Abstract:
A polyaxial screw head remobilizer system for remobilizing a screw body member relative to a head of a polyaxial bone screw includes a barrel body, a handle assembly, an inner shaft, a slide assembly, and a lever. The barrel body includes proximal and distal ends. The distal end includes a plurality of prongs for releasably engaging a plurality of yokes of the polyaxial screw body member to center the inner shaft over the head of the screw. The handle assembly couples to the proximal end of the barrel body. The inner shaft, disposed within the barrel body, includes proximal and distal ends. An engagement feature of the inner shaft mates with pockets of a bushing of the screw body member. The slide assembly is operably coupled to the barrel body and effect translations of the inner shaft. The lever extends from the slide assembly and rotates to actuate the slide assembly.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation-in-part of U.S. patent application Ser. No. 14/056,573 filed on Oct. 17, 2013, which claims priority from U.S. Provisional Application Ser. No. 61/716,413 filed on Oct. 19, 2012 and entitled “Instrument and Method for Restoring Motion to a Polyaxial Screw” which is incorporated by reference in its entirety herein. 
     
    
     FIELD 
       [0002]    The present invention relates generally to an apparatus for internal fixation of the spine and, more specifically, to a remobilizer for restoring polyaxial motion to a polyaxial screw head that has been locked. 
       BACKGROUND 
       [0003]    Certain spinal conditions, including a fracture of a vertebra and a herniated disc, indicate treatment by spinal immobilization. Several methods of spinal immobilization are known, including surgical fusion and the attachment of pins and bone plates to the affected vertebras. 
         [0004]    Spinal immobilization systems typically require the threaded securement of some form of bone anchor or bone screw-assembly into two or more vertebrae, which entails the drawing of the rod to the anchors/screw-assemblies, or drawing the anchors/screw-assemblies to the rod. Spinal screw-assemblies are used to secure a stabilization rod and comprise various components including a pedicle screw and a body member. The design of the spinal screw-assemblies allows for variable angular movement of the body member with respect to the pedicle screw with a threaded shaft portion of the screw extending through an opening in an end of the body member. 
         [0005]    The next generation of pedicle screws is polyaxial screws, with a body member which pivots and rotates about the spherical head of a bone screw. The bone screw is captured in the body member with a bushing; the bushing in turn accepts a rod after the screw has been placed in the pedicle, and the rod is captured in the bushing/body member assembly by inserting a set screw into the threads of the body member. As with most polyaxial pedicle screws, tightening of the set screw applies pressure onto the rod, which translates pressure onto the bushing, which then applies pressure on the spherical head of the bone screw, locking the polyaxial motion. Unlike other polyaxial pedicle screws, the new pedicle screw achieves additional locking because of the design of the screw bushing; the lower portion of the bushing acts like a wedge so when force is applied, the bottom of the bushing wedges between the spherical head of the bone screw and the body member, providing additional locking force. 
         [0006]    While this feature provides optimum performance with regards to strength of the construct in maintaining correction, it can make screw removal difficult, since the polyaxial motion remains locked due to the wedging effect, even after the set screw is removed. In order to restore polyaxial motion, the bushing must be un-wedged from between the bone screw head and the body member. The wedge can be knocked loose by tapping the body member of the bone screw with enough force to break the friction lock of the wedge, but this method may not be considered feasible in the case of patients with very poor bone. 
         [0007]    As a result, a tool is needed which can interact with the bushing and pull up on it, restoring the bushing to its position prior to locking and thereby removing the wedge and restoring polyaxial motion. 
         [0008]    Previously there has been no reliable method for restoring polyaxial motion to the screw. There has been no feature on the pedicle screw or bushing which allowed a tool to apply an upward force and remove the wedge. Tools have been attempted which rotate the bushing to “break” the wedge force, but these caused damage to the bushings and could not reliably effect the unlocking. The method of tapping on the screw body member to “break” the wedge has already been identified as one which cannot be recommended for patients with poor bone quality. 
       SUMMARY OF THE INVENTION 
       [0009]    Provided herein are apparatuses, systems, and methods of use for a polyaxial screw head remobilizer. 
         [0010]    The polyaxial screw head remobilizer system for remobilizing a screw body member relative to a head of a polyaxial bone screw generally comprises a polyaxial screw assembly, a barrel body, a handle assembly, an inner shaft, a slide assembly, and a lever. 
         [0011]    The barrel body has a proximal end and a distal end. In some embodiments, the distal end of the barrel body includes engagement features configured to engage with a plurality of yokes of a polyaxial screw body member and a polyaxial screw, so as to center the polyaxial screw head remobilizer on the head of the screw. The engagement features may comprise rounded rectangular prongs positioned on the distal end, such that the prongs may be seated in yokes of the screw body member. The barrel body may be made from any suitable material as known in the art including, by way of example and not limitation, stainless steel, a thermoplastic or other materials. The barrel body is generally cylindrical in shape; however, it may assume alternative shapes such as square, rectangular, polygonal, and the like. 
         [0012]    The handle assembly is coupled to the proximal end of the barrel body for holding of the polyaxial screw head remobilizer by an operator. The handle assembly may be coupled to the barrel body by any suitable method of attachment such as, for example, a fastener, an aperture, a nut or bolt connection, or the like. In some embodiments, the handle assembly further comprises a mount arm, fixedly coupled to the handle assembly and the barrel body, the mount arm configured to retain the slide assembly. In some embodiments, the mount arm has an aperture adapted to receive the inner shaft. In some embodiments, the mount arm is configured to slidably couple with the slide assembly, such as, without limitation, by a rail or track. In some embodiments, the mount arm further comprises a pin or other structure configured to limit the degree of distal translation of the inner shaft. 
         [0013]    The inner shaft is disposed within the barrel body. The distal end of the inner shaft further comprises an engagement feature. The engagement feature is configured to permit positioning of the barrel body and inner shaft within the polyaxial screw body member, engagement of the engagement feature with a polyaxial screw bushing, application of a force to unlock the screw bushing, disengagement of the inner shaft from the polyaxial screw bushing, and removal of the remobilizer from the polyaxial screw body member. In one embodiment, the engagement feature is a plurality of extensions configured to couple with a plurality of pockets of the polyaxial screw bushing. In some embodiments, the inner shaft further comprises a helical trough disposed near the proximal end of the inner shaft. 
         [0014]    The inner shaft is generally rounded-rectangular in cross-section. However, the inner shaft may assume alternative shapes, such as circular, square, cylindrical, polygonal, and the like, having an engagement feature that is adapted for entry into the screw body member and to frictionally lock with the pockets of the bushing. Alternatively, the inner shaft may be any shape which may be customized for the particular barrel body utilized. The inner shaft may be made from any suitable material as known in the art including, by way of example and not limitation, stainless steel, a thermoplastic or other materials. In many embodiments, the inner shaft is fixedly coupled to a stop element. 
         [0015]    The slide assembly is slidably coupled to the handle assembly (and/or the mating arm) and the inner shaft. In some embodiments, the mount arm and slide assembly may have apertures configured to permit a portion of the inner shaft to be disposed therethrough. In many embodiments, the proximal end of the inner shaft is fixedly coupled to a stop element, the stop element positioned proximal the slide assembly. The stop element is configured to impede translation of the slide assembly proximally along the inner shaft. In some embodiments, the slide assembly further comprises a pin configured to interact with the helical trough of the inner shaft. In use, the interaction of the pin with the helical trough causes rotation of the inner shaft as the pin travels the length of the trough. 
         [0016]    The lever rotatably associates with the slide assembly. The lever may extend from the slide assembly via mechanical attachment by any suitable method of attachment, for example, a fastener, an aperture, a nut-bolt connection, a washer, or the like. The lever is further pivotally coupled to the handle assembly by a suitable mechanical attachment, such as a pin or the like. The inner shaft may be slidably disposed within the barrel body and configured such that the inner shaft may be longitudinally displaced within the barrel body by actuation of the lever and the slide assembly. 
         [0017]    In a further embodiment, a spring member is operably coupled to the lever and the handle assembly, such that the spring member urges the lever from an actuated position back to its original position subsequent to actuation of the lever in either the proximal or distal direction. 
         [0018]    In use, when the lever is actuated, the lever causes the slide assembly to slide proximally along the inner shaft. As the slide assembly translates, the rotation pin coupled to the slide assembly engages with the helical trough on the inner shaft, causing the inner shaft to rotate as the pin travels the length of the trough. The rotation of the inner shaft causes the engagement feature to couple with pockets of the screw bushing. Once the pin has travelled the full length of the helical trough, the slide assembly reaches the stop element, configured to impede translation of the slide assembly along the inner shaft. Once the slide assembly reaches the stop, continued proximal translation of the slide assembly also translates the stop proximally. Because the stop is fixedly coupled to the proximal end of the inner shaft, the inner shaft is also translated proximally. Because the engagement feature of the inner shaft is coupled with the pockets of the screw bushing, the bushing is pulled proximally, thereby releasing its fixation on the head of the screw. Thus, the polyaxial screw assembly is remobilized. 
         [0019]    A polyaxial pedicle screw assembly comprises a screw body member, a screw bushing, and a polyaxial pedicle screw. The screw body member is generally cylindrical in configuration and adapted to receive a head portion of the pedicle screw. The bushing is adapted to fit within the screw body member between the screw body member and the head portion, and prevent polyaxial motion of the screw when the bushing is locked or pressed into position. The bushing further comprises pockets configured to engage with the inner shaft of the remobilizer. 
         [0020]    The bushing of the polyaxial screw was designed with undercut pockets to give the remobilizer tool a means of attachment. The remobilizer has an outer tube which can be inserted into the yokes of the screw body member to center the tool on the head of the screw. Inside the outer tube is a shaft which has extensions on the tip which, when rotated, can be inserted in the pockets of the bushing. The tip is actuated by squeezing the handle; squeezing the handle first pulls a pin in the inner shaft up a helical trough, causing the tip to rotate 90 degrees and inserting the extensions into the mating bushing pockets. Once the pin has traveled the full distance of the helical trough, it hits a stop, such that continuing to squeeze the handle then pulls the tip of the shaft towards the handles. Since the shaft is now mated with the bushing, this pulls the bushing upwards as well, removing the wedge from the bone screw and body member and restoring polyaxial motion. Releasing the handle restores the tip to its original position so it can be removed from the screw. 
         [0021]    A method of using the polyaxial screw head remobilizer tool comprises the steps of: inserting an outer tube of the remobilizer into yokes of a screw body member to center the tool and an inner shaft disposed within the outer tube on a head of the screw, in proximity to a bushing member of the screw body; actuating the tool to rotate the inner shaft such that an engagement feature on the tip of the inner shaft mates with a plurality of pockets in the bushing member of the screw; continuing actuation of the tool such that a force is applied to the bushing member to release a fixation hold between the bushing, the screw head, and the screw body member, thereby remobilizing the screw head; releasing the actuation of the tool such that the inner shaft derotates and the engagement feature at the tip of the inner shaft disengages from the pockets in the bushing member of the screw; and removing the remobilizer tool from the screw body member. 
         [0022]    The apparatuses, systems, and methods of use are set forth in part in the description which follows, and part will be obvious from the description or can be learned by practice of the methods, apparatuses, and systems. The advantages of the methods, apparatuses, and systems will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the methods, apparatuses, and systems, as claimed. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0023]    In the accompanying figures, like elements are identified by like reference numerals among the several preferred embodiments of the present invention. 
           [0024]      FIG. 1  is an illustration of one embodiment of the polyaxial screw head remobilizer. 
           [0025]      FIG. 2  is a close up view of the distal end of the remobilizer of  FIG. 1 . 
           [0026]      FIG. 3A  is an isometric view of a polyaxial screw for use with the remobilizer. 
           [0027]      FIG. 3B  is a cutaway view of a polyaxial screw for use with the remobilizer. 
           [0028]      FIG. 4A  is a side view of the distal end of the inner shaft. 
           [0029]      FIG. 4B  is a side view of the distal end of the inner shaft taken from view IVB in  FIG. 4A . 
           [0030]      FIG. 5  is a close up view of the distal end of the tube of the remobilizer, coupled to a polyaxial screw. 
           [0031]      FIG. 6  is a side view of one embodiment of the polyaxial screw head remobilizer. 
           [0032]      FIG. 7  is a perspective view of one embodiment of the barrel body and the inner shaft, the inner shaft having an engagement feature at a distal end and a helical trough near a proximate end. 
           [0033]      FIG. 8  is an exploded view of the barrel body, inner shaft, mount arm, slide assembly, and stop element. 
           [0034]      FIG. 9  is a cutaway view of a remobilizer tip inserted in a polyaxial screw, upon initial insertion. 
           [0035]      FIG. 10  is a cutaway view of a remobilizer tip inserted in a polyaxial screw after rotation of the remobilizer tip into bushing pockets of the screw. 
           [0036]      FIG. 11  is an exploded view of one embodiment of the polyaxial screw head remobilizer. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0037]    The foregoing and other features and advantages of the invention are apparent from the following detailed description of exemplary embodiments, read in conjunction with the accompanying drawings. The detailed description and drawings are merely illustrative of the invention rather than limiting, the scope of the invention being defined by the appended claims and equivalents thereof. 
         [0038]    The words proximal and distal are applied to denote specific ends of components of the current invention described herein. A proximal end refers to the end of a component nearer to a medical professional when operating the component. A distal end refers to the end of the component further from the medical professional when operating the component. 
         [0039]    As shown in  FIGS. 1, 6, and 11 , a polyaxial screw head remobilizer system  500  includes a polyaxial screw head remobilizer  100  generally comprises a barrel body  102 , a handle assembly  101  operably coupled to a slide assembly  106 , an inner shaft  124  coaxially disposed within the barrel body, and a lever  112  operably coupled to the slide assembly. Generally speaking, the screw head remobilizer  100  interacts with a bushing of a polyaxial screw assembly and longitudinally displaces the bushing to restore the bushing to an unlocked position, thereby removing the bushing wedge, and restoring polyaxial motion of a screw. 
         [0040]    The barrel body  102  has a generally longitudinal axis, wherein the barrel body  102  includes a proximal end  108  and a distal end  110  generally along the longitudinal axis. As shown in  FIGS. 1-2 and 5-11 , the distal end  110  of the barrel body  102  includes engagement features  111  configured to engage with a plurality of yokes (or U-shaped channels)  223  of a polyaxial screw body member  222  and a polyaxial screw  230 , so as to center the polyaxial screw head remobilizer  100  on the head of the screw  230 . The engagement features  111  may comprise rounded rectangular prongs positioned on the distal end  110 , such that the prongs  111  may be seated in the yokes  223  of the screw body member  222 . In alternative embodiments, the engagement features  111  may comprise any shape suitable for seating in the yokes  223  of the screw body member  222 , such as, without limitation, rectangular, square, triangular, ovoid, polygonal, and/or the like. Preferably, the engagement features  111  are shaped such that, when engaged, the yokes  223  are not permitted to rotate about an axis. The barrel body  102  may be made from any suitable material as known in the art including, by way of example and not limitation, stainless steel, a thermoplastic or other materials. The barrel body  102  is generally cylindrical in shape; however, it may assume alternative shapes such as square, rectangular, polygonal, and the like. 
         [0041]    The handle assembly  101  is coupled to the proximal end  108  of the barrel body  102  for holding of the polyaxial screw head remobilizer  100  by an operator. The handle assembly  101  may be coupled to the barrel body  102  by any suitable method of attachment such as, for example, a fastener, a rivet, an aperture, a nut or bolt connection, or the like. In some embodiments, the handle assembly  101  further comprises a mount arm  105 , fixedly coupled to the handle assembly  101  and the barrel body  102 , the mount arm  105  configured to retain the slide assembly  106 . In some embodiments, the mount arm  105  has an aperture adapted to receive the inner shaft  124 . In some embodiments, the mount arm  105  is configured to slidably couple with the slide assembly  106 , such as, without limitation, by a rail or track. In some embodiments, the mount arm  105  further comprises a pin or other structure configured to limit the degree of distal translation of the inner shaft  124 . 
         [0042]    The inner shaft  124  is coaxially disposed within the barrel body  102  and longitudinally displaced therein. The distal end of the inner shaft  124  further comprises an engagement feature  125 . As shown in  FIGS. 9 and 10 , the engagement feature  125  is configured to permit positioning of the barrel body  102  and inner shaft  124  within the polyaxial screw body member  222 , engagement of the engagement feature  125  with a polyaxial screw bushing  228 , application of a force to unlock the screw bushing  228 , disengagement of the inner shaft  124  from the polyaxial screw bushing  228 , and removal of the remobilizer  100  from the polyaxial screw body member  222 . 
         [0043]    In one embodiment, as shown in  FIGS. 4A and 4B , the engagement feature  125  includes a plurality of extensions  126  configured with a stepped down portion  128  on the distal end of the inner shaft  124 . The stepped down portion  128  allows the engagement feature  125  to coaxially pass through the plurality of yokes  223 , whereby the stepped down portion  128  includes a Width W S  that is less than a Length L E  of the engagement feature  125  and the inner shaft. The engagement feature  125  includes a width W E , whereby the length L E  is greater than the Width W E , as shown in  FIGS. 4A and 4B . Preferably, the Width W E  is less than the Width W Y  of the yokes  223 , such that the engagement feature  125  may longitudinally pass through the Width W Y  of the yokes  223 , as shown in  FIG. 3B . Preferably, the Length L E  is greater than the Width W Y  of the yokes  223 , such as to engage with a plurality of pockets  229  of the polyaxial screw bushing  228  (as shown in  FIGS. 3A-3B and 9-10 ) when the inner shaft  124  is rotated after the extensions  126  pass through the yokes  223 . 
         [0044]    Preferably, a quarter-turn rotation of the inner shaft  124  engages the extensions  126  with the plurality of pockets  229 . In one embodiment, the plurality of pockets  229  include a Width W P  that is greater than the Width W Y  of the yokes  223 , and preferably, the Width W P  is about the length L E  of the engagement feature  125 , as shown in  FIG. 3B , such as to allow fixedly engagement of the engagement feature  125  and the plurality of pockets  229 . As such, the engagement feature  125  is able to unlock the bushing  228  that wedges the screw head  234  by locking with the plurality of pockets  229  and longitudinally moving the bushing proximally away from the screw head  234  and restoring polyaxial motion of the screw  230 . In alternative embodiments, the engagement feature  125  may comprise generally rectangular lips. More generally, the engagement feature  125  may have any shape suitable for mating with the particular shape of the pockets  229  of the bushing  228 . For example, and without limitation, the engagement feature  125  could be rounded, domed, square, triangular, and/or the like. 
         [0045]    As shown in  FIGS. 7 and 8 , in many embodiments, the inner shaft  124  further comprises a helical trough  127  disposed near the proximal end of the inner shaft  124 .  FIG. 7  shows the inner shaft  124  disposed within the barrel body  102 , with the helical trough  127  disposed proximally from the proximate end  108  of the barrel body  102 . The inner shaft  124  is generally rounded-rectangular in cross-section. However, the inner shaft  124  may assume alternative shapes, such as circular, square, cylindrical, polygonal, and the like, having an engagement feature  125  that is adapted for entry into the screw body member  222  and to frictionally lock with the pockets  229  of the bushing  228 . Alternatively, the inner shaft  124  may be any shape which may be customized for the particular barrel body  102  utilized. The inner shaft  124  may be made from any suitable material as known in the art including, by way of example and not limitation, stainless steel, a thermoplastic or other materials. In some embodiments, the proximal end of the inner shaft  124  may be fixedly coupled to a stop element  122 . The inner shaft  124  may be fixedly coupled to the stop element  122  by any suitable method of attachment such as, for example, a threaded element, a fastener, a rivet, an aperture, a nut or bolt connection, or the like. 
         [0046]      FIG. 8  shows an exploded view of the barrel body  102 , inner shaft  124 , slide assembly  106 , stop element  122 , and mating arm  105 . The slide assembly  106  is slidably coupled to the handle assembly  101  (and/or the mating arm  105 ) and the inner shaft  124 . In some embodiments, the mount arm  105  and slide assembly  106  may have apertures configured to permit a portion of the inner shaft  124  to be disposed therethrough. In many embodiments, the proximal end of the inner shaft  124  is fixedly coupled to the stop element  122 , the stop element  122  positioned proximal the slide assembly  106 . The stop element  122  is configured to impede translation of the slide assembly  106  proximally along the inner shaft  124 . In some embodiments, the slide assembly  106  further comprises a pin  107  configured to interact with the helical trough  127  of the inner shaft  124 , as the slide assembly  106  translates along the length of the inner shaft  124 . In use, the interaction of the pin  107  with the helical trough  127  causes rotation of the inner shaft  124  as the pin  107  travels the length of the trough  127 . In some embodiments, the helical trough  127  is configured to cause a 90 degree rotation of the inner shaft  124  as the remobilizer  100  is actuated. In some embodiments, the degree of rotation is any rotation sufficient to permit the engagement feature  125  to couple with the pockets  229  of the bushing  228 . 
         [0047]    The lever  112  rotatably associates with the slide assembly  106 . The lever  112  may extend from the slide assembly  106  via mechanical attachment by any suitable method, including, for example, a fastener, an aperture, a nut-bolt connection, a washer, or the like. The lever  112  is further pivotally coupled to the handle assembly  101  by a suitable mechanical attachment, such as a pin or the like. The inner shaft  124  may be slidably disposed within the barrel body  102  and configured such that the inner shaft  124  may be longitudinally displaced within the barrel body  102  by actuation of the lever  112  and the slide assembly  106 . 
         [0048]    The lever  112  may assume any polygonal shape having a distal end that can be longitudinally displaced. The slide assembly  106  and the lever  112  may be made from any suitable material as known in the art including, by way of example and not limitation, stainless steel, a thermoplastic or other materials. In some embodiments, the lever  112  and the slide assembly  106  may be associated with a locking and/or moving mechanism  133  at the proximal end  108 , for incrementally locking and/or proximally moving the inner shaft  124  towards the proximal end  108  and subsequently releasing the inner shaft  124  to be moved towards the distal end  110  of the barrel body  102 . Alternative spring locked or spring hinged mechanisms may be coupled to the slide assembly  106  and the lever  112  to move the inner shaft  124  proximally and distally within the barrel body  102 . 
         [0049]    In one embodiment, the locking moving mechanism is a spring member  133   a . The spring member  133   a  is operably coupled to the lever  112  and the handle assembly  101 , such that the spring member  133   a  urges the lever  112  from an actuated position back to its original position subsequent to actuation of the lever  112  in either the proximal or distal direction. 
         [0050]    In use, when the lever  112  is actuated, the lever  112  causes the slide assembly  106  to slide proximally along the inner shaft  124  and the mounting arm  105 . As the slide assembly  106  translates, the pin  107  coupled to the slide assembly  106  engages with the helical trough  127  on the inner shaft  124 , causing the inner shaft  124  to rotate as the pin  107  travels the length of the trough  127 . The rotation of the inner shaft  124  causes the engagement feature  125  to couple with pockets  229  of the screw bushing  228 . Once the pin  107  has travelled the full length of the helical trough  127 , the slide assembly  106  reaches the stop element  122 , configured to impede translation of the slide assembly  106  along the inner shaft  124 . Once the slide assembly  106  reaches the stop  122 , continued proximal translation of the slide assembly  106  also translates the stop  122  proximally. Because the stop  122  is fixedly coupled to the proximal end of the inner shaft  124 , the inner shaft  124  is also translated proximally. Because the engagement feature  125  of the inner shaft is coupled with the pockets  229  of the screw bushing  228 , the bushing  228  is pulled proximally, thereby releasing its fixation on the head of the screw  230 . Thus, the polyaxial screw assembly is remobilized. 
         [0051]    As shown in  FIGS. 3A and 3B , a polyaxial pedicle screw assembly  240  comprises a screw body member  222 , a screw bushing  228 , and a polyaxial pedicle screw  230 . Polyaxial pedicle screws are more fully disclosed in U.S. publication 2010/0318136, “Polyaxial bone screw assembly,” and in U.S. publication 2008/0243189, “Variable Angle Spinal Screw Assembly” both of which are hereby incorporated by reference in their entirety. The screw body member  222  is generally cylindrical in configuration and adapted to receive a head portion  234  of the pedicle screw  230 . The screw body member  222  further comprises a plurality of yokes  223 , adapted to receive engagement features  111  of the distal end  110  of the barrel body  102 . Generally, the screw body member  222  has a generally tulip shape to form U-shaped yokes  223 ; however, the screw body member  222  may have alternative shapes to form the yokes  223 . In alternative embodiments, the screw body member  222  may have other shapes, such as rectangular, square, diamond, and/or the like. The bushing  228  is adapted to fit within the screw body member  222  between the screw body member  222  and the head portion  234 , and prevent polyaxial motion of the screw  230  when the bushing  228  is locked or pressed into position. The bushing  228  further comprises pockets  229  configured to mate with an engagement feature  125  at the distal end of the inner shaft  124  of the remobilizer  100 . The pockets  229  generally have a rectangular lipped shape; however, in alternative embodiments, the pockets  229  may have any shape suitable for mating with the engagement feature  125  of the inner shaft  124 , such as square, round, domed, circular, rectangular, triangular, slot, and/or the like. 
         [0052]      FIG. 9  shows the prongs  111  of the barrel body  102  and the engagement feature  125  of the inner shaft  124  coupled with the screw body member  222 , prior to the lever  112  being actuated. The engagement feature  125  is aligned with the prongs  111 , so that the barrel body  102  and inner shaft  124  may be inserted into the screw body member  222 . 
         [0053]      FIG. 10  shows the engagement of the engagement feature  125  with the bushing pockets  229  as the lever  112  is actuated and the slide assembly  106  initially reaches the stop element  122 . The inner shaft  124  has been rotated 90 degrees to couple the engagement feature  125  with the bushing pockets  229 . In some embodiments, the degree of rotation is any rotation sufficient to permit the engagement feature  125  to couple with the pockets  229  of the bushing  228 . At this stage, if actuation of the lever  112  is continued, the engagement feature  125  will exert an upward force on the bushing  228 , thereby releasing the bushing  228  from fixation with the screw head  234 , remobilizing the polyaxial screw assembly  240 . 
         [0054]    In some embodiments, the degree of rotation is any rotation sufficient to permit the engagement feature  125  to couple with the pockets  229  of the bushing  228 . 
         [0055]      FIG. 11  shows an exploded view of the polyaxial screw head remobilizer  100  with like reference numerals mentioned previously. 
         [0056]    A method of using the polyaxial screw head remobilizer tool comprises the steps of: inserting an outer tube of the remobilizer into yokes of a screw tulip to center the tool and an inner shaft disposed within the outer tube on a head of the screw, in proximity to a bushing member of the screw body; actuating the tool to rotate the inner shaft such that an engagement feature on the tip of the inner shaft mates with a plurality of pockets in the bushing member of the screw; continuing actuation of the tool such that a force is applied to the bushing member to release a fixation hold between the bushing, the screw head, and the screw tulip, thereby remobilizing the screw head; releasing the actuation of the tool such that the inner shaft derotates and the engagement feature at the tip of the inner shaft disengages from the pockets in the bushing member of the screw; and removing the remobilizer tool from the screw tulip. 
         [0057]    While the invention has been described in connection with various embodiments, it will be understood that the invention is capable of further modifications. This application is intended to cover any variations, uses or adaptations of the invention following, in general, the principles of the invention, and including such departures from the present disclosure as within the known and customary practice within the art to which the invention pertains.