Patent Publication Number: US-2020281608-A1

Title: Bone Screws, Instrumentation, and Methods of Using of Same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of the filing date of U.S. Provisional Patent Application No. 62/814,505 filed on Mar. 6, 2019, the disclosure of which is hereby incorporated by reference herein. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention generally relates to fixation devices, and more particularly, to spinal fasteners for single step insertion. 
     A technique commonly referred to as spinal fixation is employed for fusing together and/or mechanically immobilizing vertebrae of the spine. Spinal fixation may also be used to alter the alignment of adjacent vertebrae relative to one another so as to change the overall alignment of the spine. Such techniques have been used effectively to treat many degenerative conditions and, in most cases, to relive pain suffered by the patient. 
     In some applications, a surgeon will install pedicle screws into the pedicles of adjacent vertebrae (along one or multiple levels of the spine) and thereafter connect the screws with a spinal rod in order to immobilize and stabilize the vertebral column Whether conducted in conjunction with interbody fusion or across single or multiple levels of the spine, the use of pedicle screws connected by fixation rods is an important treatment method employed by surgeons. 
     There remains room for improvement in the design and use of pedicle screws, particularly for surgical efficiency while maintaining safety and accuracy during screw insertion. 
     BRIEF SUMMARY OF THE INVENTION 
     According to an embodiment of the present disclosure, a method of spinal repair includes the steps of inserting a stylet through a lumen of a screw such that a distal tip of the stylet extends distally from a distal end of the screw, the stylet extending along an axis; advancing the screw and the stylet toward a bone until the distal tip of the stylet contacts the bone; and rotating the screw about the axis of the stylet in a first direction and simultaneously oscillating rotation of the stylet about the axis between the first direction and a second direction opposite to the first direction. 
     In other embodiments, the step of rotating may include advancing the screw into bone. The step of oscillating may include retracting the stylet away from the bone. When the screw is rotated in the first direction and the stylet is rotated in the second direction, the screw and the stylet may move in opposite directions along the axis. The method may include the step of removing the stylet from the bone. The screw may have a distal cutting edge. The method may include the step of inserting the stylet into the bone to a depth that is less than an intended insertion depth of the screw. 
     Another embodiment of the disclosure includes a system for spinal repair. The system includes a screwdriver that includes a drill adaptor that has an internal surface and is rotatable in a first direction and a second direction opposite the first direction. The screwdriver includes a gear system that has a driving gear, a driven gear, and one or more connector gears, the driving gear has a splined internal surface and an external surface configured to mate with the internal surface of the drill adaptor such that rotation of the drill adaptor causes rotation of the driving gear in the same direction. The driven gear has a splined internal surface, the driving gear and the driven gear are connected by the one or more connector gears such that rotation of the driving gear causes rotation of the driven gear in the opposite direction. The screwdriver includes a first ratchet pawl that has a splined outer surface configured to engage the splined inner surface of the driving gear and a second ratchet pawl that has a splined outer surface configured to engage the splined inner surface of the driven gear. The first and second ratchet pawls are splined in the same direction such that when one of the driving gear and the driven gear engages the respective first or second pawl, the other gear is disengaged from the respective first or second pawl. A shaft is connected to the first and second ratchet pawls. The system also includes a stylet that has a threaded portion and a housing surrounding the first and second ratchet pawls and rotationally locked relative to the shaft. The housing has a threaded inner surface to engage the threaded portion of the stylet. 
     In other embodiments, the first and second ratchet pawls may each connected to the shaft by a pin. The shaft may rotate in a single direction. Rotation of the drill adaptor may cause rotation of the stylet in the same direction as the drill adaptor. The threaded portion of the stylet may include threads having the same pitch as internal threads of the threaded portion of the housing. Rotation of the drill adaptor in the first direction about the axis may cause the stylet to remain axially fixed and rotation of the drill adaptor in the second direction about the axis may cause the stylet to retract axially. The system may include a fastener defining a lumen for receiving the stylet. Rotation of the drill adaptor in the first direction and the second direction about the axis may cause the bone screw to advance into the bone. The fastener may include a channel adapted to receive a spinal rod, a shaft extending from the head to a distal tip, the distal tip having at least one cutting edge. 
     Another embodiment of the present disclosure includes a fastener that includes a head which has a channel adapted to receive a spinal rod, and a shaft extending from the head to a distal tip. The shaft has a thread, and the distal tip has at least one cutting edge. 
     In other embodiments, the fastener may be cannulated. The threads may continuously transition into the at least one cutting edge. The threads may terminate at a location spaced apart from the at least one cutting edge. 
     Yet another embodiment of the present disclosure includes a stylet control system for selectively advancing and retracting a stylet that includes a stylet that has a first end and a second end. The second end is threaded. The system includes a screwdriver that defines a bore for receiving the stylet and has a screw-engaging end for engaging a screw, the stylet is rotationally fixed relative to the screwdriver. The system includes a control device that is attachable to the screwdriver and has an inner surface defining a lumen for receiving the stylet. A portion of the inner surface is threaded for engaging the threaded second end of the stylet. When the control device is rotated in a first rotation direction and the screwdriver is prevented from rotating, the stylet advances in a first axial direction, and when the screwdriver is rotated in the first rotation direction and the control device is prevented from rotating, the screwdriver advances the screw in the first axial direction and the stylet retracts in a second axial direction, opposite the first axial direction. 
     In other embodiments, the threaded portion of the stylet may be an integral and monolithic part of the stylet. The stylet may be keyed and the screwdriver includes a corresponding keyed feature such as a hex feature on an inner surface to rotatably lock the stylet to the screwdriver. The system may include a quick connect feature to couple the control device to the screwdriver. The control device and the screwdriver may each include a robotic end effector. 
     Yet another embodiment of the present disclosure includes a stylet control system for selectively advancing and retracting a stylet that includes a stylet that has a first end and a second end. The second end is threaded. The system includes a screwdriver that defines a bore for receiving a portion of the stylet and has a screw-engaging end for engaging a screw, the stylet is rotationally fixed relative to the screwdriver. The system includes a control device that is operatively connected to the screwdriver and has an inner portion defining a lumen for receiving the portion of the stylet. The inner portion is threaded for engaging the threaded second end of the stylet. When the screwdriver is rotated in the first rotation direction and the control device is prevented from rotating, the screwdriver advances the screw in the first axial direction and the stylet retracts in a second axial direction, opposite the first axial direction. 
     In other embodiments, the stylet may be keyed and the screwdriver includes a corresponding keyed feature such as a hex feature on an inner surface to rotatably lock the stylet to the screwdriver. The system may include a robotic end effector and a cap to couple the screwdriver to the robotic end effector. The control device may be operatively connected to a robotic end effector. The control device may include an ultrasonic transducer for imparting an ultrasonic force to the stylet. The ultrasonic transducer may be positioned within a housing of the control device. The ultrasonic transducer may be detachable from and external to a housing of the control device. The ultrasonic transducer may include piezoelectric material. The inner portion of the control device may include at least one threaded pawl for engagement with the threads of the stylet. The system may be part of a kit which includes a robotic end effector. The kit may include a bone screw attachable to the screwdriver. The bone screw may be self-drilling. The bone screw may be cannulated. The control system of the kit may include an ultrasonic transducer for imparting an ultrasonic force to the stylet. 
     Yet another embodiment of the present disclosure includes a stylet control system for selectively advancing and retracting a stylet including a stylet having a first end and a second end, a screwdriver defining a bore for receiving the stylet and having a screw-engaging end for engaging a screw, the stylet being rotationally fixed relative to the screwdriver, robotic end effector having a passage therethrough, a cap configured to be received within a portion of the passage of the robotic end effector and being operatively connected to the screwdriver, a retraction feeder receivable within a lumen of the cap and having a mating engagement member for engaging the engagement member of the stylet, when the screwdriver is rotated in a first rotation direction, the screwdriver advances the screw in the first axial direction and the stylet engages the engagement member of the retraction feeder to retract the stylet in a second axial direction, opposite the first axial direction. 
     In other embodiments, the engagement members of the stylet and retraction feeders may include mating threads, and the retraction feeder includes a threaded pawl for one-way engagement of the threaded stylet. The stylet may be keyed and the screwdriver may include a corresponding keyed feature such as a hex feature on an inner surface to rotatably lock the stylet to the screwdriver. The control system may further include an ultrasonic transducer for imparting an ultrasonic force to the stylet. The retraction feeder may be rotatably locked within the end effector. 
