Low friction rod persuader
Instruments are provided for shifting elongate members, such as spinal rods, with respect to coupling members of spinal fixation systems. The instruments include a low friction drive mechanism having one or more rolling elements that ride along a helical groove or track in order to transform rotational movement of a drive member into linear shifting of a reducer member that shifts the elongate member. A one-way locking mechanism may be provided to selectively prevent unwanted counter-rotation of the low friction drive mechanism. The one-way locking mechanism may include annular ratchet teeth arranged on the exterior of the drive member and a ratchet pawl located adjacent to the teeth and selectively engageable therewith.
1. A reducer instrument for reducing a spinal rod, the reducer instrument comprising:
a clamp member having a distal portion configured for being secured to a coupling member of a spinal fixation system;
a reducer member configured to engage the spinal rod;
a drive member rotatable relative to both the clamp member and the reducer member;
a rotary coupling between the drive member and the reducer member to convert an input rotary drive force applied to the drive member to translatory motion of the reducer member along the clamp member; and
a selectively operable one-way lock that allows a user to select an operative mode of the one-way lock which permits the drive member to be rotated in a spinal rod reducing rotary direction causing the reducer member to translate in a distal direction along the clamp member away from the drive member and keep the reducer member from translating in a proximal direction opposite to the distal direction,
wherein the selectively operable one-way lock has an inoperative mode for selection by the user to allow the drive member to be rotated in both the spinal rod reducing rotary direction and in an opposite rotary direction with rotation in the opposite rotary direction causing the reducer member to translate in the proximal direction, and
wherein the one-way lock includes ratchet teeth of the drive member and a pawl mechanism coupled to the clamp member, the pawl mechanism including a pawl that is pivoted away from the ratchet teeth when the drive member is rotated in the opposite rotary direction with the one-way lock in the inoperative mode without requiring initial rotation of the drive member in the spinal rod reducing rotary direction.
2. The reducer instrument of claim 1 , wherein the one-way lock includes a user-operated selector member that is shiftable between a lock engagement position with the one-way lock in the operative mode thereof and a lock disengagement position with the one-way lock in the inoperative mode thereof.
3. The reducer instrument of claim 2 , wherein the user-operated selector member is a rotary selector member that the user rotates between the lock engagement and disengagement positions.
4. A reducer instrument for reducing a spinal rod, the reducer instrument comprising:
a clamp member having a distal portion configured for being secured to a coupling member of a spinal fixation system;
a reducer member configured to engage the spinal rod;
a drive member rotatable relative to both the clamp member and the reducer member;
a rotary coupling between the drive member and the reducer member to convert an input rotary drive force applied to the drive member to translatory motion of the reducer member along the clamp member; and
a selectively operable one-way lock that allows a user to select an operative mode of the one-way lock which permits the drive member to be rotated in a spinal rod reducing rotary direction causing the reducer member to translate in a distal direction along the clamp member away from the drive member and keep the reducer member from translating in a proximal direction opposite to the distal direction,
wherein the one-way lock includes ratchet teeth of the drive member and a pawl mechanism including a pivotal arm and a pivotal pawl that is pivotal relative to the pivotal arm, the pivotal arm being pivoted toward the ratchet teeth which causes the pivotal pawl to pivot into engagement with the ratchet teeth in the operative mode of the one-way lock, the pivotal arm being configured to allow the pivotal pawl to pivot as the drive member is rotated in the spinal rod reducing rotary direction and to keep the pivotal pawl from pivoting to stop rotation of the drive member in an opposite rotary direction to the spinal rod reducing rotary direction.
5. The reducer instrument of claim 4 , wherein the pivotal arm has an abutment surface that engages the pivotal pawl to keep the pivotal pawl in engagement with the ratchet teeth to stop rotation of the drive member in the opposite rotary direction in the operative mode of the one-way lock.
6. The reducer instrument of claim 4 , wherein the one-way lock includes a user-operated, rotary mode selector member including a variable thickness annular wall having a thicker portion and a thinner portion, the user-operated, rotary mode selector member being rotatable relative to the drive member so that the annular wall thicker portion is radially aligned with the pivotal arm in the operative mode of the one-way lock to pivot the pivotal arm radially inward toward the ratchet teeth causing the pivotal pawl to be pivoted into engagement therewith, the user-operated rotary mode selector member being further rotatable so that the annular wall thinner portion is radially aligned with the pivotal arm in an inoperative mode of the one-way lock so that the pivotal arm and the pivotal pawl pivot radially away from the ratchet teeth to allow the drive member to be rotated in both the spinal rod reducing rotary direction and the opposite rotary direction.
7. A reducer instrument for reducing a spinal rod, the reducer instrument comprising:
a clamp member having a distal portion configured for being secured to a coupling member of a spinal fixation system;
a reducer member configured to engage the spinal rod;
a drive member rotatable relative to both the clamp member and the reducer member;
a rotary coupling between the drive member and the reducer member to convert an input rotary drive force applied to the drive member to translatory motion of the reducer member along the clamp member; and
a selectively operable one-way lock that allows a user to select an operative mode of the one-way lock which permits the drive member to be rotated in a spinal rod reducing rotary direction causing the reducer member to translate in a distal direction along the clamp member away from the drive member and keep the reducer member from translating in a proximal direction opposite to the distal direction,
wherein the rotary coupling includes a rolling ball element held by the reducer member and a helical groove of the drive member in which the rolling ball element is received to travel therein to convert the input rotary drive force applied to the drive member to the translatory motion of the reducer member along the clamp member.
8. The reducer instrument of claim 7 , wherein the clamp member has an axial slit, and rotating the drive member causes the rolling ball element to travel axially along the axial slit as rolling ball element travels in the helical groove of the drive member.