Abstract:
An instrument for inserting, adjusting and engaging an implant, such as a polyaxial screw of a spinal fixation system, includes at least one retractable tab for engaging a corresponding recess on the implant and a shaft that moves relative to the retractable tab. The movable shaft selectively moves the tab between an expanded position for engaging the recess and a retracted position out of engagement with the recess. The shaft selectively engages a portion of the implant to rigidify the implant after the retractable tab engages the recess. The axially extending shaft may be disposed within an axially extending passageway of a body assembly. A rotatable collar surrounding the body assembly is coupled to the shaft for moving the shaft relative to the retractable tab.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to implantable surgical devices used in surgical procedures. More particularly, the present invention relates to an instrument for inserting, adjusting and removing a spinal implant, such as a polyaxial pedicle screw.  
       BACKGROUND OF THE INVENTION  
       [0002]     Various surgical implants have been used in numerous forms of reconstructive and corrective surgical procedures. One example is a spinal fixation systems used to align, stabilize and/or fix a desired relationship between adjacent vertebral bodies. Such systems typically include a spinal fixation element, such as a relatively rigid fixation rod or plate, that is coupled to adjacent vertebrae by attaching the element to various anchoring devices, such as hooks, bolts, wires or screws. The spinal fixation element may take numerous forms, including a preconfigured shape specific to the implantation site within a patient. Following installation, this spinal fixation element serves to hold the vertebrae in a desired spatial relationship. The spinal fixation element may be implanted for a fixed period of time, to allow healing or fusion to occur. Additionally, the spinal fixation element may be designed for prolonged implantation during the life of a patient.  
         [0003]     Each spinal fixation element must be anchored to various regions of a patient. For example various vertebrae sites may be designed by a surgeon as locations for a spinal fixation element. Each of these sites may vary in shape, location, composition and landscape. Therefore, a variety of anchoring devices have been developed to provide for engagement of a particular portion of the bone. Pedicle screw assemblies, for example, have a shape and size that is configured to engage pedicle bone. Such screws typically include a threaded shank that is adapted to be threaded into a vertebra and a head portion. The head portion is typically sized and orientated to allow for a spinal rod to be captured and held in position. This capture of a spinal rod is typically accomplished by providing a U-shaped recess in the head of the pedicle screw which is capable of accepting the spinal rod. Various retention mechanisms, such as a setscrew, plug, or cap, may further be employed to fix the spinal rod in place within the U-shaped recess. In use, the shank portion of each screw is then threaded into a vertebra, and once properly positioned, a fixation rod is seated through the rod-receiving portion of each screw and the rod is locked in place by tightening a cap or similar type of closure mechanism to securely interconnect each screw and the fixation rod. Other anchoring devices include hooks and other types of bone screws  
         [0004]     In many pedicle screws, the head is designed to allow motion in along a plurality of axes relative to the shank of the threaded engagement portion. This freedom of motion of the head thereby aids in alignment and seating of a rod connecting a plurality of screws. Furthermore, the range of motion available may differ based on the direction of head displacement relative to the shank of the pedicle screw. For example, a head may have 30 degrees of motion along a first axis, and only 5 degrees of motion along a second axis. These types of polyaxial screws are generally known as “favored angle” or “biased angle” polyaxial screws.  
         [0005]     Polyaxial screws and other implants having movable components are often difficult to manipulate during a surgical procedure, thereby requiring time consuming surgical procedures to properly orient the implant within a patient. Furthermore, surgeons oftentimes must make several attempts at proper implant insertion. To insert and remove the screw, the components of the implant must be made rigid relative to each other, to enable rotation of the shaft in a desired direction by engaging the head. Current drivers for inserting polyaxial screws accomplished this using several techniques, but are generally incapable of inserting a favored angle polyaxial screw in a manner such that he head position is maintained during insertion. Maintaining head position is essential when using a favored angle screw as the range of mobility of the head may be sufficiently small along non favored angle axis such that it may be impossible to use the implanted screw unless the head is orientated properly.  
       SUMMARY OF THE INVENTION  
       [0006]     The present invention provides an instrument for inserting, adjusting and removing an implant in a spinal fixation system, such as a polyaxial pedicle screw with a favored angle position. The instrument includes an engagement mechanism for engaging a first portion of the implantable device and an alignment mechanisms for engaging a second portion of the implantable device. In one embodiment the first portion may be a shank of the polyaxial screw and the second portion may be the head of the polyaxial screw. Following engagement of the alignment mechanism the head and shank are coupled together as a rigid assembly, thereby allowing implantation. Additionally the instrument may contain a counter-rotation mechanism associated with the engagement and alignment mechanisms, such that the counter-rotation mechanism provides for the orientation of the second portion of the implantable device. When used with a pedicle screw having a favored angle, these counter-rotation mechanisms can be utilized in orientating the head (i.e. the second portion of the implantable device) such that the favored angle region is aligned according to a surgeons needs.  
         [0007]     According to a first aspect, an instrument for engaging an implant is provided. The instrument comprises an engagement mechanism for selectively engaging a first portion of the implant, an alignment mechanism moveable relative to the engagement mechanism for selectively engaging a second portion of the implantable device and a counter-rotation mechanism moveable relative to the alignment mechanisms wherein the counter-rotation mechanism may be used in orientating the second portion of the implantable device according to a surgeon&#39;s needs.  
         [0008]     According to another aspect, a driver device for a polyaxial screw comprises an engagement mechanism for engaging the shaft of the polyaxial screw, an alignment mechanism for engaging the head of the polyaxial screw and a counter-rotation mechanism for orientating the head portion of the polyaxial screw is recited. The engagement mechanism defines a first axis and is further sized and orientated for engaging the shaft portion of a polyaxial screw. The engagement of the engagement mechanism with the shaft portion of a polyaxial screw may take numerous forms, including but not limited to the use of a hex shaped driver and recess arrangement. The alignment mechanism of the driver device is additionally orientated along the same axis defined by the engagement mechanism. The alignment mechanism is capable of engaging the head portion of the polyaxial screw such that the head and shaft portions are rigidified relative to each other. The engagement of the head portion of the polyaxial screw may take numerous forms, including the use of a threaded male and female arrangement for rigidifying the head portion of the polyaxial screw. Additionally, a counter-rotation mechanism is orientated along the same axis as the engagement mechanism and the alignment mechanisms such that the counter-rotation mechanism can be used to orientate the head portion of the polyaxial screw relative to the shaft portion of the polyaxial screw by rotating independently of the alignment mechanism and engagement mechanism.  
         [0009]     According to another aspect of the invention, a method of implanting a polyaxial screw having a head and shaft portion is further recited. This method includes the steps of engaging the shaft portion of the polyaxial screw with an engagement mechanism, rigidifying the head portion following engagement such that the head portion is maintained in a rigid arrangement relative to the shaft portion and then driving the rigidified head and shaft. The driving of the head and shaft can be in a forward direction, to drive the screw into a patient, or can be in a reverse direction to drive the screw out from a patient. Additionally, the orientation of the head portion of the polyaxial screw can be fixed to a know position following or during the driving of the screw. When used with a favored angle polyaxial screw this fixing of the orientation of the head portion allows for the orientating of the favored angle polyaxial screw in a manner that is most beneficial for the intended operation. Following the driving and fixing of orientation of the head portion of the polyaxial screw each of the engagement mechanism, alignment mechanism and counter-rotation mechanism may be disengaged from the implantable polyaxial screw and removed from a patient. 
     
    
     BRIEF DESCRIPTION OF THE FIGURES  
       [0010]      FIG. 1  is an exploded view of an instrument for engaging an orthopedic implant according to an embodiment of the invention.  
         [0011]      FIG. 2A  is a side view of the assembled instrument of  FIG. 1  wherein the counter-rotation mechanism is in an extended position.  
         [0012]      FIG. 2B  is a side view of the assembled instrument of  FIG. 1  wherein the counter-rotation mechanism is in a retracted position.  
         [0013]      FIG. 3  illustrates a side view of a polyaxial screw suitable for use with the instrument of  FIG. 1 .  
         [0014]      FIG. 3A  illustrates a favored angle orientation of a favored angle polyaxial screw.  
         [0015]      FIG. 3B  illustrates a non favored angle orientation of a favored angle polyaxial screw.  
         [0016]      FIG. 4  is a detailed view of the shank portion of the polyaxial screw of  FIG. 3 .  
         [0017]      FIG. 5  is a detailed view of the head portion of the polyaxial screw of  FIG. 3 .  
         [0018]      FIG. 6  is a side view of the engagement mechanism for use with the instrument of  FIG. 1 .  
         [0019]      FIG. 7  is a side view of the alignment mechanism for use with the instrument of  FIG. 1 .  
         [0020]      FIG. 8A  is a side view of the counter-rotation mechanism for use with the instrument of  FIG. 1 .  
         [0021]      FIG. 8B  is a side view of the counter-rotation mechanism for use with the instrument of  FIG. 1 .  
         [0022]      FIG. 8C  is an illustration of the assembled instrument wherein the counter-rotation element is in an extended position.  
         [0023]      FIG. 8D  is an illustration of the assembled instrument wherein the counter-rotation element is in a retracted position.  
         [0024]      FIG. 9  is an assembled view of an alternate instrument for engaging an implantable polyaxial screw  FIG. 10  is a flow chart illustrating the steps involved in implanting a polyaxial screw using the instrument of  FIGS. 1-9 .  
         [0025]      FIG. 11A  is an embodiment of a the present invention in a disengaged state according to a first aspect.  
         [0026]      FIG. 11B  is is an embodiment of a the present invention in an engaged state according to a first aspect.  
         [0027]      FIG. 12  is an embodiment of the present invention according to a second aspect.  
         [0028]      FIG. 13  is a flow chart illustrating the steps involved in adjusting a polyaxial screw using the instrument of  FIGS. 1-9 .  
         [0029]      FIG. 14  is a flow chart illustrating the steps involved in removing a screwdriver from a polyaxial bone screw.  
         [0030]      FIG. 15  is a flow chart illustrating the steps involved in inserting a favored angle polyaxial screw.  
         [0031]      FIG. 16  is a flow chart illustrating the steps involved in implanting a polyaxial screw using the instrument of  FIGS. 1-9 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0032]     The present invention provides an improved instrument for manipulating an implant, such as a polyaxial screw. The implant may be used in numerous surgical procedures, including spinal fixation surgeries. The instrument of the present invention may be manufactured from a variety of bio-compatible materials, including but not limited to various grades of titanium, stainless steel or plastics. The instrument can be used to straighten, insert, adjust and/or remove an implant without modification or replacement of the instrument. The present invention will be described below relative to an illustrative embodiment directed toward spinal surgery. Those skilled in the art will appreciate that the present invention may be implemented in a number of different applications and embodiments and is not specifically limited in its application to the particular embodiments depicted herein.  
         [0033]      FIG. 1  illustrates an exploded view of an instrument  100  for engaging an orthopedic implant, such as a favored angle polyaxial screw used in a spinal fixation system, according to an illustrative embodiment of the invention. The instrument  100  can be used with any suitable orthopedic implant, such as monoaxial screw assemblies or hooks and is not limited to use with polyaxial screws per se. In the present embodiment, the instrument  100  is a polyaxial driver device capable of inserting and removing a favored angle polyaxial screw.  FIG. 2  is a side view of the assembled instrument  100 . The instrument  100  includes a engagement mechanism  10  for engaging a first portion of the orthopedic implant. The engagement mechanism may have a hex tip  18  disposed at its end for use in engaging the first portion of the implant. This first portion of the implant may be the shaft of a favored angle screw. The instrument  100  further includes an alignment mechanism  20  having a tip  26  sized and orientated for coupling with a second portion of the implantable device, such as the head of a favored angle pedicle screw. The alignment mechanism  20  is such that it may slideably move relative to the engagement mechanism  10 . A first collar  22  is provided on the alignment mechanism  20  wherein the first collar includes a mechanical stop (not shown) that may prevent linear motion of the alignment mechanism  20  relative to the engagement mechanism  10 . This collar  22  may engage first and second circular stop  12 , 14 . These stops  12 , 14  assist in defining multiple positions of the alignment mechanism when used in the removal and insertion of a polyaxial screw. When the first collar  22  is position over the first stop  12 , the alignment mechanism  20  is deemed “extended”, while positioning the alignment mechanism over the second stop  14  results in a “retracted” alignment mechanism  20  position. Looking briefly to the assembled view of  FIG. 2A , the first collar  22  is orientated to engage a first stop  12  such that the depicted alignment mechanism of the instrument of  FIG. 2  is in an extended position. Alternatively,  FIG. 2B  illustrates the alignment mechanism in a retracted position. While in ether an extended or retracted position, the alignment mechanism  20  remains free to rotate around the axis defined by the engagement mechanism  10 . Further associated with the alignment mechanism  20  may be a alignment mechanism coupling element  26 . In the illustrated embodiment this coupling element  26  is shown as a threaded fastener capable of engaging a second portion of the implantable device. One skilled in the art will readily recognize that numerous alternative coupling elements  26  may be utilized in practicing the present invention.  
         [0034]     A counter-rotation mechanism  30  is further associated with the alignment mechanism  20  and the engagement mechanism  10  of the present invention. The counter-rotation mechanism  30  may slideably move along the alignment mechanism  20  and may simultaneously rotate about the axis defined by the engagement mechanism  10 . The counter-rotation mechanism may further include a second collar  32  which provides a readily accessible region for use in rotating and sliding the counter-rotation mechanism  30  along the alignment mechanism  20 . The counter-rotation mechanism may further include an anti-rotation finger element  34  disposed along the end of the counter-rotation mechanism  30 . This counter-rotation element is sized and orientated to allow engagement with the second portion of the implantable device.  
         [0035]     The instrument for operating the implantable device may further include a handle  16  assembly coupled to the engagement mechanism  10  which provides a convenient location for rotating the engagement mechanism  10 .  
         [0036]      FIG. 3  illustrates a side view of a polyaxial screw suitable for use with the instrument of  FIG. 1 . This polyaxial screw is solely an illustrative implantable device for use in practicing the present invention and is not intended to be limiting of acceptable implantable devices. In one embodiment the polyaxial screw  300  may be a favored angle polyaxial screw.  
         [0037]     The polyaxial screw  300  of the present invention has a first portion, namely a shank  302 , and a second portion, namely a head  304 . The shank  302 , as illustrated herein, may include threads which allow translation of rotary motion into a longitudinal displacement. Associated with the shank  302  is a drive feature  306  for receiving the engagement mechanism  10  of  FIGS. 1 and 2 . In the illustrated embodiment the drive feature  306  take the form of a female hex arrangement, yet one skilled in the art will readily recognize that the drive feature may be of varying sizes and shaped. For example, the drive feature  306  may be, but is not limited to, a square shape, a triangular shape or a Torx® shape. The tip  18  of the engagement mechanism  10  must be sized and shaped appropriately to engage the drive feature  306  of the illustrated polyaxial screw  300 .  
         [0038]     Associated with the shank  302  of the polyaxial screw assembly  300  is a head  304 . In the present embodiment, the head  304  is allowed to move relative to the shank  302  using a ball and socket arrangement. Using a traditional ball and socket arrangement allows for uniform angular displacement of the head  304  relative to the longitudinal axis of the shank  320 . Furthermore, the use of a ball and socket joint between head and shank allows for unimpeded rotary motion of the head  304  relative to the shank  302 . In an alternate embodiment, namely a favored angle polyaxial screw, the available angular displacement of the head  304  relative to the longitudinal axis of the shank  320  may be variable.  
         [0039]     A favored angle polyaxial screw arrangement is illustrated in  FIGS. 3A and 3B . Examples of favored angled screws are disclosed in U.S. Patent Application Publication No. 2002/0058942 and U.S. Patent Application Publication No. U.S. 2003/0055426. In  FIG. 3A  a first angular displacement “A” is defined as the angular measurement bound by the longitudinal centerline of the shank  320  and the longitudinal centerline of the head  340 . As the ball and socket arrangement of the present embodiment allows for angular displacements in numerous directions, a second angular displacement, namely A′ may be defined. One such secondary angular displacement is shown in  FIG. 3B . Using similar measurement techniques, this second angular measurement A′ is again the maximum displacement defined by the longitudinal centerline of the shank  320  and the head  340 . In the present case the angular displacement of A′ is clearly less than that of A. In lieu of this, the angular displacement associated with the orientation of  FIG. 3A  is deemed the favored angle.  
         [0040]     The use of favored angle polyaxial screws allows a surgeon to implant a polyaxial screw designed for a specific range of angular displacement based upon treatment requirements. As the favored angle feature is only applicable to a specific direction and only covers a small range of potential head  304  locations it is essentially to properly orientate the polyaxial screw  304  such that the favored angle feature is appropriately situated. Orientation of the head  304  appropriately is accomplished using the counter-rotation mechanism  30  illustrated in  FIGS. 1 and 2 . During insertion of the screw into bone the surface of the bone is typically uneven. With polyaxial screws the head  304  may start to angulate relative to the shank  302  once the head contacts the surface of the bone. This can cause the hex tip of the screwdriver to become lodged in polyaxial screw assembly making it difficult to remove screwdriver from the screw.  
         [0041]      FIG. 4  is a cutaway illustration of the shank  302  portion of a polyaxial screw assembly  400 . In this illustration the drive feature  306  is readily apparent. The illustrated drive feature  306  is depicted as a female hex arrangement, yet one skilled in the art will readily recognize that the hex  306  may take numerous shapes such as a triangular shape, square shape or Torx® shape. The drive feature  306  must be sized for coupling with an applicable male tip  18  (not shown) of the engagement mechanism  10  of  FIG. 1  and  FIG. 2 . A longitudinal axis  320  is further defined as passing through the centerline of the shank portion of the polyaxial screw. Additionally, the shank  302  may have an exterior screw thread arrangement  402  such that rotation of the shank using the drive feature  306  results in motion along the longitudinal axis  320 . One skilled in the art will recognize that the screw thread arrangement  402  of the shank  302  may be of a fixed or variable pitch, or some combination thereof. Furthermore the screw arrangement  402  may cover the entirety of the shank  302 , a portion of the shank  302  or any combination thereof.  
         [0042]      FIG. 5  is a isometric view of the head portion  304  of a polyaxial screw. In the illustrated embodiment the head portion  304  includes a U-shaped recess  502  disposed along opposing sides of the head  304 . This U-shaped recess  502  serves numerous functions. Firstly additional implantable devices may be disposed within the recess defined by the U-shaped recess  502 . For example, during spinal surgery a spinal surgical rod may be disposed across the opposing U-shaped recess  502 . Following insertion of the spinal rod, a screw (not shown) may be threaded into the threaded setscrew recess  308  for use in retaining the spinal rod. Additionally, the U-shaped recess  502  allows for the insertion of the anti-rotation element  34 , disposed at the end of the anti-rotation mechanism  30 , into the head  304  of the polyaxial screw. During insertion or removal of the polyaxial screw into a patient the anti-rotation mechanism  30  allows for proper orientation of head position using the opposing U-shaped recesses  502  of the head  304 .  
         [0043]      FIG. 6  is a side view of the engagement mechanism  10  for use with the instrument of  FIG. 1 . The engagement mechanism includes a hex tip  18  for coupling with a drive feature  306  disposed on the shank of a polyaxial screw (not shown) The engagement mechanism further includes a first and second stop  12 , 14  disposed within the engagement mechanism  10 . In the present embodiment these stops  12 ,  14  are illustrated as circumferential grooves within the engagement mechanism  10 . One skilled in the art will readily recognize that the stops  12   14  may take numerous alternative forms such as protruding circumferential regions. Additionally, an engagement mechanism tang  62  is illustrated. This tang  62  may be used to couple the engagement mechanism  10  to an appropriate handle which may be used by a surgeon to provide rotary motion to the engagement mechanism  10 . Rotation of the engagement mechanism  10  thereby occurs along the central axis of the engagement mechanism  60 .  
         [0044]      FIG. 7  illustrates the alignment mechanism  20  as illustrated in the exploded view of  FIG. 1 . The alignment mechanism  20  is oriented to surround the engagement mechanism and is capable of moving both longitudinally and rotationally along the central axis of the engagement mechanism  60 . The alignment mechanism  20  may include a coupling mechanism  26  sized for coupling to the setscrew recess  308  of the polyaxial screw head  304 . Coupling of the alignment mechanism  20  coupling mechanism  26  to the setscrew recess  308  may occur after insertion of the engagement mechanism  10  into the drive feature  306  of the shank of the polyaxial screw. In use during a surgical procedure, the engagement mechanisms is first deployed such that the drive feature  306  of the shank  302  of the polyaxial screw is properly engaged by the hex tip  18  of the engagement mechanism. During insertion of the engagement mechanism  10  to engage the drive feature  306  of the shank of the polyaxial screw  302  the alignment mechanism  20  is oriented in a retracted position wherein the first collar  22  engages a second stop position  14  of the engagement mechanism. Upon engagement of the engagement mechanism with the drive feature  306  of the shank  302  of the polyaxial screw, the first collar  22  may be moved to engage a first stop position  12 . Engagement of this first stop may occur following depression of a spring loaded release button  70  associated with the first collar  22  such that the first collar  22  is initially disengaged from the second stop  14  and is capable of moving to a first stop  12  position. The orientation of the first collar  22  over the first stop position is herein refereed to as an “engaged position” of the alignment mechanism. In contrast, the location of the first collar  22  over the second stop  14  is herein referred to as a “retracted position” of the alignment mechanism  20 .  
         [0045]     Following the positioning of the alignment mechanism  20  into a engaged position, the fist collar  22  is manipulated to couple the alignment mechanism  20  with the head  304  of the polyaxial screw. In the illustrated embodiment a threaded coupling mechanism  26  is illustrated for coupling with the setscrew recess  308  of the head  304 . One skilled in the art will readily recognize alternative coupling mechanisms such as a helical dovetail may be employed in keeping with the present invention. The coupling of the alignment mechanism  20  with the head of the polyaxial screw  304  is accomplished by rotating the first collar  22  to engage the threads of the coupling element  26  with the threads of the setscrew recess  308 .  
         [0046]     Upon coupling of the head of the polyaxial screw  304  with the alignment mechanism  20  a rigid polyaxial screw assembly, comprising a head  304  and shank  302 , is formed. The coupled alignment mechanism  20  and polyaxial screw head  304  is such that angular displacement away from the longitudinal axis of the screw  320  is no longer possible. In such an arrangement a surgeon may drive both polyaxial screw shank  302  and head  304  as a single unit into a patient using a handle  16  disposed upon the end of the engagement mechanism  10 . Such a rigidified head  304  and shank  302  assembly prevents unintended loss of engagement of the hex tip  18  with the drive feature  306  of the shank. Furthermore, as the polyaxial screw is rigidly affixed to the surgical instrument of the present invention, unintended loss of the polyaxial screw within a body cavity is prevented. As a surgeon is often times working in a view impaired setting, loss of a polyaxial screw assembly may result in difficulties in relocating the screw as well as relocating the drive feature  306  for further driving of the screw. Additionally, unintended contact of the head  304  with the surgical site is prevented, as compared to existing polyaxial screw devices which allow the head  304  to move freely during insertion of the polyaxial screw. It is equally important that the screwdriver can be unthreaded from the polyaxial screw. In the event that the screwdriver tip becomes lodged in the screw the mechanical advantage of threads in the head of the polyaxial screw to remove the driver from the screw.  
         [0047]     Further disposed along the length of the alignment mechanism  20  is a third and fourth stop  74 ,  76  for use in conjunction with the counter-rotation mechanism. As illustrated in  FIGS. 8A and 8B , the anti-rotation element  30  includes a second collar  82  as well as a anti-rotation finger element  34 . The second collar  82  may include a spring loaded setscrew  86  designed for engaging the third or forth stop of the alignment mechanism  20  as required by a surgeon during use. When the spring loaded setscrew  86  engages the fourth stop  76  the counter-rotation mechanism is deemed to be in a “retracted” position. In contract, the engagement of the spring loaded setscrew  86  with the third stop  74  the counter-rotation mechanism is considered to be in a “extended” position.  FIGS. 8C and 8D  illustrate the anti-rotation mechanism of the assembled instrument in an extended and retracted position respectively. As understood by one skilled in the art, the engagement of the counter-rotation mechanism in a retracted and extended position may be accomplished using a variety of suitable techniques beyond the spring loaded setscrew depicted in the present embodiment such as employing a bal-seal or spring loaded button. The use of the depicted arrangement, therefore, is not intended to be limiting of the scope of the present invention.  
         [0048]     Upon selecting an engaged position for counter-rotation mechanism  30 , a surgeon may manipulate the second collar  82  to allow the engageable protraction  34  to mate with the U-shaped recess  502  of the head  304  of the polyaxial screw.  
         [0049]     Additionally associated with the counter-rotation element  30  is an indicating mechanism capable of informing a user of the orientation of the head of the polyaxial screw during a surgical procedure. As depicted in  FIG. 8A  for example, the indicating mechanism  84 , which corresponds to a known position of the engageable protrusion, informs a surgeon that the favored angle position is orientated along the axis noted by the indicating mechanism  84 . This is achieved by utilizing a favored angle screw wherein the underside of the head includes a slanted region which provides a region wherein additional range of motion of the head relative to the shank is provided. In view of this, an indicating mechanism  84  may be aligned with this slanted underside region of the favored angle screw when the screw is attached to the driver. In contrast, as illustrated in  FIG. 8B , a second indicating mechanism, which corresponds to a different engageable protrusion  34  orientation, denotes that a secondary orientation of the head  304  of the polyaxial screw  300  has been achieved.  
         [0050]     During a surgical procedure, a surgeon may use the counter-rotation mechanism to selectively oriented the head of the polyaxial screw in an appropriate position such that the favored angle arrangement can be exploited for use in a surgical procedure. Additionally When using a non favored angle polyaxial screw the indicating mechanism  84   86  may be utilized in selectively orientating the head  304  of a polyaxial screw  300  such that subsequent surgical procedures, such as insertion of spinal bars, is readily accomplished due to the proper orientation of the u-shaped slots within the head  304  of the polyaxial screw  300 .  
         [0051]      FIG. 9  is a cutaway view of an embodiment of the present invention, wherein engagement of the drive feature  306  of the head  304  is accomplished using an moveable engagement mechanisms  902  that is actuated by a lever  920  arrangement. The present embodiment couples rotation of the engagement mechanism and the alignment mechanism together, such that rotation of the handle  918  results in rotation of both the engagement mechanism and the alignment mechanism.  
         [0052]     In use the integral lever is operated to extend the engagement mechanism. Following extension of the engagement mechanism  902  the engagement mechanism may engage a drive feature  306  of a polyaxial screw shank  302 . Additionally, rotation of the handle  918  allows for rotation of the integral alignment mechanism such that the alignment mechanism by rigidify the polyaxial screw assembly. A surgeon may then selectively drive the polyaxial screw in a variety of directions. Additionally, a counter-rotation mechanism capable of slideably moving along the length of the alignment mechanism may be employed to selectively orient the head of the polyaxial screw as needed by a surgeon. The exterior of the counter-rotation mechanism may have a variety of indicators for use in properly orientating the counter-rotation mechanism as required by an surgeon such that the benefits of a favored angle polyaxial screw can be exploited.  
         [0053]      FIG. 10  is a flowchart illustrating the steps necessary in practicing the present invention. In accordance with step  1002 , the shaft portion of a polyaxial screw is first engaged by an engagement mechanism. Following engagement of the shank portion, the head portion is rigidified relative to the shaft portion using a alignment mechanism associated with the engagement mechanism. (step  1004 ) The rigidified head and shank of the polyaxial screw may be driven by a surgeon in accordance with step  1006  as required for the surgical procedure. The driving of the rigidified head and shank arrangement may be in a forward or reverse direction thereby allowing insertion of removal of the polyaxial screw assembly. Additionally, the orientation of the head portion of the polyaxial screw may be accomplished using a counter-rotation mechanism (step  1008 ) Proper orientation of the polyaxial screw head is beneficial when using a favored angle polyaxial screw. Orientation of the head may be accomplishing using a variety of means, including but not limited to the use of a indicating mechanism associated with the counter-rotation mechanism which provides a visual indicator of polyaxial screw head position. Upon proper orientation the engagement mechanisms, alignment mechanism and counter-rotation mechanism may be selectively disengaged from the polyaxial screw such that the driver may be removed from the implantable device (step  1010 ).  
         [0054]      FIG. 11  is an embodiment of an alternate aspect of the present invention. As illustrated in  FIGS. 11A and 11B , a moveable engagement mechanism  1102  is defined, wherein this moveable engagement mechanism  1102  has a hex tip  1118  for engaging a recess  306  in a polyaxial screw. As illustrated in the present embodiment, this moveable engagement mechanism  1102  is free to rotate in an unimpeded manner relative to a shaft  1164  when in a disengaged state ( FIG. 11A ) and is in a coupled state relative to the shaft  1164  ( FIG. 11B ) when properly engaged.  
         [0055]     Engagement of the moveable engagement mechanism  1102  is accomplished using a male splined element  1150  and a female splined region  1152 , wherein the male splined element is sized to engage the female splined region  1152  upon application of an external force. One skilled in the art will recognize that the use of a splined mating assembly is solely for illustrative purposes, and may be readily replaced by a suitable engagement mechanism as understood by a skilled practitioner. In the present embodiment of  FIG. 11A , the male splined element  1150  and the female splined region  1152  is in a relieved position  1140 , wherein the moveable engagement mechanism  1102  is not coupled to the instrument shaft  1162 . In such an arrangement rotary motion delivered to the instrument shaft  1162  will not be translated to the moveable engagement mechanism  1102 .  
         [0056]     Should a surgeon elect to deliver rotary motion provided to a instrument shaft  1164  to the integral assembly  1102 , the male splined element  1150  must first engage the female splined region  1152 . Engagement is accomplished by slideably moving the counter-rotation sleeve  1130  in a rearward direction (i.e. away from the integral assembly and toward a handle (not shown)) A rearward motion results in the movement of the counter-rotation sleeve engagement region  1170 , which is disposed within the counter-rotation sleeve  1130 , in a rearward direction. After an appropriate displacement rearward, the counter-rotation sleeve engagement region  1170  will contact the actuator protrusion  1162  of an actuator assembly  1160 . Further rearward displacement will in turn move the actuator  1160  in a similar rearward direction. Rearward motion of the actuator  1160  in turns causes subsequent engagement of the male splined element  1150 , in communication with the actuator  1160 , with the female splined region  1152  of the moveable engagement mechanism  1102 . Following engagement of the male splined element  1150  with the female splined region  1152  the moveable engagement mechanism  1102  is now rigidly coupled to the shaft  1164 . Rotational energy provided to the shaft  1164  is herein translated to the moveable engagement mechanism  1102 . One skilled in the art will recognize that numerous engagement mechanism may be employed to couple the moveable engagement mechanism  1102  to the shaft  1164 . An embodiment wherein the moveable engagement mechanism  1102  is coupled to the shaft  1164  is illustrated in  FIG. 1B .  
         [0057]     An alternate embodiment illustrating the engagement of a moveable engagement mechanism  1202 , having a hex tip  1218  disposed at its end, is illustrated in  FIG. 12 . Following displacement of the counter-rotation sleeve  1230  in a rearward direction the engagement tab  1280  is displaced to engage a annular recess  1282  of the moveable engagement mechanism  1202 , thereby coupling the moveable engagement mechanism  1202  to the shaft  1264 . One skilled in the art will recognize that the illustrated coupling embodiments are solely for illustrative purposes and are not intended to be limiting in scope.  
         [0058]     The present invention furthermore provides various methods for the insertion and adjustment of a polyaxial screw during surgery. As illustrated in the flowchart of  FIG. 13 , a polyaxial screw that has been implanted in vertebrae may be adjusted by a surgeon. In adjusting this screw an alignment mechanism of a driver device is connected to the head portion of a polyaxial screw implanted in a vertebra. (step  1302 ) The head is then orientated using the alignment mechanism to align the longitudinal axis of the head with the longitudinal axis of the shank of the polyaxial screw in accordance with step  1304 . A drive feature of an engagement mechanisms is then advances ( 1306 ) such that the depth of the implanted polyaxial screw may be adjusted using this engagement mechanism. (step  1308 )  
         [0059]     In accordance with  FIG. 14 , a polyaxial bone screw may further be removed from a screwdriver used in driving this screw. Removal occurs by first advancing an engagement mechanism into the shank of a polyaxial screw (step  1402 ) such that the engagement mechanism is capable of providing rotational energy to the shank of the polyaxial screw. The polyaxial screw is then driven into the region of bone (step  1404 ) as required by a surgeon. A sleeve may then be advanced wherein this sleeve moves relative to the engagement mechanism to engage the head of the polyaxial bone screw (step  1406 ). The sleeve is then fixed in location relative to the engagement mechanism in accordance with step  1408 ) and then the engagement mechanism may be retracted from the shank of the polyaxial screw by retracting the sleeve from the head of the polyaxial bone screw (step  1410 ).  
         [0060]     In accordance with an embodiment of the present invention a method for inserting a favored angle polyaxial screw is recited. This method is represented by the flowchart of  FIG. 15 . In accordance with this method a drive tip of a shaft of a screwdriver is engaged with the shank of a favored angle screw (step  1502 ). A sleeve is then advanced relative to the shaft such that the sleeve is coupled to the head of the polyaxial screw (step  1504 ). In accordance with step  1506  the head of the screw is aligned using an alignment indicator provided on the sleeve during the driving of the polyaxial screw with the shaft of the screwdriver.  
         [0061]     In accordance with  FIG. 16 , a method for implanting a polyaxial screw having a head and a shank is provided. A drive tip of a shaft of a screwdriver is engaged with the shank of a polyaxial screw (step  1602 ) and a sleeve is advanced in a direction relative to the longitudinal axis of the shaft of the screwdriver such that the head of the polyaxial screw is engaged (step  1604 ). The screwdriver is then driven with the sleeve in an advanced position relative to the shaft of the screwdriver in accordance with step  1606 . The screwdriver is then removed from the polyaxial screw (step  1608 ). The drive tip may then reengage the shank of the polyaxial screw (step  1610 ) such that the polyaxial screw can be driven with the sleeve in a retracted position relative to the shaft of the screwdriver (step  1612 )  
         [0062]     The present invention has been described relative to an illustrative embodiment. Since certain changes may be made in the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings be interpreted as illustrative and not in a limiting sense. For example, one skilled in the art will recognize that the instrument of the illustrative embodiment of the invention is not limited to use with polyaxial screws and can be used with any suitable implant for any suitable orthopedic system.  
         [0063]     It is also to be understood that the following claims are to cover all generic and specific features of the invention described herein, and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween.