Patent Publication Number: US-2021186575-A1

Title: Instrument for use with a bone anchoring device

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     The present application claims priority to and the benefit of U.S. Provisional Patent Application No. 62/949,877, filed Dec. 18, 2019, the contents of which are hereby incorporated by reference in their entirety, and claims priority from European Patent Application EP 19 217 722.8, filed Dec. 18, 2019, the contents of which are hereby incorporated by reference in their entirety. 
    
    
     BACKGROUND 
     Field 
     The application relates to an instrument for use with a bone anchoring device that includes a receiving part for connecting a bone anchoring element to a rod. The invention further relates to a system including such an instrument and a bone anchoring device. In particular, the instrument may be used to finally tighten or lock a bone anchoring element and/or a rod with respect to the bone anchoring device. 
     Description of Related Art 
     US 2006/0293666 A1 describes a counter-holding tool for use with a receiving part of a polyaxial screw. It has a grip portion, a hollow shaft and a holding portion that is configured to be placed over the receiving part. A screwing-in tool can be guided through the hollow shaft. 
     U.S. Pat. No. 10,349,986 B2 describes a surgical instrument for use with a bone fastener. The instrument includes an outer sleeve that has a drive engageable with a drive socket of the bone fastener. An inner shaft is provided within the outer sleeve and provided with a screw that can be connected to an inner thread of a receiver of the bone fastener. The inner shaft is rotatable relative to the outer sleeve. 
     SUMMARY 
     It is an object of the present invention to provide an alternative and/or improved instrument suitable for use with a bone anchoring device and a system including such an instrument and a bone anchoring device, where the instrument is easy to handle, has a reduced size, and/or can be used with different anchoring devices. 
     An instrument according to an embodiment includes a hollow tube which has at least one protruding portion at an end portion thereof that is configured to engage a recess of the receiving part adapted to accommodate the rod therein. The tube can act as a counter holder for an inner shaft, such as a shaft with a drive portion, for final tightening of a screw. Thus, a rotational movement of the tube relative to the receiving part can be inhibited. 
     As the at least one protruding portion engages the rod recess of the receiving part, an amount of space or footprint needed by the instrument may be reduced. This permits use of narrow channels through the tissue of the human body to approach the implantation site. Hence, the instrument can be particularly applicable in minimally invasive surgery (MIS). 
     Moreover, no additional structures or elements are required at an outer surface of the receiving part to prevent the tube from rotating relative to the receiving part. Hence, the structure of the receiving part and/or the tube may be simplified, when compared to the structure of a receiving part and/or tube that engages an outer surface of the receiving part. In particular, the engagement of the tube and the receiving part is implemented by means of the rod recess, which is already provided in the receiving part as an essential feature thereof. 
     In particular, the tube may be placed within a central passage of the receiving part, with only the at least one protruding portion protruding out of the central passage in a radial direction. Hence, a system including the bone anchoring device and the attached instrument as a whole is slim, which renders the combination useful for MIS. 
     The tube may in particular have an internal channel that allows the shaft of the instrument, in particular the shaft having an engagement or drive portion, to be advanced through and guided by the tube. This guidance may facilitate engagement of the shaft or an engagement portion provided at its end, such as a drive portion, with an element located within the receiving part, such as a fixation element, for example a set screw. 
     In a further embodiment, the tube is a first tube, and the instrument includes an additional second tube configured to be arranged outside at least a portion of the receiving part to encompass the respective portion of the receiving part, in particular the legs of the receiving part. Encompassing the receiving part at its outside may provide for additional support and/or guidance of the first tube. The second tube may be very thin. Such a design of reduced thickness renders the instrument more suitable for MIS. If the second tube is arranged substantially around the legs of the receiving part, splaying of the legs may be prevented. 
     When the second tube is used with a bone anchoring device that has long extensions provided at the legs of the receiving part, the second tube may be configured to substantially encompass merely the legs of the receiving part and not the long extensions. On the other hand, when used with a bone anchoring device without such long extensions, the second tube may serve for prolonging the central passage of the receiving part. 
     The second tube may be provided as a member separate from the first tube and/or separate from other portions of the instrument. For example, the second tube can be a sleeve used for various surgical steps, such as guiding parts and/or instruments to the implantation site or as a sleeve extension for a receiving part. In this case, the second tube may also have a considerably reduced thickness. At the end of the procedure, the first tube may be inserted into the second tube, and an inner shaft with a drive portion may be used for final tightening of a locking screw. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further features and advantages will become apparent from the detailed description of embodiments by means of the accompanying drawings. In the drawings: 
         FIG. 1  shows a perspective view of a part of a spinal column with a plurality of polyaxial bone anchoring devices and an instrument according to a first embodiment of the present disclosure coupled to one of the polyaxial bone anchoring devices. 
         FIG. 2  shows an exploded perspective view of the instrument of  FIG. 1 . 
         FIGS. 3 a  to 3 d    show different views of a rear portion of a tube member of the instrument of  FIGS. 1 and 2 . In particular,  FIG. 3 a    shows an upper perspective view of the rear portion,  FIG. 3 b    shows a lower perspective view of the rear portion,  FIG. 3 c    shows a cross-sectional view of the rear portion, the cross-section taken along line A-A in  FIG. 3 d   , and  FIG. 3 d    shows a plan view of the rear portion from above. 
         FIGS. 4 a  to 4 d    show different views of a front portion of the tube member of the instrument of  FIGS. 1 and 2 . In particular,  FIG. 4 a    shows an upper perspective view of the front portion,  FIG. 4 b    shows a lower perspective view of the front portion,  FIG. 4 c    shows a cross-sectional view of the front portion, the cross-section taken along line B-B in  FIG. 4 d   , and  FIG. 4 d    shows a plan view of the front portion from below. 
         FIG. 5  shows a perspective view of a polyaxial bone anchoring device according to an embodiment in an assembled state, where the polyaxial bone anchoring device is suited for use with the instrument shown in  FIGS. 1 to 4   d.    
         FIG. 6  shows an exploded perspective view of the polyaxial bone anchoring device of  FIG. 5 . 
         FIGS. 7 a  to 7 c    show perspective views of the instrument shown  FIGS. 1 to 4   d , with the spinal column and polyaxial bone anchoring devices shown in  FIGS. 1 and 2 , wherein  FIGS. 7 a  to 7 c    show a use of the instrument. 
         FIGS. 8 a  and 8 b    are enlarged views of a portion of the polyaxial bone anchoring device and the instrument shown in  FIGS. 7 b  and 7 c   , to show steps of coupling the instrument to the polyaxial bone anchoring device in greater detail. 
         FIGS. 9 a  to 9 c    show cross-sectional views of a portion of the polyaxial bone anchoring device and the instrument shown in  FIGS. 7 b    and  7   c.    
         FIG. 10  shows a perspective view of a part of a spinal column with a plurality of polyaxial bone anchoring devices and an instrument according to a second embodiment of the present disclosure coupled to one of the polyaxial bone anchoring devices. 
         FIG. 11  shows an exploded perspective view of the instrument of  FIG. 10 . 
         FIGS. 12 a  to 12 d    show different views of a rear portion of an inner tube of the instrument of  FIGS. 10 and 11 . In particular,  FIG. 12 a    shows an upper perspective view of the rear portion,  FIG. 12 b    shows a lower perspective view of the rear portion,  FIG. 12 c    shows a cross-sectional view of the rear portion, the cross-section taken along line C-C in  FIG. 12 d   , and  FIG. 12 d    shows a plan view of the rear portion from above. 
         FIGS. 13 a  to 13 c    show different views of a front portion of the inner tube of the instrument of  FIGS. 10 and 11 . In particular,  FIG. 13 a    shows an upper perspective view of the front portion,  FIG. 13 b    shows a lower perspective view of the front portion, and  FIG. 13 c    shows a cross-sectional view of the front portion, the cross-section taken in a plane including a longitudinal axis of the inner tube. 
         FIG. 14  shows a side view of an outer tube of the instrument of  FIGS. 10 and 11 . 
         FIGS. 15 a  to 15 c    show different views of an upper portion of the outer tube of  FIG. 14  and of a snap ring and a pin of the instrument shown in  FIGS. 10 and 11 . In particular,  FIG. 15 a    shows an upper perspective view of the upper portion, the snap ring, and the pin,  FIG. 15 b    shows a lower perspective view of the upper portion, the snap ring, and the pin, and  FIG. 15 c    shows a cross-sectional view of the upper portion, the snap ring, and the pin, the cross-section taken in a plane including a longitudinal axis of the outer tube in a state where the snap ring and the pin are coupled to the outer tube. 
         FIGS. 16 a  to 16 d    show different views of a lower portion of the outer tube of  FIG. 14 . In particular,  FIG. 16 a    shows an upper perspective view of the lower portion,  FIG. 16 b    shows a lower perspective view of the lower portion,  FIG. 16 c    shows a cross-sectional view of the lower portion, the cross-section taken along line D-D in  FIG. 16 d   , and  FIG. 16 d    shows a plan view of the lower portion from below. 
         FIG. 17  shows a perspective view of a polyaxial bone anchoring device according to a further embodiment in an assembled state, where the polyaxial bone anchoring device is suited for use with the instrument shown in  FIGS. 10 to 16   d.    
         FIG. 18  shows an exploded perspective view of the polyaxial bone anchoring device of  FIG. 17 . 
         FIGS. 19 a  and 19 b    are enlarged perspective views of a lower portion of the instrument shown in  FIGS. 10 to 16   d  and a portion of the polyaxial bone anchoring device inserted into a part of a spinal column to show a use of the instrument, wherein in  FIG. 19 b   , the outer tube is shown in an upper position to provide a better view of the inner tube. 
         FIGS. 20 a  and 20 b    show cross-sectional views of the lower and upper portions, respectively, of the polyaxial bone anchoring device and the instrument shown in  FIGS. 10, 11, 19   a , and  19   b  to show a use of the instrument. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIGS. 1 and 2 , the instrument  1  of a first embodiment includes a tube member  2 , a grip member  3 , and a screwing-in tool such as a screw driver  4 .  FIGS. 1 and 2  further show a plurality of vertebral bodies  101  of a spinal column  100 , each vertebral body  101  being provided with a bone anchoring device  10  inserted into the respective vertebral body  101 . The bone anchoring devices  10  are connected to one another by means of a rod  110 . The bone anchoring device  10  will be described further below with reference to  FIGS. 5 and 6 . 
     Returning to the instrument  1 , the tube member  2  extends between a rear end  2   a  and a front end  2   b  along a longitudinal axis I. Adjacent to the rear end  2   a , the tube member  2  has a rear portion  5 , which is configured to be coupled to the grip member  3 . Furthermore, the tube member  2  has a front portion  6  adjacent the front end  2   b , where the front portion  6  is configured to be coupled to a receiving part  34  of the bone anchoring device  10 . Coupling of the tube member  2  to the bone anchoring device  10  will be explained in greater detail below. A middle portion  7  of the tube member  2  is disposed between the rear portion  5  and the front portion  6  along the longitudinal axis I. 
     The grip member  3  includes a grip portion formed as a handle  11  and an engagement portion  12  for engagement with the rear portion  5  of the tube member  2 . The engagement portion  12  depicted in  FIGS. 1 and 2  has a through-hole  12   a  for form fit engagement with the rear portion  5 , and can be, for example, shaped as a polygon such as an octagon. In the engaged state, as shown in  FIG. 1 , the handle  11  may be arranged substantially perpendicular to the longitudinal axis I of the tube member  2 . 
     The screw driver  4  includes a grip portion formed as a handle  13  and a shaft  14  extending therefrom. At an end of the shaft  14  opposite to the handle  13 , a drive portion  15  is provided that is configured to engage a screw member provided within the receiving part  34  of the bone anchoring device  10 , and in particular, a fixation element described further below. The shaft  14  of the screw driver  4  is configured to be received in the tube member  2 , such that at least the handle  13  of the screw driver  4  protrudes from the tube member  2  and the shaft  14  is displaceable within the tube member  2  along its longitudinal axis I. 
     Hereafter, the tube member  2  is described in greater detail with reference to  FIGS. 3 a  to 4 d   .  FIGS. 3 a  to 3 d    show views of the rear portion  5  and a part of the middle portion  7 , whereas  FIGS. 4 a  to 4 d    show views of the front portion  6  and a part of the middle portion  7 . 
     The tube member  2  includes a first tube  16  that extends between the rear end  2   a  and the front end  2   b  along the longitudinal axis I of the tube member  2 . The first tube  16  has an inner surface  16   a  that forms an internal channel  17  of the tube member  2 . The internal channel  17  has a cylinder shape, with its axis extending along the longitudinal axis I of the tube member  2  and a diameter d 1  that is substantially constant along the longitudinal axis I. The internal channel  17  is open to the rear end  2   a  as well as to the front end  2   b  of the tube member  2 , and thus forms an open central passage through the tube member  2 . The internal channel  17  is shaped so as to accommodate at least a portion of the shaft  14  of the screw driver  4  therein and to guide the shaft  14  therethrough. In particular, the diameter dl of the internal channel substantially corresponds to an outer diameter of the shaft  14  of the screw driver  4  or is slightly greater than the outer diameter of the shaft  14 . 
     The middle portion  7  of the tube member  2  is formed by a part of the first tube  16  that has a cylindrical outer shape, and preferably has a substantially constant cross section along the longitudinal axis I, in particular a constant outer diameter d 2 . The outer diameter d 2  is selected such that the middle portion  7  is configured to be received in a space formed between two extensions  37   a ,  37   b  of the polyaxial bone anchoring device, shown in  FIGS. 1-2 and 5-6 , and serve to provide an extension for a coaxial bore of the receiving part  34 . In particular, the outer diameter d 2  of the first tube  16  at the middle portion  7  may be slightly less than a distance between the two extensions  37   a ,  37   b , i.e., a diameter or width of the coaxial bore of the receiving part  34 , such that the tube member  2  can be guided by the extensions  37   a ,  37   b.    
     Referring to  FIGS. 3 a  to 3 d   , the rear portion  5  of the tube member  2  includes a widened section of the first tube  16 . The rear portion  5  has a cylindrical section  18  and an engagement section  19 . The engagement section  19  has an outer shape in a circumferential direction which corresponds to the inner shape of the through-hole  12   a  of the grip member  3 , to provide a form-fit engagement. Preferably a polygonal, such as an octagonal, shape is used. Thus, the engagement section  19  is configured to enter the through-hole  12   a  of the grip member  3  to connect the grip member  3  and the tube member  2 . The form-fit engagement prevents rotation of the grip member  3  relative to the tube member  2  around the longitudinal axis I. Preferably a length of the engagement section  19  in the direction of the longitudinal axis I substantially corresponds to a length of the through-hole  12   a  of the grip member  3  in an axial direction of the through-hole  12   a . Thus, the entire engagement section  19  may be received within the through-hole  12   a  of the grip member  3 . A circumferential groove  19   c  may divide the engagement section  19  into an upper engagement section  19   a  and a lower engagement section  19   b  along the longitudinal axis I. The upper engagement section  19   a  is located adjacent the rear end  2   a  of the tube member  2  and the lower engagement section  19   b  is located adjacent the cylindrical section  18 . The circumferential groove  19   c  may, for example, engage a protrusion (not shown in the figures) formed in the inner surface of the through-hole  12   a  of the grip member  3 , to better retain the grip member at a set axial position relative to the tube member  2 . 
     The cylindrical section  18  has an outer diameter that is greater than an outer diameter of at least part of the engagement section  19 , so as to form a shoulder  18   a  at a transition between the engagement section  19  and the cylindrical section  18 . The shoulder  18   a  forms a stop for the engagement portion  12  of the grip member  3 , in order to prevent the grip member  3  from advancing beyond the shoulder  18   a  in a direction towards the front end  2   b  of the tube member  2 . The cylindrical section  18  has an outer diameter that may exceed the outer diameter d 2  of the first tube  16  at the middle portion  7 . A transition  18   b  between the cylindrical section  18  and the middle portion  7  may be a smooth transition as shown in  FIGS. 3 a    to  3   c.    
     Referring now to  FIGS. 4 a  to 4 d   , the front portion  6  of the tube member  2  is formed by the first tube  16  and a second tube  20  provided around the first tube  16 . As best seen in  FIG. 4 c   , the first tube  16  has a reduced outer diameter d 3  at the front portion  6  that is less than the outer diameter d 2  of the first tube  16  at the middle portion  7 . The internal channel  17  ends at an end  17   a  at a distance from the front end  2   b  of the tube member  2 , i.e., the internal channel does not extend all the way to the front end  2   b . The first tube  16  includes a first protruding portion  21   a  and a second protruding portion  21   b  that each project radially outward from an outer surface of the first tube  16  at least at the front portion  6  of the tube member  2 . The protruding portions  21   a ,  21   b  also project axially from the end  17   a  parallel to the longitudinal axis I up to the front end  2   b  of the tube member  2 . The first and second protruding portions are each located in a circumferential direction of the tube member  2  and shaped such that they are configured to enter a recess for the rod  110  formed in the receiving part  34  of the polyaxial bone anchoring device  10  (see  FIGS. 5 and 6 ). In particular, the first protruding portion  21   a  and the second protruding portion  21   b  are arranged on opposite sides along the circumferential direction of the first tube  16 , and each have a width along the circumferential direction of the first tube  16  that substantially corresponds to a width of the recess of the receiving part  34 . In particular, a thickness t of the first and second protruding portions  21   a ,  21   b  in a radial direction of the first tube  16  perpendicular to the longitudinal axis I, may be at least a thickness or substantially equal to the thickness of the wall (or the legs) of the receiving part  34  perpendicular to the central axis. A length of the first and second protruding portions  21   a ,  21   b  along the longitudinal axis I substantially corresponds to a height of the recess of the receiving part  34  between an upper or first end of the receiving part and an inserted rod  110 . 
     The first and second protruding portions  21   a ,  21   b  each has a cylindrical recess that forms respective first and second front surfaces  22   a ,  22   b  at the front end  2   b  of the tube member  2 . A radius of said cylindrical recess substantially corresponds to a radius of the rod  110  of the polyaxial bone anchoring device  10 . 
     Furthermore, at the front portion  6 , the first tube  16  forms first and second intermediate portions  23   a ,  23   b  that are located at circumferential positions of the first tube  16  where the protruding portions  21   a ,  21   b  are not provided. Hence, the intermediate portions  23   a ,  23   b  are each located between the first and second protruding portions  21   a ,  21   b  in a circumferential direction of the first tube  16 . When the first and second protruding portions  21   a ,  21   b  enter the recess formed in the receiving part  34 , as explained above, the intermediate portions  23   a ,  23   b  may thus be located at those circumferential positions that correspond to the positions of the legs of the receiving part formed by the recess. 
     The second tube  20  extends along the longitudinal axis I from the front end  2   b  of the tube member  2  to a distance thereof. In particular, the second tube  20  extends for a length s along the longitudinal axis I. The second tube  20  is firmly attached to the projecting portions  21   a ,  21   b  of the first tube  16 , or is monolithically provided with the first tube  16 , wherein the projecting portions  21   a ,  21   b  form connecting portions that connect the first tube  16  and the second tube  20 . A shape of the second tube  20  may be cylindrical. The second tube  20  is configured to be arranged around the receiving part  34 . In particular, an inner diameter d 4  of the second tube  20  is greater than an outer diameter of the receiving part  34 . The inner diameter d 4  of the second tube  20  is also greater than the outer diameter d 3  of the first tube  16 , so that a gap  24  is provided between outer surfaces of the intermediate portions  23   a ,  23   b  of the first tube  16  and the inner surface of the second tube  20 . The width b of the gap  24  in the radial direction perpendicular to the longitudinal axis I is selected such that the legs of the receiving part  34 , as well as the extensions  37   a ,  37   b , can be received within the gap  24 . In particular, the width b of the gap  24  substantially corresponds to a thickness of the wall (or legs) of the receiving part  34  measured perpendicular to the central axis. 
     Furthermore, the second tube  20  has a front surface  25  at the front end  2   a  of the tube member  2 . Cylindrical recesses  25   a ,  25   b  are provided at the front surface  25  at positions that correspond to the positions of the projecting portions  21   a ,  21   b  in the circumferential direction. A radius of said cylindrical recesses substantially corresponds to a radius of the rod  110  of the polyaxial bone anchoring device  10 . 
     Next, with reference to  FIGS. 5 and 6 , an example of a polyaxial bone anchoring device that is suitable for use with the instrument  1  will be explained. The polyaxial bone anchoring device  10  according to an embodiment includes a bone anchoring element  30  with a shank  31  and a head  32  having a spherically-shaped outer surface portion. The bone anchoring element  30  may be a bone screw with a threaded shank. The head  32  may have a recess  33  that is provided for engagement with a tool, such as a driver. A receiving part  34  is adapted for receiving the head  32  and for connecting the bone anchoring element  30  to the rod  110 . In addition, a fixation element  35  in the form of an inner screw or a set screw is provided for fixing the rod  110  in the receiving part  34 . The fixation element  35  has a recess  35   a  for engagement with the drive portion  15  of the screw driver  4  and an outer thread  35   b . Also, the bone anchoring device  10  includes a locking ring  36  for locking the head  32  in the receiving part  34 . The bone anchoring device  10  further includes first and second extensions  37   a ,  37   b  connected to the receiving part  34 . 
     The receiving part  34  has a first or upper end  34   a  and a second or lower end  34   b . Adjacent to the upper end  34   a , a rod receiving portion  38  is provided, and adjacent to the lower end  34   b , a head receiving portion  39  is provided. The rod receiving portion  38  is substantially cylindrical and has a central passage formed as a coaxial bore  40  that extends from the upper end  34   a  into the head receiving portion  39  along a central axis C. The bore  40  has an internal thread  40   a  in at least a portion thereof that cooperates with the outer thread  35   b  of the fixation element  35 . A substantially U-shaped recess  41  that forms a channel for receiving the rod  110  extends from the upper end  34   a  to almost the beginning of the head receiving portion  39 . The recess  41  defines a first leg  45   a  and a second leg  45   b  of the receiving part. At a distance from the upper end  34   a , a groove or otherwise weakened section  42  may be formed that allows breaking off of the upper portions of the receiving part formed by the U-shaped recess that serve as extended tabs. The first and second extensions  37   a ,  37   b  are provided at the first and second legs  45   a ,  45   b , respectively, and extend beyond the upper edge  34   a  of the receiving part parallel the central axis C. The extensions  37   a ,  37   b  extend or form a continuation of the bore  40  beyond the receiving part  34 , and may be useful for minimally invasive surgeries (MIS). 
     The head receiving portion  39  has a substantially cap-like shape with a hollow substantially spherical interior portion (not shown in the figures) for receiving the head  32  pivotably therein. A plurality of slits  46  render the head receiving portion flexible, so that when pressure is exerted onto the head receiving portion  39  by the locking ring  36 , the head  32  can be clamped and finally locked. 
     The locking ring  36  is designed to encompass the head receiving portion  39  and has an internal surface structure that cooperates with the head receiving portion  39  to provide a full locking of the head  32  in the head receiving portion  39  when the locking ring  36  is at a lowermost position, and a pre-locking when the locking ring  36  is at a position slightly above the lowermost position, where pivoting of the head  32  in the head receiving portion is still possible but removal of the head  32  from the head receiving portion  39  is prevented. The locking ring  36  further has upstanding slightly flexible sections  47  that may serve for engagement with the receiving part to preliminarily hold the locking ring in a pre-locking position. Also, two opposing ones of said projections  47  may be provided at an upper side of the locking ring for supporting the rod  110 . In the embodiment shown, the locking ring  36  also includes two upstanding arms  48  that are arranged on opposite sides of the locking ring. The upstanding arms may provide for engagement of the locking ring with a further instrument (not shown in the figures) other than the instrument  1  described above. 
     Use of the instrument  1  will now be explained, with reference to  FIGS. 7 a  to 9 c   . The bone anchoring element  30  may be implanted in a vertebra  101  or other bone. The locking ring  36  may be at an axial position where the head  32  is locked in the head receiving portion  39 . In this position, the rod  110  located in the substantially U-shaped recess  41  is still movable. Also, the fixation element  35  may already be screwed into the bore  40  of the receiving part  34  but not yet tightened. 
     Referring to  FIGS. 7 a , 8 a , and 9 a   , the tube member  2  with the grip member  3  is attached to a polyaxial bone anchoring device  10 . To do so, the front end  2   b  of the tube member  2  is advanced over the free ends of the extensions  37   a ,  37   b , so that the first tube  16  is located at a position of the bore  40 , i.e., in the space formed between the extensions  37   a  and  37   b , and the second tube  20  is located around the extensions  37   a ,  37   b . The protruding portions  21   a ,  21   b  protrude out of the space formed between the extensions  37   a ,  37   b  at circumferential positions that correspond to the recess  41  of the receiving part  34 . Next, the tube member  2  is advanced along the central axis C towards the bone anchoring element  30  until its front end  2   b  contacts the inserted rod  110 . In doing so, the first tube  16  advances within the space formed between the extensions  37   a ,  37   b  and is guided by the extensions  37   a ,  37   b . Further guidance of the tube member  2  is provided by the second tube  20  sliding along the outer surfaces of the extensions  37   a ,  37   b . The tube member  2  may be held and advanced manually by an operator such as a surgeon who holds the handle  11 . 
     The final position of the tube member  2 , in which the front end  2   b  contacts the inserted rod  110 , is shown in  FIGS. 7 b , 8 b  and 9 b   . In this position, the protruding portions  21   a ,  21   b  of the first tube  16  are arranged within the substantially U-shaped recess  41  of the receiving part  34 , and preferably abut against the lateral sides of the recess  41 . Hence, the tube member  2  is prevented from rotating relative to the receiving part  34  around the longitudinal axis I. The front surfaces  22   a ,  22   b  of the protruding portions  21   a ,  21   b  and the front surface  25  of the second tube  20  abut against the inserted rod  110 . The legs  45   a ,  45   b  of the receiving part  34  are provided within the gap  24  of the tube member  2  formed between the first tube  16  and the second tub  20  at the positions of the intermediate portions  23   a ,  23   b . The internal channel  17  extends through the tube member  2  from its rear end  2   a  to the end  17   a  of the channel located at or slightly above the fixation element  35 . 
     Next, as shown in  FIGS. 7 c  and 9 c   , the shaft  14  of the screw driver  4  is introduced into the internal channel  17  of the tube member  2  at its rear end  2   a  and advanced through and guided by the channel  17  towards the front end  2   b , until the drive portion  15  of the screw driver  4  exits the channel  17  at its end  17   a  and engages the recess  35   a  of the fixation element  35 . The fixation element  35  can then be tightened by rotating the handle  13 , and thus also the drive portion  15  of the screw driver  4 , around the longitudinal axis I. While rotating the handle  13  of the screw driver  4 , in particular manually rotating the handle  13 , the tube portion  2  may be held, e.g. manually held, at its handle  11  to act as a counter holder while tightening the fixation element  35 . By tightening the fixation element  35 , the rod  110  is locked within the receiving part  34 , thus locking the relative position of the rod  110  and the bone anchoring element  30 . 
     A second embodiment of the instrument is shown in  FIGS. 10 to 16   d . For the sake of brevity, the description of parts and portions of the instrument of the second embodiment that are the same as or similar to parts and portions of the instrument of the first embodiment described above will not be repeated. The tube member  2 ′ of the instrument  1 ′ of the second embodiment differs from that of the instrument of the first embodiment. Referring to  FIGS. 10 and 11 , the tube member  2 ′ according to the second embodiment includes a first or inner tube  116  and a second or outer tube  120 , as well as a snap ring  50  and a pin  51 . It shall be noted that the outer tube  120  may be a part that is used for other surgical procedures and may be combined with the inner tube to form an instrument according to the second embodiment. Such an outer tube may be used, for example, for guiding other parts or instruments to the implantation site or as extension for a receiving part. The outer tube  120  extends from an upper or first end  120   a  to a lower or second end  120   b , and forms a hollow shaft configured to receive the inner tube  116  therein. A length of the second tube  120  measured between its first end  120   a  and its second end  120   b  is less than a length of the inner tube  116  measured between its rear end  2   a  and its front end  2   b . In particular, the length of the second tube  120  is selected such that at least the cylindrical section  18  and the engagement section  19  of the rear portion  5 ′ of the inner tube  116  protrude from the first end  120   a  of the outer tube  120  in an assembled state, i.e., when the inner tube  116  is located within the outer tube  120 . 
     With reference to  FIGS. 12 a  to 13 c   , the inner tube  116  will now be described. Referring first to  FIGS. 12 a  to 12 d   , The rear portion  5 ′ of the inner tube  116  differs from the rear portion of the tube member of the first embodiment described above in that the inner tube  116  includes a further cylindrical section  118  arranged below the transition  18   b , i.e., adjacent to the transition  18   b  closer to the front end  2   b  along the longitudinal axis I. An outer surface of the cylindrical section  118  has a substantially constant outer diameter that is greater than the outer diameter d 2  of the middle portion  7 ′ of the inner tube  116 . The outer diameter of the cylindrical section  118  substantially corresponds to an inner diameter d 5  of the outer tube  120  (see below), or is slightly smaller than the inner diameter d 5  of the outer tube  120 , so that the outer surface of the cylindrical section  118  is configured to contact an inner surface of the outer tube  120 . A circumferential groove  118   c  divides the cylindrical section  118  into an upper cylindrical section  118   a  and a lower cylindrical section  118   b  along the longitudinal axis I. Preferably, the circumferential groove  118   c  extends along the entire circumference of the cylindrical section  118 . The upper cylindrical section  118   a  is located adjacent the transition  18   b  and the lower cylindrical section  118   b  is located adjacent the middle portion  7 ′ of the inner tube  116 . Furthermore, a longitudinal recess  118   d  is formed in the outer surface of the lower cylindrical section  118   b . The longitudinal recess  118   d  may extend along the entire length of the lower cylindrical section  118   b  along the longitudinal axis I, i.e., from the circumferential groove  118   c  to the middle portion  7 ′ of the inner tube  116 . The longitudinal recess  118   d  preferably does not extend through the entire thickness of the inner tube  116  in its radial direction, i.e., does not form a transversely open slit of the inner tube. The longitudinal recess  118   d  is configured to receive the pin  51  therein when the pin  51  extends through and protrudes out of a hole of the outer tube  120 . 
     Referring now to  FIGS. 13 a  to 13 c   , the front portion  6 ′ of the tube member  2 ′ differs from the front portion of the first embodiment in that it is formed by the inner tube  116  alone. Hence, the protrusion portions  21   a ,  21   b  and the intermediate portions  23   a ,  23   b  are not enclosed by a tubular portion. 
     Next, the outer tube  120  will be described with reference to  FIGS. 14 to 16   d . The outer tube  120  has a substantially cylindrical outer shape and has an inner surface  117   a  that forms an internal channel  117  of the outer tube  120 . The internal channel  117  extends from the first end  120   a  to the second end  120   b  in a longitudinal direction of the outer tube corresponding to the direction of the longitudinal axis I of the instrument  1 ′ in an assembled state. The internal channel  117  has a substantially cylindrical shape with an inner diameter d 5  that is substantially constant along the entire length of the outer tube  120  in the longitudinal direction. The inner diameter d 5  of the internal channel  117  of the outer tube  120  substantially corresponds to the outer diameter d 2  of the inner tube  116  at the middle portion  7 ′ of the inner tube  116  or is slightly greater than the outer diameter d 2  of the inner tube  116 , to permit the inner tube  116  to be guided within the internal channel  117  of the outer tube  120 . Furthermore, the inner diameter d 5  of the internal channel  117  substantially corresponds to an outer diameter of the receiving part  34  of the polyaxial bone anchoring device  10 ′ or is slightly greater than the outer diameter of the receiving part  34 , to accommodate at least a portion of the receiving part  34 , in particular its legs, within the internal channel  117 . 
     As shown in  FIGS. 15 a  to 15 c   , the outer tube  120  has an upper portion adjacent its first end  120   a . A groove  52  is provided in the upper portion of the outer tube  120 . The groove  52  is configured to receive the snap ring  50  therein. With respect to the direction of the longitudinal axis I, the groove  52  is provided at an axial position that corresponds to the axial position of the groove  118   c  provided in the cylindrical section  118  of the inner tube  116  described above. The snap ring  50  is an open ring having ends  54   a ,  54   b  in a circumferential direction of the ring. Moreover, the snap ring  50  is provided with first and second protrusions  50   a ,  50   b  formed at a distance from the respective ends  54   a ,  54   b  at an inner surface of the ring. The first and second protrusions  50   a ,  50   b  protrude further into an interior region enclosed by the ring than non-protruding portions of the ring adjacent the protrusions. In the present embodiment, the first and second protrusions  50   a ,  50   b  are arranged opposed to one another. Due to the shape of the snap ring  50  as an open ring, the snap ring  50  is resilient. 
     Referring back to the outer tube  120 , the groove  52  extends along a circumferential portion of the outer tube  120  but does not encompass the entire circumference of the outer tube  120 . The groove  52  may extend around approximately three quarters, i.e., around 270°, of the circumference of the outer tube  120 , for example. The circumferential length of the groove  52  corresponds to a circumferential length of the snap ring  50  between the ends  54   a ,  54   b . Furthermore, a first opening  52   a  and a second opening  52   b  are formed in the groove  52  to receive the protrusions  50   a ,  50   b  of the snap ring  50  therein. The openings  52   a ,  52   b  are through-holes that extend from an outer surface of the outer tube  120  through its wall to the internal channel  117 , whereas portions of the groove  52  aside from the openings  52   a ,  52   b  do not extend entirely through the wall of the outer tube  120  in the radial direction. At a distance below the groove  52 , i.e., further towards the second end  120   b  in the direction of the longitudinal axis I, a through-hole  53  is provided that extends from an outer surface of the outer tube  120  through its wall to the internal channel  117 . The through-hole  53  is shaped to receive the pin  51  therein. The through-hole  53  is located at a position of the outer tube  120  such that the pin  53  inserted into the through-hole  53  extends into the longitudinal recess  118   d  of the lower cylindrical section  118   b  of the inner tube  116  described above. 
     As shown in  FIG. 15 c   , when the snap ring  50  is arranged in the groove  50 , the protrusions  50   a ,  50   b  of the snap ring  50  extent through the respective openings  52   a ,  52   b  of the groove  52  into the internal channel  117  of the outer tube  120 . Likewise, the pin  51  extends through the through-hole  53  into the internal channel  117 . Hence, in the assembled state of the instrument  1 ′ as shown in  FIGS. 10 and 20   b , the inner tube  116  is located within the channel  117  of the outer tube  120 , while the grip member  3  is attached to the engagement section  19  of the inner tube  116  which protrudes away from the first end  120   a  of the outer tube  120 . The first and second protrusions  50   a ,  50   b  of the snap ring  50  provided within the groove  52  of the outer tube  120  extend through the openings  52   a ,  52   b  of the groove  52 , respectively, and engage the circumferential groove  118   c  provided in the outer surface of the inner tube  116 . The pin  51  extends through the through-hole  53  of the outer tube  120  and engages the longitudinal recess  118   d  provided in the outer surface of the inner tube  116 . As the protrusions  50   a ,  50   b  of the snap ring  50  and the pin  53  protrude inwardly from the outer tube  120  and extend into indentations (i.e., the groove  118   c  and the recess  118   d ) provided in the outer surface of the inner tube  116 , translational and rotational movement of the inner tube  116  relative to the outer tube  120  is inhibited. Thus, the position of the inner tube  116  relative to the outer tube  120  can be locked. 
     Turning now to  FIGS. 16 a  to 16 d   , the outer tube  120  further has a recess  60  adjacent its second end  120   b  to accommodate the rod  110  therein. The recess forms first and second legs  61   a ,  61   b  of the outer tube adjacent its second end  120   b . A distance between the first leg  61   a  and the second leg  61   b , i.e., a width of the recess  60  in the circumferential direction of the outer tube  120 , substantially corresponds to a diameter of the rod  110  or is slightly greater than the diameter of the rod. In the direction of the longitudinal axis I, a depth of the recess  60  is preferably greater than the diameter of the rod  110 . When the outer tube  120  is arranged around the legs of the receiving part  34  of the polyaxial bone anchoring device  10 ′ as shown in  FIG. 10 , the rod  110  is located in the recess  60  of the outer tube  120 . 
     The instrument  1 ′ of the second embodiment is suited for use with a polyaxial bone anchoring device  10 ′ depicted in greater detail in  FIGS. 17 and 18 . This polyaxial bone anchoring device  10 ′ differs from the polyaxial bone anchoring device  10  for use with the instrument of the first embodiment described above in that the extensions  37   a ,  37   b  (see  FIGS. 5, 6 ) are omitted. Hence, the outer tube  120  of the instrument  1 ′ of the second embodiment can serve as an extension of the coaxial bore  40  of the receiving part  34 . 
     Use of the instrument  1 ′ of the second embodiment can be substantially similar to the use of the instrument  1  of the first embodiment, and is shown in  FIGS. 19 a  to 20 b   . Instead of providing the second tube  20  of the tube member  2  of the first embodiment to encompass the legs  45   a ,  45   b  of the receiving part  34 , in the second embodiment, the outer tube  120  is provided to encompass the legs  45   a ,  45   b , and serve to extend the coaxial bore  40  beyond the receiving part  34  in the direction of the longitudinal axis I, to provide for additional stabilization and guidance of the inner tube  116 . When assembling the instrument  1 ′, first the outer tube  120  is placed on and around the receiving part  34  and subsequently the inner tube  116  is inserted into the channel  117  of the outer tube and coupled to the outer tube by means of the snap ring  50  and the pin  51 . 
     It should be noted that, instead of providing the snap ring  50  and pin  51  used for coupling the outer tube  120  to the inner tube  116 , any other suitable means or elements, such as a screw or any other detachable or non-detachable connection, may be used for coupling the tubes to one another. Alternatively, the first tube  116  may be integrally provided with the second tube  120 . 
     In the second embodiment described above, the outer tube  120  forms part of the instrument  1 ′. However, in a modification of the second embodiment, the instrument  1 ′ may only include the inner tube  116 , the grip member  3 , and the screw driver  4 . In this case, the outer tube  120 , the snap ring  50 , and the pin  51  may be provided as parts separate from the instrument. In particular, in this case, the outer tube  120  may also be used for other purposes, or with any other tools or instruments, in order to provide a channel that extends from the first end  120   a  to the receiving part  34 , i.e., that serves to extend the coaxial bore  40  of the receiving part  34  to thus, for example, provide guidance for tools or instruments, etc. It should be noted that the instrument of the second embodiment may also be used without the outer tube  120 . Likewise, the tube member  2  of the instrument  1  of the first embodiment may also be provided without the second tube  20 . 
     Further modifications of the embodiments described above are also possible without deviating from the scope of the present disclosure. For example, the instrument may be used with a bone anchoring device different than the ones described above. The specific shape of the first and second tube and/or the inner and outer tube may vary. In particular, the receiving part may be configured for inserting the bone anchoring element from above, i.e., the receiving part may be a top loader instead of the bottom loader described above. As another possible modification, the receiving part may be configured such that the head and the rod are fixed simultaneously by advancing the fixation element  35  in the coaxial bore  40  between the legs. Furthermore, the present disclosure is not limited to an instrument for use with a polyaxial bone anchoring device but may also be used with a monoaxial bone anchoring device. In general, the instrument described above may be used with any receiving part that has a recess defining two legs. 
     Furthermore, the present disclosure is not limited to the use of the instrument for advancing the fixation element  35  within the receiving part. Rather, the screw driver may also engage another screw member provided within the receiving part or the recess in the head of the bone anchoring element. 
     Although connection of the grip member  3  and the tube member  2  is implemented by a polygonal through-hole  12   a  and the polygonal engagement section  19  described above, it should be understood that any other suitable connection can be applied that prevents rotation of the grip member  3  around the longitudinal axis I while at the same time providing access to the internal channel  17 . Alternatively, the grip member  3  and the tube member  2  can also be provided integrally, i.e., as a single part, or can be otherwise firmly attached to one another. 
     In the above embodiments, the first and second tubes have a substantially cylindrical shape with a substantially circular cross-section. It should be understood that the shape of the first and/or second tube and/or the internal channel of the second tube may have any other shape or cross-section. For example, the inner channels of the second tube may have a polygonal, such as a hexagonal, cross-section at least in a section thereof, and the first tube may have a correspondingly shaped polygonal, e.g. hexagonal, outer surface at least in a section thereof. 
     The instrument  1 ,  1 ′ and the bone anchoring device  10 ,  10 ′ may be provided as separate parts, or may in some cases be provided together as a system including both the bone anchoring device  10 ,  10 ′ and the instrument  1 ,  1 ′. 
     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.