Low friction rod persuader
View Patent ↗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. An instrument for reducing a spinal rod, the instrument comprising:
an elongate clamp member having an axial throughbore and configured for holding a coupling member of a spinal fixation system;
a rotatable drive member distinct from the clamp member, and sized to be received in the clamp member axial throughbore to be rotatably coupled to the clamp member, the drive member including a helical groove;
at least one rolling ball element partially disposed in the helical groove of the drive member;
an elongate reducer member configured to be linearly shifted with respect to the clamp member, the reducer member including at least one opening sized and configured to receive the at least one rolling ball element such that rotation of the drive member causes the reducer member to be linearly advanced by converting an input rotary drive force applied to the rotatable drive member to translatory motion of the elongate reducing member along the elongate clamp member with the rolling ball element transmitting drive forces therebetween to provide a low friction drive interface between the drive member and the reducer member; and
a one-way locking mechanism that is operable to maintain the reducer member in a distally advanced position thereof by restricting proximal linear shifting thereof.
2. The instrument of claim 1 wherein the one-way locking mechanism is a ratchet mechanism that selectively inhibits rotation of the drive member in at least one direction, the ratchet mechanism including a plurality of ratchet teeth, a pivotable pawl configured to interact with the ratchet teeth, and a moveable ratchet arm coupled to the pawl that shifts the pawl toward and away from the ratchet teeth to engage and disengage the one-way locking mechanism.
3. The instrument of claim 1 wherein the reducer member is a sleeve disposed about the clamp member.
4. The instrument of claim 1 wherein shifting of the reducer member causes clamping and unclamping of the clamp member.
5. An instrument for reducing a spinal rod comprising:
an elongate clamp member for receiving a coupling member of a spinal fixation system, the clamp member comprising a hollow, generally cylindrical first end and a second end comprising a plurality of clamping arms, the generally cylindrical first end having at least one elongate slit disposed therein;
a drive member rotatably disposed in the generally cylindrical first end of the clamp member, the drive member including a helical groove extending thereabout;
at least one rolling element partially disposed in the helical groove of the drive member and partially disposed within the elongate slit of the clamp member;
an elongate reducer sleeve disposed about the clamp member and configured to be linearly shifted with respect to the clamp member, the reducer member including at least one opening sized and configured to receive the at least one rolling element; and
a one-way locking mechanism comprising:
an annular array of ratchet teeth coupled to the exterior of the drive member;
a ratchet pawl disposed adjacent to the ratchet teeth; and
a ratchet control member that holds the ratchet pawl against the ratchet teeth when shifted to a first position and allows the ratchet pawl to shift away from the ratchet teeth when the control member is shifted to a second position;
wherein rotation of the drive member causes linear shifting of the reducer sleeve due to the interaction between the helical groove, the rolling element, and the reducer sleeve; and
wherein the one-way locking mechanism allows rotation of the drive member in two directions when the control member is in the first position but allows rotation of the drive member in only one direction when the control member is in the second position.
6. The instrument of claim 5 , wherein the helical groove of the drive member has a varied pitch along the length of the drive member to automatically adjust the amount of linear shifting of the reducer sleeve accomplished with a given amount of rotation of the drive member depending upon the linear position of the reducer member.
7. The instrument of claim 5 , wherein the ratchet control member is an annular structure surrounding the ratchet teeth and ratchet pawl, with an interior surface contoured so that rotating the annular structure to a first position maintains the position of the ratchet pawl in close enough proximity to the ratchet teeth to prevent rotation of the teeth in one direction and so that the ratchet pawl has room to shift away from the ratchet teeth when the control member is rotated to a second position.
8. The instrument of claim 5 , further comprising pins associated with the reducer sleeve and disposed between the clamping arms, wherein the clamping arms are shaped so that movement of the reducer sleeve and associated pins in one direction forces apart the clamping arms for receiving a coupling member therebetween.
9. The instrument of claim 5 , further comprising a locking member insertion instrument disposable within the drive member and clamping member and capable of interacting with a coupling member when the coupling member is held between the clamping arms.