Pedicle screws

Abstract

A modular pedicle screw assembly for immobilisation and stabilisation of spinal segments in a patient. One example of the modular pedicle screw assembly includes a bone screw, a uniaxial inner collet arranged to cooperate with a head of the bone screw, a seat arranged to provide seating for retention of the inner collet, and an inner collet actuator designed to engage the seat to activate the inner collet for clamping about the head of the bone screw.

1 . A uniaxial pedicle screw assembly of a modular construction comprising:
 a bone screw having a threaded bone shaft adapted for insertion in a vertebra;   a uniaxial inner collet configured in an operative position to clamp about a head of the bone screw, said head being substantially ball-shaped with a truncated surface arranged to cooperate with a corresponding bearing surface of the uniaxial inner collet in an inoperative position to permit tilting of the uniaxial inner collet about a tilt axis of the head of the bone screw;   a seat arranged to provide seating for retention of the uniaxial inner collet, the seat designed to tilt in conjunction with the uniaxial inner collet in the inoperative position about the tilt axis of the head of said bone screw;   a rod for securement to the seat;   an inner collet actuator configured to engage the seat to activate the uniaxial inner collet for movement into the operative position for clamping about the head of the bone screw to lock the uniaxial inner collet and the seat to the head of said bone screw;   the seat including (a) a pair of legs defining a pair of opposing and axially oriented channels arranged for receipt of the rod for locking to the seat via the inner collet actuator, and (b) a recess within which the uniaxial inner collet seats for retention in either the inoperative or operative positions, the uniaxial inner collet being movable via the inner collet actuator from i) the inoperative position where the head of the bone screw is received within the uniaxial inner collet with radial separation of the uniaxial inner collet into the recess of the seat, to ii) the operative position where the head of the bone screw is clamped within the uniaxial inner collet;   the uniaxial inner collet including a pair of radially extending arms aligned with one another and arranged for seating within the pair of opposing channels of the seat thereby orienting the rod at a fixed angular disposition relative to the tilt axis of the head of the bone screw, said angular disposition determined by the angular position of the bearing surface of the uniaxial inner collet relative to the pair of radially extending arms;   the uniaxial inner collet being selected from either (1) a first uniaxial inner collet wherein said pair of radial arms are directionally parallel with the selected bearing surface of the uniaxial inner collet wherein the rod is oriented substantially perpendicular with the tilt axis of the head of the bone screw about which the selected uniaxial inner collet in the operative position is arranged to tilt, or (2) a second uniaxial inner collet wherein the pair of radial arms of the selected uniaxial inner collet are directionally perpendicular with the bearing surface of said selected inner collet wherein the rod is oriented substantially parallel with the tilt axis of the head of the bone screw.   
     
     
         2 . The uniaxial pedicle screw assembly as claimed in  claim 1  wherein the uniaxial inner collet includes a plurality of claw elements together configured in the inoperative position of the inner collet to permit tilting of the inner collet about the tilt axis of the head of the bone screw. 
     
     
         3 . The uniaxial pedicle screw assembly as claimed in  claim 2  wherein one of the claw elements includes a bearing surface defining the corresponding bearing surface of the uniaxial inner collet configured to cooperate with the truncated surface of the head of the bone screw to permit tilting of the uniaxial inner collet in the inoperative position about the fixed tilt axis of the head of said bone screw. 
     
     
         4 . The uniaxial pedicle screw assembly as claimed in  claim 3  wherein the bearing surface of the claw element is one of a pair of opposing bearing surfaces formed in respective of an opposing pair of the plurality of claw elements, the pair of opposing bearing surfaces arranged to cooperate with respective of a pair of the truncated surfaces in the head of the bone screw. 
     
     
         5 . The uniaxial pedicle screw assembly as claimed in  claim 1  wherein the seat includes an aperture formed continuous with the recess and arranged for receipt of the head of the bone screw into the inner collet which is retained in the inoperative position for seating in the recess of the seat. 
     
     
         6 . The uniaxial pedicle screw assembly as claimed in  claim 5  wherein the recess of the seat includes an annular rebate configured, with the inner collet in the inoperative position, to permit the radial separation of the claw elements of the inner collet into the annular rebate on receipt of the head of the bone screw into the inner collet. 
     
     
         7 . The uniaxial pedicle screw assembly as claimed in  claim 5  wherein the seat includes an annular flange defining the aperture through which the head of the bone screw is received, said flange configured with the inner collet in the operative position to urge the claw elements of the inner collet for clamping about the head of the bone screw. 
     
     
         8 . The uniaxial pedicle screw assembly as claimed in  claim 1  further comprising a locking element operatively coupled to the seat to lock the rod to the seat. 
     
     
         9 . The uniaxial pedicle screw assembly as claimed in  claim 8  wherein the inner collet actuator serves as the locking element wherein the inner collet actuator is in the form of a set screw arranged to engage the seat for activation of the inner collet and to lock the rod to the seat. 
     
     
         10 . The uniaxial pedicle screw assembly as claimed in  claim 8  wherein the inner collet actuator is independent of the locking element wherein the inner collet actuator is in the form of an external set screw arranged to engage the seat for activation of the inner collet, and the locking element is in the form of an internal set screw arranged to engage the external set screw for locking of the rod to the seat. 
     
     
         11 . The uniaxial pedicle screw assembly as claimed in  claim 9  wherein the seat also includes a pair of legs defining a pair of opposing and axially oriented channels arranged for receipt of the rod for locking to the seat via the locking element. 
     
     
         12 . The uniaxial pedicle screw assembly as claimed in  claim 11  wherein the inner collet also includes a pair of legs disposed either side of the pair of radially extending arms, said legs of the inner collet defining a pair of opposing and axially oriented channels substantially aligned with the channels of the seat and arranged for receipt of the rod. 
     
     
         13 . The uniaxial pedicle screw assembly as claimed in  claim 12  wherein each of the legs of the inner collet include a protrusion designed for releasable retention within a corresponding opening in the legs of the seat to retain the inner collet within the seat in both the inoperative and operative positions. 
     
     
         14 . The uniaxial pedicle screw assembly as claimed in  claim 11  wherein the set screw of the inner collet actuator threadably engages the legs of the seat for contact with the inner collet to effect its movement in a sliding action from the inoperative position to the operative position where the annular flange of the seat contacts the claw elements of the inner collet for clamping about the head of the bone screw with increasing pressure. 
     
     
         15 . The uniaxial pedicle screw assembly as claimed in  claim 14  wherein the radially extending arms of the inner collet are arranged to rest at a base of the respective channels of the seat within which they are seated when in the operative position the inner collet is clamped about the head of the bone screw with sufficient locking pressure. 
     
     
         16 . The uniaxial pedicle screw assembly as claimed in  claim 14  wherein the protrusion of each of the legs of the inner collet is retained for sliding movement within the corresponding opening of the legs of the seat during movement of the inner collet between the inoperative and operative positions. 
     
     
         17 . The uniaxial pedicle screw assembly as claimed in  claim 9  wherein the set screw of the inner collet actuator during movement of the inner collet from its inoperative to operative positions also effects locking of the rod to the seat. 
     
     
         18 . The uniaxial pedicle screw assembly as claimed in  claim 10  wherein the external set screw includes a threaded aperture within which the internal set screw is received for independent locking of the rod to the seat. 
     
     
         19 . The uniaxial pedicle screw assembly as claimed in  claim 1  wherein the modular construction of the uniaxial pedicle screw assembly enables the uniaxial pedicle screw assembly to be intraoperatively installed.