Spinal fixation system and method
In an example system, a screw tower includes a rigid screw tower body with flexible tulip retaining clips for releasably securing the screw tower to a tulip. An elongate rod channel receives a spinal fixation rod transversely through the screw tower body. A drive shaft rotatably received in the screw tower body includes opposing first and second threaded members for threadedly engaging an outwardly threaded portion of a drive shaft. Each threaded member rides on a corresponding ramped portion on the driver body to guide the threaded members proximately and radially inwardly to an engaged position with the threaded portion of the drive shaft and distally and radially outwardly to a disengaged position from the threaded portion of the drive shaft.
1 . A screw tower for a spinal fixation procedure, comprising:
a screw tower body defining a central axis and including a proximal end, a distal end with a distal opening sized for receiving a tulip, and rigid, axially extending first and second walls defining an elongate rod channel therebetween sized for receiving a spinal fixation rod to extend transversely through the screw tower body between the first and second walls; and
one or more tulip retaining clips each coupled to the screw tower body and having a free end adjacent the distal end of the screw tower body, whereby each tulip retaining clip is radially flexible with respect to the first and second walls in response to receiving a tulip at the distal opening, the one or more tulip retaining clips including retention features that retain the received tulip,
wherein opposing first and second threaded members disposed in the proximal end of the screw tower body, each threaded member having an inwardly facing threaded portion for threadedly engaging an outwardly threaded portion of a drive shaft received in the screw tower body, wherein each threaded member rides on a corresponding ramped portion extending transversely to the central axis to guide the threaded members proximately and radially inwardly toward an engaged position and distally and radially outwardly toward a disengaged position.
2 . The screw tower of claim 1 , wherein the one or more tulip retaining clips comprise a plurality of the tulip retaining clips circumferentially spaced about the central axis.
3 . The screw tower of claim 2 , wherein the plurality of the tulip retaining clips comprise a first tulip retaining clip coupled to the first wall with the free end extending through an aperture in the first wall and an opposing second tulip retaining clip coupled to the second wall with the free end extending through an aperture in the second wall.
4 . The screw tower of claim 1 , further comprising:
a plurality of circumferentially spaced flat sections along the proximal end of the screw tower body for receiving a counter-torque instrument.
5 . The screw tower of claim 1 , further comprising:
a tulip shaped for fastening by a pedicle screw and for being received at the distal opening of the screw tower body, the tulip including a dovetail feature, wherein the dovetail feature and the retention features of the tulip retaining clips cooperate to automatically lockingly engage the tulip to the screw tower body in response to receiving the tulip at the distal opening of the screw tower body.
6 . The screw tower of claim 1 , further comprising:
at least one of an anti-rotation feature and an anti-splay feature on the distal end of the screw tower body and one or more corresponding anti-rotation or anti-splay features on the tulip that are respectively engaged in response to receiving the tulip into the distal opening to prevent relative rotation and radial detachment of the screw tower body with respect to the tulip.