Bone anchor and elongated instrument system

Abstract

To provide a system of a bone anchor and an elongate instrument.SOLUTION: A system includes a bone anchor (1) comprising a shank (2) having a first end (3) and a second end (4), and a channel (7) extending through the shank from the first end to the second end, with the channel defining a channel axis (L), wherein at or close to the second end of the shank an internal advancement structure (8) is provided at an inner wall of the channel. The system includes an elongate instrument (20, 30, 40, 50) that is configured to extend through the channel. The elongate instrument comprises a tip portion (23, 31, 42, 51) and an external advancement structure (25, 32, 43, 53). The external advancement structure cooperates with the internal advancement structure of the shank so as to permit the tip portion to advance in the channel in a direction towards the second end and to be moved back in an opposite direction towards the first end. The elongate instrument with the tip portion is removable from the channel.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present application relates to a system of a bone anchor with a cannulated shank and an elongated instrument insertable into the cannulated shank. [Background technology]

[0002] In certain minimally invasive surgery (MIS) spinal surgery procedures, it is known to use guide wires, such as Kirschner wires (K-wires), that penetrate the skin and are percutaneously placed into the vertebrae of the spine at the desired location for a bone anchor. In some cases, holes for the bone anchor are pre-drilled and pre-threaded for the bone anchor. A bone anchor having a cannulated shank is then guided along the guide wire and finally screwed into the pedicle. The guide wire is then removed. Such bone anchors and procedures are known, for example, from U.S. Pat. No. 8,690,930 B2.

[0003] Other bone anchors that are cannulated for guiding through a guide pin or drill are known in the art. For example, U.S. Pat. No. 5,098,435 discloses a bone stabilization system including a guide pin and a cannula for forming a bone anchor. The forward end of the guide pin is provided with a drilling means for drilling a guide hole into the fractured bone at a predetermined location. Using the system includes inserting the guide pin into the bone, placing a cannula over the guide pin, and advancing the cannula into the bone.

[0004] US Patent No. 7,938,848 B2 discloses a pedicle screw having a channel extending along the longitudinal axis of the screw, with a drill extending through the channel, and a first end of the drill extending out of a distal opening of the channel.

[0005] US9,095,395B2 discloses a surgical K-wire for guiding a bone screw, which includes a longitudinal channel. A closure element is formed at the distal end of the K-wire to close the distal end outlet opening of the longitudinal channel of the bone screw. In some embodiments, the closure element is connected to the longitudinal channel by a screw. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] US8,690,930B2 [Patent Document 2] US5,098,435 [Patent Document 3] US7,938,848B2 [Patent Document 4] US9,095,395B2 Summary of the Invention [Problem to be solved by the invention]

[0007] SUMMARY OF THE INVENTION It is an object of the present invention to provide a system of bone anchors and elongated instruments that has broad application and simplifies the surgical procedure in certain MIS procedures. [Means for solving the problem]

[0008] This object is solved by a system according to claim 1. Further developments are described in the dependent claims. [Appendix 1] 1. A bone anchor and elongate instrument system comprising: a bone anchor (1) including a shank (2) having a first end (3) and a second end (4), and a channel (7) extending from the first end (3) through the shank (2) to the second end (4), the channel (7) defining a channel axis (L); an internal advancement structure (8) is provided on the inner wall of the channel (7) at or near the second end (4) of the shank (2); A bone screw (5) is provided on at least a portion of the outer surface of the shank (2); The system further comprises: an elongated instrument (20, 30, 40, 50) configured to extend through the channel (7); the elongated instrument (20, 30, 40, 50) includes a tip portion (23, 31, 42, 51) and an external advancement structure (25, 32, 43, 53) that cooperates with the internal advancement structure (8) of the shank (2) to enable the tip portion (23, 31, 42, 51) to be advanced in the channel (7) in a direction toward the second end (4) and retracted in an opposite direction toward the first end (3); the elongate instrument with the distal end portion (23, 31, 42, 51) is removable from the channel (7); the tip portion includes at least one cutting edge (24) configured to cut into bone; The system further includes a tool; the bone anchor is grasped by the tool; The elongate instrument (20, 30, 40, 50) further includes a first engagement structure. ,before The first engagement structure is configured to cooperate with a second engagement structure on the tool to prevent rotation of the elongated instrument (20, 30, 40, 50) relative to the bone anchor. [Appendix 2] 2. The system of claim 1, wherein the internal advancement structure (8) is an internal thread and the external advancement structure (25, 32, 43, 53) is an external thread. [Appendix 3] 3. The system of claim 2, wherein the female thread and the male thread are cylindrical threads. [Appendix 4] 4. The system of any one of claims 1 to 3, wherein the tip portion (23, 31, 42, 51) is configured to advance within the channel (7) from the first end (3) to the second end (4). [Appendix 5] The tip portion (23, 31, 42, 51) advances within the channel (7) from the first end (3) to the second end (4) until it extends out from the second end (4). 5. The system of claim 4, configured as follows: [Appendix 6] 6. The system of any one of claims 1 to 5, wherein the elongated instrument (20, 30, 40, 50) has a length such that the tip portion (23, 31, 42, 51) extends out from the first end (3) of the shank (2) when the tip portion (23, 31, 42, 51) is at or near the second end (4) of the channel (7). [Appendix 7] 7. The system of any one of claims 1 to 6, wherein the internal advancement structure (8) and the external advancement structure (25, 32, 43, 53) are configured to cooperate in such a manner that the position of the elongated instrument (20, 30, 40, 50) relative to the bone anchor is axially fixed to prevent displacement. [Appendix 8] 8. The system of any one of claims 1 to 7, wherein the axial length of the outer advancement structure (25, 32, 43, 53) is equal to or greater than the axial length of the inner advancement structure (8). [Appendix 9] 9. The system of any one of claims 1 to 8, wherein the elongated instrument (20, 30, 40, 50) includes a rear end (21) opposite the tip portion (23) and a neck portion (26, 44) adjacent to or proximate the external advancement structure (25, 43) on the rear end (21) side. [Appendix 10] 8. The system of any one of claims 1 to 7, wherein the axial length of the outer advancement structure (25, 32) is shorter than the axial length of the inner advancement structure (8). [Appendix 11] 11. The system of claim 10, wherein the axial length of the external advancement structure (25, 32) is sufficient to secure the elongated instrument (20, 30, 40, 50) against axial sliding. 。 [ Additional notes 12 ] A stop (9) is provided on the inner wall of the channel (7) to limit the insertion of the elongated instrument into the bone anchor. 11 10. The system according to claim 1, wherein [Addendum 13 ] the tip portion includes a sensor element (46), 12 The system described in [Addendum 14 ] The tip portion includes a marker element (52). 12 The system described in [Addendum 15 ] The elongated instrument (20, 30, 40, 50) includes a tube (51). 14 The system according to any one of claims 1 to 5, 。

[0009] The elongated instruments of the system may be, for example, cutting devices, K-wires, sensors for detecting features or markers at the implantation site, or any other instrument. Each elongated instrument and bone anchor together form a unit that can be placed at the implantation site. Furthermore, a surgical procedure involving the elongated instrument can be performed. The instrument can then be removed from the channel of the bone anchor. If desired, another type of elongated instrument can be inserted into the channel. Thus, the bone anchor can be selectively combined with various instruments depending on the specific function of the instrument required. This increases the range of applications of the system.

[0010] When the elongated instrument is a cutting device, the system allows for the placement of a bone anchor with the cutting device inserted without the use of K-wires, pre-drilling, or pre-threading, thereby saving time during the surgical procedure. Additionally, a cutting device with a cutting portion having a shape and length appropriate for the particular clinical situation in which the bone anchor is to be used can be selected.

[0011] If the elongated instrument is a K-wire, the system allows the bone anchor to be placed on the bone surface together with the K-wire as a unit, driving the tip of the K-wire into the bone, after which the K-wire can be used as a guide.

[0012] If the elongate instrument is a marker, the bone anchor and the marker element may have a defined positional relationship to each other so that the position of the bone anchor can be accurately detected.

[0013] Further features and advantages will become apparent from the following description of embodiments of the invention, which proceeds with reference to the accompanying drawings. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is an exploded perspective view of one embodiment of a system of bone anchors and elongated instruments in the form of cutting devices. FIG. [Figure 2] FIG. 2 is a perspective view of the system of FIG. 1 in an assembled state. [Figure 3a] FIG. 3 is a cross-sectional view of the system of FIGS. 1 and 2 taken along a plane extending through the channel axis of the bone anchor. [Figure 3b] FIG. 3b shows an enlarged portion of FIG. 3a. [Figure 4] FIG. 4 is a perspective view of a tool attached to the system of FIGS. 1-3b during the step of implanting a bone anchor into the pedicle of the vertebra. [Figure 5a] FIG. 4 is a cross-sectional view showing the system of FIGS. 1 to 3b being inserted into the pedicle of the vertebral bone. [Figure 5b] FIG. 4 is a cross-sectional view showing the system of FIGS. 1 to 3b being inserted into the pedicle of the vertebral bone. [Figure 5c] FIG. 4 is a cross-sectional view showing the system of FIGS. 1 to 3b being inserted into the pedicle of the vertebral bone. [Figure 6] FIG. 10 is a cross-sectional view of the inserted bone anchor after removal of the elongated instrument. [Figure 7]1 is a perspective view showing bone anchors to form a system and various elongated instruments that can each be used with the bone anchors; [Figure 8] FIG. 10 is a cross-sectional view of a portion of the system with an elongated instrument including an improved K-wire. [Figure 9] FIG. 1 is a cross-sectional view of a portion of a system including an elongate instrument containing a sensor. [Figure 10] FIG. 10 is a cross-sectional view of a portion of the system with an elongate instrument including a marker. DETAILED DESCRIPTION OF THE INVENTION

[0015] 1 to 4 show one embodiment of a system of a bone anchor 1 and an elongated instrument in the form of a cutting device 20. The bone anchor 1 comprises a shank 2 with a head 3 at a first end and a free second end 4. The head 3 may have a spherical outer surface portion that defines the maximum outer diameter of the bone anchor 1. A bone thread 5 may be provided on at least a portion of the outer surface of the shank 2. The shank 2 may be slightly tapered towards the second end 4. An engagement recess 6 for engagement with a tool may be formed in the free end face of the head 3.

[0016] As shown in more detail in FIGS. 3a and 3b, the bone anchor 1 is cannulated. The bone anchor 1 includes a channel 7 extending from the head 3 all the way through the bone anchor to the second end 4. The channel 7 is defined by a coaxial bore extending from the first end to a certain distance from the second end 4. The bore axis defines the longitudinal axis L of the channel. Adjacent to the second end 4, the diameter of the channel 7 is slightly smaller than the coaxial bore. An internal advancement structure in the form of an internal thread 8 is provided within the channel adjacent or near the second end 4. A shoulder 9 may be formed between the coaxial bore and the advancement structure. The shoulder 9 functions as an abutment to limit the insertion of an elongated instrument, thereby enabling precise positioning between the bone anchor 1 and the elongated instrument. The minimum internal diameter of the channel 7 in the bone anchor 1 is defined by the internal thread 8.

[0017] At least one (preferably multiple) radial openings 10 (shown in Figure 6) may be provided in the wall of the shank 2 for the purpose of forming an outlet for bone cement or medical substance to be injected into the bone anchor 1.

[0018] The elongate instrument in the form of cutting device 20 is a substantially rod-like member including a first or rearward end 21 (shown in FIG. 4) and an opposite second or forward end 22. Essentially, cutting device 20 is formed as a cylindrical rod, having a length from rearward end 21 to forward end 22 that is greater than the length of bone anchor 1. Specifically, the length of cutting device 20 is configured such that cutting device 20 extends through passageway 7 of bone anchor 1 and protrudes from second end 4 of bone anchor 1 on one side, while rearward end 21 is positioned at the distal end of bone anchor 1. tool To insert the bone anchor, protrude from 100 (as shown in Figure 4). tool 100.

[0019] A tip portion 23 including a cutting edge 24 is provided adjacent the forward end 22. For example, the cutting edge 24 may be formed by an indentation in the outer surface of the tip portion 23, with at least one edge of the indentation configured to perform a cutting function. Although only one cutting edge 24 is shown in the figures, multiple cutting edges may be provided. The cutting edge or edges may be linear in shape. The cutting edge 24 may extend longitudinally, be helical, or have any other shape configured to cut bone. The cutting device 20 includes a section adjacent to or spaced apart from the tip portion 23 that includes an external advancement structure in the form of external threads 25 configured to cooperate with the internal threads 8 of the bone anchor 1. The axial length of the section with external threads 25 may be equal to or greater than the length of the section with internal threads 8 of the bone anchor 1, so that the position of the cutting device 20 can be precisely adjusted over a certain range when inserted into the passageway 7 of the bone anchor 1. The section with the external threads 25 may be followed by a small neck portion 26. The remainder or main portion 27 of the cutting device may be formed as a smooth cylindrical rod having an outer diameter slightly smaller than the inner diameter of the coaxial bore of the passage 7 so that the cutting device 20 can slide within the coaxial bore.

[0020] Furthermore, the cutting device 20 may be configured such that, when the cutting device is inserted into the channel 7, at a position of the main portion 27 outside the bone anchor 1, tool 100. Such engagement portion is intended to rotatably secure the cutting device 20 relative to the bone anchor 1 when the cutting device 20 is inserted into the bone anchor and the tip portion 23 extends out of the first end 4 of the bone anchor 1.

[0021] The bone anchor 1 and the cutting device 20 may each be constructed from a biocompatible material, such as titanium or stainless steel, a biocompatible alloy, such as a NiTi alloy, such as Nitinol, magnesium or a magnesium alloy, or a biocompatible plastic material, such as polyether ether ketone (PEEK) or poly-l-lactide acid (PLLA). Additionally, the components can be made of the same or different materials.

[0022] For assembly, the bone anchor 1 is secured in such a manner that the length of the cutting portion 23 of the cutting device that protrudes from the second end 4 of the bone anchor 1 is adjusted by the cooperating screws 8 and 25. tool 100, and the cutting device 20 is inserted into the channel 7 of the bone anchor 1. Note that the cutting device 20 and the bone anchor 1 may be pre-assembled. tool It should be noted that the cutting device 20 can be gripped with a screw 8. By selecting the type of cutting device 20 (i.e., with respect to the shape of the cutting edge 24 and the length of the tip portion 23) and by adjusting the length of the portion that protrudes out of the second end 4 of the threaded bone anchor 1, a system can be provided that is adapted to the specific requirements of the implantation site. Finally, the cutting device 20 is axially fixed to the bone anchor by the screws 8 and 25, and the cutting device 20 and the screw 8 are fastened to the bone anchor. tool 100. The bone anchor 1 and cutting device 20 are therefore adapted to be inserted into bone as a unit.

[0023] 5a-5c, a bone anchor 1 with a cutting device 20 and tool A portion of 100 is shown. tool 100 is shown as an exemplary embodiment. tool 100 includes a first head engaging portion 101 that engages with the head 3 from the outside, a second head engaging portion 102 that engages with the head 3 in the recess 6, and a head 3 of the bone anchor 1. tool 5a, the bone anchor 1 is inserted into the vertebral column 500. The first head engaging portion 102 is pressed against the head 3, and the second head engaging portion 102 includes a clamping sleeve 103 that presses the first head engaging portion 102 toward the head 3 so that the bone anchor 1 is firmly clamped to the head 3. The second head engaging portion 102 includes a passage for the cutting device 20 to pass through. As shown in FIG. 5a, the unit consisting of the bone anchor 1 and the cutting device 20 is placed at the position where the bone anchor 1 should be inserted (e.g., the pedicle of the vertebral column 500). The cutting edge 24 is used to penetrate the cortical bone. The tip portion 23 therefore prepares a path for the bone anchor 1 so that the bone anchor 1 can be easily screwed into it. The hole does not need to be pre-drilled.

[0024] The bone anchor 1 is then screwed into the pedicle until the shank 2 is finally embedded and the head 3 protrudes from the bone surface, as shown in Figures 5b and 5c. The placement of the bone anchor 1 with the cutting device 20 may be performed with the aid of imaging methods.

[0025] When the bone anchor is in its final position, the cutting device 20 is unthreaded and removed from the bone anchor as shown in Figure 6. If desired, the second end 4 can be closed by inserting a plug member and / or injecting bone cement or another substance that may flow out of the opening 10.

[0026] 7 shows a bone anchor 1 and various elongated instruments. Such instruments may include, for example, a cutting device 20, a medical guidewire 30 such as a modified K-wire, a sensor 40, and a marker 50. Each of the instruments forms a unit with the bone anchor 1. The various instruments and bone anchors may form a modular system that allows one elongated instrument to be selectively combined with the bone anchor 1 depending on the application.

[0027] An elongate device in the form of a medical guidewire 30, such as a modified K-wire, is shown in more detail in FIG. 8 . The guidewire 30 has a substantially smooth outer surface and an outer diameter slightly smaller than the inner diameter of the threads 8 so that it can be guided through the channel 7 of the bone anchor 1. Conventionally, the guidewire 30 has a distal end 31 configured to be driven into bone. Spaced apart from the distal end 31 is an external advancement structure in the form of external threads 32 configured to cooperate with the internal threads 8 of the bone anchor 1. Preferably, the axial length of the external threads 32 is shorter than the axial length of the internal threads 8. More specifically, the axial length of the external threads 32 includes as many turns of thread as necessary to axially secure the guidewire 30 against sliding within the channel 7. In this case, the number of turns may be at least one or fewer. The external threads 32 may be positioned away from the distal end 31 so that the distal end 31 and preferably a portion 33 adjacent to the distal end 31 protrude from the second end 4 when the external threads 32 engage the internal threads 8.

[0028] In use, the guide wire 30 and bone anchor 1 are combined by threading the guide wire 30 into the bone anchor 1, and the system is then positioned as a unit on the bone surface so that the distal portion 31 of the guide wire is driven into the bone. The bone anchor 1 can then be threaded downward until the threads disengage. In this state, the guide wire can be used like a regular guide wire, and the bone anchor 1 and other components may be guided along the guide wire toward the implantation site. Alternatively, the bone anchor and modified K-wire can be positioned as a unit on the bone surface, and the K-wire can be driven into the bone and further down along the internal threads.

[0029] An elongate instrument in the form of a sensor 40 is shown in FIG. 9. As shown in FIG. 9, the sensor 40 includes a housing 41. The housing 41 is substantially tubular and configured to pass through the channel 7 of the bone anchor 1. The housing 41 has a distal portion 42 that can extend through the second end 4. The housing 41 includes an advancement structure adjacent the distal portion 42. The advancement structure is in the form of external threads 43 configured to cooperate with the internal threads 8 of the bone anchor 1. The axial length of the external threads 43 may be equal to or greater than the axial length of the internal threads 8. A neck portion 44 may be present adjacent the external threads 43. The neck portion 44 may be followed by a main portion 45 of the housing 41 having a smooth outer surface. A sensor element 46 is positioned in the housing 41. The sensor element 46 includes a distal portion 47. The distal portion 47 is configured to detect a respective characteristic, such as bone density, or to monitor a nerve. Any other suitable sensor elements may be contemplated.

[0030] The sensor 40 may be inserted with the bone anchor already inserted into the bone, or may be pre-assembled with the bone anchor 1 and inserted into the bone together with the bone anchor 1.

[0031] An elongated instrument in the form of a marker 50, such as a marker for detecting its location on a bone by X-ray and / or marking, is shown in more detail in FIG. 10 . The marker 50 is substantially rod-shaped and has an inner diameter slightly smaller than the inner diameter of the coaxial bore of the bone anchor 1. A distal portion 51 is provided, which includes a marker element 52 (e.g., an X-ray detectable element). An external advancement structure in the form of an external thread 53 configured to cooperate with the internal thread 8 of the bone anchor 1 is provided at a distance from the distal portion 51. The axial length of the external thread 53 may be equal to or less than the axial length of the internal thread 8. A shoulder 54 may be adjacent to the external thread 53 and configured to abut against a shoulder or step 9 in the channel 7 to limit insertion of the marker 50 into the bone anchor. The shoulder 54 is positioned such that the marker element is positioned at the second end 4 and may protrude slightly therefrom when the shoulder 54 abuts the shoulder 9. The stop provided by the shoulder 9 defines the position of the marker 50 relative to the bone anchor 1. Thus, the marker 50 can accurately indicate the position of the bone anchor 1.

[0032] At the time of use, the marker 50 and the bone anchor 1 may preferably be pre-assembled and inserted into the bone.

[0033] Further variations of the above-described system may be envisaged. The shape of the bone anchor is not limited to the shape shown in the embodiment. Any type of bone anchor may be used, for example a bone anchor without a bone screw, such as a bone nail. The head of the bone anchor is shown as spherical. However, any other suitable head may be envisaged. In particular, a receiving part for providing a polyaxial bone anchor may be attached to the head.

[0034] The channel of the bone anchor may have a shape other than cylindrical. The opening in the wall of the bone anchor may have any shape; in particular, a longitudinally extending slit may also be contemplated. Finally, the opening may be omitted.

[0035] The advancement structure is shown as a screw; however, multiple concentric ribs may be used to form the advancement structure, or another advancement structure may be used that allows for continuous or incremental advancement of the cutting device within the channel.

[0036] Various features of the elongate instruments may be combined to provide other embodiments of the elongate instruments. [Explanation of symbols]

[0037] 1 bone anchor, 2 shank, 3 first end, 4 second end, 7 channel, 8 internal advancement structure, 20, 30, 40, 50 elongated instrument, 23, 31, 42, 51 distal end portion, 25, 32, 43, 53 external advancement structure, L channel shaft.

Claims

1. 1. A bone anchor and elongate instrument system comprising: a bone anchor (1) including a shank (2) having a first end (3) and a second end (4), and a channel (7) extending from the first end (3) through the shank (2) to the second end (4), the channel (7) defining a channel axis (L); an internal advancement structure (8) disposed on an inner wall of the channel (7) at or near the second end (4) of the shank (2), and a bone screw (5) disposed on at least a portion of an outer surface of the shank (2), the system further comprising: an elongated instrument (20, 30, 40, 50) configured to extend through said channel (7); the elongate instrument (20, 30, 40, 50) includes a tip portion (23, 31, 42, 51) and an external advancement structure (25, 32, 43, 53) that cooperates with the internal advancement structure (8) of the shank (2) to enable the tip portion (23, 31, 42, 51) to be advanced in the channel (7) in a direction toward the second end (4) and retracted in an opposite direction toward the first end (3); the elongate instrument with the distal end portion (23, 31, 42, 51) is removable from the channel (7); the tip portion includes at least one cutting edge (24) configured to cut into bone; The system further includes a tool; the bone anchor is grasped by the tool; The elongated instrument (20, 30, 40, 50) further includes a first engagement structure configured to cooperate with a second engagement structure on the tool to prevent rotation of the elongated instrument (20, 30, 40, 50) relative to the bone anchor.

2. 2. The system of claim 1, wherein the internal advancement structure (8) is an internal thread and the external advancement structure (25, 32, 43, 53) is an external thread.

3. The system of claim 2 , wherein the female thread and the male thread are cylindrical threads.

4. 4. The system of claim 1, wherein the tip portion (23, 31, 42, 51) is configured to advance within the channel (7) from the first end (3) to the second end (4).

5. 5. The system of claim 4, wherein the tip portion (23, 31, 42, 51) is configured to advance within the channel (7) from the first end (3) to the second end (4) until it extends out from the second end (4).

6. 6. The system of claim 1, wherein the elongated instrument (20, 30, 40, 50) has a length such that the tip portion (23, 31, 42, 51) extends out from the first end (3) of the shank (2) when the tip portion (23, 31, 42, 51) is at or near the second end (4) of the channel (7).

7. 7. The system of claim 1, wherein the inner advancement structure (8) and the outer advancement structure (25, 32, 43, 53) are configured to cooperate in such a manner that the position of the elongated instrument (20, 30, 40, 50) relative to the bone anchor is axially fixed to prevent displacement.

8. 8. The system of claim 1, wherein the axial length of the outer advancement structure (25, 32, 43, 53) is equal to or greater than the axial length of the inner advancement structure (8).

9. 9. The system of claim 1, wherein the elongated instrument (20, 30, 40, 50) includes a rearward end (21) opposite the tip portion (23) and a neck portion (26, 44) adjacent to or proximate the external advancement structure (25, 43) on the rearward end (21) side.

10. 8. The system according to any one of claims 1 to 7, wherein the axial length of the outer advancement structure (25, 32) is shorter than the axial length of the inner advancement structure (8).

11. 11. The system of claim 10, wherein the axial length of the external advancement structure (25, 32) is sufficient to secure the elongate instrument (20, 30, 40, 50) against axial sliding.

12. 12. The system according to any one of claims 1 to 11, wherein a stop (9) is provided on the inner wall of the channel (7) to limit the insertion of the elongated instrument into the bone anchor.

13. The system of claim 12, wherein the tip portion includes a sensor element (46).

14. The system of claim 12 , wherein the tip portion includes a marker element (52).

15. The system of any one of claims 1 to 14, wherein the elongated instrument (20, 30, 40, 50) comprises a tube (51).

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