     Another embodiment of the present disclosure includes a stylet control system for selectively advancing and retracting a stylet including a stylet having a first end and a second end, the second end being threaded, a screwdriver defining a bore for receiving the stylet and having a screw-engaging end for engaging a screw, the stylet being rotationally fixed relative to the screwdriver, a robotic end effector having a passage therethrough, a cap configured to be received within a portion of the passage of the robotic end effector and being operatively connected to the screwdriver, and a retraction feeder receivable within a lumen of the cap and having a threaded pawl for one-way engagement with the threads of the second end of the stylet, when the screwdriver is rotated in a first rotation direction, the screwdriver advances the screw in the first axial direction and the threads of the stylet engages the threaded pawl of the retraction member to retract the stylet in a second axial direction, opposite the first axial direction. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a fastener and stylet in accordance with a first embodiment of the present disclosure; 
         FIG. 2  is an enlarged perspective view of the distal end of the fastener of  FIG. 1 ; 
         FIGS. 3 and 4  are enlarged perspective views of an alternative embodiment according to another embodiment of the present disclosure; 
         FIG. 5  is a perspective view of a fastener in accordance with another embodiment of the present disclosure; 
         FIG. 6  is an enlarged perspective view of the distal end of the fastener of  FIG. 5 ; 
         FIG. 7  is a perspective view of a fastener and stylet in accordance with another aspect of the present disclosure; 
         FIG. 8  is an enlarged view of the distal end of the fastener of  FIG. 7 ; 
         FIG. 9  is a perspective view of a fastener and stylet in accordance with yet another aspect of the present disclosure; 
         FIG. 10  is an enlarged view of the distal end of the fastener of  FIG. 9 ; 
         FIG. 11  is a cross-sectional view of the proximal end of the fastener in conjunction with the Stylet of  FIG. 9 ; 
         FIG. 12  is a perspective view of another fastener in conjunction with a stylet according to another embodiment of the present disclosure; 
         FIG. 13  is an enlarged perspective view of the distal end of the fastener of  FIG. 12 ; 
         FIG. 14  is an enlarged view of a distal end of an alternative fastener according to another embodiment of the present disclosure; 
         FIG. 15  is a perspective view of a fastener according to yet another embodiment of the present disclosure; 
         FIG. 16  is an enlarged view of the distal end of the fastener of  FIG. 15 ; 
         FIG. 17-21  are enlarged perspective views of the distal ends of fasteners according to various alternative embodiments of the present disclosure; 
         FIGS. 22-23  are schematic representations of the fastener of  FIG. 3  during implantation into a pedicle bone; 
         FIGS. 24-27  are schematic representations of the fastener of  FIG. 1  during implantation into a pedicle bone; 
         FIG. 28  is a schematic view of an advancement device in conjunction with a robotic end effector in accordance with an aspect of the present disclosure; 
         FIG. 29  is a cross-sectional view of the advancement device of  FIG. 28 ; 
         FIG. 30  is a perspective view of a placement device according to another embodiment of the present disclosure; 
         FIG. 31  is an enlarged view of a drive mechanism of the placement device of  FIG. 30 ; 
         FIG. 32  is an exploded view of the placement device of  FIG. 30 ; 
         FIGS. 33 and 34  are cross-sectional views of the placement device of  FIG. 30 ; 
         FIG. 35  is a side view of the placement device of  FIG. 30 ; 
         FIG. 36  is a perspective side view of the driving gear of the placement device of  FIG. 30 ; 
         FIG. 37  is a side view of the double drive mechanism of the placement device of  FIG. 30 ; and 
         FIGS. 38-41  are schematic representations of the placement device of  FIG. 30  in conjunction with a stylet and a screw; 
         FIG. 42  is a perspective side view of a stylet control system according to an embodiment of the present disclosure; 
         FIG. 43  is an exploded view of the stylet control system of  FIG. 42 ; 
         FIG. 44  is an enlarged view of the exploded view of the proximal end of the stylet control system of  FIG. 43 ; 
         FIG. 45  is a cross-sectional view of a quick connect feature of the stylet control system of  FIG. 42 ; 
         FIG. 46  is a perspective side view of the proximal end of the screwdriver of the stylet control system of  FIG. 42 ; 
         FIG. 47  is a cross-sectional view of the control device of the stylet control system of  FIG. 42 ; and 
         FIG. 48  is a perspective side view of a robotically operative stylet control system in conjunction with a robotic device according to an aspect of the present disclosure; 
         FIGS. 49-53  are perspective side views of a robotically operative stylet control system in conjunction with a robotic device according to an aspect of the present disclosure; 
         FIG. 54  is a cross-sectional view of the control system of  FIGS. 49-53 ; 
         FIG. 55  is a perspective side view of an ultrasonic stylet control device in conjunction with a robotic device according to an aspect of the present disclosure; 
         FIG. 56  is a cross-sectional view of the control device of  FIG. 55 ; 
         FIG. 57  is a cross-sectional view of the stylet and bone screw of the system of  FIG. 55  at the bone interface; 
         FIG. 58  is a perspective side view of a cannulated drill for use in conjunction with the control device of  FIG. 55 ; 
         FIG. 59  is a perspective side view of a robotically operative stylet control device in conjunction with a ultrasonic transducer; 
         FIG. 60  is a perspective view of a fastener in accordance with another aspect of the present disclosure; 
         FIG. 61  is an enlarged view of the distal end of the fastener of  FIG. 60 ; 
         FIG. 62  is a perspective view of a fastener in accordance with another aspect of the present disclosure; 
         FIG. 63  is an enlarged view of the distal end of the fastener of  FIG. 62 ; 
         FIG. 64  is a perspective view of a fastener in accordance with another aspect of the present disclosure; 
         FIG. 65  is an enlarged view of the distal end of the fastener of  FIG. 64 ; 
         FIG. 66  is a perspective view of a fastener in accordance with another aspect of the present disclosure; 
         FIG. 67  is an enlarged view of the distal end of the fastener of  FIG. 66 ; 
         FIG. 68  is a perspective view of a fastener in accordance with another aspect of the present disclosure; 
         FIG. 69  is an enlarged view of a distal end of a fastener according to another aspect of the present disclosure; and 
         FIG. 70  is a perspective view of a fastener in accordance with another aspect of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The present invention generally relates to a fastener to be used in conjunction with spinal rods during spinal surgery. Those of skill in the art will recognize that the following description is merely illustrative of the principles of the invention, which may be applied in various ways to provide many different alternative embodiments. 
     The various embodiments of the bone screws or fasteners described below are designed to facilitate efficient and accurate screw insertion during surgery. In some embodiments, the fasteners are cannulated for receiving a stylet extending through the length of the channel. In such cases, the stylet includes a sharp tip to create a pilot hole. In other embodiments, certain fasteners are solid along the shaft rather than being cannulated. In such embodiments, the distal tip of the shaft of the fastener includes a sharp cutting tip for forming a pilot hole and drilling into the bone. The use of the fasteners and/or stylet for creating the pilot hole and cutting into the bone until the threads of the fasteners engage and pull the screw into the bone eliminates the steps of reaming, awling, tapping the hole, or otherwise preparing the hole, before the screw can be placed into the prepared hole. As a result, the fasteners in the present disclosure provide for more efficient implantation. 
       FIGS. 1-2  depict a first embodiment of a fastener  100  and a Kirschner wire or stylet  150  that is configured for spinal applications, and in particular, for the use of fastener  100  as a pedicle screw, as will be described in detail below. Fastener  100  includes a screw shaft  103  and a tulip  104 , which has a channel adapted to receive a spinal rod. A spinal rod can be installed into tulip  104  and held in place by a set screw (not shown), which can be threaded into internal threads of tulip  104 . 
     Fastener  100  is polyaxial in that shaft  103  is separate from and polyaxially movable with respect to tulip  104 . Tulip  104  and a proximal end  107  of shaft  103  can generally be referred to as a head of fastener  100 . Shaft  103  extends along a longitudinal axis from its proximal end  107  to a distal tip  109 . Proximal end  107  of shaft  103  forms an interference fit connection with a distal opening of tulip  104  to create the polyaxial connection. Tulip  104  can swivel to form different angles with respect to shaft  103  which allows for proper rod placement. In alternative embodiments, the fastener may be a monolithic structure with the tulip statically connected with the proximal end of shaft  103 . 
     Shaft  103  includes threads  112  extending between proximal end  107  and distal tip  109 . As seen in  FIGS. 1 and 2 , fastener  100 , including shaft  103  and tulip  104 , is cannulated through its entire length for receiving stylet  150  as shown. Stylet  150  terminates at a sharp distal point  156 . 
     With reference to  FIG. 2 , distal tip  109  of shaft  103  is an annular surface that includes at least one cutting edge  115  for cutting into the cortical bone and facilitating initial engagement with the bone during insertion of fastener  100  such that distal tip  109  may be referred to as a drill tip. Cutting edges  115  are shaped to propagate a hole in the bone during advancement of fastener  100 . The annular surface of distal tip  109  forms two flat surfaces between cutting edges  115  in the form of notches for cutting the bone. 
     Threads  112  extend along shaft  103  to a distal end  112   a  adjacent the distal tip  109  and cutting edges  115 . With the placement of thread  112  in close proximity to the cutting edges  115 , the threading facilitates the pulling motion of fastener  100  into the bone immediately after cutting edges penetrate cortical bone. 
     The embodiment of fastener  100  shown in  FIGS. 1 and 2  includes a double lead thread. With a double lead thread, there are, as shown, two cutting edges  115 . Other embodiments may include a single or a triple lead thread, or may include more threads around shaft  103 . For example,  FIGS. 3 and 4  show a fastener  100 ′ which is substantially similar to fastener  100  except that the threading includes a triple lead thread, and fastener  100 ′ includes three cutting edges  115 ′ at distal tip  109 ′ for cutting into the cortical bone until threads  112 ′ engage the bone and pull fastener  100 ′ into placement. The cutting edges  115 ′ are formed by the thread exiting the bottom of the screw tip. A triple lead thread advantageously provides a more balanced approach that prevents grabbing of the bone by only one of the cutting edges. The number of cutting edges  115  does not have to equal the number of threads  112  along shaft  103 , since the function of cutting edges  115  to penetrate the bone is not always aligned with the function of threads  112  to advance fastener  100  along its trajectory within the bone. 
       FIGS. 5 and 6  depict a fastener  200  according to another embodiment of the present disclosure. Fastener  200  differs from fastener  100  in that shaft  203  is not cannulated but rather includes a cutting drill point  216  at the distal end  209  of the shaft. Threads  212  transition into the cutting point  216  at distal end  209 , such that cutting point  216  forms the drill tip to cut into the bone to form the hole without the use of a stylet. The distal portion of the shaft  203  may include one or more flutes  214 . Fastener  200  is polyaxial, though it can also be constructed as a monoaxial embodiment. 
     The fasteners of  FIGS. 3-6  include a smooth transition region between the cutting features and the threads. The smooth transition region allows the cutting features to continuously cut into bone until the cutting blends into the threads, which create the axial force to push the threads forward into the bone. In  FIG. 4  the geometry is similar to an end mill, and in  FIG. 5  the geometry is similar to a brad point drill tip. 
     As a result of cutting drill point  216 , fastener  200  can be inserted into the bone in one step which eliminates a separate step of reaming or drilling the hole with a separate tool before inserting fastener  200  into the bone. This advantageously reduces the number of steps and tools required during surgery. Additionally, the sharp cutting point  216  facilitates accuracy of the placement of the bone screw during insertion because it can be pushed into the bone to penetrate slightly and dock fastener  200  to prevent skiving during insertion. 
       FIGS. 7 and 8  depict a fastener  300  similar to fasteners  100  and  200 . Like fastener  100 , fastener  300  is cannulated for receiving stylet  350 . Fastener  300  includes distal end  309  formed into a drill point  316  with two cutting edges  315 . Drill point  316  is sized and configured to cut into the bone to form the hole during insertion of fastener  300  into a pedicle. As with fastener  100 , stylet  350  can be pushed into the bone to prevent skiving of fastener  300  during insertion. 
     Another embodiment of the present disclosure is a fastener  400 , shown in  FIGS. 9-11 . Fastener  400  includes channel  415  extending through the entirety of the shaft  403  for receiving stylet  450 . 
     Stylet  450  includes elongated shaft body  452  extending along a longitudinal axis and terminating at sharp distal tip  456 . Body  452  of stylet  450  extends through a proximal end of the shaft  403  and out of distal end  409  such that the sharp tip  456  of stylet  450  extends beyond the distal end  409  of the shaft  403  of fastener  400 . 
     Body  452  of stylet  450  includes a keyed stop  458  that is engageable with a corresponding stop member, ledge, or shoulder positioned on or near a proximal end of shaft  403 . In an engaged position, the stylet is rotationally and axially fixed with respect to shaft  403  of fastener  400 . Stylet  450  can be disengaged from the locked relationship between the stylet and the shaft  403  so that the stylet can be removed from the cannulated channel of the fastener. Alternatively, stylet  450  may be frangibly connected to the screw, such that the frangible connection can be fractured for removal of the stylet after the bone screw is inserted into bone. 
     Keyed stop  458  may be in the form of a flat section running along at least a length of body  452  of stylet  450  to ensure that the body remains in an axially-fixed and rotatably-fixed position relative to shaft  403 . The cross-section of stylet  450  is non-circular to include the flat section or to be hexagonally shaped so that it can be rotationally locked with the internal lumen of fastener  400 . Thus, once stylet  450  is in place, the tip  456  coupled with distal end  409  of fastener  400  is configured similarly to cutting point  216  of non-cannulated fastener  200 . 
     During use, stylet  450  is first positioned within channel  415  of shaft  403  such that the keyed stop is engaged and the stylet is axially and rotationally fixed relative to the shaft. With the stylet  450  secured to the shaft  403 , the sharp tip  456  of the stylet  450  extends further distally than the fastener to form the cutting point. With stylet  450  secured to shaft  403 , distal end  409  of fastener  400  has the same shape and geometry of fastener  200 . Fastener  400  and stylet  450  rotate simultaneously as the fastener and stylet are advanced into bone. After fastener  400  is implanted to the desired depth in the bone, the keyed stop is disengaged and stylet  450  can be removed from the fastener. The removal of stylet  450  may be advantageous in certain instances because the sharp point  456  of the stylet is removed from the anatomy which may result in less damage to the surround area over time. 
       FIGS. 12 and 13  depict a fastener  500  according to yet another embodiment of the present disclosure. Fastener  500  includes a cannulated threaded shaft  503  that terminates at distal tip  509 . Distal tip  509  includes saw tooth members  540  positioned around the circumference thereof. Each saw tooth member  540  is in the shape of a triangular member terminating in a point. In the illustrated embodiment, there are six saw tooth members  540 ; however, in other embodiments there may be more or less of the saw tooth members positioned around the circumference of the distal tip. Additionally, the saw tooth members may be larger or smaller depending on the number of members around the circumference. Although shown as triangularly shaped, in other examples, the saw tooth members may be trapezoidal, rectangular, etc. 
       FIG. 14  depicts a fastener  600  according to another embodiment of the present disclosure. Fastener  600  includes cannulated shaft that includes thread having serrations  634  along a portion of the shaft. Serrations  634  include alternating peaks and valleys. Serrations  634  may be in the form of the various embodiments of serrations described in U.S. application Ser. No. 15/645,264 filed on Jul. 10, 2017 and titled Spinal Fastener with Serrated Thread. The inclusion of the serrations reduces insertion torque, which reduces the chance of bone fracture and breaching. The shaft terminates at distal tip  609  which includes sharp triangular-shaped saw tooth members  640  positioned around the circumference of the distal tip. 
       FIGS. 60-61  show a fastener  1300  according to another embodiment of the present disclosure. Fastener  1300  includes cannulated shaft  1303  that is threaded along its length to distal tip  1309 . Shaft  1303  tapers toward distal tip  1309 , and distal tip  1309  includes substantially V-shaped saw tooth members  1340  positioned around the circumference of the distal tip  1309 , as best shown in  FIG. 61 . 
       FIGS. 62-63  show fastener  1400  according to another embodiment of the present disclosure. Fastener  1400  is similar in most respects to fastener  1300  except that shaft  1403  has a constant major diameter. 
       FIGS. 64-65  show fastener  1500  according to another embodiment of the present disclosure. Fastener  1500  includes cannulated shaft  1503  which tapers to distal tip  1509 . Fastener  1500  includes substantially C-shaped saw tooth members  1540  such that between adjacent tooth members is a curved edge rather than the pointed edge shown in  FIG. 61  in connection with fastener  1300 .  FIGS. 66-67  show fastener  1600  according an embodiment that is substantially identical to fastener  1500  except that fastener  1600  includes shaft  1603  with major constant diameter rather than a tapering profile, as in fastener  1500 .  FIG. 68  shows fastener  1700  which is another variant of fasteners  1500  and  1600 , with fastener  1700  including shaft  1703  with a constant major diameter and tapering minor diameter.  FIG. 69  shows the distal tip of fastener  1800 , which is another variant to fastener  1500 . Fastener  1800  includes saw tooth members  1840  angled relative to one another. 
       FIG. 70  shows fastener  1900  according to another embodiment of the present disclosure. Fastener  1900  includes cannulated threaded shaft  1903  which terminates at distal tip  1909 . Distal tip  1909  includes a only single cutting member  1940  for cutting into the bone. The single cutting member  1940  may have a rectangular, trapezoidal, triangular, or c-shape. 
     Referring to  FIGS. 15 and 16 , a fastener  700  includes a non-cannulated threaded shaft  703  terminating at rounded distal tip  709  that includes burr members  722  that allow for high speed cutting of the cortical bone. The burr members  722  are positioned around the circumference of the distal tip and are separated from one another by cut-out portions. 
     In another embodiment, shown in  FIG. 17 , a fastener  800  includes a self-drilling distal tip  809  with one or more flutes  828  positioned at a distal portion of shaft  803 . Threading  812  extends to the distal tip  809  which allows the shaft to engage and anchor into the bone immediately upon contact. 
     In an alternative embodiment, shown in  FIG. 18 , a fastener  900  includes self-drilling distal tip  909  of the shaft which includes a helically threaded portion  932 . The pitch of threaded portion  932  is less than that of threads  912  of the shaft. As shown in the illustrated embodiment, the distal end of the shaft may include one or more flutes that do not cut across the entire helically threaded portion  932 . 
     In yet another embodiment,  FIG. 19  shows a fastener  1000  having a distal tip that includes first threaded portion  1014  and second unthreaded portion  1016  which tapers inwardly to form a pointed tip  1009  to facilitate a self-drilling tip. The shaft also includes a cutting flute extending to pointed tip  1009 . 
       FIG. 20  shows a fastener  1100  which includes a threaded portion  1112  adjacent a distal portion of the shaft that has tap threads  1132 . Tap threads  1132  extend along less than half of the length of the shaft and may extend along about one-third of the length of the shaft. Tap threads  1132  are of a smaller pitch than the threads of threaded portion  1112 , and also include a helical flute extending along tap threads  1132  to facilitate threading of the hole through the cortical bone. 
     In another embodiment, shown in  FIG. 21 , a fastener  1200  includes a shaft that terminates at awl tip  1209 . Awl tip  1209  is configured to create the pilot hole during implantation of fastener  1200 . Threads  1212  may overlap a portion of the awl tip or, as shown, threads  1212  may terminate at the proximal-most end of the awl tip. 
     It is contemplated that each of the non-cannulated fasteners can alternatively be cannulated for use with a stylet. 
     The method of using the solid, non-cannulated fasteners (i.e. fasteners  200 ,  700 ,  800 ,  900 ,  1000 ,  1100 ,  1200 ) will now be described with specific reference to fastener  200 , although the method applies to each of the aforementioned non-cannulated fasteners. As shown in  FIG. 22 , fastener  200  is positioned on the pedicle bone and distal tip  209  is docked onto the bone. The fastener  200  is pushed into the bone until the distal tip penetrates the bone to dock the fastener. This allows for an accurate point of entry during initial insertion of the fastener into the bone and prevents skiving of the screw. Torque is applied to the fastener, either by manual insertion, robotic or power insertion. The distal tip  209  cuts the bone until threads  212  catch bone and advance the screw into the bone, shown in  FIG. 23 . 
     A similar method of implantation is used with fastener  400  as the stylet  450  and fastener become “integral” with one another while stylet  450  is in the engaged position and axially and rotationally locked with respect to fastener  400 . After implantation of fastener  400 , stylet  450  is removed from the bone. 
     The method of using the cannulated fasteners (i.e. fasteners  100 ,  300 ,  500 ,  600 ) will now be described with specific reference to fastener  100 , although the method applies to each of the aforementioned cannulated fasteners. As shown in  FIG. 24 , stylet  150  is positioned within the channel of the shaft  103  of fastener  100 . Sharp tip  156  of stylet  150  is used to form the pilot hole. The stylet is then advanced into the bone, while shaft  103  remains placed on or above the bone surface. The stylet is advanced into bone about 5 to 30 millimeters, as shown in  FIG. 25 . Torsion is applied to fastener  100  such that the screw rotates with respect to stylet  150 , which remains at its same depth within the bone during insertion of fastener  100 , and the cutting feature of the distal end of fastener  100  cuts into the cortical bone. For fastener  100 , the cutting feature includes cutting edges  115 . As fastener  100  cuts into bone, stylet  150  remains axially fixed and does not advance farther into the bone. The securement of stylet  150  in the bone at the desired depth of screw placement while fastener  100  is being advanced into the bone helps to prevent skiving. The advancement of fastener  100  relative to the secured stylet  150  helps to maintain the accurate trajectory of the fastener. Fastener  100  is advanced to the desired depth by continuing to rotate fastener  100  until its threads engage the bone and advance fastener  100  down stylet  150 , as shown in  FIG. 26 . The depth to which fastener  100  is inserted is just smaller than the depth to which stylet  150  has been inserted. After final placement of the fastener, stylet  150  is pulled proximally and removed from the shaft of fastener  100 , as shown in  FIG. 27 . Removal of the sharp tip of stylet  150  is advantageous in that it prevents damage that could otherwise be caused by the sharp feature to the surrounding area after the procedure. 
     The use of the stylet to maintain the proper trajectory during screw placement is advantageous particularly in instances where a fastener is screwed into a first surface of a first bone, is passed out of a second surface of the first bone, is made to traverse a gap between bone segments, and is screwed into a second bone segment. Typically, without the use of a stylet, as the screw exits the first bone and traverses the gap, the screw&#39;s path loses its accuracy before entering the second bone. In the present disclosure, the movement of the screw over the previously positioned and secured stylet maintains the placement of the screw along the proper position of the second bone despite having to traverse a gap. This technique is particularly useful in surgeries involving smaller pedicles, such as the pedicles of the thoracic spine. Placement of the stylet through the bone portions across the gap does not present the same difficulties, particularly given its sharp tip and the fact that it can be pushed or oscillated during insertion as opposed to being rotated. Often the skiving of a bone screw occurs based on the tip of the screw moving along the bone surface as it attempts to penetrate the surface while it is rotating. The fasteners of the present invention are aimed at eliminating this problem. 
     The step of advancing the stylet into the bone can be performed with the use of a robotic end effector  2000  and an advancement mechanism  2100  positioned at a proximal end of robotic end effector  2000 . In the illustrated embodiment, shown in  FIGS. 28 and 29 , advancement mechanism  2100  includes threaded knob  2105  which engages the stylet as threaded knob  2105  is rotated in a first direction. As threaded knob  2105  is advanced distally, the stylet translates distally through a screwdriver  2200  and through the cannulated channel of the attached fastener. The stylet is connected to a sliding coupler  2107  that travels axially within the advancement mechanism. The coupler is attached to the stylet via a set screw to secure the stylet to the coupler. Once the stylet is advanced to the desired depth, threaded knob  2105  can be disengaged from the stylet and removed such that the stylet remains secured within the bone while the fastener is then rotated to advance the fastener into the bone. In alternative embodiments, advancement mechanism  2100  can include a spring, cam or gear in place of the threading to advance the stylet distally through screwdriver  2000  and the attached fastener. 
       FIGS. 30-37  show a placement device  3100  that may be used to place a stylet and fastener into the bone. Placement device  3100  may be used with robotic end effector  2000  or may be used during manual insertion. Placement device  3100  allows the stylet to oscillate back and forth between clockwise and counter clockwise directions while the fastener is advanced over the stylet in just one of those rotational directions and threaded into bone. 
     Placement device  3100  includes a drill adaptor  3130  through which the motor of end effector  2000  can be connected to device  3100 . Drill adaptor  3130  communicates with a double drive mechanism  3120 , as best shown in  FIGS. 31, 32, and 37 . Double drive mechanism  3120  includes gear system  3125  formed of a driving gear  3129  and a driven gear  3127 . Driving gear  3129  has a splined outer surface at its proximal end that mates with a complimentary splined internal surface (not shown) of the drill adaptor  3130  so that rotation of drill adaptor  3130  is translated into rotation of driving gear  3129 . Driving gear  3129  is connected to driven gear  3127  through two connector gears  3131 ,  3132  disposed at opposite sides of a collar  3133 . Through this connection, rotational movement of driving gear  3129  in one direction, e.g. clockwise, corresponds to rotational movement of driven gear  3127  in the opposite direction, e.g. counter clockwise. 
     A housing  3134  is disposed within the circumferences of driving gear  3129 , driven gear  3127 , and collar  3133 . Housing  3134  has two recesses  3135 ,  3137  in which ratcheted pawls  3136 ,  3138 , respectively, are disposed, as shown in  FIG. 37 . In  FIG. 37 , driven gear  3127  is shown in a misaligned state so that pawl  3136  is exposed, and driving gear  3129  is removed to expose pawl  3138 . As shown in  FIG. 36 , an internal circumferential surface  3139  of driving gear  3129  is splined for communication with the ratcheted outer surface of pawl  3138 . An internal circumferential surface (not shown) of driven gear  3127  is similarly splined for communication with the ratcheted outer surface of pawl  3136 . Both of pawls  3136 ,  3138  are ratcheted in the same direction about the axis of device  3100 . When one gear is in ratcheted connection with its pawl, the other gear slips past its pawl, and vice versa. 
     Pawl  3136  is connectable to a screw driver shaft  3141  through a pin  3142 . Similarly, pawl  3138  is connectable to screw driver shaft  3141  through a pin  3143 . Since pawls  3136 ,  3138  are both ratcheted in the same direction while gears  3127 ,  3129  disposed circumferentially above them are connected in opposite rotational directions, this dictates that rotational motion of housing  3134  will always only be driven by one of gears  3127 ,  3129  through its respective pawl  3136 ,  3138 . That is, when driving gear  3129  is rotated in a direction to engage with pawl  3138 , pawl  3138  engages screw driver shaft  3141  so that housing  3134  is rotationally locked with screw driver shaft  3141 . Also, when driven gear  3127  is rotated in a direction to engage with pawl  3136 , pawl  3136  engages screw driver shaft  3141  so that housing  3134  is rotationally locked with screw driver shaft  3141 . The opposite rotational directions of gears  3127 ,  3129  therefore dictate that screw driver shaft  3141  will always be rotationally locked with housing  3134  and that housing  3134  will always be rotated in the same direction regardless of the direction in which drill adaptor  3130  is rotated. 
     Based on the structural makeup of device  3100  as described above, rotation of drill adaptor  3130  in either direction (i.e. clockwise or counter clockwise) will result in rotation of screw driver shaft  3141  in a single direction (i.e. only clockwise or only counter clockwise). As device  3100  is configured for insertion of a fastener, the direction screw driver shaft  3141  rotates is clockwise by right-hand rule. A distal end of screw driver shaft  3141  is noncircular to mate with the tulip of the fastener to facilitate insertion. A screw driver sleeve  3144  is disposed about screw driver shaft  3141  such that screw driver shaft  3141  can rotate therein. A distal end of screw driver sleeve  3144  has an annular depression in which interior flanges of each prong of the tulip can be seated to maintain the fastener at the end of device  3100 , particularly as it is advanced toward the surgical site. 
     The operation of gear system  3125  is made possible because an outer housing  3145  is held stationary (i.e. non rotatable) during operation of device  3100 . Outer housing  3145  is either held by the user or connected to the end effector  2200  during operation. Pins  3146 ,  3147  are anchored to outer housing  3145 , through connector gears  3131 ,  3132 , respectively, and into collar  3133 . This allows drill adaptor  3130  to be rotationally connected to driving gear  3129  and driven gear  3127 , and ultimately to housing  3134  to drive screw driver shaft  3141 , which in turn drives the fastener. 
     Another simultaneous function of driver  3100  is that it can rotate a stylet  3180  through a threaded proximal end  3181  of stylet  3180 . A threaded internal surface  3182  of housing  3134  is threadedly connected with threaded proximal end  3181 . Also, a pin  3149  is disposed through housing an aperture in threaded proximal end  3181  and protrudes through a slot in drill adaptor  3130  at either end, so that rotation of drill adaptor  3130  in one direction (i.e. clockwise or counter clockwise) always corresponds with rotation of stylet  3180  in the same direction (i.e. clockwise or counter clockwise, respectively) as drill adaptor  3130 . Thus, when drill adaptor  3130  is oscillated, stylet  3180  is also oscillated. When drill adaptor  3130  is rotated in one direction, stylet  3180  is rotated along with it. 
     The threaded connection of stylet  3180  with housing  3134  adds a further useful dimension to device  3100  since housing  3134  is axially stationary along device  3100  though it rotates in one direction due to double drive mechanism  3125 . Assuming device  3100  is configured so that clockwise rotation by right-hand rule advances the fastener distally, during clockwise rotation of drill adaptor  3130 , torque is transmitted by the slot in drill adaptor  3130  via pin  3149  to stylet  3180 , and stylet  3180  is simply driven in the same clockwise direction, though no translation of stylet  3180  occurs. The threads of threaded proximal end  3181  and housing  3134  are of the same pitch. When stylet  3180  and housing  3134  both rotate in the same direction, there is no relative movement between their threads. When the input motion is reversed to counter clockwise rotation of drill adaptor  3130 , stylet  3180  once again follows in the same counter clockwise direction of drill adaptor  3130 , but since it is threaded to housing  3134  that is rotating in the opposite clockwise direction, the relative motion between the mating threads causes an axial translation of stylet  3180 , having the effect of incremental retraction. The slot in drill housing  3130  through which pin  3149  is disposed accommodates translation of stylet  3180 . The position of the pin  3149  along the length of the slot can serve as an indicator for where the tip of stylet  3180  is relative to the tip of the fastener, and could include depth markings to give a more precise indication. Selecting a particular pitch and lead of threads dictates how much axial translation occurs for a given angular rotation of drill housing  3130 . Additionally selecting a particular pitch and lead of thread on the fastener dictates how much relative axial translation occurs between the bone and stylet  3180 . 
     Any of the previously described rotations or translations could be reversed to achieve alternative surgical goals, such as progressively advancing stylet  3180  or maintaining a constant stylet  3180  depth relative to the bone. A simple switch can also be provided to allow the user to mechanically select between “forward” (as described above) and “reverse” modes of device  3100 . 
     Spine surgeons currently use a natural oscillating motion to advance instruments into the spine to create a pilot hole in the pedicle to prepare for screw insertion. For example, a surgeon will twist an awl, gearshift, or jamshidi needle back and forth to carefully advance it to the desired depth. While device  3100  can be utilized either electronically (via power or a robot) or manually by hand, it captures this desired oscillating motion while simultaneously driving the fastener over the stylet in a single, efficient tool. 
     During use of device  3100 , stylet  3180  is first loaded by setting it to the proper depth relative to the length of the intended fastener. Since device  3100  is configured to either maintain the axial position of stylet  3180  or retract it, this is the furthest distally that the tip of stylet  3180  will be positioned relative to the handle of device  3100  during the procedure. A fastener  3300  is then loaded onto device  3100  by placing it over stylet  3100  and connecting it to screw driver shaft  3141 . Device  3100  is advanced until the distal tip of stylet  3100  is docked to the bone, as shown in  FIG. 38 . At this point or during docking, the surgeon can begin to oscillate drill housing  3130  by hand or robotically by keeping outer housing  3145  stationary and not rotating it. This oscillating motion of stylet  3180  during docking prevents tugging on the local tissue and tendons so that the procedure can be carried out most efficiently and with the least disruption to the surrounding anatomy. While this practice is currently used by surgeons, the oscillation of stylet  3180  even when device  3100  is used robotically provides surgeons with comfort that the same technique is being applied during the procedure. 
     Continued oscillation of drill housing  3130  while device  3100  is being pushed distally embeds the tip of stylet  3180  into the bone until fastener  3300  meets the bone surface. At this point, further oscillation of drill housing  3130  engages the threads of fastener  3300  into the bone to advance fastener  3300 , all while fastener is guided by the path set by stylet  3180 . Upon each small counter clockwise rotation of drill housing  3130 , stylet  3180  retracts along the length of fastener  3300  so that stylet  3180  is retracted simultaneously. In this way, the surgeon can cannulate the pedicle via oscillating rotational motion of a sharp cutting tool such as a stylet or stylet  3180 , while simultaneously advancing a cannulated screw or fastener  3300  over stylet  3180 , all driven by a single oscillating input motion to device  3100 . 
     In other embodiments similar to device  3100 , the threaded connection and automatic retraction of stylet  3180  can be omitted and stylet  3180  can simply be pulled from the surgical site once fastener  3300  is implanted to the appropriate depth. 
     According to another embodiment of the present disclosure,  FIGS. 42-47  show a stylet control system  4000  for selective and controlled axial movement (i.e. advancement and/or retraction) of a stylet for use during surgery in which a cannulated bone screw is inserted into bone around the stylet. Stylet control system  4000  includes control device  4120  for use in conjunction with a threaded stylet  4150  and a screwdriver  4170  during a spinal surgery in which a pedicle screw  4010  is implanted in bone. Control device  4120  may be controlled manually or with a robotic device, such as a robotic end effector. 
     Bone screw  4010  includes a head portion, a threaded shaft  4011 , and a tulip  4020  for coupling the screw to an orthopedic rod. Bone screw  4010  may be a standard size pedicle screw or it may be a screw adapted for use in minimally invasive surgery. Any of the above-described screws are suitable for use in stylet control system  4000 . Bone screw  4010  is cannulated such that stylet  4150  can extend through the cannulation and can extend beyond a distal tip of the screw. Bone screw  4010  has a threaded shaft  4011  and its head is received within tulip  4020 . Tulip  4020  is designed to receive a stabilizing rod therethrough. An inner surface of tulip  4020  includes threads capable of engaging with the screwdriver  4170 , described in further detail below. Further, bone screw  4010  includes a self-cutting feature at its distal end, such as sharp cutting edges. 
     Stylet  4150  extends between proximal end  4152  and distal end  4158 , which terminates at a sharp distal point to allow the stylet to cut through bone to form a cannulation for ease of insertion of bone screw  4010 , as described above. At proximal end  4152 , stylet  4150  includes monolithic threaded portion  4159  that facilitates axial translation of the stylet relative to screwdriver  4170  and control device  4120 . Stylet  4150  also includes an anti-rotation feature to prevent relative rotation between stylet  4150  and screwdriver  4170 . For example, in the illustrated embodiment, stylet  4150  includes keyed hex portion  4153  that has a hexagonal cross section extending along a portion of its length which corresponds to a hex feature on screwdriver  4170 , described below. As shown in  FIG. 43 , hex portion extends from a distal end of threaded portion  4159 . Although described herein as a hex, the mechanically keyed feature may be square, oval, triangular, trapezoidal etc. 
     Control device  4120  includes proximal assembly  4121  that is rotatable relative to screwdriver  4170 . Proximal assembly  4121  includes inner core  4125 , coupling member  4132 , and outer handle  4140 . Inner core  4125  defines central lumen  4126  extending therethrough for receiving stylet  4150 . As shown in  FIG. 44 , control device  4120  includes coupling member  4132  with base  4134  having a generally cylindrical shape and top portion  4135  having a planar surface and a sidewall with opposing cut-outs  4135  for receiving screws  4138 , which secure base  4134  to inner core  4125 . Base  4134  is sized to fit within central lumen  4126  of inner core  4125 . Coupling member  4132  includes a threaded opening  4136  extending through base  4134  and top portion  4135  for engaging threaded portion  4159  of stylet  4150 . 
     Inner core  4125  includes an attachment feature to attach coupling member  4132  to proximal end  4130  of inner core  4125 . In the illustrated embodiment, the attachment feature is in the form of two threaded bores  4128  extending into proximal end  4130  of inner core  4125  that are sized for receiving set screws  4138 . With coupling member  4132  axially and rotationally secured to inner core  4125 , threaded opening  4136  of the coupling member is coaxial with central lumen  4126  of the inner core so that stylet  4150  can extend through the assembly. In other examples, coupling member  4132  may be integral or monolithic with inner core  4125 . 
     Control device  4120  also includes outer handle  4140  housing coupling member  4132  and inner core  4125 . Outer handle  4140  defines central lumen  4146  extending longitudinally through its entirety. Central lumen  4146  is sized to accommodate inner core  4125 . Outer handle  4140  has a rounded outer surface to allow for a user to comfortably grip the handle. Outer handle  4140  is axially and rotatably fixed to inner core  4125  and coupling member  4132  such that when the outer handle  4140  is rotated in a first direction, e g manually or robotically, inner core  4125  and coupling member  4132  are also rotated in the first direction. In the illustrated embodiment shown in  FIG. 46 , a proximal end of coupling member  4132  extends farther proximally than the proximal end of outer handle  4140 , such that threaded opening  4136  is positioned proximal to outer handle  4140 . Further, when stylet  4150  is positioned within inner core  4125 , a portion of stylet  4150  extends proximally to outer handle  4140  as shown in  FIG. 42 . 
     Control device  4120  includes quick connect system  4141  that facilitates a simple and efficient connection to the proximal end of screwdriver  4170 , as shown in detail in  FIGS. 45-47 . Quick connect system  4141  includes a collar  4144  that surrounds a distal shaft  4127  of inner core  4125 . An inner shaft  4180  of screwdriver  4170  is connected to collar  4144  via at least one a spring-loaded ball bearing  4148  received within a radial groove  4178  on inner shaft  4180  of screwdriver  4170 . When collar  4144  is located radially outside of radial groove  4178  with the ball bearing disposed within the groove  4178 , collar  4144  does not permit the ball bearing  4148  to leave groove  4178 , thereby connecting control device  4120  and screwdriver  4170 . The engagement of ball bearing  4148  and groove  4178  prevents axially movement of control device  4120  relative to screwdriver  4170  but allows rotation of the control device  4120  relative to the screwdriver  4170 . When collar  4144  is moved away, the ball bearing can move radially outward so that control device  4120  and screwdriver  4170  can be disconnected. Screwdriver  4170  also includes recess  4176  for attaching an alternative quick connect in the event the user wants to use a standard handle to manually drive the screw into bone. 
     The quick connect system  4141  may be released by applying an axial force in the proximal direction, which may be applied by a user to collar flange  4149 , to remove the radial load applied against the screwdriver  4170  to disengage the screwdriver from the control device  4120 . 
     Referring to  FIGS. 42 and 43 , screwdriver  4170  extends between proximal end  4172  and distal end  4184 . Distal end  4184  is configured for securing to and engaging a screw, such as pedicle screw  4010 . Screwdriver  4170  may be used with mono-axial pedicle screws, poly-axial pedicle screws, reduction screws, or screws designed for minimally invasive surgeries (MIS screws). 
     At distal end  4184 , screwdriver  4170  engages screw  4010 . An outer sleeve may include external threaded portion configured to thread into corresponding threads on the inner surface of the tulip  4020  of screw  4010 . Inner shaft  4180  is positioned concentrically within the outer sleeve and includes a driving member for engagement within a corresponding opening of the head of bone screw  4010 . The driving member may be hexagonally shaped designed to torque bone screw  4010  to advance the screw into bone. Alternatively, inner shaft  4180  may include threads to engage the threads of tulip  4020  of screw  4010 . 
     Inner shaft  4180  is cannulated along its length and defines inner lumen  4181  to allow stylet  4150  to extend entirely through the shaft and through bone screw  4010 . Inner shaft  4180  includes an anti-rotation feature at its proximal end to prevent stylet  4150  from rotating relative to screwdriver  4170 . In this manner, stylet  4150  is rotationally coupled with screwdriver  4170 , and both are rotatable relative to proximal handle assembly  4121 . In the illustrated embodiment, the anti-rotation feature includes a hex-shaped inner surface  4182  surrounding inner lumen  4181  on at least the proximal end of the screwdriver  4170 . Hex portion  4153  on stylet  4150  is sized and shaped to fit within inner shaft  4180  without relative rotational movement between the hex members  4153 ,  4182 , thus rotationally coupling the elements. 
     System  4000  is also designed for use in robot-assisted surgery and can be connected to a robotic device to facilitate the torqueing of bone screw  4010  into the bone and/or to facilitate the movement of stylet  4150 . In other examples, system  4000  can be manually operated in part, i.e. control device  4120  may be manually operated while the screwdriver is robotically operated, or both pieces can be either robotically or manually operated. For example, as shown in  FIG. 48 , a robotic device  4200  including a robotic arm with a rotatable end effector coupled to the end of the robotic arm can interface with a robotic unit coupler positioned on proximal end  4172  of screwdriver  4170 . The robotic coupler includes at least one tab for transmitting torque to the screwdriver. End effector  4210  transmits torque to inner shaft  4180  to rotate the shaft  4180  in a clockwise direction to advance the screw in bone. When the control device  4120  is held stationary during this robotic rotation of screwdriver  4170 , stylet  4150  retracts proximally. 
     To assemble system  4000 , stylet  4150  is first advanced through control device  4120  and threaded portion  4159  of stylet  4150  is threaded into threaded opening  4136  of coupling member  4132 . Control device  4120  is then loaded onto screwdriver  4170  via quick connect system  4141 , while stylet  4150  is positioned through the assembled device such that it extends through the distal end of bone screw  4010 . When the stylet  4150  is loaded into the screwdriver  4170 , stylet  4150  is rotationally fixed relative to the screwdriver due to the mating hex features  4182 ,  4153  of the screwdriver and the stylet. 
