Patent Publication Number: US-9408716-B1

Title: Percutaneous posterior spinal fusion implant construction and method

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to the percutaneous insertion of spinal fusion implants into the body of a patient and the affixation of those implants to the spine. In particular, the invention includes percutaneous posterior spinal fusion systems, devices used in conjunction with such systems, and associated methods. 
     Pedicle screw fixation constructs have been in use for decades in order to fuse adjacent vertebral segments to improve spinal stability or correct certain spinal deformities. Older approaches for inserting these fixation constructs involved open procedures, in which relatively large skin incisions were created to expose a substantial portion of the patient&#39;s spinal column, in order to allow for insertion of the pedicle screws and manipulation of spinal rods through openings adjacent to the heads of the screws. 
     Over time, less invasive approaches have been developed. Typically, in such approaches, pedicle screws are inserted into the pedicles of the same or adjacent vertebrae of a patient&#39;s spine through individual percutaneous incisions corresponding to the pedicle screws. Fixation or fusion rods are then inserted into the body through one of those incisions, or through an additional incision adjacent to the most cephalad or caudal pedicle screw, and the rod is rigidly connected to the pedicle screws such that the rod extends along the longitudinal axis of the spine (i.e., along the cephalad/caudal direction) in order to fix the relative positions of the adjacent vertebrae to which the rod is connected. In some such minimally invasive procedures, a device (e.g., a cannula, tower, or portal) is connected to each of the pedicle screws and extends through the respective percutaneous incision. Moreover, it is known to utilize separate elongate blades connected with the screws. Such devices provide a percutaneous passageway through the tissue from each incision to the respective pedicle screw, in order to aid in the insertion of a spinal rod. Examples of such passageway devices are described in commonly-assigned U.S. Pat. No. 7,955,355 (“the &#39;355 Patent”) and U.S. Pat. No. 8,002,798 (“the &#39;798 Patent”), the entireties of which are hereby incorporated by reference herein as if fully set forth herein. 
     Although considerable effort has been devoted in the art to optimization of such minimally invasive systems, still further improvement would be desirable. 
     BRIEF SUMMARY OF THE INVENTION 
     One aspect of the present invention provides a system for manipulating portions of a spinal fusion system. The system according to this aspect of the invention desirably includes a connecting element, a passageway device, and a tubular member. The connecting element is preferably attachable to a vertebra of the spine, and a distal end of the passageway device is preferably connected to the connecting element. The tubular member preferably has an opening through its sidewall between its proximal and distal ends, and the tubular member is preferably removably positionable over the passageway device in an inserted position. In that position, an open interior portion of the tubular member preferably receives the passageway device within it. 
     According to another aspect of the invention, the tubular member may be structured such that, when it is positioned in the inserted position, its distal end is positioned proximate the connecting element and a feature of the passageway device is positioned adjacent to the opening. According to a further aspect of the invention, the feature may be the proximal end of the passageway device. According to yet another aspect of the invention, the sidewall of the tubular member may include a visible marking proximate the opening. In accordance with a further aspect of the invention, the visible marking may be indicative of a length of the passageway device. According to another aspect of the invention, the tubular member may include a second opening through its sidewall between the proximal and distal ends. 
     According to other aspects of the invention, the tubular member may be a counter torque tube having a handle projecting laterally therefrom. According to a further aspect of the invention, the distal end of the tubular member may be structured to engage the connecting element in the inserted position so as to prevent relative rotation between the connecting element and the tubular member. 
     According to another aspect of the invention, the system may further include a second connecting element, a second passageway device, and a second tubular member. The second connecting element is preferably attachable to a second vertebra of the spine, and a distal end of the second passageway device is preferably connected to the second connecting element. The second tubular member is desirably removably positionable over the second passageway device in a second inserted position. In that position, a second open interior portion of the tubular member preferably receives the second passageway device within it. The second tubular member may be movably connectable to the tubular member to allow for compression and distraction of the first and second vertebrae. 
     According to yet another aspect of the invention, the passageway device may include a first blade having a distal end connected to the connecting element, and the open interior portion of the tubular member may receive the first blade in the inserted position. In accordance with a further aspect of the invention, the open interior portion of the tubular member may include a first channel that receives the first blade when the tubular member is positioned in the inserted position. According to another aspect of the invention, the passageway device may include a second blade having a distal end connected to the connecting element, and the open interior portion of the tubular member may receive the second blade in the inserted position. In accordance with a further aspect of the invention, the open interior portion of the tubular member may include first and second channels that receive the respective first and second blades when the tubular member is positioned in the inserted position. 
     Another aspect of the present invention that provides a system for manipulating portions of a spinal fusion system desirably includes a connecting element attachable to a vertebra of the spine; a tubular member; and first and second blades, each of which has a distal end connected to the connecting element. The tubular member preferably has first and second channels formed therein that receive the respective first and second blades when the tubular member is positioned in an inserted position in which its distal end is proximate the connecting element. 
     According to yet another aspect of the invention, the system desirably further includes a second connecting element attachable to a second vertebra of the spine; a second tubular member; and third and fourth blades, each of which has a distal end connected to the second connecting element. The second tubular member preferably has third and fourth channels formed therein that receive the respective third and fourth blades when the second tubular member is positioned in a second inserted position in which its distal end is proximate the second connecting element. 
     According to other aspects of the invention, the tubular member may have an opening through its sidewall between proximal and distal ends of the tubular member. In accordance with a further aspect of the invention, the sidewall of the tubular member may include a visible marking proximate the opening. 
     Yet another aspect of the present invention that provides a system for manipulating portions of a spinal fusion system desirably includes a first shaft, a second shaft, and a manipulation device. The first and second shafts preferably have a respective first and second connector, and the distal ends of the first and second shafts are preferably connectable to respective first and second connecting elements affixed to respective first and second vertebrae of the spine. Desirably, the first connector is rotatable about the longitudinal axis of the first shaft. The manipulation device may be connectable to the first and second connectors and adapted to move the first and second shafts with respect to one another to induce relative movement between the first and second vertebrae. 
     According to one aspect of the invention, the second connector may be rotatable about the longitudinal axis of the second shaft. According to another aspect of the invention, the manipulation device may be a compressor adapted to move the first and second shafts towards one another. According to yet another aspect of the invention, the manipulation device may be a distractor adapted to move the first and second shafts away from one another. According to a further aspect of the invention, the first connector may be positioned in a middle portion of the first shaft between the proximal and distal ends of the first shaft. In accordance with another aspect of the invention, the proximal ends of the first and second shafts may be movably connectable to one another. In accordance with a further aspect of the invention, the proximal ends of the first and second shafts may be pivotably connectable together at a pivot point. 
     According to another aspect of the invention, the first shaft may have an open interior portion adapted to receive a passageway device extending proximally from the first connecting element. According to a further aspect of the invention, the passageway device may include a first blade having a distal end connected to the connecting element, and the open interior portion of the first shaft may include a first channel adapted to receive the first blade when the passageway device is received within the open interior portion. In accordance with another aspect of the invention, the first and second connecting elements may each include a respective anchoring element and coupling element, the anchoring element being affixable to a pedicle of a respective vertebra, and the coupling element being adapted to receive a spinal fusion element. In accordance with this aspect of the invention, the distal ends of the first and second shafts may be connectable to the respective first and second coupling elements. 
     Another aspect of the present invention that provides a system for manipulating portions of a spinal fusion system desirably includes a first shaft, a second shaft, and a manipulation device. The first and second shafts preferably have a respective first and second connector, and the distal ends of the first and second shafts are preferably connectable to respective first and second connecting elements affixed to respective first and second vertebrae of the spine. Desirably, the first and second connecting elements each have a passageway device extending proximally therefrom, and the first and second shafts desirably each have an open interior portion adapted to receive the respective passageway device therein when the distal end of the respective shaft is connected to the respective connecting element. The manipulation device may be connectable to the first and second connectors and adapted to move the first and second shafts with respect to one another to induce relative movement between the first and second vertebrae. 
     In accordance with other aspects of the invention, a first passageway device extending proximally from the first connecting element may include first and second blades each having a distal end connected to the first connecting element. In accordance with this aspect of the invention, the open interior portion of the first shaft may include a first and second channel adapted to receive the respective first and second blades when the first passageway device is received within the open interior portion of the first shaft. According to a further aspect of the invention, a second passageway device extending proximally from the second connecting element may include third and fourth blades each having a distal end connected to the second connecting element. In accordance with this aspect of the invention, the open interior portion of the second shaft may include a third and fourth channel adapted to receive the respective third and fourth blades when the second passageway device is received within the open interior portion of the second shaft. 
