Polyaxial facet fixation screw system with cannula inserter
A screw system includes a screw and a washer assembly captive to the screw. The washer assembly is polyaxially pivotable relative to the screw. The screw may be freely rotated in one direction relative to the washer assembly, but frictionally binds with the washer assembly when rotated in a second direction. A cannula insertion system includes an instrument and a cannula. The instrument may include a dilator. The cannula insertion system may have a locked setting in which the dilator is fixed relative to the cannula, and an unlocked setting in which the dilator is slidable relative to the cannula. A surgical method uses the cannula insertion system to implant the screw system.
1. A system, comprising:
a handle;
a dilator coupled to the handle;
a tubular cannula removably coupled to the handle;
a selector having a first pin coupled to the dilator; and
a second pin coupled to the dilator, said second pin adapted to provide rotational and axial motion constraints for the system;
wherein the system is transformable between a first setting and a second setting by rotating the first pin into or out of engagement with a groove of the dilator;
wherein, in the first setting, the dilator is fixed to the handle in an extended position in which a first length of the dilator protrudes from the handle and the cannula is fixed to the handle so that a length of the cannula protrudes from the handle and the dilator extends through the cannula less than the first length of the dilator;
wherein, in the second setting, the dilator is slidable relative to the handle between the extended position and a retracted position in which a second length of the dilator protrudes from the handle, the second length being less than the first length and the cannula being removable from the handle,
wherein the dilator is biased toward the extended position to temporarily overcome the retracted position,
wherein the dilator comprises the groove and a flat; wherein, in the first setting, the first pin engages the groove to fix the dilator to the handle; wherein, in the second setting, the first pin engages the flat to permit the dilator to slide relative to the handle between the extended position and the retracted position, wherein the dilator is rotationally fixed to the handle in the extended and retracted positions.
2. The system of claim 1 , comprising:
a center longitudinal axis;
wherein the handle and the dilator are aligned with the axis;
wherein the system transforms between the first and second settings in response to rotation of the selector about the axis.
3. A system, comprising:
a cannula comprising a proximal segment, a distal segment, and a central longitudinal hole, wherein the distal segment is opposite the proximal segment, wherein the central longitudinal hole extends through the proximal and distal segments; and
an instrument comprising a dilator, the dilator comprising a distal portion, said instrument further comprising a first pin and a second pin coupled to the dilator, said second pin adapted to provide rotational and axial motion constraints for the system;
wherein the system is transformable between a first setting and a second setting by rotating the first pin into or out of engagement with a groove of the dilator;
wherein, in the first setting, the cannula proximal segment is fixed to the instrument and the dilator is fixed to the instrument in an extended position in which a first length of the dilator protrudes from the instrument, at least a portion of the dilator is inside the cannula hole, and the dilator distal portion protrudes at least partially from the cannula distal segment;
wherein, in the second setting, the dilator is slidable relative to the instrument between the extended position and a retracted position in which a second length of the dilator protrudes from the instrument, the cannula is slidable relative to the instrument, and the dilator is slidable relative to the cannula, the second length being less than the first length and the cannula being removable from the instrument,
wherein the dilator comprises the groove and a flat, wherein, in the first setting, the first pin engages the groove to fix the dilator to the instrument, wherein, in the second setting, the first pin engages the flat to permit the dilator to slide relative to the instrument, wherein the dilator is rotationally fixed to the instrument in the extended and retracted positions.
4. The system of claim 3 , wherein, in the second setting, the dilator is slidable relative to the instrument between a distal position and a proximal position; wherein, in the distal position, a first distal position length of the dilator protrudes from the instrument; wherein, in the proximal position, a second proximal position length of the dilator protrudes from the instrument, wherein the second proximal position length is less than the first distal position length.
5. The system of claim 4 , wherein the dilator is biased toward the distal position; wherein, in the second setting, sliding the dilator toward the proximal position temporarily overcomes the bias.