Instrument for guiding a rod into an implant holder
An instrument for guiding a rod into a holder of an implant, in particular a pedicle screw, includes a coupling unit for coupling the instrument to the implant, in particular a head of the pedicle screw, a threaded rod that can be positioned in the axial direction relative to the coupling unit, and at least one internally threaded segment that is arranged in an axially fixed manner relative to the coupling unit, and can be positioned in a radial direction relative to the threaded rod, and prestressed toward the threaded rod by a prestressing element applying a radial force. The internally threaded segment can be brought into engagement with, and disengaged from, the male thread of the threaded rod by radial positioning. Thread flanks of the threaded rod and thread flanks of the internally threaded segment face each other and are each formed with an undercut.
1. An instrument for guiding a rod into a head of a pedicle screw, the instrument comprising:
a coupling unit for coupling the instrument to the head of the pedicle screw,
a threaded rod provided with a male thread and first thread flanks, the threaded rod being positionable in an axial direction relative to the coupling unit, and
at least one internally threaded segment comprising second thread flanks and arranged in an axially fixed manner relative to the coupling unit, the at least one internally threaded segment positionable in a radial direction relative to the threaded rod and prestressed toward the threaded rod by a prestressing element applying a radial force,
wherein the internally threaded segment can be brought into engagement with, and disengaged from, the male thread of the threaded rod by radial positioning,
wherein the first thread flanks of the threaded rod and the second thread flanks of the internally threaded segment face each other, and are each formed with an undercut, and
wherein at least one unlocking element is arranged in a tangential direction of the at least one internally threaded segment and is positionable in the radial direction by user-side actuation.
2. The instrument according to claim 1 , wherein the first and second thread flanks formed with an undercut have a negative flank angle α inclined relative to a normal to a respective thread axis, said angel α being in a range approximately −10° to approximately −1°.
3. The instrument according to claim 1 , wherein the flank angle α of the threaded rod is arranged distally and the flank angle α of the at least one internally threaded segment is arranged proximally.
4. The instrument according to claim 1 , wherein the at least one internally threaded segment is received in a housing and is prestressed toward the threaded rod by a spring.
5. The instrument according to claim 1 , wherein the at least one internally threaded segment comprises two internally threaded segments that are arranged radially opposite one another on both sides of the threaded rod.
6. The instrument according to claim 1 , wherein the threaded rod is frictionally inhibited during an axial movement in a proximal direction.
7. The instrument according to claim 6 , wherein, when the threaded rod is unscrewed from the internally threaded segment it is displaced outwards in the radial direction against its preload.
8. The instrument according to claim 1 , wherein the threaded rod is hollow with a passage channel continuously extending in the axial direction.
9. The instrument according to claim 1 , further comprising a rod pushing unit with a stop and a locking element arranged in a axially fixed manner relative to a latch that cooperates with the stop, which can be positioned in the radial direction with respect to the threaded rod and is prestressed toward the threaded rod into engagement with the stop by the prestressing element applying the radial force.
10. The instrument according to claim 9 , further comprising an unlocking element disposed around the at least one internally threaded segment or around the locking element and capable of displacing the at least one internally threaded segment and/or the locking element in the radial direction.
11. The instrument according to claim 10 , wherein the unlocking element has at least one stop pin that moves the at least one internally threaded segment or the locking element outwards in the radial direction by user-side actuation.
12. The instrument according to claim 9 , wherein an outer diameter of the stop is smaller than a base diameter of the male thread.
13. The instrument according to claim 9 , wherein the locking element has a smooth surface facing the threaded rod.
14. An instrument for guiding a rod into a head of a pedicle screw, the instrument comprising:
a coupling unit for coupling the instrument to the head of the pedicle screw,
a threaded rod provided with a male thread and first thread flanks, the threaded rod being positionable in an axial direction relative to the coupling unit, and
at least one internally threaded segment comprising second thread flanks and arranged in an axially fixed manner relative to the coupling unit, the at least one internally threaded segment positionable in a radial direction relative to the threaded rod and prestressed toward the threaded rod by a prestressing element applying a radial force,
wherein the internally threaded segment can be brought into engagement with, and disengaged from, the male thread of the threaded rod by radial positioning, and
wherein the first thread flanks of the threaded rod and the second thread flanks of the internally threaded segment face each other, and are each formed with an undercut,
the instrument further comprising two unlocking elements arranged in a tangential direction on both sides of the at least one internally threaded segment and positionable in the radial direction by user-side actuation.
15. The instrument according to claim 14 , wherein each of the unlocking elements is in contact with the at least one internally threaded segment via an inclined plane.