     Another aspect of the present invention provides a method of manipulating portions of a spinal fusion system. The method according to this aspect of the invention desirably includes: connecting a distal end of a first shaft to a first connecting element affixed to a first vertebra of a spine, the first shaft including a first connector; connecting a distal end of a second shaft to a second connecting element affixed to a second vertebra of the spine, the second shaft including a second connector; and manipulating a manipulation device connected to the first and second connectors so as to move the first and second shafts with respect to one another to induce relative movement between the first and second vertebrae. In accordance with this aspect of the invention, the first connector is preferably rotatable about the longitudinal axis of the first shaft. 
     In accordance with a further aspect of the invention, the first connector may rotate about the longitudinal axis of the first shaft during the step of manipulating the manipulation device. In accordance with another aspect of the invention, the second connector may be rotatable about a longitudinal axis of the second shaft. According to yet another aspect of the invention, the step of manipulating the manipulation device may include pivoting first and second arms of the manipulation device, each arm being connected to the respective first and second connector. 
     In accordance with another aspect of the invention, where the first vertebra may be located on a first side of the second vertebra, the method preferably further includes: disconnecting the distal end of the first shaft from the first connecting element; repositioning the first shaft on a second side of the second vertebra opposite the first side; and connecting the distal end of the first shaft to a connecting element affixed to a third vertebra located on the second side of the second vertebra. In accordance with a further aspect of the invention, the method may further include rotating the second connector of the second shaft towards the first shaft. In accordance with yet a further aspect of the invention, the method may further include connecting the manipulation device to the first and second connectors. According to a further aspect of the invention, the method may further include disconnecting a proximal end of the first shaft from a proximal end of the second shaft before the step of repositioning the first shaft on the second side of the second vertebra. According to yet a further aspect of the invention, the method may further include reconnecting the proximal end of the first shaft with the proximal end of the second shaft after the step of repositioning the first shaft on the second side of the second vertebra. In accordance with yet a further aspect of the invention, the step of disconnecting the proximal end of the first shaft from the proximal end of the second shaft may comprise uncoupling a receiver element at the proximal end of the second shaft from an engagement end at the proximal end of the first shaft, and the step of reconnecting the proximal end of the first shaft with the proximal end of the second shaft may include reorienting the receiver element and coupling the receiver element to the engagement end. According to yet a further aspect of the invention, the step of reorienting the receiver element may include rotating the receiver element from the first side of the second vertebra to the second side of the second vertebra. 
     According to another aspect of the invention, the first and second connectors may each be positioned in a middle portion of the respective first and second shafts between the proximal and distal ends of the respective shafts. According to yet another aspect of the invention, the method may further include receiving a first passageway device within the first shaft and receiving a second passageway device within the second shaft, which first and second passageway devices extend proximally from the respective first and second connecting elements. In accordance with yet another aspect of the invention, the method may further include connecting a proximal end of the first shaft to a proximal end of the second shaft. In accordance with a further aspect of the invention, the proximal ends of the first and second shafts may be connected such that, during the step of manipulating the manipulation device connected to the first and second connectors, the first and second shafts pivot about a pivot point proximate the proximal ends of the first and second shafts. 
     Another aspect of the present invention provides a method of constructing a monolithic blade-screw. The method according to this aspect of the invention desirably includes providing a connecting element including a screw coupled to a cage. The cage is preferably adapted to receive a spinal fusion rod in it, and the cage preferably has a reduction portion connected to it at a frangible portion. The method according to this aspect of the invention desirably also includes affixing a distal end of a blade extension to a proximal end of the reduction portion. 
     According to another aspect of the invention, the method may further include integrally forming the cage and the reduction portion from a single piece of material. According to a further aspect of the invention, the cage and the reduction portion may include threads therealong, and the blade extension may not be threaded. According to yet a further aspect of the invention, the threads may have a generally horizontal flank facing towards the screw. According to yet another aspect of the invention, the step of affixing the distal end of the blade extension to the proximal end of the reduction portion may include welding the distal end of the blade extension to the proximal end of the reduction portion. According to another aspect of the invention, the screw may be polyaxially coupled to the cage. In accordance with another aspect of the invention, the method may further include modifying the shape of a component forming the blade extension. According to further aspects of the invention, the step of modifying the shape of the component may occur either before or after the step of affixing the distal end of the blade extension to the proximal end of the reduction portion. According to yet another aspect of the invention, the step of modifying the shape of the component may be performed by wire-cut electrical discharge machining. In accordance with yet another aspect of the invention, the method may further include coupling the screw to the cage before the step of providing the connecting element. 
     Another aspect of the present invention provides a monolithic blade-screw. The blade-screw according to this aspect of the invention desirably includes a connecting element and a blade extension. The connecting element preferably includes a screw coupled to a cage. The cage may be adapted to receive a spinal fusion rod in it, and the cage may have a reduction portion connected to it at a frangible portion. Desirably, a distal end of the blade extension may be affixed to a proximal end of the reduction portion. 
     According to another aspect of the invention, the cage and the reduction portion may be integrally formed from a single piece of material. According to a further aspect of the invention, the cage and the reduction portion may include threads therealong, and the blade extension may not be threaded. According to yet a further aspect of the invention, the threads may have a generally horizontal flank facing towards the screw. According to yet another aspect of the invention, the distal end of the blade extension may be affixed to the proximal end of the reduction portion by a weld. In accordance with another aspect of the invention, the screw may be polyaxially coupled to the cage. In accordance with yet another aspect of the invention, a profile of the blade extension may vary between its proximal and distal ends. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a system of blade-screws connected to a spine, in accordance with an embodiment of the present invention. 
         FIG. 2A  is a perspective view of a blade-screw of  FIG. 1 . 
         FIG. 2B  is a sectional view of the blade-screw of  FIG. 2A . 
         FIG. 3A  is a perspective view of a system of blade-screws connected to a spine and being used for contouring a rod, in accordance with an embodiment of the present invention. 
         FIG. 3B  is a plan view of a template rod, in accordance with an embodiment of the present invention. 
         FIG. 4A  is a partial, perspective view of a rod inserter and rod, in accordance with an embodiment of the present invention. 
         FIGS. 4B-C  are perspective views of the rod inserter of  FIG. 4A  inserting the rod into a body through the system of blade-screws of  FIG. 1 . 
         FIG. 5A  is a perspective view of a set screw, in accordance with an embodiment of the present invention. 
         FIG. 5B  is a partial, perspective view of the set screw of  FIG. 5A  engaged with a set screw driver, in accordance with an embodiment of the present invention. 
         FIG. 6  is a perspective view of the system of blade-screws of  FIG. 1 , the rod inserter and rod of  FIGS. 4A-C , the set screw driver of  FIG. 5B , and a counter torque tube, all being used together, in accordance with an embodiment of the present invention. 
         FIG. 7A  is a perspective view of the counter torque tube of  FIG. 6 . 
         FIG. 7B  is a partial, sectional view of the counter torque tube of  FIG. 7A . 
         FIGS. 8A-B  are partial, elevational views of the counter torque tube of  FIG. 7A . 
         FIG. 9A  is a perspective view of the system of blade-screws of  FIG. 1  being used with components of a compression and distraction system in one configuration, in accordance with an embodiment of the present invention. 
         FIG. 9B  is a perspective view of the system of blade-screws of  FIG. 1  being used with the components of the compression and distraction system of  FIG. 9A  in another configuration, in accordance with an embodiment of the present invention. 
         FIGS. 10A-B  are elevational views of a hinge shaft of the compression and distraction system of  FIGS. 9A-B . 
         FIGS. 11A-B  are elevational views of a ball shaft of the compression and distraction system of  FIGS. 9A-B . 
         FIG. 12A  is a plan view of a distractor for use with a compression and distraction system in accordance with an embodiment of the present invention. 
         FIG. 12B  is a perspective view of the distractor of  FIG. 12A  being used with the components of the compression and distraction system in the configuration of  FIG. 9B . 
         FIG. 13A  is a plan view of a compressor for use with a compression and distraction system in accordance with an embodiment of the present invention. 
         FIG. 13B  is a perspective view of the compressor of  FIG. 13A  being used with the components of the compression and distraction system in the configuration of  FIG. 9B . 
         FIG. 14A  is an elevational view of a blade remover, in accordance with an embodiment of the present invention. 
         FIGS. 14B-C  are perspective views of the blade remover of  FIG. 14A  being used with the system of blade-screws of  FIG. 1 . 
         FIG. 14D  is an elevational view of the blade remover of  FIG. 14A  ejecting a blade of a blade-screw, in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Where reference is made herein to directional terms such as “proximal,” “proximal most,” “distal,” and “distal most,” it is to be understood that “proximal” and “proximal most” refer to locations closer to a user or operator of the device or method being described and that “distal” and “distal most” refer to locations further from a user or operator of the device or method being described. 
       FIG. 1  illustrates a system of connecting elements  30 , passageway devices  31 , and a spinal fusion element or rod  44  connected to a spine  10 . The spine  10  has a cephalad direction  12 , a caudal direction  14 , an anterior direction  16 , a posterior direction  18 , and a medial/lateral axis  20 , all of which are oriented as shown by the arrows bearing the same reference numerals. In this application, “left” and “right” are used with reference to a posterior view, i.e., a view from behind the spine  10 . “Medial” refers to a position or orientation toward a sagittal plane (i.e., plane of symmetry that separates left and right sides from each other) of the spine  10 , and “lateral” refers to a position or orientation relatively further from the sagittal plane. 
     As shown in  FIG. 1 , the spine  10  includes a first vertebra  22 , a second vertebra  24 , and a third vertebra  26 . The systems and methods herein may be applicable to any vertebra or vertebrae of the spine  10  and/or the sacrum  11 . As such, the term “vertebrae” may be broadly interpreted to include all vertebrae, as well as the sacrum. As shown in the figure, the connecting elements  30  and associated passageway devices  31  are connected to respective pedicles  36 ,  38 ,  40  on the right side of the respective first, second, and third vertebrae  22 ,  24 ,  26 . Although the system illustrated in  FIG. 1  spans three vertebrae, other embodiments of systems in accordance with the present invention may span fewer or more vertebrae. For example, additional connecting elements  30  and passageway devices  31  may be connected to additional vertebrae along the spine  10 . 
     The connecting elements  30  each include an anchoring element or screw  32  (see  FIGS. 2A-B ) implanted in the respective pedicles  36 ,  38 ,  40  and a coupling element or cage  42  for receiving the spinal fusion rod  44  therein. The cages  42  may be coupled to the respective screws  32  in various ways known in the art. For example, as shown in  FIG. 2B , the cages  42  and the screws  32  may be polyaxially coupled. In other embodiments (not shown), the coupling between the cages  42  and the screws  32  may be a monoaxial coupling or a uniplanar coupling, or the cages  42  may be rigidly fixed to (e.g., integrally formed with) the screws  32 . Each connecting element  30  may also include a set screw  45  for securing the rod  44  within the cage  42 . The connecting elements  30  may have the same or similar structure as the connecting elements described in the &#39;798 Patent. Alternatively, the connecting elements  30  may have the same or similar structure as the pedicle screws described in U.S. Pat. No. 7,988,713 (“the &#39;713 Patent”) or the pedicle screws, pedicle hooks, or lamina hooks described in U.S. Pat. No. 6,074,391 (“the &#39;391 Patent”). The entire disclosures of the &#39;713 Patent and the &#39;391 Patent are hereby incorporated by reference herein as if fully set forth herein. Although the anchoring elements are illustrated herein as screws  32 , it is to be understood that other types of anchoring elements capable of being secured to vertebral bone may be used, such as the above-referenced hooks described in the &#39;391 Patent. Moreover, although the spinal fusion element  44  is illustrated herein as a rod  44 , it is to be understood that other types of elements capable of securing together adjacent vertebrae may be used, such as plates, wires, rods, or articulating versions thereof. 
     The connecting elements  30  may be percutaneously inserted in the body in the same manner as described in the &#39;798 Patent. That is, each of the connecting elements  30  may be inserted along a respective guide wire through a separate incision  46 ,  48 ,  50  in the skin  51 . Sequential dilators may be used to enlarge the passageway between the incisions  46 ,  48 ,  50  and the respective pedicles  36 ,  38 ,  40 . The screws  32  of the connecting elements  30  may be implanted in previously tapped bores in the associated pedicles, or the screws  32  may self-tap into the pedicles. The advancement of each screw  32  into a pedicle may be driven by a driver (not shown) having a distal end engaged with a driver interface  34  on the head  35  of the screw  32  (see  FIG. 2B ), such that a shaft of the driver extends proximally within the passageway device  31 . The driver interface  34  of the head  35  may take the form of that disclosed in U.S. Pat. No. 8,231,635 (“the &#39;635 Patent”), the entire disclosure of which is hereby incorporated by reference herein as if fully set forth herein, and the driver may take the form of any one of the screwdrivers disclosed in that patent. The driver may be a powered or a manually operated driver. Additionally, before the connecting elements  30  are inserted into the body, spinal navigation software and/or robotics may be used to help locate the appropriate pedicles  36 ,  38 ,  40  and to implant or help guide the implantation of the connecting elements  30  into the pedicles. 
     The passageway devices  31  are connected to the connecting elements  30  such that the passageway devices  31  extend proximally from the connecting elements  30  though the respective incisions  46 ,  48 ,  50 . In particular, as shown in  FIGS. 2A-B , the distal ends  52  of the passageway devices  31  are connected to the proximal ends  54  of the cages  42 . The passageway devices  31  each provide a passageway  55  extending along an axis  57  from the incision  46 ,  48 ,  50  to the respective connecting element  30  to aid the percutaneous insertion of the rod  44 . The axis  57  (and the associated passageway device  31 ) may be straight, as illustrated in the figures herein, or the passageway device  31  may define an angled or curved longitudinal axis, as disclosed in certain embodiments of U.S. patent application Ser. No. 14/034,021 (“the &#39;021 Application”), filed on Sep. 23, 2013 and entitled “Lumbar-Sacral Screw Insertion and Manipulation,” the entire disclosure of which is hereby incorporated by reference herein as if fully set forth herein. Each passageway device  31  may take the form of two blades  56  attached to opposing arms  58  of the associated cage  42 . The blades  56  may be separately formed from and detachably connectible to the cages  42 , as described in the &#39;798 Patent. Alternatively, the blades  56  may be formed as a single piece with the associated cages  42 , as also described in the &#39;798 Patent. For example,  FIGS. 1-2B  illustrate an embodiment in which the blades  56  are integrally connected to the associated cages  42  to form monolithic blade-screws  60 . In such an embodiment, the blades  56  may be connected to the cages by frangible portions  62 . Each frangible portion  62  may include a reduced thickness portion, which may be defined by grooves formed in either or both of the interior and exterior surfaces of the blade-screws  60  at the junction between the blades  56  and the respective arms  58  of the cages  42 . In the embodiment illustrated in  FIG. 2B , the frangible portions  62  are defined by a groove  64  along the exterior of the blade-screw  60  and a groove  66  along the interior of the blade-screw  60  that is aligned with the exterior groove  64 . The frangible portions  62  provide a location for the blades  56  to be broken away from the cages  42  when desired. 
     The interior of each cage  42  may include threads  68  along the arms  58 , and the passageway device  31  may include reduction threads  70  at least along the distal end  52  thereof. In other embodiments (not shown), the reduction threads  70  of the passageway device  31  may not be present while the threads  68  of the cage  42  are present. The set screw  45  (see  FIG. 5A ) is an externally threaded component structured to engage the reduction threads  70  of the passageway device  31  and the threads  68  of the cage  42 . Both threads  68  and  70  are aligned such that the set screw  45  can be rotatably advanced distally along the reduction threads  70  of the passageway device  31 , after which continued rotation of the set screw  45  will cause the set screw  45  to engage and advance along the threads  68  of the cage  42 . 
     The threads  68  and/or the reduction threads  70  may have a tooth shape as disclosed in the &#39;391 Patent. That is, as disclosed in the &#39;391 Patent, and as illustrated in  FIG. 2B  herein, the flank of each thread facing in the distal direction (i.e., towards the screw  32 ) may be steep and, preferably, is generally horizontal, and the flank of each thread facing in the proximal direction (i.e., away from the screw  32 ) may be angled at about 30° with respect to the horizontal. The threads  106  of the set screw  45  are preferably complementary to the threads  68  and/or the reduction threads  70  (i.e., the steep flank of each thread  106  of the set screw  45  may be aligned oppositely to the steep flanks of the threads  68 ,  70 ). 
     As discussed above, the blades  56  of the passageway devices  31  are integrally connected to the cages  42  in the monolithic blade-screws  60 . Such blade-screws  60  may be constructed by fabricating each cage  42  with its respective passageway device  31  as one piece. For example, a cage  42  with two blades  56  extending therefrom may be machined out of a single piece of material. In another example, the cage  42  with both blades  56  may be cast or molded as a unitary component. In other embodiments, however, subcomponents of the cage  42  and passageway device  31  may be formed separately and then integrally connected together, such as by welding. For example, the blades  56  and the cages  42  may be separately formed (e.g., by machining, casting, or molding), and the distal ends  52  of two blades  56  defining a passageway device  31  may be connected (e.g., by welding) to the proximal ends  54  of the arms  58  of a cage  42 . In the case of welding, the welded regions may form the frangible portions  62 . In yet another embodiment, each cage  42  may be integrally formed (e.g., by machining, casting, or molding) with two reduction portions  61  extending proximally from the proximal ends  54  of each of the arms  58  of the cage  42 . The reduction portions  61  desirably include the reduction threads  70  of what will become the blades  56 . Two blade extensions  63  may be separately formed, and the distal ends  65  of those extensions  63  may be integrally connected (e.g., welded) to the proximal ends  67  of the reduction portions  61  at connection  69 . As shown in  FIGS. 2A-B , each blade extension  63  may have a particular shape or profile that changes along its length. The final shape of the blade extensions  63  may be created when the separately formed blade extensions  63  are initially fabricated (e.g., machined, casted, or molded). Alternatively, the blade extensions  63  may initially be formed into larger pieces, which are then further refined to arrive at their final shape. For example, wire-cut electrical discharge machining (“EDM”) may be used to modify the shape of the initially formed larger pieces in order to arrive at the final shape of the blade extensions  63 . Such modifications (e.g., using wire-cut EDM) may be performed either before or after the blade extensions  63  are integrally connected to the reduction portions  61 . 
     In some embodiments, the height of the cages  42  (i.e., the length along longitudinal axis  57 ) may be about 1.5 cm. The blades  56  may range between about 5 cm long and about 15 cm long. The reduction portions  61  may represent any portion of the length of the blades  56 , e.g., about 1 cm to about 4 cm, but may preferably be about 2 cm in length. Systems in accordance with embodiments of the invention may include blade-screws  60  having blades  56  of different lengths, for example, because the distances to be traversed between the skin along a patient&#39;s back and the underlying pedicles may be different for different sized patients. For example, such systems may include blades  56  of two different lengths (i.e., long blades and short blades). In an exemplary embodiment, the long blades may be about 11 cm long, and the short blades may be about 7 cm long. Although the reduction portions  61  may represent any portion of that length, the reduction portions  61  may have the same length in both the long and short blades. For example, in an embodiment in which the reduction portions are about 2 cm, as discussed above, the blade extensions  64  of the short blades may be about 5 cm long and the blade extensions  64  of the long blades may be about 9 cm long. 
     Referring to  FIG. 1 , a coupling  72  may be connected to the blades  56  of each passageway device  31  along the length of the passageway device  31 . The couplings  72  may take the form of those disclosed in U.S. Provisional Patent Application No. 61/783,098 (“the &#39;098 Application”), filed on Mar. 14, 2013 and entitled “Systems and Methods for Percutaneous Spinal Fusion,” the entire disclosure of which is hereby incorporated by reference herein as if fully set forth herein. In other embodiments, the coupling may take the form of the abutment members disclosed in the &#39;798 Patent. In addition, the couplings  72  may be connected to the blades  56  in the same manner as disclosed in the &#39;098 Application or the &#39;798 Patent. For example, as disclosed in the &#39;098 Application, the couplings  72  may include flexible tabs  74  having a boss or protuberance (not shown) extending inwardly therefrom for engaging holes  76  along the length of the blades  56 . The couplings  72  may also include recesses  78  to provide an extracorporeal template for contouring or selecting the rod  44  to be implanted, as disclosed in the &#39;098 Application. Such contouring or selection may also be done in the manner disclosed in commonly owned U.S. Pat. No. 8,177,817 (“the &#39;817 Patent”) or U.S. Patent Application Publication No. 2007/0233079 (“the &#39;079 Publication”), the entireties of which are hereby incorporated by reference herein as if fully set forth herein. 
     Referring to  FIG. 3A , a rod  44  is shown seated in the recesses  78  of the couplings  72  attached to two adjacent passageway devices  31 . The rod  44  may be contoured (e.g., with a French bender or with an automated or robotic rod bending system in the operating room), selected from a kit of pre-shaped rods, or custom fabricated (e.g., by a CNC procedure) such that the rod  44  provides an optimal fit within the recesses  78 , and thus, in turn, within the cages  42  of the connecting elements  30 . Alternatively, a template rod  80 , as shown in  FIG. 3B , may be seated in the recesses  78  of the couplings  72 . The template rod  80  may be similar in shape to rod  44  but may be easier to bend, particularly by hand, and may also include measurement markings  82  along its length. The template rod  80  may be bent and seated within the recesses  78 , which steps may be repeated as necessary until the template rod  80  approximates the desired shape of the rod  44  to be implanted in the cages  42 . The template rod  80  may then be used as a reference in contouring, selecting, or fabricating the rod  44  to be implanted. 
     Once a rod  44  having the desired contour has been selected, it may be connected to a rod inserter  84 , as shown in  FIG. 4A . The rod inserter  84  is an elongate tool having a handle (see  FIGS. 4B-C ) at its proximal end  88  and a connection structure  90  at its distal end  92  for detachably connecting to the rod  44 . The proximal end  88  of the rod inserter  84  may also include an actuator  94  configured to operate the connection structure  90  so as to selectively secure and release the rod  44  to the connection structure  90 . The rod  44  may be designed with a particular shape at one end for secure gripping by the connection structure  90  of the rod inserter  84 . For example, the outer surface of the rod  44  at one end may have one or more flat sides (e.g., the rod may have a hexagonal cross-sectional profile at that end), and the interaction between the flat sides and the connection structure  90  may prevent rotation of the rod  44  about its longitudinal axis. The connection structure  90  may also be structured to securely grip the rod  44  while the rod  44  extends away at an angle to the rod inserter  84 . For example, the rod  44  may extend at an approximately 90° angle to the rod inserter  84 , as shown in  FIG. 4A . In another embodiment, the rod  44  may extend at a 110° angle. In yet another embodiment, the connection structure  90  may be adjustable such that the angle of the rod  44  with respect to the rod inserter  84  can be varied. 
     Once the rod  44  is attached to the rod inserter  84 , the handle  86  of the rod inserter  84  may be grasped and used to manipulate the rod  44  into the body, as shown in  FIGS. 4B-C , until the rod  44  extends between the cages  42  of the implanted connecting elements  30 . For example, as shown in  FIG. 4B , the far end  96  of the rod  44  opposite to the end  98  connected to the rod inserter  84  may be inserted through an incision  46  at one end of the system of blade-screws  60 . That far end  96  of the rod  44  may then be passed subcutaneously across between the blades  56  of the passageway devices  31  until it is seated in the cage  42  of the connecting element  30  at the other end of the system of blade-screws  60 . Then, as shown in  FIG. 4C , the rod inserter  84  may be used to manipulate the end  98  of the rod  44  connected to the inserter  84  downwards until that end  98  is seated in the cage  42  of the connecting element  30  beneath the incision  46 . 
     Once the rod  44  is seated in the cages  42  of the connecting elements  30  attached to the vertebrae  22 ,  24 ,  26 , a set screw  45 , as shown in  FIG. 5A , may be advanced into each of the cages  42 . The set screw  45  includes a driving interface  100  engageable with the distal end  102  of a set screw driver  104 , as shown in  FIG. 5B , for advancing the set screw  45  along the passageway devices  31  and into the cages  42 . The set screw  45  may include threads  106  along its outer surface for rotatably engaging the reduction threads  70  of the passageway devices  31  and the threads  68  of the cages  42 . 
     As shown in  FIG. 6 , the set screw driver  104  having a set screw  45  connected to its distal end is inserted distally through incision  50  and along the passageway device  31  extending through that incision  50 . A counter torque tube  108  can be used in conjunction with the insertion and advancement of the set screw  45  with the set screw driver  104 , as also shown in  FIG. 6 . 
     A perspective view of the counter torque tube  108  is shown in  FIG. 7A . The counter torque tube  108  includes a tubular body  110  having a proximal end  112  and a distal end  114 . A handle  116  is connected to the body  110  at the proximal end  112  by a connection member  118 . The connection member  118  may be a substantially tubular structure projecting laterally from the proximal end  112  of the body  110 , the tubular structure being configured to receive a stem  120  of the handle  116  therein. The stem  120  may be secured within the connection member  118  by one or more set screws (not shown) within one or more holes  122  in the connection member  118 . When connected to the connection member  118 , the handle  116  extends transverse to the longitudinal axis  119  of the body  110  and may extend substantially perpendicular to the longitudinal axis  119 . 
     The tubular body  110  of the counter torque tube  108  has an open interior  124  designed to receive a passageway device  31  therein. A cross section of the counter torque tube  108  normal to the longitudinal axis  119  of the body  110  and taken along the axis of the handle  116  is shown in  FIG. 7B . As shown in the figure, the interior surface  126  defining the open interior  124  includes opposing recessed grooves  128  or channels therein extending along the length of the body  110 . The grooves  128  are structured to receive the blades  56  of the passageway device  31  when the counter torque tube  108  receives the passageway device  31  therein. As shown in  FIG. 7B , the grooves  128  may have an arcuate shape along the plane normal to the longitudinal axis  119  of the body  110 , which shape substantially matches the shape of the blades  56  in that plane. The grooves  128  include end surfaces  130  that constrain the blades  56  to remain in the grooves  128 . As shown in  FIG. 7B , the handle  116  preferably extends from the body  110  along an axis  132 , which is perpendicular to an axis  134 . When the counter torque tube  108  is advanced over one of the passageway devices  31  illustrated in  FIGS. 1 and 6 , and the blades  56  are received within the grooves  128 , the axis  132  and the handle  116  desirably extends along the medial/lateral axis  20 , and the axis  134  desirably extends along the cephalad and caudal directions  12 ,  14 . 
       FIGS. 8A and 8B  illustrate elevational views of a distal portion of the body  110  of the counter torque tube  108 , taken along orthogonal directions. In particular,  FIG. 8A  is a view along axis  132 , and  FIG. 8B  is a view along axis  134 . As shown in the figures, the counter torque tube  108  may include a distal edge  136  arranged to abut the proximal end  54  of the cage  42  of the connecting element  30  when the body  110  of the counter torque tube  108  is fully advanced along the passageway device  31 . In that regard, the cage  42  may be at least slightly wider than the passageway device  31  such that further distal movement of the counter torque tube  108  is prevented when the distal edge  136  of the body  110  comes into contact with the proximal end  54  of the cage  42 . The distal edge  136  may be chamfered in order to ease bodily tissue aside during insertion of the counter torque tube  108 . The counter torque tube  108  may also include opposing extensions  138  extending distally beyond the distal edge  136 . At the distal ends of each of the extensions  138  is an arcuate cut-out  140  shaped to abut the rod  44 . The length of each extension  138  may be dimensioned such that, when the counter torque tube  108  is fully advanced against the cage  42  of a connecting element  30 , the contact between the cut-outs  140  and the rod  44  force the rod  44  to be fully seated within the cage  42 . When the counter torque tube  108  is fully advanced, each of the extensions  138  is preferably positioned along a respective opening  139  (see  FIG. 2A ) defined between the arms  58  of the cage  42 . Moreover, the width of each extension  138  may be dimensioned such that the opposite edges  141  of each extension  138  engage the respective edges  143  of the arms  58  along each opening  139 . In that way, the engagement between the edges  141  of the extensions  138  and the edges  143  of the arms  58  of the cage  42  desirably constrains the rotational orientation of the cage  42  with respect to the body  110  of the counter torque tube  108  about the longitudinal axis  119 . Alternatively, or in addition, the engagement between the blades  56  of the passageway device  31  and the grooves  128  of the counter torque tube body  110  desirably provides a similar constraint in the rotational orientation of the blade-screw  60  with respect to the body  110  of the counter torque tube  108 . 
     One or more windows  142  may be positioned on the counter torque tube body  110  in alignment with the grooves  128  in the interior surface  126  of the body  110 . The windows  142  are positioned such that the proximal edges  144  of the blades  56  (see  FIGS. 2A-B ) are visible through one or more of the windows  142  when the counter torque tube  108  is fully advanced against the connecting element  30 . One or more laser markings, such as a line  146  bisecting the windows  142 , may also be located on the counter torque tube body  110 , such that the lines  146  are aligned with the proximal edges  144  of the blades  56  when the counter torque tube  108  is fully advanced against the connecting element  30 . Multiple windows  142  (with or without corresponding lines  146 ) may be spaced apart along the longitudinal axis  119  of the body, and, as shown in  FIG. 8B , one or more of those windows  142  may have an opposing window  142  located across the longitudinal axis  119  of the body. The locations of the various windows  142  and lines  146  along the longitudinal axis  119  of the body  110  desirably correspond to the different lengths of blades  56  provided with systems in accordance with some embodiments of the invention. As discussed above, different length blades  56 , or blade-screws  60  having blades  56  of different lengths, may be provided with such systems to accommodate different distances to be traversed for different sized patients. Reference markings  148  may be positioned near each window  142  and/or line  146  to indicate which blade  56  length is associated with that window  142  and/or line  146 . 
     The counter torque tube  108  may also include one or more holes  150  along at least a portion of the length of the body  110 , preferably in alignment with the grooves  128  in the interior surface  126 . Such holes  150  may be sized and positioned such that any fluid (bodily or otherwise) and/or tissue that may have become trapped between the blades  56  and the body  110  of the counter torque tube  108  (e.g., during insertion of the counter torque tube  108 ) may be released through the holes  150 . 
     Returning to  FIG. 6 , the counter torque tube  108  may be advanced over one of the passageway devices  31 , as shown in that figure. The counter torque tube  108  may be used in different ways. For example, when advancing the set screw  45  into engagement with the threads  70  of the blades  56  using the set screw driver  104 , positioning the body  110  of the counter torque tube  108  around the passageway device  31  may help to align the set screw driver  104  along the longitudinal axis  57  of the blade-screw  60 , and thus help prevent cross-threading of the set screw  45 . In some embodiments, the coupling  72  may need to be removed from the blades  56  in order to allow the counter torque tube  108  to advance along the passageway device  31 . In such cases, without the stability provided to the blades  56  by the coupling  72 , the blades  56  may tend to pivot or flex slightly inwardly towards one another under pressure from the surrounding tissue. The grooves  128  in the counter torque tube body  110 , along with their end surfaces  130 , however, preferably constrain the desired positions of the blades  56  and provide stability to the blades  56  when the counter torque tube  108  is advanced along the passageway device  31 . That stability provided by the counter torque tube  108  desirably protects portions of the blade-screw  60 , such as the frangible portions  62  and the connections  69  between the blade extensions  63  and the reduction portions  61 , by preventing the blades  56  from becoming prematurely disconnected from the connecting element  30  and by preventing the blade extensions  63  from becoming separated from the reduction portions  61 . If the blades  56  pivot or flex slightly inwardly upon removing the coupling  72 , the set screw driver  104  may be advanced together with the counter torque tube  108  such that the set screw driver  108  is positioned within the open interior  124  of the counter torque tube body  110  and such that the distal end of the set screw driver  104  (with or without the set screw  45  connected to it) projects distally from the distal end  114  of the body  110 . Beneficially, in this arrangement, the set screw driver  104  (and the set screw  45 , if connected to it) will first pass between the proximal edges  144  of the blades  56  and will help to keep the proximal edges  144  apart when they are engaged by the distal end  114  of the counter torque tube body  110  and guided into the grooves  128 . If the proximal edges  144  of the blades  56  are not kept apart, the blades  56  might not properly be guided into the grooves  128 . 
     If, after being inserted in the body, the rod  44  is not fully seated in one or more of the cages  42  (e.g., the rod  44  is slightly proud), the rod  44  can be further directed into a particular cage  42  in various ways. For example, the set screw  45  and set screw driver  104  can be used to advance the rod  44  towards the cage  42 . In one example, the set screw driver  104  having a set screw  45  connected to its distal end can be advanced within the passageway device  31  until the set screw  45  engages the rod  44  and pushes it distally. If the rod  44  is located proximally of the reduction threads  70 , the set screw driver  104  can be used to push the rod  44  distally until the set screw  45  contacts the reduction threads  70 . The rod  44  can then be further advanced towards the cage  42  by rotating the set screw driver  104  to advance the set screw  45  along the reduction threads  70 , which will further push the rod  44  towards the cage  42 . Continued rotation of the set screw  45  will cause the set screw  45  to engage and advance along the threads  68  of the cage  42  until the rod  44  is fully seated within the cage. 
     In another example, the counter torque tube  108  can be used to push the rod  44  towards the cage  42  by advancing the body  110  of the counter torque tube  108  distally along a passageway device  31  until the cut-outs  140  at the distal end  114  of the body  110  engage the rod  44  and push it distally. The counter torque tube  108  can be used in this manner to advance the rod  44  for all or part of the distance to the cage  42 . For example, the counter torque tube  108  can be used to advance the rod  44  until the rod is within the region of the passageway device  31  having the reduction threads  70 , after which the set screw  45  and set screw driver  104  can be used to reduce the rod  44  the remaining distance into the cage  42 , as discussed above. 
     During the advancement of the set screw  45  along the reduction threads  70  and/or the threads  68  of the cage  42 , the body  110  of the counter torque tube  108  is desirably received around at least a portion of the passageway device  31 . Preferably, the distal end  114  of the tube body  110  is positioned close to the set screw  45 , and, more preferably, the distal end  114  is advanced distally along the passageway device  31  while the set screw  45  is advanced. By positioning the counter torque tube body  110  around the passageway device  31 , the body  110  preferably constrains the blades  56  of the passageway device  31  to prevent the blades  56  from splaying outwardly during the threaded advancement of the set screw  45 . Moreover, by positioning the counter torque tube  110  body near or in contact with the cage  42 , the body  110  preferably constrains the arms  58  of the cage  42  to prevent the arms  58  from splaying outwardly during the threaded advancement of the set screw  45 . 
     During final tightening of the set screw  45  against the rod  44  within the cage  42 , the counter torque tube  108  is desirably fully advanced against the cage  42 . The full and proper advancement of the counter torque tube  108  can be checked by confirming that a proximal edge  144  of one of the blades  56  of the passageway device  31  is aligned with the appropriate window  142  of the counter torque tube body  110 , and, in some embodiments, is aligned with the appropriate laser marking or line  146 . With the counter torque tube  108  fully advanced against the cage  42 , the counter torque tube  108  desirably constrains the rotational orientation of the cage  42  and/or the blades  56  of the passageway device  31 , as discussed above. Therefore, during final tightening of the set screw  45 , the surgeon or other user preferably firmly holds the handle  116  of the counter torque tube  108  and/or provides any necessary torque to the handle  116  in the direction opposite to the direction of rotation of the set screw  45 . This will desirably prevent the torque being applied to the set screw  45  by the set screw driver  104  from being transmitted to the associated vertebra of the spine  10  via the connecting element  30 , or at least reduce the amount of torque that is transmitted to the spine. 
     The final tightening of the set screw  45  in the cage  42  may be performed by the set screw driver  104 , or the final tightening may be performed by a torque wrench (not shown). The torque wrench may have a similar structure to the set screw driver  104 , except that it may be constructed such that the torque applied by the torque wrench to the set screw  45  is limited to a pre-selected amount (e.g., 8 Nm (newton-meters)). Once a set screw  45  is finally tightened in one of the cages  42 , as described above, the other cages  42  may be secured to the rod  44  by set screws  45  in the same manner. Preferably, after the rod  44  is secured within at least one of the cages  42  by a set screw  45 , the rod inserter  84  may be disconnected from the rod  44  and removed from the body. 
     Before final tightening of the set screw  45  in the cage  42 , the relative positions of the vertebrae may be adjusted. For example, while the rod  44  is positioned within the cages  42  but before the set screw  45  is tightened to the point that the cages  42  are locked with respect to the rod  44 , two or more vertebrae may be moved in the cephalad and caudal directions  12 ,  14  towards one another (i.e., compression) and/or away from one another (i.e., distraction). One system and method for performing such compression and distraction is disclosed in U.S. Pat. No. 8,157,809 (“the &#39;809 Patent”), the entire disclosure of which is hereby incorporated by reference herein as if fully set forth herein. Another similar system is illustrated in  FIGS. 9A-13B  and is discussed herein. 
       FIGS. 9A-B  illustrate a hinge shaft  202  and a ball shaft  204  of a compression and distraction system  200 . As shown in those figures, the hinge shaft  202  and the ball shaft  204  have been inserted into the patient&#39;s body over and along a respective one of the passageway devices  31 . Similar to the compression and distraction assembly disclosed in the &#39;809 Patent, the proximal end  206  of the hinge shaft  202  includes a fulcrum or hinge  208 , and the proximal end  210  of the ball shaft  204  includes a ball  212 . The hinge  208  can receive the ball  212  therein, as illustrated in  FIG. 9B , and the hinge  208  can be rotated about the proximal end  206  of the hinge shaft  202  from the position illustrated in  FIG. 9A  to the position illustrated in  FIG. 9B  in order to receive the ball  212 . Once the ball  212  is received within the hinge  208  in the manner shown in  FIG. 9B , a polyaxial fulcrum  214  is formed between the proximal ends  206 ,  210  of the shafts  202 ,  204  similar to that disclosed in the &#39;809 Patent. Like the polyaxial fulcrum of the &#39;809 Patent, the polyaxial fulcrum  214  desirably allows all rotational degrees of freedom such that the fulcrum  214  does not impart ancillary stresses or motion to the vertebrae during compression or distraction. 
       FIGS. 10A-B  illustrate elevational views of the hinge shaft  202 , taken along orthogonal directions. The hinge shaft  202  has a proximal end  206  and a distal end  216 , with the hinge  208  being at the proximal end  206 . The hinge shaft  202  includes a proximal shaft  218  and a distal shaft  220 , with an eyelet ring  222  disposed therebetween. The distal shaft  220  may have a similar structure to the body  110  of the counter torque tube  108 . That is, the distal shaft  220  desirably has a tubular shape with an open interior designed to receive a passageway device  31  therein. The open interior may have the same grooved structure as the counter torque tube  108 , in order to similarly receive and constrain the blades  56  of the passageway device  31 . The distal end  216  may also have the same structure for engaging the cage  42  of a connecting element  30  as the distal end  114  of the counter torque tube body  110 . That is, the distal end  216  may have a chamfered distal edge  224  arranged to abut the proximal end  54  of the cage  42  of the connecting element  30  when the hinge shaft  202  is fully advanced against the cage  42 . The distal end  216  may also include opposing extensions  226  with a cut out  228  shaped to abut the rod  44  and/or edges  230  for engaging the respective edges  143  of the arms  58  of the cage  42 . Also, the distal shaft  220  may include one or more windows  232  and one or more laser markings, such as lines  234 , arranged in the same manner as that described above with respect to the counter torque tube  108 , such that the full and proper advancement of the hinge shaft  202  can be determined based on alignment with the proximal edges  144  of the blades  56 . The distal shaft  220  may also include one or more holes  236  along at least a portion of the length of the distal shaft  220 , preferably in alignment with the grooves in its interior surface. Such holes  236  are desirably sized and positioned in the same manner as the holes  150  in the counter torque tube  108 , in order to similarly release any trapped fluid and/or tissue. 
     The proximal shaft  218  of the hinge shaft  202  may be narrower along at least a portion of its length, in order to reduce weight and material, and thus proximal shaft  218  may include a tapered portion  238 . The hinge  208  is a generally U-shaped component sized to fit the proximal end  206  of the hinge shaft  202  between its ends  240 . Each end  204  of the hinge  208  is connected to the proximal end  206  by a respective pin  242  such that the hinge  208  may rotate from one side to the other (as shown in  FIGS. 9A-B ) about the pins  242 . The proximal shaft  218  preferably includes a passageway along its length that is open at each end of the proximal shaft  218  and that communicates with the open interior of the distal shaft  220 . In that way, a tool, such as the set screw driver  104 , can be passed down within the hinge shaft  202  through the open proximal end  206  in order to lock the position of the connecting element  30  with respect to the rod  44  by tightening the set screw  45 . 
     An eyelet ring  222  is located between the proximal shaft  218  and the distal shaft  220 . The eyelet ring  222  includes a laterally extending tab  244  having a bore  246  formed within it. The bore  246  is configured to receive a portion of one or more compression or distraction tools, as discussed below. Although the bore  246  may have an hourglass shape along its central axis, as disclosed in the &#39;809 Patent, the bore  246  may alternatively have another shape, such as a substantially cylindrical shape along its central axis. The eyelet ring  222  is rotatable about the longitudinal axis of the hinge shaft  202 , such that the angular position of the tab  244  around the hinge shaft  202  can be varied. The hinge shaft  202  may be structured such that the eyelet ring  222  (and its tab  244 ) is positioned in approximately the middle of the hinge shaft  202  along its longitudinal axis, but the eyelet ring  222  could be positioned at other locations along the length of the hinge shaft  202 . 
     The distal end  248  of the proximal shaft  218  may include a distal extension (not shown) which is received in the proximal end  250  of the distal shaft  220 . For example, the distal extension may be in the form of a sleeve which extends through the eyelet ring  222  and is press fit within the open interior of the proximal end  250  of the distal shaft  220 . The hinge shaft  202  may thus be assembled by advancing the distal extension of the proximal shaft  218  through the eyelet ring  222  and into the open proximal end of the distal shaft  220 . The proximal shaft  218  is preferably not advanced too far into the distal shaft  220 , so that the eyelet ring  222  received therebetween will not be compressed and have difficulty rotating freely about the longitudinal axis of the hinge shaft  202 . Once the proximal shaft  218  is properly received by the distal shaft  220 , the position of the shafts  218 ,  220  may be secured by inserting one or more pins  252  through respective aligned bores passing through the overlapping walls of the proximal and distal shafts  218 ,  220 . In one example, four such pins  252  are used for each hinge shaft  202 , spaced at 90° intervals about the longitudinal axis. After the pins  252  are inserted, they are welded and blended within the bores until the outer surface of the hinge shaft  202  extending over the pins  252  is smooth. 
       FIGS. 11A-B  illustrate elevational views of the ball shaft  204 , taken along orthogonal directions. The ball shaft  204  has a proximal end  210  and a distal end  254 , with the ball  212  being at the proximal end  210 . The ball shaft  204  includes a proximal shaft  256  and a distal shaft  258 , with an eyelet ring  260  disposed therebetween. The ball shaft  204  includes numerous structures which are similar or identical to corresponding structures of the hinge shaft  202 . For example, the distal shaft  258  and the eyelet ring  260  of the ball shaft  204  may be identical to the respective distal shaft  220  and eyelet ring  222  of the hinge shaft  202 . 
     As with the distal shaft  220  of the hinge shaft  202 , the distal shaft  258  of the ball shaft  204  may have a similar structure to the body  110  of the counter torque tube  108 . That is, the distal shaft  258  desirably has a tubular shape with an open interior designed to receive a passageway device  31  therein. The open interior may have the same grooved structure as the counter torque tube  108 , in order to similarly receive and constrain the blades  56  of the passageway device  31 . The distal end  254  may also have the same structure for engaging the cage  42  of a connecting element  30  as the distal end  114  of the counter torque tube body  110  or the distal end  216  of the hinge shaft  202 . That is, the distal end  254  may have a chamfered distal edge  262  arranged to abut the proximal end  54  of the cage  42  of the connecting element  30  when the ball shaft  204  is fully advanced against the cage  42 . The distal end  254  may also include opposing extensions  264  with a cut out  266  shaped to abut the rod  44  and/or edges  268  for engaging the respective edges  143  of the arms  58  of the cage  42 . Also, the distal shaft  258  may include one or more windows  270  and one or more laser markings, such as lines  272 , arranged in the same manner as described above with respect to the counter torque tube  108  or the hinge shaft  202 , such that the full and proper advancement of the ball shaft  204  can be determined based on alignment with the proximal edges  144  of the blades  56 . The distal shaft  258  may also include one or more holes  274  along at least a portion of the length of the distal shaft  258 , preferably in alignment with the grooves in its interior surface. Such holes  274  are desirably sized and positioned in the same manner as the holes  150  in the counter torque tube  108  or the holes  236  in the hinge shaft  202 , in order to similarly release any trapped fluid and/or tissue. 
     The proximal shaft  256  of the ball shaft  204  may be narrower along at least a portion of its length, in order to reduce weight and material, and thus proximal shaft  256  may include a tapered portion  276 . The ball  212  is a generally spherical component sized to fit within the hinge  208  to form the polyaxial fulcrum  214 . The proximal shaft  256  preferably includes a passageway along its length that is open at each end of the proximal shaft  218  and that communicates with the open interior of the distal shaft  258 . In that way, a tool, such as the set screw driver  104 , can be passed down within the ball shaft  204  through the open proximal end  210  in order to lock the position of the connecting element  30  with respect to the rod  44  by tightening the set screw  45 . 
     An eyelet ring  260  is located between the proximal shaft  256  and the distal shaft  258 . The eyelet ring  260  includes a laterally extending tab  278  having a bore  280  formed within it. The bore  280  is configured to receive a portion of one or more compression or distraction tools, as discussed below. Although the bore  280  may have an hourglass shape along its central axis, as disclosed in the &#39;809 Patent, the bore  280  may alternatively have another shape, such as a substantially cylindrical shape along its central axis. The eyelet ring  260  is rotatable about the longitudinal axis of the ball shaft  204 , such that the angular position of the tab  278  around the ball shaft  204  can be varied. The ball shaft  204  may be structured such that the eyelet ring  260  (and its tab  278 ) is positioned in approximately the middle of the ball shaft  204  along its longitudinal axis, but the eyelet ring  260  could be positioned at other locations along the length of the ball shaft  204 . 
     The ball shaft  204  may be assembled in the same manner as the hinge shaft  202 . In particular, the proximal shaft  256  may be press fit or otherwise received within the distal shaft  258 , and then the position of the shafts  256 ,  258  may be secured by inserting one or more pins  282  through respective aligned bores passing through the overlapping walls of the proximal and distal shafts  256 ,  258 . Four such pins  282  may be inserted into the ball shaft  204 , spaced at 90° intervals about the longitudinal axis, after which the pins  282  may be welded and blended within the bores until the outer surface of the ball shaft  204  extending over the pins  282  is smooth. 
       FIG. 12A  illustrates an embodiment of a distractor  284  for use in conjunction with the present invention. The distractor  284  may be identical in structure and function to the distraction pliers disclosed in the &#39;809 Patent. For example, the distractor  284  may include a first handle  286  and a second handle  288  pivotably connected together at a pivot point  287 . Each of the first and second handles  286 ,  288  has a tip end  290  and a ratchet end  292 . A tip  294 , which may have a generally cylindrical shape, is formed at the tip end  290  of each handle  286 ,  288 , and a ratchet  296  for locking the distraction position of the distractor  284  extends between the handles  286 ,  288  at the ratchet end  292 . 
       FIG. 13A  illustrates an embodiment of a compressor  298  for use in conjunction with the present invention. The compressor  298  may be identical in structure and function to the compression pliers disclosed in the &#39;809 Patent. For example, the compressor  298  may include a first handle  300  and a second handle  302  pivotably connected together at a pivot point  301 . Each of the first and second handles  300 ,  302  has a tip end  304  and a ratchet end  306 . A tip  308 , which may have a generally cylindrical shape, is formed at the tip end  304  of each handle  300 ,  302 , and a ratchet  310  for locking the compression position of the compressor  298  extends between the handles  300 ,  302  at the ratchet end  306 . 
     One method of using the compression and distraction system  200  is by inserting the hinge shaft  202  and the ball shaft  204  over and along respective passageway devices associated with connecting elements  30  attached to the vertebrae  24 ,  26  that the surgeon or other user desires to move relative to one another. It is noted that the hinge shaft  202  and ball shaft  204  can be inserted without regard to the orientation of the tabs  244 ,  278  of the respective eyelet rings  222 ,  260 . Indeed, because the eyelet rings  222 ,  260  are rotatable about the longitudinal axes of the respective hinge shaft  202  and ball shaft  204 , the tabs  244 ,  278  can be properly oriented after the hinge shaft  202  and ball shaft  204  are inserted. In order to align the tabs  244 ,  278 , the ring  222  of the hinge shaft  202  is rotated until the tab  244  is directed away from the ball shaft  204  along the cephalad or caudal direction  12 ,  14 , and the ring  260  of the ball shaft  204  is rotated until the tab  278  is directed away from the hinge shaft  202  along the cephalad or caudal direction  12 ,  14 , as shown in  FIGS. 9A-B . Similarly, the hinge shaft  202  and ball shaft  204  can desirably be inserted without regard to the orientation of the hinge  208  of the hinge shaft  202 . That is, the hinge  208  is preferably symmetrical, such that it can engage the ball  212  of the ball shaft  204  (whether the ball shaft  202  is displaced in the cephalad direction  12  or the caudal direction  14  from the hinge shaft  202 ) by rotating the hinge  208  about the proximal end  206  of the hinge shaft  202  and towards the ball shaft  204  in either the cephalad direction  12  or the caudal direction  14 . Thus, after the hinge shaft  202  and ball shaft  204  are inserted, the hinge  208  is rotated about the proximal end  206  of the hinge shaft  202  until the ball  212  of the ball shaft  204  is received within the hinge  208  as shown in  FIG. 9B . Next, the hinge shaft  202  and ball shaft  204 , and the associated vertebrae  24 ,  26 , are distracted apart using the distractor  284  or compressed towards one another using the compressor  298 , as shown in  FIGS. 12B and 13B , respectively, and discussed below. 
       FIG. 12B  illustrates the distractor  284  engaging the hinge shaft  202  and the ball shaft  204  to distract apart the vertebrae  24 ,  26  connected thereto. In particular, the tips  294  of the distractor  284  are inserted into respective bores  246 ,  280  of the hinge shaft  202  and ball shaft  204 , respectively. Then, the handles  286 ,  288  are pressed together, which causes the tips  294  to move away from each other. The hinge shaft  202  and ball shaft  204  are thus caused to pivot about the polyaxial fulcrum  214  such that the distal ends  216 ,  254  of the respective hinge shaft  202  and ball shaft  204  separate the respective connecting elements  30  and distract the associated vertebrae  24 ,  26 . Once the first and second handles  286 ,  288  are pressed to impart an appropriate amount of distraction to the vertebrae, they are locked in that position by the ratchet  296 . The vertebrae  24 ,  26  may then be held in that position by the distractor  284  until the surgeon or other user fixes the relative positions of the vertebrae  24 ,  26 . That fixation may be performed by inserting a tool, such as the set screw driver  104 , through each of the hinge shaft  202  and ball shaft  204 , and then tightening a set screw  45  against the rod  44  in each of the connecting elements  30  connected to the vertebrae  24 ,  26  to be fixed. 
       FIG. 13B  illustrates the compressor  298  engaging the hinge shaft  202  and the ball shaft  204  to compress together the vertebrae  24 ,  26  connected thereto. In particular, the tips  308  of the compressor  298  are inserted into respective bores  246 ,  280  of the hinge shaft  202  and ball shaft  204 , respectively. Then, the handles  300 ,  302  are pressed together, which causes the tips  308  to move towards each other. The hinge shaft  202  and ball shaft  204  are thus caused to pivot about the polyaxial fulcrum  214  such that the distal ends  216 ,  254  of the respective hinge shaft  202  and ball shaft  204  move the respective connecting elements  30  closer together and compress the associated vertebrae  24 ,  26 . Once the first and second handles  300 ,  302  are pressed to impart an appropriate amount of compression to the vertebrae, they are locked in that position by the ratchet  310 . The vertebrae  24 ,  26  may then be held in that position by the compressor  298  until the surgeon or other user fixes the relative positions of the vertebrae  24 ,  26 . That fixation may be performed by inserting a tool, such as the set screw driver  104 , through each of the hinge shaft  202  and ball shaft  204 , and then tightening a set screw  45  against the rod  44  in each of the connecting elements  30  connected to the vertebrae  24 ,  26  to be fixed. 
     If performing final tightening of a set screw  45  into a connecting element  30  to which a hinge shaft  202  or a ball shaft  204  are connected, the counter torque tube  108  can be advanced against the cage  42  of an adjacent vertebra to help reduce the amount of torque that is transmitted to the spine  10 . 
     During compression or distraction, the eyelet rings  222 ,  260  may rotate about the respective longitudinal axes of the hinge shaft  202  and ball shaft  204  while engaged with the tips  294 ,  308  of the respective compressor  298  or distractor  284 . That is, if the bores  246 ,  280  of the respective eyelet rings  222 ,  260  have a substantially cylindrical rather than an hourglass shape along their central axes, as discussed above, such rotation may permit the tips  294 ,  308  to follow an arcuate path about the pivot points  287 ,  301  of the respective compressor  298  or distractor  284 . Also, during the compression or distraction, the connecting elements  30  connected to the hinge shaft  202  and ball shaft  204  may move with respect to the rod  44  as the connecting elements  30  are displaced relative to one another. In one alternative, one of the set screws  45  (either the one associated with the connecting element  30  connected to the hinge shaft  202  or the one associated with the connecting element connected to the ball shaft  204 ) may be tightened against the rod  44  before compression or distraction is performed. In that way, a one-way displacement may be induced, where the non-tightened connecting element  30  is moved along the rod  44  during compression or distraction. 
     After completing compression or distraction between two adjacent vertebrae  24 ,  26 , the compression and distraction system  200  may be used to perform compression or distraction between two other vertebrae (e.g., one vertebra  24  previously engaged for compression/distraction and the next adjacent vertebra  22 ). In that case, the entire compression and distraction system  200  need not be removed from the body. Rather, one of the hinge shaft  202  or ball shaft  204  may be moved to that next adjacent vertebra  22 , and the tabs  244 ,  278  may be rotated accordingly, and the hinge  208  may be flipped to engage the ball  212  of the ball shaft  204 . For example, with reference to  FIGS. 9A-B , after compression or distraction is completed between vertebrae  24  and  26 , the ball shaft  24  may be repositioned over and along the passageway device  31  connected to vertebra  22 . Then the ring  222  of the hinge shaft  202  is rotated until the tab  244  is directed away from the ball shaft  204  along the cephalad or caudal direction  12 ,  14 , and the ring  260  of the ball shaft  204  is rotated until the tab  278  is directed away from the hinge shaft  202  along the cephalad or caudal direction  12 ,  14 . The hinge  208  can then be rotated about the proximal end  206  of the hinge shaft  202  in the caudal direction  14  and into engagement with the ball  212  of the ball shaft  204 . Compression or distraction can then be performed between the vertebrae  22 ,  24  as described above. 
     After the various set screws  45  are finally tightened into the cages  42 , the passageway devices  31  can be detached from the respective connecting elements  30  and removed from the body. For example, the blades  56  of the passageway devices  31  may be separately disconnected from the connecting elements  30  and removed from the body. If monolithic blade-screws  60  were used, the blades  56  may be disconnected from the connecting element  30  by breaking each of the blades  56  away from the connecting element  30  at the frangible portions  62 . 
     One method for breaking the blades  56  of the blade-screw  60  away from the connecting element  30  is by using a blade remover  312 , illustrated in  FIG. 14A . The blade remover  312  is an elongate tool having a proximal end  314  and a distal end  316 . The blade remover  312  may include a handle  318  at the proximal end  314  and may have a channel (not shown) formed therein open to the distal end  316 . The channel may be constructed to receive a blade  56  of a blade-screw  60  therein. The blade remover  312  may also include a window and a laser marking (not shown) (or multiple windows and laser markings, if multiple blades  56  with different lengths are used), as described above with respect to the counter torque tube  108 , the hinge shaft  202 , and the ball shaft  204 , in order to determine whether the blade remover  312  has been fully and properly advanced along the blade  56 . The blade remover  312  may include a spring clip  322  in communication with the channel such that the spring clip  222  securely engages a blade  56  when the blade  56  is positioned within the channel, preferably in order to retain the blade  56  within the blade remover  312  after the blade  56  has been detached from the connecting element  30 . The blade remover  312  may also include a release mechanism for ejecting the blade  56  from the channel after the detached blade  56  has been removed from the body. That release mechanism may include a slider  324  received within a longitudinal track, such as a slot  326 , extending along the blade remover  312 . The release mechanism is structured such that distal movement of the slider  324  along the track will push the blade  56  out of the channel at the distal end  316  of the blade remover  312 . 
     In use, the blade remover  312  is engaged to a blade  56  by sliding the blade remover  312  distally over the blade  56  until the blade is received within the channel, as illustrated in  FIG. 14B . Using the handle  318 , a surgeon or other user may pivot the blade remover  312 , and thus the blade  56  received therein, about the frangible portion  62  until the frangible portion  62  fractures, thus disconnecting the blade  56  from the connecting element  30 . As illustrated in  FIG. 14C , each blade  56  may be pivoted away from the adjacent blade  56  of the same blade-screw  60 . The blade remover  312  may then be removed from the body, and desirably the spring clip  322  may retain the blade  56  within the blade remover  312  until the blade remover  312  is removed from the body. After the blade remover  312  is removed from the body, the detached blade  56  may be ejected from the channel by actuating the release mechanism. As shown in  FIG. 14D , the slider  324  is moved distally along the blade remover  312  until the blade  56  is ejected from the distal end  316  of the blade remover  312 . The blade remover  312  may then be used again by repeating the above steps to remove other blades  56  from the connecting elements  30 . 
     If one or both blades  56  of one of the passageway devices  31  were to become prematurely disconnected from a connecting element  30 , and further access to the connecting element  30  is desired, one or more of the blade rescue retractors of the blade rescue system disclosed in the &#39;098 Application may be used as functional replacements for the missing blade(s), as disclosed in that application. In order to ease the insertion of such a blade rescue retractor into the body, a series of sequential dilators may be inserted to gently enlarge a path to the targeted connecting element  30 , with the largest of the dilators being sized to receive one of the blade rescue retractors inside of it. Thereafter, all but the largest of the sequential dilators may be removed, and then the blade rescue retractor may be advanced within the largest dilator to the connecting element  30 . After the blade rescue retractor reaches the connecting element  30 , the largest dilator may be removed from the body. 
     Although various components described herein, such as the counter torque tube  108 , the hinge shaft  202 , and the ball shaft  204 , have been described and illustrated as being designed to interact with the blades  56  of passageway devices  31 , it is to be understood that those components could be designed to interact with different types of passageway devices, such as cannulas, towers, or portals, some of which may not have blades  56 . In such cases, those components may be designed to interact similarly with those other types of passageway devices. For example, the open interiors of the counter torque tube  108 , hinge shaft  202 , and ball shaft  204  may be structured to receive such other type of passageway device, and the interior surfaces of those components may have recessed grooves that have a correspondingly different shape, or the interior surfaces may have other structures for receiving or otherwise engaging corresponding structures of the passageway device. Moreover, the windows and the laser markings (e.g., lines) may be designed to align with a predetermined portion of the passageway device, such as the proximal end of the passageway device. 
     The various components described herein are preferably constructed of materials safe for use in the body. In one embodiment, many of the components to be permanently implanted in the body, such as the blade-screws  60  and the rod  44 , may be constructed from titanium or a titanium alloy. In one alternative, some or all of such permanently implantable components may be constructed from a cobalt-chromium alloy, such as the material sold under the trademark VITALLIUM® by Howmedica Osteonics Corp. Many or all of the instruments for use in implanting and manipulating the permanently implantable components, such as the rod inserter  84 , the counter torque tube  108 , the blade remover  312 , and the components of the compression and distraction system  200  (including the hinge shaft  202 , the ball shaft  204 , the distractor  284 , and the compressor  298 ), may be entirely, largely, or partially constructed from stainless steel. 
     Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims.