Methods and devices for minimally invasive spinal fixation element placement

Abstract

Minimally invasive methods and devices for introducing a spinal fixation element into a surgical site in a patient's spinal column are provided. In general, the method involves advancing a spinal fixation element in a first, lengthwise orientation along a pathway extending from a minimally invasive percutaneous incision to a spinal anchor site. As the spinal fixation element approaches the spinal anchor site, the fixation element can be manipulated to extend in a second orientation, which is preferably substantially transverse to the first orientation, to position the fixation element in relation to one or more spinal anchors.

1 .- 20 . (canceled) 
     
     
         21 . A cannulated polyaxial bone anchor assembly implantable in a bone and for mechanically coupling a stabilization member to the bone, the cannulated polyaxial bone anchor assembly comprising:
 an anchor member comprising a first proximal end portion, a first distal end portion, and a central opening extending entirely through the anchor member along a first central longitudinal axis of the anchor member and opening onto a top end of the first proximal end portion and a bottom end of the first distal end portion, the central opening being closed laterally along an entire length thereof and having a constant diameter along the first distal end portion through to the bottom end opening, the top end of the first proximal end portion comprising a radiused upper surface, the first distal end portion comprising an implant portion to be implanted into the bone; and   a head member comprising:
 a second proximal end portion and a second distal end portion, the head member defining a second central longitudinal axis extending through the second proximal end portion and the second distal end portion; 
 a channel extending through the head member perpendicularly to, and 
   intersecting, the second central longitudinal axis, the channel extending proximally through the second proximal end portion, the channel configured to receive the stabilization member and a closure so that the stabilization member can be mechanically coupled to the bone;
 a distal opening at the second distal end portion centered about the second central longitudinal axis; and 
 a chamber in communication with the channel and the distal opening, the chamber pivotally receiving the first proximal end portion therein as the first distal end extends through the head member distal opening so that the first central longitudinal axis is orientable coaxially with the second central longitudinal axis and at any of a plurality of angles relative to the second central longitudinal axis, 
 wherein when the anchor member and head member are coupled together, the cannulated polyaxial bone anchor assembly is insertable over a guide wire as a fully assembled unit and implantable into the bone with only the stabilization member and the closure remaining to be inserted into the head member channel. 
   
     
     
         22 . The cannulated polyaxial bone anchor assembly of  claim 21 , wherein the central opening is unthreaded along at least the first distal end portion. 
     
     
         23 . The cannulated polyaxial bone anchor assembly of  claim 21 , the chamber comprising an at least partially spherical internal surface, the first proximal end portion being positionable within, and pivotally orientable relative to, the at least partially spherical internal surface. 
     
     
         24 . The cannulated polyaxial bone anchor assembly of  claim 21 , the head member further comprising:
 a base located at the second distal end portion; and   a first arm and a second arm extending proximally from the base to the second proximal end portion, the first arm and the second arm defining the channel.   
     
     
         25 . The cannulated polyaxial bone anchor assembly of  claim 21 , wherein the anchor member comprises a bone screw. 
     
     
         26 . The cannulated polyaxial bone anchor assembly of  claim 21 , wherein:
 the first distal end implant portion of the anchor member further comprises a helically wound threaded portion of a shank member;   the first proximal end portion of the anchor member comprises a capture structure of the shank member; and   the cannulated polyaxial bone anchor assembly further includes a retainer positionable within the chamber prior to the capture structure and having an axially-aligned through-and-through opening operative to engage the capture structure within the chamber so as to hold the shank member in the head member.   
     
     
         27 . The cannulated polyaxial bone anchor assembly of  claim 21 , wherein the closure threadably cooperates with the channel to retain the stabilization member within the channel. 
     
     
         28 . The cannulated polyaxial bone anchor assembly of  claim 27 , wherein the closure further comprises a closure top configured to threadably engage the channel at the second proximal end portion and to urge the stabilization member against the radiused proximal surface of the first proximal end portion to maintain a current angle of the second central longitudinal axis relative to the first central longitudinal axis. 
     
     
         29 . The cannulated polyaxial bone anchor assembly of  claim 21 , the stabilization member comprising a rod. 
     
     
         30 . The cannulated polyaxial bone anchor assembly of  claim 21 , the central opening exiting the top end of the first proximal end portion through the radiused upper surface. 
     
     
         31 . The cannulated polyaxial bone anchor assembly of  claim 21 , an external surface of the head member comprising an attachment feature shaped to engage at least one tool to hold the head member. 
     
     
         32 . The cannulated polyaxial bone anchor assembly of  claim 21 , the first proximal end portion comprising at least one tool recess to receive a driving tool to drive the implant portion of the anchor member into the bone. 
     
     
         33 . The cannulated polyaxial bone anchor assembly of  claim 21 , the anchor member further comprising a neck portion coupling the first proximal end portion to the implant portion, the neck portion having a width that is less than a width of a proximal end of the adjacent implant portion. 
     
     
         34 . The cannulated polyaxial bone anchor assembly of  claim 21 , the implant portion comprising an external helically wound thread. 
     
     
         35 . The cannulated polyaxial bone anchor assembly of  claim 21 , wherein at least a portion of the first proximal end portion is inserted through the distal opening and into the chamber. 
     
     
         36 . The cannulated polyaxial bone anchor assembly of  claim 21 , the anchor member being implanted in the bone via the guide wire extending through the anchor member central opening and a central opening of a driving tool. 
     
     
         37 . The cannulated polyaxial bone anchor assembly of  claim 21 , the first proximal end portion comprising a tool mating structure so as to be able to drive the implant portion of the bone screw into the bone. 
     
     
         38 . The cannulated polyaxial bone anchor assembly of  claim 37 , wherein the tool mating structure includes a faceted surface. 
     
     
         39 . The cannulated polyaxial bone anchor assembly of  claim 38 , wherein the faceted surface extends parallel to the first central longitudinal axis of the bone screw. 
     
     
         40 . A cannulated polyaxial bone anchor assembly implantable in a bone and for mechanically coupling a stabilization member to the bone, the cannulated polyaxial bone anchor assembly comprising:
 a bone screw comprising:
 a first proximal end, a first distal end, and a central opening extending along a first central longitudinal axis of the bone screw between the first proximal end and the first distal end, the central opening extending to a top and a bottom of the bone screw and being closed laterally by parallel internal surfaces along at least a distal length of the bone screw and as exiting the first distal end at the bottom of the bone screw and the first proximal end at the top of the bone screw, the first proximal end comprising a radiused upper surface; and 
 an implant portion extending from the first proximal end towards the first distal end, the implant portion comprising an external helically wound thread for implantation into the bone; 
   a head member comprising:
 a second proximal end and a second distal end, the head member defining a second central longitudinal axis from the second proximal end to the second distal end; and 
 a channel extending through the head portion perpendicularly to, and intersecting, the second central longitudinal axis and configured to receive the stabilization member to be mechanically coupled to the bone; 
 a distal opening at the second distal end centered about the second central longitudinal axis; and 
 a chamber in communication with the channel and the distal opening, the chamber pivotally receiving the first proximal end therein as the implant portion extends from the distal opening so that the first central longitudinal axis is orientable coaxially with the second central longitudinal axis and at any of a plurality of angles relative to the second central longitudinal axis; and 
   a closure component to cooperate with the channel to retain the stabilization member within the channel, and to maintain a current angle of the second central longitudinal axis relative to the first central longitudinal axis when urging the stabilization member toward the radiused proximal surface,   wherein when the bone screw and head member are coupled together, the bone screw and head member are insertable together over a guide wire and implantable into the bone with only the stabilization member and the closure component remaining to be inserted into the head member channel.   
     
     
         41 . The cannulated polyaxial bone anchor assembly of  claim 40 , the closure component to urge the stabilization member against the radiused proximal surface. 
     
     
         42 . A cannulated polyaxial bone screw assembly implantable in a bone and for mechanically coupling a rod member to the bone, the cannulated polyaxial bone screw assembly comprising:
 an anchor member comprising a first proximal end portion, a first distal end portion and a central opening extending entirely through the anchor member along a first central longitudinal axis from the first proximal end portion to the first distal end portion, the central opening being closed laterally and having a constant width along an entire length of the first distal end portion, the first proximal end portion comprising a radiused upper surface with the central opening exiting onto a top end thereof, the first distal end portion comprising an implant portion to be implanted into the bone;   a head member comprising:
 a second proximal end portion and a second distal end portion, the head member defining a second central longitudinal axis from the second proximal end portion to the second distal end portion; 
 a channel extending through the head member perpendicular to, and intersecting, the second central longitudinal axis and configured to receive the rod member to be mechanically coupled to the bone; 
 a distal opening at the second distal end portion centered about the second central longitudinal axis; and 
 a chamber in communication with the channel and the distal opening and having an internal surface, the chamber pivotally receiving the first proximal end portion of the anchor member therein as the implant portion extends through the distal opening so that the first central longitudinal axis is orientable coaxially with the second central longitudinal axis and at any of a plurality of angles relative to the second central longitudinal axis; and 
   a closure member comprising a body with a head member mating structure thereon, the body at least partially positionable within the head member second proximal end portion so as to lock the anchor member at a fixed angle with respect to the head member,   wherein when the anchor member and head member are coupled together, the anchor member and head member are insertable over a guide wire as a unit and implantable into the bone with only the rod member and the closure member remaining to be inserted into the head member channel.   
     
     
         43 . The cannulated polyaxial bone screw assembly of  claim 42 , wherein the head member mating structure is a helically wound guide and advancement structure. 
     
     
         44 . The cannulated polyaxial bone screw assembly of  claim 42 , wherein the internal surface of the chamber includes at least a partial spherical surface portion. 
     
     
         45 . The cannulated polyaxial bone screw assembly of  claim 42 , wherein when mechanically coupling the rod to the bone, the rod engages the channel of the head member before the body of the closure member is positioned within the second proximal end portion of the head member. 
     
     
         46 . The cannulated polyaxial bone screw assembly of  claim 42 , wherein the head member includes a tool attachment structure recessed within an external surface thereof so as to not extend outwardly beyond the external surface. 
     
     
         47 . The cannulated polyaxial bone screw assembly of  claim 42 , wherein the closure member body includes a bottom surface in direct locking engagement with the rod. 
     
     
         48 . The cannulated polyaxial bone screw assembly of  claim 42 , the first proximal end portion comprising a tool mating structure so as to be able to drive the implant portion of the anchor member into the bone. 
     
     
         49 . The cannulated polyaxial bone screw assembly of  claim 48 , wherein the tool mating structure includes a faceted surface. 
     
     
         50 . The cannulated polyaxial bone screw assembly of  claim 49 , wherein the faceted surface extends parallel to the first central longitudinal axis of the anchor member.