure.