Instrument and method for restoring motion to a polyaxial screw
A polyaxial screw head remobilizer system for remobilizing a screw body member relative to a head of a polyaxial bone screw includes a barrel body, a handle assembly, an inner shaft, a slide assembly, and a lever. The barrel body includes proximal and distal ends. The distal end includes a plurality of prongs for releasably engaging a plurality of yokes of the polyaxial screw body member to center the inner shaft over the head of the screw. The handle assembly couples to the proximal end of the barrel body. The inner shaft, disposed within the barrel body, includes proximal and distal ends. An engagement feature of the inner shaft mates with pockets of a bushing of the screw body member. The slide assembly is operably coupled to the barrel body and effect translations of the inner shaft. The lever extends from the slide assembly and rotates to actuate the slide assembly.
1. A polyaxial screw head remobilizer system, comprising:
a polyaxial screw assembly including a polyaxial screw body member that includes a yoke, a polyaxial screw member, and a polyaxial bushing member; and
a remobilizer tool, the remobilizer tool comprising:
a barrel body having a proximal end and a distal end;
a handle assembly coupled to the proximal end of the barrel body;
an inner shaft having a proximal end and a distal end, the inner shaft disposed within the barrel body, wherein the distal end of the inner shaft further comprises an engagement feature configured to mate with at least one pocket of the bushing member of the polyaxial screw assembly, wherein the engagement feature includes a Length LE and a Width WE, whereby the Length LE is greater than the Width WE and the Width WE is less than a Width WY of the yoke, such that the engagement feature may longitudinally pass through the Width WY of the yoke;
a slide assembly operably coupled to the barrel body, the slide assembly configured to effect translation of the inner shaft; and
a lever extending from the slide assembly, the lever being rotatable to actuate the slide assembly;
wherein actuation of the slide assembly rotates the engagement feature of the inner shaft to engage the at least one pocket of the polyaxial bushing member;
wherein the engagement features of the inner shaft are a plurality of prongs;
wherein one of the plurality of prongs is configured to releasably engage the yoke;
wherein the engagement feature further comprises a plurality of extensions configured with a stepped down portion on the distal end of the inner shaft; and
wherein the stepped down portion allows the engagement feature to coaxially pass through the yoke.
2. The system of claim 1 , wherein the Length LE is greater than the Width WY of the yoke, such that the Length LE of the engagement feature engages with the at least one pocket of the polyaxial bushing member of the polyaxial screw assembly.
3. The system of claim 2 , wherein the at least one pocket includes a Width WP that is greater than the Width WY of the yoke, and the Width WP is about the length LE of the engagement feature, to allow the engagement feature to unlock the bushing from a head of the polyaxial screw member.
4. The system of claim 3 , wherein the handle assembly further comprises a mount arm fixedly coupled to the handle assembly, the mount arm configured to retain the slide assembly and the mount arm further comprises an aperture adapted to receive the inner shaft.
5. The system of claim 4 , wherein the mount arm is configured to slidably couple with the slide assembly.
6. The system of claim 5 , wherein the mount arm further comprises a pin or other structure configured to limit the degree of distal translation of the inner shaft.
7. The system of claim 1 , further comprising a spring member operably coupled to the lever and the handle assembly, such that the spring member urges the lever from an actuated position back to its original position subsequent to actuation of the lever in either the proximal or distal direction.
8. The system of claim 1 , wherein the polyaxial bushing member is disposed between the polyaxial screw body member and a head of the polyaxial screw member.
9. The system of claim 8 , wherein actuation of the slide assembly rotates the engagement feature of the inner shaft to engage the at least one pocket of the polyaxial bushing member and longitudinally displaces the inner shaft towards the proximal end to proximally translate the polyaxial bushing member disposed between the polyaxial screw body member and the head of the polyaxial screw member, remobilizing the head of the polyaxial screw member.
10. The system of claim 1 , wherein the inner shaft further comprises a helical trough configured to interact with a pin coupled to the slide assembly so as to rotate the inner shaft as the slide assembly translates along the inner shaft.
11. The system of claim 10 , further comprising a stop member fixedly coupled to the proximal end of the inner shaft, wherein the stop member is configured to impede proximal translation of the slide assembly along the inner shaft such that continued proximal translation of the slide assembly also translates the inner shaft proximally.
12. The system of claim 11 , wherein the lever further comprises a polygonal shape having a distal end that can be longitudinally displaced.
13. The system of claim 1 , further comprising a locking or moving mechanism associated with the lever and the slide assembly and located at the proximal end of the barrel body, for incrementally locking or proximally moving the inner shaft towards the proximal end of the barrel body and subsequently releasing the inner shaft to be moved towards the distal end of the barrel body.
14. The system of claim 1 , further comprising a spring locked or spring hinged mechanism coupled to the slide assembly and the lever, to move the inner shaft proximally and distally within the barrel body.