Abstract:
An instrument for provisionally tightening a screw body member to a head of a polyaxial bone screw includes a barrel body, an inner shaft, a handle and lever, and a load link assembly. The barrel body includes a distal end with a pair of rotatable tangs configured to engage the screw body member. The inner shaft includes a distal end configured to engage a bushing within the screw body member. The lever pivotally couples to one of the handle and the barrel body. The load link assembly couples to the inner shaft and the lever. Actuation of the lever towards causes the load link assembly to longitudinally displace the inner shaft toward the distal end to contact the bushing and advance the bushing into frictional fit between the screw body member and the head of the polyaxial bone screw.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority to U.S. Provisional Application Ser. No. 61/716,458 entitled “Instrument and Method for Provisionally Locking a Polyaxial Screw” which was filed on Oct. 19, 2012 and is incorporated herein by reference in its entirety. 
    
    
     FIELD 
     The present invention relates generally to systems for fixation of screws in the spine or bone, and more particularly to an instrument for provisionally tightening a screw body of the screw. 
     BACKGROUND 
     The spine is a flexible column formed of a plurality of bones called vertebrae. The vertebrae are hollow and piled one upon the other, forming a strong hollow column for support of the cranium and trunk. The hollow core of the spine houses and protects the nerves of the spinal cord. The different vertebrae are connected to one another by means of articular processes and intervertebral, fibrocartilaginous bodies. Various spinal disorders may cause the spine to become misaligned, curved, and/or twisted or result in fractured and/or compressed vertebrae. It is often necessary to surgically correct these spinal disorders. 
     The spine includes seven cervical (neck) vertebrae, twelve thoracic (chest) vertebrae, five lumbar (lower back) vertebrae, and the fused vertebrae in the sacrum and coccyx that help to form the hip region. While the shapes of individual vertebrae differ among these regions, each is essentially a short hollow shaft containing the bundle of nerves known as the spinal cord. Individual nerves, such as those carrying messages to the arms or legs, enter and exit the spinal cord through gaps between vertebrae. 
     The spinal disks act as shock absorbers, cushioning the spine, and preventing individual bones from contacting each other. Disks also help to hold the vertebrae together. The weight of the upper body is transferred through the spine to the hips and the legs. The spine is held upright through the work of the back muscles, which are attached to the vertebrae. While the normal spine has no side-to-side curve, it does have a series of front-to-back curves, giving it a gentle “S” shape. If the proper shaping and/or curvature are not present due to scoliosis, neuromuscular disease, cerebral palsy, or other disorder, it may be necessary to straighten or adjust the spine into a proper curvature. 
     Generally the correct curvature is obtained by manipulating the vertebrae into their proper position and securing that position with a rigid system of screws, rods, intervertebral spaces, and/or plates. The various components of the system may be surgically inserted through open or minimally invasive surgeries. The components may also be inserted through various approaches to the spine including anterior, lateral, and posterior approaches and others in between. 
     Spinal fixation systems may be used in surgery to align, adjust, and/or fix portions of the spinal column, i.e., vertebrae, in a desired spatial relationship relative to each other. Many spinal fixation systems employ a spinal rod for supporting the spine and for properly positioning components of the spine for various treatment purposes. Vertebral anchors, comprising pins, bolts, screws, and hooks, engage the vertebrae and connect the supporting rod to different vertebrae. The size, length, and shape of the cylindrical rod depend on the size, number, and position of the vertebrae to be held in a desired spatial relationship relative to each other by the apparatus. 
     During spinal surgery, a surgeon first exposes the spine posterior and attaches the vertebral anchors to selected vertebrae of the spine. The surgeon then inserts a properly shaped spinal rod into rod-receiving portions of the vertebral anchors to connect the selected vertebrae, thereby fixing the relative positions of the vertebrae. Generally, a controlled mechanical force is required to bring together the spinal rod and a spinal implant, such as the vertebral anchors, in a convenient manner. After insertion, a surgeon must insert a locking mechanism, such as a set screw, into the vertebral anchor to lock the spinal rod to the implant after the force for inserting the rod is removed. 
     Patients suffering from orthopedic injuries, deformities, or degenerative diseases often require surgery to stabilize an internal structure, promote healing, and/or relieve pain. In the spinal field, surgeries to correct spinal abnormalities often involve positioning one or more elongate stabilization elements such as rods, plates or other types of elongate members along a portion of the spinal column, and anchoring each of the elongate stabilization elements to two or more vertebrae via screws, hooks or other types of bone anchors. Prior to anchoring the elongate stabilization element to the spinal column, the surgeon may need to measure the distance between the bone anchors or between two reference locations along the spinal column in order to determine the appropriate length of the elongate stabilization element. In some instances, the bone anchors may be arranged at varying angular orientations, thereby presenting difficulties in accurately measuring the distance between the bone anchors to provide a properly sized elongate stabilization element having a length sufficient for coupling to the bone anchors. 
     Certain spinal conditions, including a fracture of a vertebra and a herniated disc, indicate treatment by spinal immobilization. Several systems of spinal joint immobilization are known, including surgical fusion and the attachment of pins and bone plates to the affected vertebrae. Known systems include screws having proximal heads and threaded shafts that may be inserted into at least two spaced-apart vertebras. Each screw includes a receiver attached over the head such that a stabilization rod can interconnect two or more receivers to immobilize the vertebras spanned by the screws. 
     Spinal immobilization systems typically require the threaded securement of some form of bone anchor and the like 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. However, in these systems, in order to tighten the spinal screw-assembly at a specific angle, a rod and a set screw must first be inserted, the components are tightened, and then the rod and set screw are removed. 
     The present invention helps to expedite the time of surgery by allowing a medical professional to provisionally tighten the spinal screw-assembly at a specific angle prior to placing a rod or set screw into the body member. 
     SUMMARY 
     Provided herein are apparatuses, systems, and methods of use for a screw head locker. The instrument for provisionally tightening or locking a screw body member to a head of a polyaxial bone screw, generally comprises: a barrel body having a proximal end and a distal end, the distal end having at least one tang for releasably engaging a screw body pocket on the screw body member; an inner shaft coaxially disposed between the tang, wherein the inner shaft includes distal engagement portion; and a lever operably coupled to the inner shaft, wherein the lever distally displaces the inner shaft to engage with a bushing member to lock the polyaxial motion of a screw displaced beneath the bushing member. 
     An instrument for tightening a screw body member to a head of a polyaxial bone screw includes a barrel body, an inner shaft, and a lever. The barrel body includes a proximal end and a distal end, the distal end having at least one tang for releasably engaging a screw body pocket on the screw body member. The inner shaft is coaxially disposed between the tangs and includes distal engagement portion. The lever is operably coupled to the inner shaft. The lever distally displaces the inner shaft to engage with a bushing member to lock the polyaxial motion of a screw displaced beneath the bushing member. 
     In other features, the lever is operably coupled to a load link assembly to distally displace the inner shaft into the screw body member to contact the bushing. The load link assembly includes first and second portions pivotally coupled together and coupled to the lever by a transfer link. 
     An instrument for provisionally tightening a screw body member to a head of a polyaxial bone screw includes a barrel body, an inner shaft, a load link assembly, and a lever. The barrel body includes a proximal end and a distal end, the distal end having a pair of tangs for releasably engaging a pair of screw body pockets on the screw body member. The inner shaft is disposed within the barrel body. The load link assembly operably couples to the inner shaft to the body. The lever extends from the load link assembly, the lever being movable to actuate the load link assembly. Actuation of the load link assembly displaces the inner shaft to engage a bushing disposed between the screw body member and the head of the polyaxial bone screw. 
     In other features, the inner shaft is longitudinally disposed between the tangs. Displacement of the lever after load link assembly actuation longitudinally displaces the inner shaft proximally from the bushing. The tangs releasably engage with the screw body pockets. 
     An instrument for provisionally tightening a screw body member to a head of a polyaxial bone screw includes a barrel body, an inner shaft, a handle and lever, and a load link assembly. The barrel body includes a distal end with a pair of rotatable tangs configured to engage the screw body member. The inner shaft includes a distal end configured to engage a bushing within the screw body member. The lever pivotally couples to one of the handle and the barrel body. The load link assembly couples to the inner shaft and the lever. Actuation of the lever towards causes the load link assembly to longitudinally displace the inner shaft toward the distal end to contact the bushing and advance the bushing into frictional fit between the screw body member and the head of the polyaxial bone screw. 
     In other features, the pair of tangs releasably engages a pair of screw body pockets. The inner shaft is coaxially disposed between the tangs. A lever extends from the load link assembly, wherein the lever is movable to actuate the load link assembly. Displacement of the lever after load link assembly actuation longitudinally displaces the inner shaft towards the proximal end of the barrel body. A bias spring biases the lever away from the handle to return the load link assembly to a rest position, wherein the inner shaft advances away from the distal end. The load link assembly comprises first and second portions pivotally coupled together such that actuation of the handle causes the at least one of the portions to advance towards a proximal end of the inner shaft. The pair of tangs are biased towards engagement with the screw body member by a pair of bias members within the distal end of the barrel body. 
     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 
         FIG. 1  is a perspective view of an instrument for tightening a screw body according to the principles of the present disclosure. 
         FIG. 2  is an enlarged view of the distal end of the instrument when the screw body is engaged with the distal end with the barrel body, according to the principles of the present disclosure. 
         FIG. 3A  is a cross-sectional view of the distal end of the instrument in a place extending through the longitudinal axis  104  and parallel to the sheet. 
         FIG. 3B  is a cross-sectional view of the distal end of the instrument engaged with the screw body. 
         FIG. 4A  is a generally top perspective view of the screw body member, the bushing, and the screw. 
         FIG. 4B  is a generally side perspective view of the screw body member, the bushing, and the screw, according to the principles of the present disclosure. 
         FIG. 5A  is side view of an inner shaft, according to the principles of the present disclosure. 
         FIG. 5B  is side view of the inner shaft, according to the principles of the present disclosure. 
         FIG. 5C  is side view of the inner shaft taken from the perspective of arrow V-C in  FIG. 5B , according to the principles of the present disclosure. 
         FIG. 6  is a perspective exploded view of a barrel body of the instrument. 
         FIG. 7  is a perspective view of the inner shaft coaxially disposed within the barrel body and being coupled to the handle and load link assembly. 
         FIG. 8  is a side view of the barrel body operably coupled to the handle. 
         FIG. 9  is a perspective exploded view of the instrument, according to the principles of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the invention will now be described with reference to the Figures, wherein like numerals reflect like elements throughout. The terminology used in the description presented herein is not intended to be interpreted in any limited or restrictive way, simply because it is being utilized in conjunction with detailed description of certain specific embodiments of the invention. Furthermore, embodiments of the invention may include several novel features, no single one of which is solely responsible for its desirable attributes or which is essential to practicing the invention described herein. The words proximal and distal are applied herein to denote specific ends of components of the instrument described herein. A proximal end refers to the end of an instrument nearer to an operator of the instrument when the instrument is being used. A distal end refers to the end of a component further from the operator and extending towards the surgical area of a patient and/or the implant. 
     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. 
     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. 
     The present invention helps to expedite the time of surgery by allowing a medical professional to provisionally tighten or lock the spinal screw-assembly at a specific angle prior to placing a rod or set screw into the body member. 
     As shown in  FIGS. 1-2 , an instrument  100  for provisionally locking a polyaxial screw body member to a screw generally comprises a barrel body  102  having a generally longitudinal axis  104 , wherein the barrel body  102  includes a proximal end  108  and a distal end  110  generally along the longitudinal axis  104 . An inner shaft  140  is coaxially disposed within the barrel body  102  and may be advanced distally along the longitudinal axis from a first position to a second position. The inner shaft  140  may be retracted proximally along the longitudinal axis to a first position. A handle  180  extends proximally from the proximal end  108  of the barrel body  102  for holding of the instrument  100  by an operator. A load link assembly  160  is operably coupled to the barrel body  102  and the inner shaft  140  near the proximal end  108  of the barrel body  102 . The load link assembly  160  may be coupled to the barrel body  102  by any suitable method of attachment such as, for example, a fastener, an aperture, a nut or bolt connection, or the like. The load link assembly  160  may include two portions,  160   a  and  160   b , coupled by one or more pins to each other and the handle  180 . The portions  160   a  and  160   b  may rotate relative to one another to permit a change in the overall length of the load link assembly  160  when acted upon by the operator. 
     A lever  170  rotatably associates with the handle  180  and the lever  170  is operably coupled with the load link assembly  160 . The lever  170  may extend from the load link assembly  160  via mechanical attachment by any suitable method of attachment, for example, a fastener, an aperture, a nut-bolt connection, a washer, or the like. Alternatively, the lever  170  and load link assembly  160  may be a unitary element that is mounted on the proximal end  108  of the barrel body  102 . 
     In a first embodiment, actuation of the lever  170  causes the inner shaft  140  to longitudinally move towards the distal end to the second position, and release of the lever  170  causes the inner shaft  140  to longitudinally move towards the proximal end to the first position. In a second embodiment, actuation of the lever  170  causes the inner shaft  140  to longitudinally move towards the proximal end to the first position, and release of the lever  170  causes the inner shaft  140  to longitudinally move towards the distal end and the second position. In the first and second embodiments, returning the lever  170  to its original position causes the inner shaft  140  to return to its original position. 
     As shown in  FIGS. 3A and 3B , the distal end  110  of the barrel body  102  includes an opening  109  to fit a screw body member  122  and a screw  130 . The inner shaft  140  is operably coupled to the load link assembly  160 , as shown in  FIG. 1 . The inner shaft  140  may be slidably disposed within the barrel body  102  and extends longitudinally through the proximal end of the barrel body  102  to the distal end  110  to the barrel body  102 , such that the inner shaft  140  may be longitudinally displaced within the barrel body  102  by operation of the lever  170  and the load link assembly  160 . The proximal end of the inner shaft  140  is operably coupled to the distal end of the load link assembly  160  to longitudinally displace the inner shaft  140  along the longitudinal axis  104  and through the opening  109 . The longitudinal displacement of the inner shaft  140  forces a bushing  128  to be wedged between the screw head  134  and the body member  122 . The lever  170  may extend downwardly from the load link assembly  160  and the barrel body  102  at an angled inclination, as shown in  FIG. 1 . 
     As shown in  FIGS. 3A and 3B , the distal end  110  includes at least two tangs  116  that generally project and pivot along the longitudinal axis  104  and towards the distal end of the barrel body  102 . The tangs  116  include at least one protrusion  117  that is positioned on the interior surface of the tang  116 , such that the screw body member  122  may be secured in the distal end  110  of the barrel body  102 , as shown in  FIG. 3B . In one embodiment, the protrusion  117  radially extends inwardly from an interior surface of each of the tangs  116  proximate to a distal end of the tangs  116 . The protrusion  117  defines a distal end of a groove  123  that may include a tapered proximal end  125 . The protrusion  117  is adapted to engage a body pocket  120  (See also  FIGS. 4A-4B ) disposed on the screw body member  122 . The distal end  121  of the groove  123  includes a generally right angled corner that is well suited for engaging the body pocket  120 , locking the body pocket  120  into the distal end  110  of the barrel body  102 , and applying a proximally directed force thereto. As such, the screw body member  122  may be locked in the distal end  110  of the barrel body  102 . The protrusions  117  may include a generally angled or tapered surface on the distal end to abut the screw body member and permit the proximal portion of the screw body member  122  to slide over the generally angles surface and lock with the protrusion  117  and the body pocket  120 . 
     In one embodiment, the protrusion  117  may include an exterior surface that may be the same general shape as the body pocket  120  to facilitate engagement of the body pocket  120  by the protrusion  117 . For example, the protrusion  117  may have an exterior surface  127  that is generally rectangular like the body pocket  120  illustrated in  FIGS. 4A-4B . However, the exterior surface of the protrusion may have any shape as desired to facilitate engagement of body pockets  120  having other shapes, including by way of example and not limitation, a circle, a rectangle, a pentagram, a hexagram, any regular polygon, any irregular polygon, and the like. 
     As shown in  FIG. 3A , the tangs  116  include a proximal bar  136  on the proximal portion, which is operably coupled to at least one spring  138 . The springs  138  may be operably coupled to the exterior portion of the barrel body  102 . The springs  138  are pre-stressed such that the proximal bar  136  is displaced axially away from the longitudinal axis  104  and the tangs  116  are proximally displaced towards the longitudinal axis  104 . The distal portion of the tangs  116  and the protrusions  117  are displaced away from the longitudinal axis  104  by rotation about the pins  135  as the barrel body  102  engages the screw body member  122 . Therefore, the bias of the spring  138  and the proximal bar  136  of the tangs  116  axially displace or rotate the distal portion of the tangs  116  and the protrusion  117  axially away from the longitudinal axis  104 , as the tangs  116  rotate about the pins  135 . In alternative embodiments, the tangs  116  are integral with the distal end  110  of the barrel body  102 . In other embodiment, the tangs  116  may be removable disposed/attachable in order to attach the tangs  116  having protrusions  117  that are able to engage screw body pockets  120  (as shown in  FIGS. 4A-4B ) having different shapes and/or sizes. 
     As shown in  FIGS. 3A-3B , the tangs  116  axially displace the protrusions  117  towards the longitudinal axis  104  and engage the screw body pockets  120 , as illustrated by the line  137 . The proximal bar  136  and the spring  138  keep the protrusions  117  engaged with the screw body pockets  120 , which allow the inner shaft  140  to engage a bushing  128  into the pedicle screw  130  to create a frictional lock. Releasing the lever  170  causes the inner shaft  140  to move proximally to disengage distal portion from the bushing  128  and the pedicle screw  130 . 
     Referring to  FIGS. 4A-4B , for example, the tangs  116  may have a generally rectangular cross-sectional shape that is similarly shaped as at least a portion of the exterior surface of the screw body member  122  when the tangs  116  are engaged with the screw body member  122 . Such a configuration of the exterior surface of the tangs  116  enhances engagement between the tangs  116  and the screw body member  122  and/or provides enhanced support against the screw body member  122  moving with respect to the tangs  116  when engaged by the tangs  116 . The tangs  116  may include a cross-sectional shape looking along the longitudinal axis  104  that such that an interior surface of the distal portion of each tang  116  is complementary to a peripheral surface of the screw body member  122 . Examples of screw body members  122  that may be useful in the current invention may be found in U.S. Patent Application Publication No. 2010/0318136, U.S. Patent Application Publication No. 2008/0243189, and U.S. Pat. No. 7,377,923, both of which are hereby incorporated by reference in their entirety herein. Alternatively, the instrument  100  may be used with any screw requiring a friction-fit bushing to be translated or displaced. 
     As shown in  FIGS. 4A-4B , a polyaxial pedicle screw assembly  145  comprises the screw body member  122 , a bushing  128 , and a polyaxial pedicle screw  130 . The screw body member  122  is generally cylindrical in configuration and adapted to receive a fixed head portion of the pedicle screw  130 . The exterior surface of the screw body member  122  includes at least two body pockets  120 , as to engage the protrusions  117 . The screw body member  122  generally includes a width W S . Traversing the exterior surface of the screw body member  122  is a generally tulip-shaped opening  132  that includes a length L T  and a diameter D T . The bushing  128  is adapted to coaxially fit within the screw body member  122  and partially extend between the screw body member  122  and a head portion  134  of the screw  130 . In one embodiment, the bushing  128  has a concave proximal surface  147  that is adapted to mate with the distal engagement portion  141  of the inner shaft  140 . In one embodiment, the concave proximal surface  147  includes a radius of curvature R B . The bushing  128  has a slotted lower skirt portion (not shown) with tapered distal surfaces adapted to provide a press fitment or wedge about the head portion  134  of the pedicle screw  130 . When the bushing  128  is compressed, it is wedged between the spherical head of the screw and the walls of the screw body member  122  for a frictional fit to resist movement of the body member  122  relative to the head portion  134 . Once the bushing  128  has been locked in place by the inner shaft  140 , the polyaxial motion of the screw head  134 , even when active pressure of the inner shaft  140  is removed from the bushing  128 , is restricted. 
     The pedicle screw  130  may include a substantially spherical or elliptical head portion  134  defining a slot therein used to drive a threaded shaft portion of the screw  130  into a vertebra or other bone. Examples of bushings  128  and polyaxial pedicle screws  130  that may be useful in the current invention may be found in U.S. Patent Application Publication No. 2010/0318136, U.S. Patent Application Publication No. 2008/0243189, and U.S. Pat. No. 7,377,923, all incorporated by reference herein. Typically, the set screw is used to compress rod into the bushing to lock the body member and head portion of the screw in a single action. 
     In operation, the instrument  100  of the present disclosure allows an operator to provisionally tighten the screw head portion  134  without inserting a rod and set screw into the pedicle screw. If the provisionally tightened screw needs to be adjusted, the screw may be loosened without the rod and the bushing being re-inserted and then removed again. An operator may apply compression and distraction forces to the screw body member  233  and achieve direct compression and distraction. Once the desired compression or distraction is achieved, the operator can then insert the rod and set screws and final tightening torques if necessary. 
     As shown in  FIG. 5A-5B , the inner shaft  140  includes a distal engagement portion  141  on the distal end and the proximal end of the inner shaft  140  includes a generally threaded portion  142  to be operably coupled to the load link assembly  160 . The distal engagement portion  141  generally includes at least two projections  143  extending from the longitudinal axis of the inner shaft  140  that include a length L P  and a width W P . In one embodiment, the Width W P  of the distal engagement portion  141  is about equal to or greater than the length L T  of the tulip-shaped opening  132  of the screw body member  122 , such that the longitudinal movement of the inner shaft  140  towards the distal end is able to engage the bushing  128 . The distal engagement portion  141  includes a radius of curvature R P , which substantially equals the radius of curvature R B  of the concave surface  147  of the bushing  128 , as to allow a flush engagement of the distal engagement portion  141  with the concave surface  147  of the bushing  128 . The distal engagement portion  141  includes a diameter D P  that is less than or equal to the diameter D T  of the tulip shaped opening  132  of the body screw member  122 , which allows the distal engagement portion  141  to be longitudinally displaced within the tulip-shaped opening  132 . 
     Alternatively, the inner shaft  140  may include generally stepped profile whereby the distal portion of the inner shaft  140  includes a smaller diameter than the middle portion, and the middle portion includes a smaller diameter than the proximal portion. Although the inner shaft  140  is generally shown to have H-shaped cross-sections, alternative configurations for the cross-section of the inner shaft  140  may be used, for example, circular, square, elliptical, polygonal cross-sections, and the like configurations. As shown in  FIGS. 5A and 5C , the inner shaft  140  may optionally include a longitudinal slide or cutout  149 , as to permit the inner shaft  140  to longitudinally slide along the inner lumen of the barrel body  102 . The inner lumen of the barrel body  102  may have a reciprocal or corresponding inner longitudinal slide or cutout to operably couple the inner shaft  140  with the barrel body  102  for longitudinal displacement. 
     As shown in  FIG. 6 , the barrel body  102  is operably coupled with the tangs  116  on the distal end  110  by way of at least two pins  105  that are fixed within holes  106  on the distal end  110 . The springs  138  operably coupled with the tangs  116  are seated within a stepped portion  103  on the distal end  110  of the barrel body  102 . The distal end  110  further includes at least two cutouts  112  that seat the at least two protrusions  143  of the distal engagement portion  141  of the inner shaft  140 . In one embodiment, the proximal end  108  of the barrel body  102  includes a threaded portion for fixedly associating the barrel body  102  to the handle  180 . In one embodiment, the distal end  110  of the barrel body  102  includes an opening  109  with a width W B  that is greater than or equal to the width W T  of the screw body member  122 , such that the screw body member  122  coaxially fits within the opening  109  on the distal end  110 . The barrel body  102  is generally cylindrical in shape; however, it may assume alternative cross-sectional shapes such as circular, elliptical, square, rectangular, polygonal, and the like. 
     As shown in  FIG. 7 , the inner shaft  140  is coaxially coupled within the barrel body  102 , whereby the proximal end  142  of the inner shaft  140  protrudes from the proximal end  108  of the barrel body  102 . In one embodiment, the proximal end  142  of the inner shaft  140  is operably associated with a retention cap  152  and a spring  156 , while the proximal end  108  of the barrel body  102  is fixedly associated with a retention collar  150 , as shown in  FIGS. 7 and 9 . As shown in  FIG. 8 , the retention cap  152  is coaxially disposed through the retention collar  150  and the distal end of the handle  180 . The retention collar  150  is fixedly associated with the distal end of the handle  180 . The retention cap  152  is operably associated with the load link assembly  160 , such that the longitudinal displacement of the load link assembly  160  longitudinally displaces the retention cap  152  along with the inner shaft  140 . 
     Operation of the lever  170  longitudinally displaces the load link assembly  160  by way of a transfer link  168  and a spring  172 , as shown in the exploded  FIG. 9 . The spring  172  biases the lever  170  away from the handle  180 , and when the lever  170  is moved towards the handle  180  by an operator, the transfer link  168  longitudinally displaces the load link assembly  160  to longitudinally displace the inner shaft  140 . For example, the transfer link  168  may act on a pivot point between portion  160   a  and  160   b . In some embodiments, the lever  170  and the load link assembly  160  may be associated with a locking and/or moving mechanism at the proximal end  108 , for example, a ratcheting mechanism, for incrementally locking and/or distally moving the inner shaft  140  towards the distal end  110  and subsequently releasing the inner shaft  140  to be moved towards the proximal end  108  of the barrel body  102 . Alternative spring locked or spring hinged mechanisms may be coupled to the load link assembly  160  and the lever  170  to move the inner shaft  140  distally and proximally within the barrel body  102  in incremental or stepped positions. 
     A screw head locker for spinal immobilization systems is presented. The screw head locker includes a screw body member that is provisionally tightened before placing a rod or set screw into the screw body member. Such provisional tightening allows the screw body member to be frictionally locked at a specific angle relative to a polyaxial pedicle screw prior to rod or set screw introduction. 
     As can be understood by one skilled in the art, the screw head locker  100  and/or any of its components may have any size, shape, length, thickness, height, weight, or any other parameters. Such parameters may be selected by the surgeon (or other qualified professional) for performance of specific procedures. Further, the screw head locker  100  and/or any of its components may be manufactured from metal, plastic, synthetic material, or other suitable materials, or any combination thereof. In one embodiment, the screw head locker  100  is composed of titanium, nitinol, or stainless steel, or any medical grade polymer, such as Polyether ether keton (PEEK). 
     In some embodiments, various lengths and configurations may also include various features to accommodate different applications for the screw head locker. The screw head locker can be constructed of various materials to aid in radio translucency, strength, flexibility, and integration with anatomy, etc. 
     It will be appreciated by those skilled in the art that changes could be made to the embodiments described hereinabove without departing from the broad concepts disclosed therein. It is understood, therefore, that this disclosure is not limited to the particular embodiments disclosed, but it is intended to cover modifications that may include a combination of features illustrated in one or more embodiments with features illustrated in any other embodiments. Various modifications, equivalent processes, as well as numerous structures to which the present disclosure may be applicable will be readily apparent to those of skill in the art to which the present disclosure is directed upon review of the present specification. Accordingly, this description is to be construed as illustrative only and is presented for the purpose of enabling those skilled in the art to make and use the screw head locker described herein and to teach the best mode of carrying out the same. 
     Example embodiments of the methods and systems of the present invention have been described herein. As noted elsewhere, these example embodiments have been described for illustrative purposes only, and are not limiting. Other embodiments are possible and are covered by the invention. Such embodiments will be apparent to persons skilled in the relevant art(s) based on the teachings contained herein. Thus, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents. 
     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.