     In operation, with distal end  4158  of stylet  4150  positioned against bone, proximal handle assembly  4121  is rotated by rotating outer handle  4140  in a first direction, such as in the clockwise direction. When outer handle  4140  is rotated in the first direction, screwdriver  4170  is held stationary and is not rotated, which produces relative rotational movement between control device  4120  and screwdriver  4170 . The rotation of outer handle  4140  causes inner core  4125  to rotate so that threads of threaded opening  4136  of inner core engage threads of threaded portion  4159  of stylet  4150 . Screwdriver  4170  is held stationary, meaning that stylet  4150  is also not rotated. Thus, as threaded portions  4136 ,  4159  engage each other, stylet  4150  advances axially through control device  4120  and screwdriver  4170 , i.e. stylet  4150  travels in the distal direction, based on the threaded engagement. As stylet  4150  moves distally it travels through bone and produces a path having the desired trajectory for the bone screw to follow, while the shaft of the bone screw  4010  remains placed on or above the bone. Once stylet  4150  is advanced to the desired depth in the bone, which may be about 5 to 30 millimeters, bone screw  4010  can be implanted over stylet  4150  to maintain the desired trajectory of the bone screw. Because bone screw  4010  advances over stylet  4150 , this helps to prevent skiving of the tip of bone screw  4010  relative to the intended entry point in the bone. In the example of robotic operation of the screwdriver  4170 , the end effector  4210  keeps the screwdriver stationary to insert stylet  4150  without impaction. 
     It is advantageous to advance bone screw  4010  into bone without further advancing stylet  4150  beyond the desired depth. In order to do so, proximal handle assembly  4121  is held stationary while screwdriver  4170  is rotated in a clockwise direction. When screwdriver  4170  is rotated clockwise, manually or robotically, inner shaft  4180  of the screwdriver  4170  rotates in this direction which drives bone screw  4010  into bone. As screwdriver  4170  is rotated, and thus stylet  4150  rotates while proximal handle assembly  4121  remains stationary, stylet  4150  travels axially in the retraction direction, i.e. proximally. It may be advantageous that the pitch of the threads of the stylet are the same as the pitch of the threads of the bone screw, which results in the stylet retracting at the same rate as the bone screw is advanced. 
     In another embodiment according to the present disclosure, control device  4120  is built into the robotic end effector  4250 . A back coupler is attached to end effector  4250  which functions as control device  4120  and facilitates the relative rotational movement of the screwdriver  4170  and the back coupler to control the movement of stylet  4150  in the proximal and distal directions, as desired. When screwdriver  4170  is driven in the counter-clockwise direction by the end effector  4250 , stylet  4150  rotates with screwdriver  4170  causing the stylet  4150  to rotate relative to the back coupler. This relative rotation causes stylet  4150  to advance axially in the distal direction to advance into bone. When the end effector  4250  rotates screwdriver  4170  clockwise, stylet  4150  translates axially in the proximal direction as screwdriver  4170  simultaneously drives the fastener into bone. 
       FIGS. 49-54  show stylet control system  7000 , which is built into end effector  7200 . Control system  7000  includes cap  7027  which forms a connection between the end effector and the instrument for use, e.g. screwdriver  7170 . Cap  7027  defines passage  7029  which extends from proximal end  7031  to distal end  7033  of cap  7027  and is sized and shaped to receive screwdriver  7170  into at least a distal portion of passage  7029 . Cap  7027  is configured to be attached to a proximal end of control system  7000 , as shown in  FIG. 50 . 
     Screwdriver  7170 , with bone screw  7010  attached to a distal end thereof, is positioned within passage  7029  and attached to cap  7027 . As shown in  FIGS. 49 and 50 , screwdriver  7170  extends distally from cap  7027 . Cap  7027  is then attached to end effector  7200  such that screwdriver  7170  is in operative engagement with the end effector. Cap  7027  may be designed as a universal cap which configured to attach to various instruments for use during preparation of the bone and implantation of an implant therein, e.g. screwdriver, drill, burr etc. 
     Control system  7000  further includes stylet  7150  which includes threaded portion  7159  at a proximal end thereof. At least a portion  7153  of the length of stylet  7150  is keyed and screwdriver  7140  includes an anti-rotation feature, such as a corresponding keyed feature to prevent relative rotation between stylet  7150  and screwdriver  7140  while allowing axial movement of the stylet within the screwdriver. In the illustrated embodiment, the keyed feature is shown as a hex, although the mechanically keyed feature may be square, oval, triangular, trapezoidal etc. Control system  7000  includes stylet feeder  7140  sized such that at least a portion of the stylet feeder  7140  is received within a proximal portion of passage  7029  of cap  7027 . A portion of stylet feeder  7140  is keyed to prevent relative rotation of the stylet feeder within cap  7027 . Stylet feeder  7140  includes hinged threaded pawl  7145 , the threads of which are configured to facilitate one-way engagement of threaded portion  7159  of stylet  7150 , e.g. engagement to cause proximal movement of the stylet during the rotation of the stylet, while disengaging for distal advancement of the stylet. In this regard, rotation of screwdriver during advancement of bone screw  7010  into bone causes rotation of stylet  7150  and thus engagement of threaded pawl  7145  with threaded portion  7159  of stylet  7150 . This engagement results in proximal movement, e.g. retraction, of stylet  7150  as the bone screw is advanced into bone. It may be advantageous that the pitch of the threads of the stylet are the same as the pitch of the threads of the bone screw, which results in the stylet retracting at the same rate as the bone screw is advanced. Of course, this is not required in all embodiments and there may be some benefit to having the stylet designed to retract at a different rate. 
     As shown in  FIG. 52 , during use, stylet  7150  is inserted into stylet feeder  7140  such that the stylet extends through screwdriver  7140  and bone screw  7010  so that the distal tip of stylet  7150  extends just beyond the distal tip of bone screw  7010 . Stylet  7150  can then be impacted to dock the screw to the bone, such impaction can be done manually such as by hammering or ultrasonically, such ultrasonic advancement of the stylet is described below with reference to  FIGS. 55-58 . Stylet  7150  may be impacted into the bone to a depth of between about 10 mm to 20 mm Once stylet  7150  is advanced to the desired depth, screwdriver  7170  is driven to advance bone screw  7010  into bone, which causes simultaneous retraction of stylet  7150 . After stylet  7150  is advanced to the desired depth in the bone, screwdriver  7170  is driven via end effector  7200  which rotates both the screwdriver and stylet  7150 , since the stylet is keyed to the screwdriver. As bone screw  7010  is driven into bone along the trajectory defined by previously implanted stylet  7150 , the threaded portion  7159  of stylet  7150  is engaged by pawls  7145 , which causes proximal movement, e.g. retraction, of stylet  7150  as the bone screw is advanced into bone. 
     According to another embodiment of the present disclosure,  FIGS. 55-58  show a robotic stylet control device  5000 . Control device  5000  shares many similar to features as control device  4000  and control system  7000 , described above in connection with  FIGS. 42-47  and  FIGS. 48-53 , respectively, although control device  5000  is designed to facilitate ultrasonic movement and oscillation of a stylet as it is advanced into bone. Control device  5000  allows for movement of a stylet through a cannulated bone fastener, such as bone fasteners  100 - 500  and  1300 - 1900  or a cannulated drill, shown in  FIG. 58 . Control device  5000  provides controlled axial movement (advancement and/or retraction) of a stylet during surgery including implantation of a cannulated bone fastener. The stylet is advanced into bone to create the initial pilot hole for subsequent insertion of the screw. Additionally, the control device  5000  ultrasonically oscillates during axial movement of the stylet. Such oscillation reduces the applied forces at the bone interface during the advancement of the stylet, which improves robotic accuracy as it minimizes the potential of deflection of the robotic arm. The reduction of force and increased accuracy may also result in a decreased likelihood of skiving. 
     Traditionally, in during manual preparation of a site for implantation of a bone screw, the process includes multiple steps including: awling, probing, tapping and then placement of the screw. Whereas, with the use of control device  5000 , the initial pilot hole is created with the stylet which is received within either a cannulated drill or a cannulated bone screw. Thus, control device  5000  is advantageously procedurally efficient as it eliminates the need for the traditional steps of pilot hole creation. 
     Turning to  FIGS. 55 and 56 , control device  5000  includes housing  5300 , retraction assembly  5140 , and end effector  5200 . Control device  5000  further includes integrated ultrasonic transducers  5275 . Housing  5300  defines passage  5310  for receiving stylet  5150 . Housing  5300  includes a low gain transducer assembly  5275  for imparting ultrasonic vibrations to stylet  5150 . Control device  5000  further includes an energy source for generating the ultrasonic energy. 
     Transducer assembly  5275  comprises a plurality of piezoelectric elements positioned within housing  5300 . Ultrasonic vibration is induced in the end effector by electrically exciting transducers  5275 . In this example, transducers  5275  are comprised of piezoelectric elements which produce ultrasonic vibrations. Transducer assembly  5275  are low gain transducers and output frequencies in the range of about 10,000 Hz to about 30,000 Hz. Such ultrasonic vibrations are transmitted to the stylet  5100  positioned within passage  5306  of body  5300 . 
       FIGS. 55 and 56  show control device  5000  in conjunction with screwdriver  5170  and bone screw  5010  attached to the screwdriver. Stylet  5150  includes threaded portion  5159  at its proximal end to facilitate the axial movement of the stylet. 
     As shown in  FIG. 57 , bone screw  5010  is positioned at or near the bone interface with the distal end of stylet  5150  substantially flush with distal end  5012  of bone screw  5010 . Upon actuation of the energy source and thus excitation of the piezoelectric elements of transducer assembly  5275 , ultrasonic vibrations are induced which oscillates stylet  5150  in a reciprocating longitudinal direction in strokes of about 20 to 100 micrometers (μm) which ultimately advances the stylet through distal end  5012  of bone screw  5010  and within the bone to create the pilot hole which is about 10 to 30 millimeters (mm) measured axially from the interface of the bone. Preferably, the stylet advances about 15 mm for creation of the pilot hole. Oscillation of stylet  5150  also occurs in a reciprocating torsional direction to twist and turn the stylet while it advances axially (shown by the arrows in  FIG. 57 ). 
     After stylet  5150  is advanced to the desired depth, e.g. about 15 mm, stylet  5150  is simultaneously retracted via retraction assembly  5140  as bone screw  5010  is driven into the bone by screwdriver  5170 . In this example, retraction assembly  5140  is positioned proximally of housing  5300  and defines passage  5123  for receiving stylet  5150  therethrough. Retraction assembly furthers includes an internally threaded portion for engaging threaded portion  5159  control device  5000  as described above in connection with control device  4120 , stylet  5150  is rotationally coupled to screwdriver  5170  such that when screwdriver  5170  and thus stylet  5150  rotates in a clockwise manner, the engagement of threaded portion  5159  of stylet  5150  and internally threaded portion of retraction assembly  5140  causes proximal axial advancement of stylet  5150 , e.g. retraction. Because the screwdriver is also rotating, this causes the bone screw  5010  to be driven into bone at the same time as stylet  5150  retracts. The pitch of the threads of threaded portion  5159  of stylet  5150  and the threads of bone screw  5010  may match to facilitate movement in opposite directions at the same rate. 
       FIG. 58  shows drill  5270  which may alternatively be utilized in conjunction with control device  5000  rather than the screwdriver/bone screw, described in connection with  FIGS. 55-57 . Drill  5270  defines passage  5275  for receiving stylet  5150  therethrough. In this example, stylet  5150  is ultrasonically advanced through drill  5270  and into bone to create an initial pilot hole. The stylet is then retracted via retraction assembly  5140 , and drill  5270  is advanced into bone. 
       FIG. 59  shows control device  6000  which is another embodiment of a device for advancing and retracting a stylet and is similar in most respects to control device  5000 , the similar features of which will not be described again. Control device  6000  includes housing  6300  which operatively connects to a separate, non-integral ultrasound transducer device  6270  to impart the ultrasonic vibrations to advance the screwdriver or drill into bone. 
     Robotic systems may be used throughout the pre-operative and intra-operative stages of the surgery. 
     Preoperative planning for surgeries may include determining the bone quality in order to optimize bone preparation. Bone quality information, such as bone density or elastic modulus, can be ascertained from preoperative scans, e.g. CT scans. The bone quality data can be used to determine optimal properties for effective implant engagement. Examples of such methods are found in U.S. Pat. No. 10,166,109 to Ferko, filed on Sep. 18, 2014, entitled “Patient Specific Bone Preparation for Consistent Effective Fixation Feature Engagement,” U.S. Patent Application Publication No. 2015/0119987 to Davignon et al., filed on Oct. 28, 2014, entitled “Implant Design Using Heterogeneous Bone Properties and Probabilistic Tools to Determine Optimal Geometries for Fixation Features,” and U.S. Pat. No. 10,070,928 to Frank et al., filed on Jul. 1, 2015, entitled “Implant Placement Planning,” each of which is hereby incorporated by reference herein in its entirety. In addition to preoperative imaging, robotic surgery techniques may employ imaging, such as fluoroscopy, during surgery. In such cases, systems integrating the surgical system with the imaging technologies facilitate flexible and efficient intraoperative imaging. Exemplary systems are described in U.S. Pat. No. 10,028,788 to Kang, filed on Dec. 31, 2013, entitled “System for Image-Based Robotic Surgery,” hereby incorporated by reference herein in its entirety. 
     As in the instant case, robotic systems and methods may be used in the performance of spine surgeries to place implants in the patient&#39;s spine as in, for example, U.S. Patent Application Publication No. 2018/0325608 to Kang et al., filed on May 10, 2018, entitled “Robotic Spine Surgery System and Methods,” the disclosure of which is hereby incorporated by reference herein in its entirety. The robotic system generally includes a manipulator and a navigation system to track a surgical tool relative to a patient&#39;s spine. The surgical tool may be manually and/or autonomously controlled. Examples of robotic systems and methods that employ both a manual and a semi-autonomous are described in U.S. Pat. No. 9,566,122 to Bowling et al., filed on Jun. 4, 2015, and entitled “Robotic System and Method for Transitioning Between Operating Modes,” and U.S. Pat. No. 9,119,655 to Bowling et al., filed on Aug. 2, 2013, entitled “Surgical Manipulator Capable of Controlling a Surgical Instrument in Multiple Modes,” each of which is hereby incorporated by reference herein in its entirety. 
     A robotic controller may be configured to control the robotic arm to provide haptic feedback to the user via the robotic arm. This haptic feedback helps to constrain or inhibit the surgeon from manually moving the screwdrivers  4170 ,  8170  of systems  4000 ,  8000  beyond predefined virtual boundaries associated with the surgical procedure. Such a haptic feedback system and associated haptic objects that define the virtual boundaries are described in, for example, U.S. Pat. No. 9,002,426 to Quaid et al., filed on Jun. 23, 2008, entitled “Haptic Guidance System and Method,” and U.S. Pat. No. 8,010,180 to Quaid et al., filed on Dec. 21, 2012, entitled “Systems and Methods for Haptic Control of a Surgical Tool,” and U.S. Pat. No. 10,098,704 to Bowling et al., filed on May 18, 2016, entitled “System and Method for Manipulating an Anatomy,” each of which is hereby incorporated by reference herein in its entirety. 
     In some cases of autonomous positioning, a tool center point (TCP) of a surgical tool, such as screwdriver  4170 ,  8170 , is brought to within a predefined distance of a starting point of a line haptic object that provides the desired trajectory. Once the tool center point is within the predefined distance of the starting point, actuation of an input causes the robotic arm to autonomously align and position the surgical tool on the desired trajectory. Once the surgical tool is in the desired position, the robotic system may effectively hold the rotational axis of the surgical tool on the desired trajectory by tracking movement of the patient and autonomously adjusting the robotic arm as needed to keep the rotational axis on the desired trajectory. Such teachings can be found in U.S. Patent Application Publication No. 2014/0180290 to Otto et al., filed on Dec. 21, 2012, entitled “Systems and Methods for Haptic Control of a Surgical Tool,” which is hereby incorporated by reference herein in its entirety. 
     During operation of a robotic surgical system, the operation of the surgical tool can be modified based on comparing actual and commanded states of the tool relative to the surgical site is described in U.S. Patent Application Publication No. 2018/0168750 to Staunton et al., filed on Dec. 13, 2017, entitled Techniques for Modifying Tool Operation in a Surgical Robotic System Based on Comparing Actual and Commanded States of the Tool Relative to a Surgical Site,” which is hereby incorporated by reference herein in its entirety. Further, robotic systems may be designed to respond to external forces applied to it during surgery, as described in U.S. Patent Application Publication No. 2017/0128136 to Post, filed on Nov. 3, 2016, entitled “Robotic System and Method for Backdriving the Same,” which is hereby incorporated by reference herein in its entirety. 
     Further, because of the non-homogeneity of bone, applying a constant feed rate, a uniform tool path, and a constant rotational speed may not be efficient for all portions of bone. Systems and methods for controlling tools for such non-homogenous bone can be advantageous as described in U.S. Pat. No. 10,117,713 to Moctezuma de la Barrera et al., filed on Jun. 28, 2016, entitled “Robotic Systems and Methods for Controlling a Tool Removing Material From a Workpiece,” which is hereby incorporated by reference herein in its entirety. 
     Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims.