Patent Publication Number: US-2023149057-A1

Title: Instrument for use in surgery

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     The present application claims priority to and the benefit of U.S. Provisional Patent Application No. 63/280,765, filed Nov. 18, 2021, the contents of which are hereby incorporated by reference in their entirety, and claims priority from European Patent Application EP 21 208 986.6, filed Nov. 18, 2021, the contents of which are hereby incorporated by reference in their entirety. 
    
    
     BACKGROUND 
     Field 
     The application relates to an instrument for use in surgery, in particular, in connection with a bone anchor insertion device. With the instrument, a position of a needle relative to the bone anchor can be adjusted. Further, the invention relates to a surgical instrument including the bone anchor insertion device and the aforementioned instrument. The surgical instrument may in particular be used in musculoskeletal surgery, and more particularly in spinal surgery. 
     Description of Related Art 
     In surgery of the spine, a known technique involves the use of Jamshidi needles for inserting Kirschner wires (K-wires), which may be used for the placement of bone anchors such as pedicle screws. According to the known method, first, a small incision is made in the skin of the patient. After that, a Jamshidi needle including a tiny awl is advanced through the incision to the bone. A bore is prepared by hammering and turning the Jamshidi needle back and forth and then the awl is removed. Subsequently, a K-wire is placed into the hole and the Jamshidi needle is removed. A thread cutter is guided by the K-wire to the hole, and a thread is cut with the thread cutter. After cutting the thread, the thread cutter is screwed back. Finally, a cannulated bone screw is guided by the K-wire to, and screwed into, the threaded hole. As a last step, the K-wire is removed. In total, these steps require the use of several instruments and several instrument passes and may be time consuming, especially in cases where many threaded bores have to be prepared. 
     A bone anchor insertion device for holding and inserting a bone anchor into the bone, in particular for use with a pedicle screw, is known, for example, from U.S. Pat. No. 10,105,165 B2. The bone anchor insertion device includes a holding member with a seat for holding the head of the bone anchor, the holding member having two arms that are configured to encompass the head of the bone anchor, and a drive shaft for engaging the head of the bone anchor to screw the bone anchor into bone, and a displacement member acting onto the holding member such that the holding member can assume a first configuration in which the head can enter the seat and a second configuration in which the head is held in the seat and the shank of the bone anchor can be screwed into bone. 
     U.S. Pat. No. 10,433,883 B2 describes surgical instruments for delivering bone anchor assemblies into bone. Use of these assemblies can eliminate one or more of the steps in a conventional bone anchor installation procedure. The surgical instrument includes a handle assembly having an elongate shaft extending distally therefrom. The handle assembly can be configured to axially translate a carrier assembly that secures a stylet extending therethrough. Translation of the stylet can be made relative to a distal end of the elongate shaft. 
     SUMMARY 
     It is an object of the invention to provide an improved instrument that allows a number of surgical steps to be reduced and that makes certain surgical steps more efficient. 
     According to a first aspect of the invention, an instrument for use in surgery, in particular, in connection with a bone anchor insertion device, includes a hollow shaft configured to connect to the drive shaft of a bone anchor insertion device, a needle holder configured to receive a needle and to be translated with respect to the hollow shaft, an actuator rotatable with respect to the hollow shaft, and a transmission member configured to be coupled to the needle holder and to convert a rotational movement of the actuator to a translational movement of the needle holder to advance and retract the needle. The transmission member has a first advancement structure that is configured to engage a second advancement structure provided at the hollow shaft for effecting the translational movement of the needle holder. 
     The term needle as used herein includes any elongate member that may extend through a cannulated shank of a bone anchor such as, for example, a Jamshidi needle, an awl, a stylet, a needle of a syringe, and others. 
     With the instrument, the needle can remain at a fixed position during insertion of the shank of the bone anchor in bone. A needle of a fixed length may be used together with bone anchors with different shank lengths. The length of the shank of the bone anchor used with the instrument can be set on a first scale and displayed on the instrument. Moreover, the length of the needle portion that protrudes out of the tip of the shank can be adjusted and displayed on a second scale on the instrument. Hence, an adjustment of the needle position can be carried out easily and safely. 
     The position of the tip of the needle in the axial direction relative to the tip of the bone anchor can be adjusted in a stepless manner or incrementally. The travel path of the needle may be around 50 mm to 70 mm. Once a position of the needle has been adjusted, this position can be maintained and the shank of the bone anchor can be screwed into the bone. Removal and/or exchange of the needle, if necessary, can be carried out in a simple and time efficient manner. It may also be possible to use the instrument with needles of different type and/or with needles of different length. 
     The instrument is compact. A cavity formed in the handle portion that drives the drive shaft of the shank inserter is used for housing the needle advancement mechanism and defines a path of translation of the needle holder. 
     The instrument may be coupled to any bone insertion device, which also may be called a shank inserter, and which includes a drive shaft to engage and rotate a bone anchor with a threaded shank into bone. Such a shank inserter may have a standard coupling at the rear end of the drive shaft, for example, a ¼ inch square connection portion, that can be coupled to the instrument via a standard coupling used for ¼ inch connection portions. Hence, the instrument can form a part of a modular system and can preferably be selectively coupled to different shank inserters. Moreover, the instrument may be used together with an adapter carrying a navigation instrument for computer aided imaging and/or navigation or robotics. 
     With the instrument according to embodiments of the invention, various techniques for anchoring a bone anchor in bone may be realized. In particular the instrument may be used in minimally invasive surgery (MIS), and preferably using bone anchors with a self-cutting thread. 
     An embodiment of a method of use includes at least the steps of connecting the instrument to a drive shaft of another instrument for inserting a bone anchor into bone before or after connecting a cannulated bone anchor to the drive shaft, inserting a needle into the instrument and fixing the needle, translating the needle via the actuator such that a tip of the needle extends out of the tip of the bone anchor to a desired distance, inserting the needle into bone, preferably further translating the needle relative to the bone anchor to a desired depth, and inserting the bone anchor along the needle by rotating the handle portion. Afterwards, the needle may be removed from the bone anchor before removing the shank inserter with the instrument, or simultaneously therewith. The method may further include a step of setting the shank length of the bone anchor used on a first scale and adjusting the length of the needle that protrudes out of the bone anchor on a second scale. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further features and advantages of the invention will become apparent from the description of embodiments by means of the accompanying drawings. In the drawings: 
         FIG.  1    shows a perspective exploded view of an embodiment of the instrument, a shank inserter, and a bone anchor attached to the shank inserter. 
         FIG.  2    shows a perspective view of the instrument and the shank inserter of  FIG.  1    in an assembled state. 
         FIG.  3    shows a perspective view of the instrument and the shank inserter of  FIGS.  1  and  2    with the bone anchor, prior to insertion of the bone anchor in a vertebra. 
         FIG.  4    shows a perspective exploded view of the instrument shown in  FIGS.  1  to  3   . 
         FIG.  5    shows a perspective view of the instrument of  FIG.  4    in an assembled state. 
         FIG.  6    shows a cross-sectional view of the instrument of  FIGS.  4  and  5   , with a needle inserted therein, the cross-section taken in a plane including an axis of rotation of a handle portion and an actuator of the instrument, wherein a needle holder is in an intermediate position. 
         FIG.  7    shows a cross-sectional view of the instrument of  FIGS.  4  to  6    without the needle, and wherein the needle holder is in a retracted or rearmost position. 
         FIG.  8    shows a cross-sectional view of the instrument of  FIGS.  4  to  7   , wherein the needle holder is in an advanced or foremost position. 
         FIG.  9    shows a perspective view from a front end of a hollow shaft that is part of the instrument of  FIGS.  4  to  8   . 
         FIG.  10    shows a perspective view from a rear end of the hollow shaft of  FIG.  9   . 
         FIG.  11    shows a cross-sectional view of the hollow shaft of  FIGS.  9  and  10   , the cross-section taken in a plane including a central longitudinal axis of the hollow shaft. 
         FIG.  12    shows an enlarged perspective view from a rear end of a needle to be used with the instrument of  FIGS.  4  to  8   . 
         FIG.  13    shows a perspective exploded view of the needle holder of the instrument of  FIGS.  4  to  8   . 
         FIG.  14    shows a perspective exploded view of the actuator of the instrument of  FIGS.  4  to  8    for actuating the movement of the needle holder. 
         FIG.  15    shows a perspective exploded view of a transmission member of the instrument of  FIGS.  4  to  8    for transmitting the movement of the actuator to the needle holder, and of a needle position indication device in the form of a ring. 
         FIG.  16    shows a perspective view from a front end of the handle portion of the instrument of  FIGS.  4  to  8   . 
         FIG.  17    shows a perspective view from a rear end of the handle portion of  FIG.  16   . 
         FIG.  18    shows a rear view of the handle portion of  FIGS.  16  and  17   . 
         FIG.  19    shows a cross-sectional view of the handle portion of  FIGS.  16  to  18   , the cross-section taken in a plane including an axis of rotation of the handle portion. 
         FIG.  20    shows a perspective view from a top of a shank length and needle position indication device of the instrument of  FIGS.  14  to  18   . 
         FIG.  21    shows a perspective view from a bottom of the shank length and needle position indication device of  FIG.  20   . 
         FIG.  22    shows another perspective view from the top of the shank length and needle position indication device of  FIGS.  20  and  21   . 
         FIGS.  23   a  to  23   d    show schematic views of steps for using the instrument together with a shank inserter, a bone anchor, and a needle. 
         FIG.  24    shows a perspective view of a second embodiment of a surgical instrument which includes the instrument of  FIGS.  1  to  23     d.    
         FIG.  25    shows a perspective exploded view of another embodiment of a needle holder and a needle. 
         FIG.  26    shows a perspective view of the needle holder and the needle of  FIG.  25    in an assembled state. 
         FIG.  27    shows a cross sectional view of the needle holder and the needle of  FIGS.  25  and  26   , with the needle inserted in the needle holder, the cross-section taken in a plane including a longitudinal axis of the needle. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIGS.  1  to  3   , an instrument  100  is configured to be used with a surgical instrument, such as a shank inserter  10 , that is adapted to insert a bone anchor  1  into bone. The bone anchor  1  usually has a threaded shank  2  with a tip  3  and may also have a head (not shown) at the end of the shank  2  opposite the tip  3 . For example, the bone anchor may be part of a polyaxial bone anchoring device, wherein the head of the bone anchor is held in a receiving part  1   a . A needle  4  may be used to place the bone anchor  1  at the desired position on the bone surface and to prepare a tiny hole in the bone that defines the insertion path for the bone anchor  1 . For this purpose, the bone anchor  1  may be cannulated so that the needle  4  can extend through the bone anchor  1  from the head to the tip  3 . The shank inserter  10  may be any known bone anchor insertion device. Such a shank inserter  10  is configured to engage the bone anchor  1 , usually at the head, with a front end of a drive shaft (not shown in detail), so that torque can be transmitted via the drive shaft to the shank  2  to screw the shank  2  into the bone. The drive shaft may have a connection portion, for example, with a polygon outer contour or a square end such as a ¼ inch connection, at its rear end that is shaped and sized to permit quick connection to and release from other instrument parts, such as a T-handle  11  or another type of handle or adapters. A gripping portion  12 , such as a thickened portion with axial grooves, may also be provided for the shank inserter  10 . To allow the use of the needle  4 , the drive shaft is cannulated. This permits the needle  4  to extend completely through the drive shaft and through the bone anchor  1 . It shall be noted that the shank inserter may also include only a drive shaft, without other holding or counter holding features that engage the bone anchor. 
     Referring further to  FIGS.  4  to  6   , the instrument  100  can be coupled via a coupling portion  15  to the shank inserter  10 , and more specifically, to the drive shaft of the shank inserter  10 . The coupling portion may optionally be part of the instrument. The instrument  100  includes a hollow shaft  20  that is configured to be connected via the coupling portion  15  to the drive shaft of the shank inserter  10 , and that is further configured to be connected to a handle portion  30 . The handle portion  30  can be rotated by a user, whereby the torque is transmitted to the hollow shaft  20  and the drive shaft of the shank inserter  10 . A fixation member  40  may be used to connect the hollow shaft  20  with the handle portion  30  in a rotationally and translationally fixed manner. Moreover, the hollow shaft  20  is housed at least partially in a cavity of the handle portion  30 . A needle holder  50  is adapted to be arranged in the hollow shaft  20 . The needle holder  50  can be translated within the hollow shaft  20  via an actuating mechanism to permit a tip  6  of the needle  4  to be advanced and retracted relative to the tip  3  of the shank  2  of the bone anchor  1 . 
     The actuating mechanism includes an actuator  60  and a transmission member  70 . The actuator  60  is rotatable relative to the hollow shaft  20  and the drive shaft of the shank inserter  10 . The transmission member  70  is guided by the actuator  60  in a manner such that when the actuator  60  is rotated, the transmission member  70  follows the rotational movement of the actuator and, at the same time, advances axially relative to the hollow shaft  20 . In addition, the transmission member  70  is connected to the needle holder  50  in a manner such that the needle holder  50  follows the axial advancement of the transmission member  70 . Thus, the transmission member  70  is configured to convert a rotational movement of the actuator  60  into a translational movement of the needle holder  50 . By means of this, the needle  4  can be advanced and retracted relative to the bone anchor  1  independently from a position of the bone anchor  1 . An axis of rotation R of the instrument  100 , which is also a central longitudinal axis of the instrument, is coaxial with the axis of rotation of the shank inserter  10  and the screw axis of the bone anchor  1 . 
     The parts of the instrument  100  will now be explained in greater detail. Referring additionally to  FIGS.  9  to  11   , the hollow shaft  20  is an elongate, substantially cylindrical part which has a front end  20   a  and a rear end  20   b . The front end  20   a  faces towards the shank inserter  10  when the instrument is mounted to the shank inserter. Moreover, the hollow shaft  20  defines a channel extending through the hollow shaft from the front end to the rear end, such that the needle  4  can extend fully therethrough. The channel has various sections described hereinafter. Adjacent to the front end  20   a , there is a connection portion  21  for connecting the hollow shaft  20  to the coupling portion  15 . The connection portion includes, at the front end  20   a , a hollow cylindrical section  21   a  with an outer diameter such that the cylindrical section  21   a  is configured to be received in the coupling portion  15 , and with an inner diameter sized to receive a portion of the drive shaft. Adjacent to the cylindrical section  21   a , there is a section  21   b  with a greater outer diameter so that a step  21   c  is formed therebetween. The step  21   c  may serve as an abutment for a spring of the connection portion  15  (see  FIGS.  6  to  8   ). Another abutment for an end surface of the coupling portion  15  may be formed by a small outwardly extending annular protrusion  21   d  adjacent to the front end  20   a . The section  21   b  has, close to the step  21   c , several equidistantly distributed circumferential compartments  22  for engagement members, such as balls  18 , that are configured to engage a groove of the drive shaft to hold an axial position of the drive shaft while allowing rotation of the drive shaft. At a side of the compartments  22  positioned closer to the rear end  20   b , a receiving section  23  for receiving the connection portion of the drive shaft is formed, that has an inner contour matching the outer contour of the connection section, to provide a form-fit connection between the drive shaft and the hollow shaft  20 . Preferably, the receiving section  23  has a standard connection contour, such as a quarter inch female square contour. At a distance from the step  21   c , a circumferential flange or annular projection  24  may be provided that is configured to cooperate with a portion of the actuator  60 . A plurality of axial grooves  24   a  are equidistantly formed in the outer surface of the projection  24 , which are adapted to be engaged by balls of the actuator  60 . Adjacent to the receiving section  23  towards the rear end  20   b , a narrowed section  25  of the channel may have a width that is only slightly greater than an outer diameter of the needle  4 . This may provide guidance for the needle  4  once the needle extends through the hollow shaft  20 . 
     The channel then widens towards the rear end  20   b  into a needle holder receiving section  26 , which serves for receiving the needle holder  50  therein. The needle holder receiving section  26  has a length such that the needle holder  50  can move therein in an axial direction along a defined length. At least one, preferably four, axially elongate slots  27  that are closed at both ends are formed in the wall of the hollow shaft  20  equidistantly in the circumferential direction. The slots  27  permit pins  73  to extend therethrough for holding the needle holder  50 , as described in greater detail below. When the pins  73  abut against or are close to the rear end of the slots  27  that are located closer to the rear end  20   b  of the hollow shaft  20 , respectively, the needle holder  50  is in a rearmost position ( FIG.  7   ). When the pins  73  abut against or are close to the opposite front end of the slots  27 , respectively, the needle holder  50  is at a foremost position ( FIG.  8   ). 
     Between the annular projection  24  and a position at a distance from the rear end  20   b , the outer surface of the hollow shaft  20  includes an advancement structure, which in this embodiment is a thread  200 . The thread  200  is configured to cooperate with an advancement structure provided on the transmission member  70  to facilitate an axial advancement of the transmission member  70  along the outer surface of the hollow shaft  20 . The outer diameter of this threaded section of the hollow shaft  20  may be smaller than that of the annular projection  24 . The type of thread depends on the application and the desired dependency between the action of the actuator  60  and the advancement of the needle holder  50 . Thus, the pitch, the threadform, and the number of thread entries may be selected accordingly. A multiple thread may be used for obtaining a greater advancement of the needle. In the embodiment, a thread with three entries is used. However, a single thread, a double thread, or any other multiple thread may also be applied. 
     Adjacent to the rear end  20   b , a reduced outer diameter section  28  with an external thread is formed that is configured to cooperate with an internal thread in a bore of the fixation member  40  ( FIGS.  4  and  6  to  8   ). In addition, a plurality, more specifically four, axial slots  29  extend through the end portion with the outer thread. Thereby, posts  280  are formed that are configured to extend through corresponding recesses in the handle portion  30  to provide a form-fit connection between the hollow shaft  20  and the handle portion  30 . In this manner, rotation of the hollow shaft  20  relative to the handle portion  30  is prevented when the fixation member  40  is screwed onto the posts  280  of the hollow shaft  20 . It shall be noted that other rotation preventing structures between the hollow shaft  20  and the handle portion  30  may also be envisaged. 
     In the following, the coupling portion  15  which couples the hollow shaft  20  to the drive shaft will be described in greater detail. The coupling portion  15  is exemplary and any outer suitable coupling can also be used. As best seen in  FIGS.  4  to  8   , the coupling portion  15  is a sleeve-like part and is configured to receive a portion of the hollow shaft  20  therein. The coupling portion  15  has a front section  16  adjacent to a front end  15   a  and a rear section  17  adjacent to a rear end  15   b . The rear section  17  has an inner diameter such that the rear section fits tightly around the lager diameter section  21   b  of the hollow shaft and an outer diameter that allows the rear section  17  to protrude into a portion of the actuator  60 . The front section  16  extends around the cylindrical section  21   a  of the hollow shaft  20 . Moreover, the front section  16  is flexible, for example, by means of axial slits  16   a , as best seen in  FIG.  5   , that are open to the front end  15   a . The slits  16   a  and an inner annular projection  16   b  at the front end enable the front section  16  of the coupling portion  15  to be snapped over the portion  21   a  of the hollow shaft  20  and to abut against the annular projection  21   d  adjacent to the front end  20   a  of the hollow shaft  20 . In the front section  16 , a compartment is formed in which a helical spring  19  is accommodated. The helical spring  19  extends around the portion  21   a  of the hollow shaft  20  and abuts against the step  21   c . By means of this, the hollow shaft  20  is biased against the annular projection  16   b  of the coupling portion  15 , so that the two parts are firmly connected. At a distance from the front end  15   a , the balls  18  are placed into the compartments  22  of the hollow shaft  20  and extend radially inwardly to some extent to permit rotation of the hollow shaft  20 . 
     Referring to  FIGS.  12  and  13   , the needle  4  and the needle holder  50  will now be described in greater detail. As depicted in  FIG.  12   , the needle  4  includes a thin rod portion  5  with a tip  6  at its front end. The tip  6  preferably is a sharp tip that is suitable for forming a hole in bone. At the side opposite to the tip  6 , a holding portion is provided that includes a cylindrical front portion  7 , an intermediate thicker portion  8 , and a head portion  9  at a rear end  4   b . Preferably, the rod portion  5  and the holding portion are separate parts. A rear end  5   b  ( FIG.  6   ) of the rod portion  5  may be mounted to the cylindrical front portion  7  of the holding portion, for example, press-fit into a bore of the cylindrical front portion  7 , so that between the rod portion  5  and the cylindrical front portion  7 , a small shoulder  7   a  is formed. At the outer surface of the intermediate portion  8 , two projections  8   a , preferably cylindrical projections, extend outward in opposite directions. The projections  8   a  serve for mounting the needle  4  to the needle holder  50 . The head portion  9  has an engagement portion  9   a  for a tool at its free end. With the tool, such as a driver, the needle  4  can be pushed and rotated to mount and release the needle from the needle holder  50 . It shall be noted that the needle can be any suitable needle, such as a Jamshidi needle or a needle having a special tip, such as a tip provided with a sensor. 
     As shown in  FIGS.  6  to  8  and  13   , The needle holder  50  is a substantially cylindrical part with a front end  50   a  and a rear end  50   b . The needle holder defines a channel extending completely through the needle holder from the front end  50   a  to the rear end  50   b , such that the tip  6  of the needle  4  can be inserted from the rear end  50   b  and can extend with the rod portion  5  all the way through the needle holder  50 . Adjacent to the front end  50   a , the channel has a front section  51  with an inner diameter large enough to guide the rod portion  5  of the needle  4  therethrough and to further house a biasing member for holding the needle in the needle holder. At a distance from the front end  50   a , four threaded radially extending through holes  52  are formed equidistantly in the circumferential direction in the wall of the needle holder  50 . The through holes  52  are configured to receive the connection pins  73  (see also  FIGS.  4  and  6  to  8   ) therein to connect the transmission member  70  to the needle holder  50 . Each connection pin  73  has a threaded front portion  73   a  that is configured to engage a corresponding one of the threaded holes  52  in the needle holder  50 . Opposite to the front portion  73   a , the connection pins  73  have a rear end  73   b  with an engagement structure, such as a slit or a polygonal recess, for screwing in the pin. The threaded front portion  73   a  has a smaller outer diameter than the remaining pin, and a length such that the connection pin  73  can be inserted into the needle holder  50  only to a depth such that the needle  4  inside the needle holder is not touched by the connection pins  73 . To limit the insertion, a counterbore  52   a  at the entrance of the threaded through hole  52  may be provided against which a portion of the pin  73  abuts. Adjacent to the rear end  50   b , a rear section  53  for the intermediate portion  8  of the needle  4  is provided. In the front portion  51  of the channel, a helical spring  55  is housed between a washer  56  that is fixed to the front end  50   a  and configured to permit the rod portion  5  of the needle to pass therethrough and a movable washer  57  against which the shoulder  7   a  of the needle  4  is configured to abut. 
     At the rear end  50   b , two axially extending recesses  58  that are offset by 180° from each other are formed in the wall of the needle holder  50 , that permit the projections  8   a  of the intermediate portion  8  of the needle  4  to be guided therethrough when the needle  4  is inserted. At a distance from the rear end  50   b , the recesses  58  continue into end portions  59  which extend in the circumferential direction, and thus are transverse to the axial portion of recesses  58 . The end portions  59  extend circumferentially in a same rotational direction, so that when the projections  8   a  of the needle  4  reach the end portions during insertion of the needle, rotation in one direction moves the projections into the end portions  59  of the recesses  58 , respectively, and rotation in the other direction moves the projections out of the end portions. 
     Referring to  FIGS.  14  and  4    as well as  FIGS.  6  to  8   , the actuator  60  will be described. The actuator  60  includes a sleeve-shaped actuator wheel  61  that has a front end  61   a  and a rear end  61   b , wherein in the mounted state, the front end  61   a  faces the connection portion  15 . At the front end  61   a , a coaxial recess  62  may be formed that is configured to receive a portion of the rear end  17  of the connection portion  15 . Following the recess  62 , the inner diameter of the sleeve is such that the annular projection  24  of the hollow shaft  20  fits therein and abuts in the axial direction against a step  62   a . Between the step  62   a  and the rear end  61   b , the inner diameter of the sleeve is such that the threaded portion of the hollow shaft  20  can pass and extend therethrough. In the free end surface of the rear end  61   b , a plurality, in the embodiment four, equidistantly arranged circumferentially extending slits  63  are formed that serve for receiving portions of an actuator tube  64  therein, for example, in a press-fit manner. The slits  63  may have enlarged end portions on both ends, respectively, for facilitating mounting of the actuator tube  64 . The outer surface of the actuator wheel  61  includes a gripping structure  65  which may include axially extending depressions or grooves that facilitate gripping and rotating the actuator wheel  61 . 
     The actuator tube  64  has a front end  64   a  and a rear end  64   b , and a plurality of axially extending slits  66 , in the embodiment four slits. The slits  66  are open towards the front end  64   a  and closed towards the rear end  64   b , so that four tube sections  67  are formed. The tube sections  67  are mounted with the front end  64   a  into the recesses  63  of the actuator wheel  61 . Thereby, the actuator tube  64  protrudes from the rear end  61   b  of the actuator wheel  61 , with a smaller diameter compared to that of the actuator wheel. The length of the actuator tube  64  is such that in the mounted state, the rear end  64   b  of the actuator tube extends up to a small distance from the rear wall of the handle portion  30 . When the actuator is mounted to the hollow shaft  20 , the mounting pins  75  that connect the ring  76  with the transmission member  70  can extend through the slits  66 , respectively. 
     The actuator  60  may be mounted to the hollow shaft  20  via a spring biased rotatable connection. As shown in particular in  FIGS.  4  and  6   , at an axial position corresponding to the position of the annular protrusion  24  of the hollow shaft  20 , the actuator wheel  61  defines a plurality of equidistantly arranged threaded through holes  68 , in the embodiment three through holes. Balls  69  are arranged in the through holes  68  and are pressed via helical springs  600  by the action of set screws  601  against the surface of the protrusion  24  of the hollow shaft  20 . The grooves  24  a provide resting positions that can be engaged by the balls  69  incrementally when rotating the actuator wheel  61 . In other words, when rotating the actuator wheel  61 , the balls  69  can move out of each of the grooves  24   a  and snap into circumferentially neighboring grooves  24   a . Thus, a haptic feedback may be given to a user when the actuator wheel is rotated. The actuator wheel  61  is prevented from axial movement since the actuator wheel is connected via the actuator tube  64  to the transmission member  70  and the needle holder  50 . 
     The transmission member is shown in greater detail in  FIG.  15   . The transmission member  70  is a sleeve-like part with a front end  70   a  and a rear end  70   b . An internal thread  71  configured to cooperate with the external thread  200  on the hollow shaft  20  is formed on the inner wall of the sleeve to allow the transmission member  70  to move back and forth on the hollow shaft  20  in the axial direction. The advancement structure in the form of the thread  71  on the transmission member  70  and the advancement structure in the form of the thread  200  on the hollow shaft  20  may be configured such that the distance per revolution which the transmission member  70  moves axially corresponds to the distance the shank  2  is advanced per revolution of the drive shaft. 
     The transmission member  70  is connected to the needle holder  50  via the connection pins  73  as shown in  FIGS.  6  to  8   , so that when the transmission member  70  moves along the hollow shaft  20  in the axial direction, the needle holder  50  within the hollow shaft  20  moves together with the transmission member  70  in the axial direction. The connection pins  73 , in the embodiment four pins, extend radially through the slots  27  of the hollow shaft  20 , respectively. The rear ends  73   b  of the connection pins extend into a circumferential groove  72  formed in the inner wall of the transmission member  70 . Thus, when the transmission member  70  advances along the threaded hollow shaft  20 , the rear ends  73   b  of the connection pins  73  can rotate in the groove  72  of the transmission member  70 . The pins  73  can be inserted through a mounting hole  79  that extends through the transmission member into the groove  72 . 
     At an axial position between the rear end  70   b  and the groove  72 , a plurality, in the embodiment four, equidistantly arranged threaded through holes  74  are formed that serve for receiving mounting pins  75  for mounting a needle position indication device in the form of a ring or sleeve  76  to the transmission member  70 . The ring  76  has substantially the same axial length and an inner diameter that permits mounting around the tube portion  64  of the actuator  60 . The inner wall of the ring  76  is threadless, so that the ring  76  can slide along the tube portion  64 . At positions corresponding to the threaded through holes  74  in the transmission member  70 , the ring  76  defines unthreaded holes  77  which permit only a threaded front portion  75   a  of the mounting pins  75  to extend therethrough and engage the threaded holes  74  of the transmission member  70 . It shall be noted that the ring  76  is thinner in the radial direction compared to the transmission member  70 , since the ring  76  has to fit into the space between the actuator and the handle portion in the radial direction. In the outer surface of the ring  76 , a circumferential indication mark  78  is provided which may be, for example, a groove, that may be provided with a coloring and/or a colored ring. Hence, when the transmission member  70  moves, the ring  76  with the indication mark  78  moves in the same way, for example, a same axial distance. Therefore, the indication mark  78  is configured to display the axial position of the needle holder  50 , and therefore the axial position of the tip  6  of the needle relative to the tip  3  of the bone anchor  1 . For this purpose, there is a window in the handle portion  30 , as explained in greater detail below. 
     Turning now in addition to  FIGS.  16  to  19   , the handle portion  30  will be described in greater detail. The handle portion  30  may be an elongate, substantially cylindrical part that has a front end  30   a  and a rear end  30   b . An outer surface portion  31  that extends from a position close to the rear end  30   b  to a distance from the front end  30   a  includes a gripping structure such as, for example, axial grooves. Between the outer surface portion  31  with the gripping structure and the front end  30   a , the outer diameter of the handle portion may include a tapered portion  33  that tapers and narrows towards the front end  30   a , so that the outer diameter of the handle portion  30  close to the actuator wheel  61  is smaller or has the same size as that of the actuator wheel  61 . The handle portion  30  further defines an elongate passage in the form of a cylindrical bore  32  extending from the front end  30   a  to a distance from the rear end  30   b . The diameter of the bore  32  is such that, in the radial direction, the hollow shaft  20 , the actuator tube  64 , the transmission member  70  and the ring  76  can extend therein. 
     Adjacent to the rear end  30   b , a cylindrical recess  34  with a bottom  34   a  is formed that is sized to receive a portion of the fixation member  40  (see  FIGS.  6  to  8   ). A coaxial opening  35  with a reduced inner diameter compared to the diameter of the bore  32  is provided in the bottom  34   a  of the recess  34 . The opening  35  has four rounded side recesses  35   a  offset from each other by 90° that are configured to receive the posts  280  of the hollow shaft  20 , in order to connect the hollow shaft  20  and the handle portion  30  to each other in a rotationally secured manner. The posts  280  can pass through the side recesses  35   a , respectively, so that free ends of the projections  280  project out therefrom. 
     In addition, a window  36  is provided in the handle portion  30  that exposes a portion of the inside of the handle portion. More specifically, the window  36  exposes at least a portion of the ring  76  with the marking  78 . Thus, the marking  78  that is indicative of the position of the needle holder  50  can be used for adjusting the position of the needle holder  50 , and thus the position of the needle  4 . The window  36  may have a rectangular shape with rounded edges, with a length that is greater than a difference between lengths of the longest and the shortest shanks of bone anchors that can be used, plus the length that the needle  4  is allowed to move. A groove  38  is formed in the wall of the handle portion  30  for receiving a shank length indication device in the form of a slide  90  that is configured to indicate the possible travel path of the needle holder  50  and which serves for setting a shank length of the bone anchor that is actually being used. The groove  38  has a substantially rectangular contour and a flat bottom. At the tapered portion  33  of the handle  30 , the height of outer wall of the groove decreases towards the front end  30   a , such that a portion of the bottom is free which permits the slide  90  to enter the groove  38  easily. Inside the groove  38  there are protrusions  38   b  along at least a portion of the length of the window for cooperating with the slide  90 . At the outer wall of the handle portion  30 , around the window  36 , are markings  39  that are configured to indicate the length of the shank of the bone anchor that is being used. In the embodiment, the length is indicated in increments wherein, for example, even numbers are indicated at one side of the window and odd numbers are indicated at the opposite side of the window. For example, if the smallest length of a shank that can be used is 35 mm and a greatest length of a shank that can be used is 60 mm, the even numbers between 40 mm and 60 mm with an increment of 10 mm are indicated on one side of the window  36  and the odd numbers between 35 mm and 55 mm are indicated on the opposite side of the window. The markings  39  are arranged such that the smallest length is displayed closer to the rear end  30   b  of the handle portion  30 , and the displayed lengths increase towards the front end  30   a.    
     As shown in  FIGS.  20  to  22   , the slide  90  includes a substantially rectangular flat plate that is configured to be slid into the groove  38  and that can be moved therein in an axial direction, i.e., along a length axis of the plate that is parallel to the longitudinal axis of the handle portion  30 . The slide  90  has a front end  90   a  and a rear end  90   b , wherein the front end is positioned closer to the actuator wheel  61  in the assembled state when the slide  90  is in the groove  38 . A longitudinal slot  91  is formed in the middle of the slide in the transverse direction which may extend almost along the whole length of the slide  90 . The slot  91  is configured to display a portion of the actuator tube  64  and the ring  76  with the marking  78  that are visible through the window  36  of the handle portion  30 . Hence the slide also forms a needle position indication device. A countersink  92  around the slot  91  may improve the visibility of the ring  76  and may carry markings. On the upper side of the slide that faces outward, a plurality of elongate gripping protrusions  93  may be formed that may be arranged along both long sides of slot  91  to allow gripping of the slide  90  and sliding of the slide in the groove  38 . 
     On the surface of the countersink  92 , markings are provided that can be aligned with the markings  39  on the handle portion  30  when the slide  90  is moved. In greater detail, close to the rear end  90   b , a first type of marking  94   b  may be provided that is configured to be aligned with one of the markings  39  around the window  36  that indicate possible shank lengths. The first type of marking can be, for example, two arrows pointing to the center of the slot  91  in the circumferential direction of the handle portion  30 , such that, when the slide  90  is at a position in which the two arrows are aligned with a marking  39  on the handle portion  30 , the marking  94   b  indicates the length of a shank of an inserted bone anchor  1 . This first type of marking  94   b  may have a color, for example, green. Moreover, a second type of marking  94   a  may be provided close to the front end  90   a  of the slide  90 . This second type of marking  94   a  may indicate the maximum admissible projection of the needle  4  out of the shank  2 . In other words, the second type of marking indicates the maximum admissible or desirable travel path of the needle holder  50  to ensure the maximum admissible projection of the needle. The marking  94   a  may also include two arrows that point with their tips towards each other. A color of the second type of marking may be red, for example, to indicate the limit of the admissible advancement of the needle  4 . In between the first and the second type of markings, there may be a third type of marking  94   c  that may include equidistantly spaced apart dashes and/or dots on each side of the slot  91 , wherein the markings  94   c  are offset from each other on one side relative to the other side. The markings  94   c  may indicate the advancement of the needle in increments. 
     Generally, the markings  39  on the handle portion  30  provide a first scale indicative of possible lengths of the shank of a bone anchor  1 , while the markings on the slide  90  provide a second scale indicative of the possible positions of the tip  6  of the needle with respect to the tip of the bone anchor  1 . Lastly, the slide  90  defines on each of the long sides, at approximately the middle of the long sides, recesses, for example, two V-shaped recesses  95  in the outer edge of the slide. The recesses  95  are configured to cooperate with the protrusions  38   b  inside the groove  38 . Thereby, the adjustment of the markings on the slide  90  relative to the markings  39  on the handle portion  30  may be more easily facilitated, and the slide may be held at specific positions. 
     As further depicted in  FIGS.  6  to  8   , the fixation member  40  fits at least partially in the recess  34  at the rear end  30   b  of the handle portion  30 . The fixation member defines a threaded bore  43  that is configured to be screwed onto the posts  280  of the hollow shaft  20 . On the side of the fixation member opposite the rear end  30   b  of the handle portion  30 , the fixation member defines a tool engagement recess  44  for screwing the fixation member  40  onto the posts  280  of the hollow shaft  20 . The inner space between the posts  280  of the hollow shaft  20  is such that the needle holder  50  can extend therein and the threaded bore  43  has a size such that insertion and/or removal of the needle  4  through the fixation member  40  is possible. The fixation member  40  is configured to abut against the bottom  34   a  of the recess  34  in the handle portion  30  ( FIGS.  7  and  8   ). 
     The parts and portions of the instrument and/or the bone anchor insertion device, the bone anchor, and/or the needle may be made of any material, preferably, however, of a bio-compatible material, such as titanium or stainless steel, or any other bio-compatible metal or metal alloy, or plastic material. For bio-compatible alloys, a NiTi-alloy, for example Nitinol, may be used. Other materials that can be used are, for example, Magnesium or Magnesium alloys, or bio-compatible plastic materials that can be used may be, for example, Polyether ether ketone (PEEK) or Poly-L-lactide acid (PLLA). The parts can be made of the same or of different materials from one another. For the instrument, a material that is easy to clean may be preferred. 
     The needle holder  50 , the hollow shaft  20 , the transmission member  70  with the ring  76 , the handle portion  30  with the slide  90 , and the actuator  60  are usually preassembled such that their respective front ends face in the direction of the connection portion  15 . When the needle holder  50  is placed into the hollow shaft  20 , the transmission member  70  is screwed onto the hollow shaft  20  from the rear end thereof, and the pins  73  are inserted through the mounting hole  79 , passed through the slots  27  of the hollow shaft  20  and screwed into the threaded holes  52  of the needle holder  50 . The actuator  60  is placed with the actuator wheel  61  around the hollow shaft  20  and the set screws  601  are tightened. The ring  76  is mounted around the actuator tube  64  and fixed with the mounting pins  75  to the transmission member  70 , and the actuator tube  64  is mounted to the actuator wheel  61 . After that, the hollow shaft  20  is fixed to the handle portion  30  via the fixation member  40  that is screwed onto the threaded posts  280  of the hollow shaft  20 . Tightening the fixation member  40  firmly fixes the hollow shaft  20  to the handle  30  so that rotation of the handle  30  also rotates the hollow shaft  20 . The actuator  60  remains rotatable with respect to the hollow shaft  20  and with respect to the handle portion  30 . 
     To use the instrument  100  with a shank inserter  10 , the optional coupling portion  15  is mounted to the connection portion  21  of the hollow shaft  20 . The instrument  100  preassembled in this manner can be connected to a shank inserter  10 . To accomplish this, the connection portion of the drive shaft is inserted into the connection portion  21  of the hollow shaft until the connection portion of the drive shaft is received in the receiving section  23 , so that the form-fit engagement allows transmission of torque to the drive shaft. The shank inserter may be already connected to a bone anchor  1  to be inserted into bone, or the bone anchor  1  can be fixed to the shank inserter  10  when the shank inserter has already been connected to the instrument  100 . 
     In operation, when the actuator wheel  61  is rotated, the rotational movement of the actuator tube  64  forces the transmission member  70  to travel in an axial direction via the engagement of the thread  71  of the transmission member  70  with the thread  200  of the hollow shaft  20 . Since the transmission member  70  is connected via the pins  73  to the needle holder  50 , the needle holder  50  will travel axially together with the transmission member  70 . 
     The needle  4  can be inserted and removed by means of a push and turn action as follows. When the projections  8   a  are received in the end portions  59 , the needle  4  is secured against inadvertent removal from the needle holder  50 . When the shoulder  7   a  of the holding portion of the needle  4  abuts against the washer  57 , the spring  55  urges the washer against the shoulder  7   a , so that the needle  4  as a whole is biased towards the rear end  50   b  of the needle holder  50 . Thereby, the projections  8   a  are held in the transverse end portions  59  of the axial recesses  58 . Removal of the needle  4  is effected by pushing the holding portion of the needle against the washer  57 , which frees the projections  8   a  so that they can be moved out of the transverse end portions  59  by rotating the needle in a counter or opposite direction compared to when the needle is attached to the needle holder. For example, in the embodiment, the end portions  59  extend in the counterclockwise direction when viewed from the read end  50   b , so that pushing and rotating the needle in the counterclockwise direction locks the needle  4  in the needle holder  50 , while pushing and rotating the needle in the clockwise direction releases the needle  4  from the needle holder  50 . This push and turn action allows for a quick and simple mounting and removal of the needle. The rod portion  5  of the needle may be exchanged relative to the holding portion, or the entire rod portion together with the holding portion of the needle  4  can be replaced or exchanged. 
     Referring to  FIGS.  23   a  to  23   d   , in clinical use, once a bone anchor with a specific shank length has been selected, the slide  90  is adjusted to the position in which its first type marking  94   b  is aligned with the marking  39  which corresponds to the shank length of the bone anchor. In the example shown, a bone anchor with a shank length of 60 mm has been selected, and the slide  90  has been adjusted correspondingly. 
     Once the needle  4  has been inserted and locked in the needle holder  50 , the position of the needle is adjusted with the actuator. By rotating the actuator wheel  61 , for example, in the clockwise direction, the needle  4  is advanced, and by rotating the actuator wheel, in this example, in the counterclockwise direction, the needle is retracted. During adjustment of the position of the needle  4 , the marking  78  on the ring  76  displayed through the window  36  and the slot  91  indicates the position of the tip  6  of the needle  4  relative to the tip  3  of the bone anchor  1 . 
     As shown in  FIG.  23   a   , the surgical instrument prepared in this manner is ready to insert the bone anchor  1  into bone, in the example, in a pedicle of a vertebra  500 . Next, as shown in  FIG.  23   b   , the bone anchor is placed onto the bone surface and the tip  6  of the needle  4  is hit or otherwise advanced into the bone until the needle  4  has penetrated the cortical bone. 
     Next, as depicted in  FIG.  23   c   , the handle portion  30  is held stationary and the actuator wheel  61  is rotated in the clockwise direction. Thereby, the needle  4  penetrates deeper into the bone. The distance of travel of the tip  6  of the needle can be seen by the position of the marking  78  of the ring  76  relative to the first type marking  94   b.    
     As further shown in  FIG.  23   d   , once the desired depth has been reached, the actuator wheel  61  of the actuator  60  is held stationary and the handle portion  30  is rotated in the clockwise direction to screw the bone anchor  1  over the needle  4  into the bone. Preferably, the bone anchor  1  is a self-tapping bone anchor that is configured to cut the thread into the bone by itself during rotation. 
     Finally, the shank inserter  10  can be decoupled from the bone anchor  1  together with the instrument  100  still attached to the shank inserter and with the needle  4  still extending through the entire device. Alternatively, the needle  4  can be removed first, and the shank inserter  10  can then be released from the bone anchor thereafter. 
     Since the path the needle can travel covers about a length of the shank of a usual bone anchor or more, the instrument  100  and the same needle  4  can be used in connection with different bone anchors having different lengths. The needle position can be monitored during use as it is displayed on the slide  90 . 
     Referring to  FIG.  24   , a second embodiment of the surgical instrument is shown. Identical or similar parts and portions are indicated with the same reference numerals, and the descriptions thereof will not be repeated. The shank inserter  10  and the instrument  100  are identical to the previous embodiment. However, between the shank inserter  10  and the instrument  100 , an adapter  1000  is mounted that has a rear end that is coupled to the hollow shaft  20  in the same manner as the drive shaft of the previous embodiment is coupled to the hollow shaft  20 . The adapter  1000  has a front connection portion that is connected to the shank inserter  10 . The hollow shaft  20  of the instrument  100  is coupled to an inner shaft (not shown) of the adapter member  1000 , which is also coupled to the drive shaft of the shank inserter  10 . Thus, torque can be transmitted from the handle portion  30  through the adapter member  1000  to the drive shaft of the shank inserter  10 . A secondary instrument  1010 , such as a navigation array for optical or any other navigation, can be mounted on the adapter member  1000  via a mounting sleeve  1001 . The mounting sleeve  1001  may be, for example, rotatable around the shaft of the adapter member  1000 . By means of this, while the torque is transmitted via the handle  30  to the drive shaft, the secondary instrument  1010  can be kept stationary by gripping the secondary instrument  1010  or the mounting sleeve  1001  with the other hand. Thereby, the orientation of the secondary instrument  1010  such as a navigation array can be maintained relative to the rest of the device, e.g., while the rest of the device is rotated. This may be used for surgery under fluoroscopy or with computer-based navigation assisted systems. 
     It shall be noted that instead of a navigation array, other secondary instruments can also be used via the adapter member  1000 . 
     Referring to  FIGS.  25  to  27   , a further embodiment of the needle holder and the needle is explained. Parts and portions that are identical or similar to the previous embodiments are indicated with the same reference numerals, and the descriptions thereof will not be repeated. The needle  4 ′ is connectable to the needle holder  50 ′ via a threaded connection. For this purpose, the holding portion of the needle  4 ′ has, between a cylindrical front portion  7 ′ in which the rod portion  5  is supported and a rearward head portion  9 ′, an intermediate threaded portion  8 ′ with an external thread  81 . The outer diameter of the threaded portion  8 ′ may be greater than that of the cylindrical front portion  7 ′ and smaller than that of the head portion  9 ′. 
     The needle holder  50 ′ is cylindrical, similar to the previous embodiment, and defines a coaxial channel for passing through the rod portion  5  of the needle  4 ′ and for receiving at least part of the holding portion of the needle. A front portion  51 ′ of the channel is configured to receive the cylindrical front portion  7 ′ of the needle. A rear portion  53 ′ of the channel has an internal thread  53   a ′ that is configured to cooperate with the external thread  81  of the holding portion of the needle. The rear portion  53 ′ may be located between the holes  52  for the pins  73  and the rear end  50   b . At the transition between the front portion  51 ′ and the rear portion  53 ′ of the channel, a step  51   a ′ may be formed that may serve as an abutment to limit the insertion of the needle into the needle holder  50 ′. Moreover, when the needle  4 ′ is screwed into the needle holder  50 ′, the needle  4 ′ can be tightened against the abutment. This may result in a stronger and safer connection. Between the rear end  50   b  and the rear portion  53 ′, a coaxial bore  53   b ′ may be formed, and the head portion  9 ′ may abut against the rear end  50   b . The needle holder  50 ′ may be used in the instrument instead of the needle holder  50 . 
     In use, when the needle holder  50 ′ is inserted into the hollow shaft  20 , the needle  4 ′ can be removed and/or exchanged by means of screwing the needle into and out of the needle holder. Preferably the needle holder  50 ′ is in the rearmost position when the needle  4 ′ is mounted or exchanged. The threaded connection simplifies the handling of the needle and allows for a quicker exchange of the needle. 
     Further modifications of the instrument or the parts thereof may be possible. In particular, the shapes of the various parts are not limited to the specific shapes shown in the embodiments. The instrument can also be used, for example, for inserting a syringe for injecting bone cement or other substances after or instead of a needle as shown in the embodiment. For the actuating mechanism, any suitable actuating mechanism that can convert a rotational motion of an actuator into a translational motion of the needle holder can be used. The instrument can also be used in connection with, for example, a drill instead of a shank inserter, or with other suitable surgical instruments. The instrument can also be used without a needle or with needles of different types and lengths. 
     While the present invention has been described in connection with certain exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but is instead intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims, and equivalents thereof.