SPINAL FIXATION ROD ADJUSTMENT SYSTEM AND METHOD
An instrument for adjusting a fixation rod within a head member of a screw assembly includes a distal portion, a first arm, a first recess, and an actuation member. The distal portion includes a rod engagement surface that engages the fixation rod. The first arm extends from the distal portion towards the head member at a first angle. The first recess is disposed along the first arm at a first distance from the rod engagement surface. The actuation member extends proximally from the distal portion and positions the first recess relative to a first projection on the head member.
1 . An instrument for adjusting a fixation rod within a head member of a screw assembly, comprising:
a distal portion including a rod engagement surface that engages the fixation rod;
a first arm extending from the distal portion towards the head member at a first angle;
a first recess on the first arm at a first distance from the rod engagement surface; and
an actuation member extending proximally from the distal portion that positions the first recess relative to a first projection on the head member.
2 . The instrument of claim 1 , further comprising:
a second arm extending parallel to the first arm to form a pair of arms; and
a second recess on the second arm at the first distance from the rod engagement surface,
wherein the actuation member positions the second recess relative to a second projection on the head member.
3 . The instrument of claim 2 , wherein the first and second arms form a U-shaped cavity that receives the head member.
4 . The instrument of claim 2 , wherein the first and second recesses mate with the first and second projections extending from the head member.
5 . The apparatus of claim 1 , wherein the first arm is perpendicular to the distal portion.
6 . The instrument of claim 1 , wherein the actuation member pivots the distal portion about the first projection to seat the fixation rod within the head member.
7 . The instrument of claim 1 , wherein the distal portion and the first arm form an L-shaped profile.
8 . The instrument of claim 1 , wherein the rod engagement surface includes a concave profile configured to engage a convex profile of the fixation rod.
9 . The instrument of claim 1 , further comprising a plurality of recesses on the first arm at a plurality of distances from the rod engagement surface.
10 . The instrument of claim 10 , wherein each of the plurality of recesses provides a plurality of magnitudes of leverage to position the fixation rod within the head member.
11 . A system for adjusting a fixation rod of a spinal fixation system, comprising:
a screw assembly having
a threaded shaft with a distal end that attaches to a vertebra and a proximal end; and
a head member including a channel for receiving the fixation rod and an outer surface including a pair of projections; and
an instrument having
a distal portion including a concave distal surface for engagement with a convex surface of the fixation rod;
a pair of arms extending perpendicularly from the distal portion towards the head member;
a plurality of recesses on proximal surfaces of the pair of arms, said plurality of recesses including a profile that mates with the pair of projections on the head member; and
an actuation member extending proximally from the distal portion that applies a force to pivot the distal portion about the projections and seat the fixation rod within the head member.
12 . The system of claim 11 , wherein inner surfaces of the pair of arms are separated by a width W 1 .
13 . The system of claim 12 , wherein the pair of projections extends from recessed portions of the outer surface separated by a width W 2 that is less than width W 1 .
14 . The system of claim 13 , wherein outer surfaces of the projections are separated by a width W 3 that is greater than the width W 1 .
15 . A method of adjusting a fixation rod relative to a head member of a screw assembly with an adjustment instrument, comprising:
engaging a distal portion the rocker head with the fixation rod;
sliding a pair of arms extending perpendicularly from the distal portion relative to the head member;
engaging recesses on proximal surfaces of the pair of arms with a mating pair of projections on the head member;
applying a force on an actuation member extending proximally from the distal portion to position the fixation rod within the head member.
16 . The method of claim 15 , wherein engaging the distal portion includes engaging a concave distal surface with a convex surface of the fixation rod.
17 . The method of claim 15 , further comprising selecting from a plurality of pairs of recesses at a plurality of distances from the distal portion to change the leverage of the adjustment instrument.