Coupling device for connecting a rod to a bone anchor, instrument for placing a coupling device on the head of a bone anchor, system of coupling devices for connecting a rod to a bone anchor and instrument, and method for placing a coupling device on the head of a bone anchor

Abstract

To provide a coupling device for coupling a rod to a bone anchor.SOLUTION: A receiving part (20) of a coupling device comprises a head receiving portion (22) including an interior seat (35) for pivotably receiving a head (3) of a bone anchor, the head receiving portion being expandable to permit insertion of the head and compressible to lock the inserted head in the seat. The receiving part further comprises a rod receiving portion (21) including a recess (24) having a first engagement structure (32) for engagement with an instrument (100). A locking ring (40) comprising a second engagement structure (44a) for the instrument is provided around the head receiving portion. When the locking ring is around the head receiving portion, the locking ring can assume an insertion position, in which the head (3) of the bone anchor is insertable into the head receiving portion, and a pre-locking position, in which the inserted head is prevented from removal from the head receiving portion.SELECTED DRAWING: Figure 24a

Description

[Technical field]

[0001] The present invention relates to a coupling device for connecting a rod to a bone anchor and to an instrument for placing the coupling device on the head of the bone anchor. More particularly, the present invention relates to a coupling device and an instrument that allows a receiving part with an outer locking ring to be placed in situ in the body, i.e. on the head protruding from the bone surface, with the bone anchor already inserted in the bone or vertebra. [Background technology]

[0002] A coupling device of the type with an outer locking ring arranged around the head receiving part is known, for example, from US 2018 / 0055545 A1. The coupling device is part of a polyaxial bone anchoring device and comprises a receiving part with a rod receiving part and a head receiving part, and a locking ring which forms a compression member for applying pressure to the inserted head and is arranged around the head receiving part. The head receiving part is provided with a number of slits, which provide flexibility to the head receiving part, so that the head can be clamped and finally locked when pressure is applied to the head receiving part by the locking ring. An instrument for moving the locking ring from the insertion position of the head to the locking position of the head and vice versa is also disclosed in the abovementioned document. Usually, the bone anchoring device is preassembled with the bone anchor.

[0003] US 10,258,390 B2 discloses a device for placing a receiving part of a bone anchoring device on a head of a bone anchoring element. The device comprises a holding part and a collet configured to be held in the holding part. The collet has a tubular body and a distal end portion configured to be radially flexibly expanded and compressed. The device further comprises a plunger configured to be positioned in the collet. The device can be used to engage the receiving part at the inner wall and place it on a bone anchor already inserted in the bone. The bone anchoring device disclosed in this document is of the type that uses an inner cap placed in the receiving part as a compression member for applying pressure to the head together with a rod or locking member for locking the head. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] US2018 / 0055545A1 [Patent Document 2] US10,258,390B2 Summary of the Invention [Problem to be solved by the invention]

[0005] While bone fixation devices using an inner cap to clamp and lock the head disclosed in the prior art may be suitable for many clinical applications, there remains a need for alternative and / or improved bone fixation devices that allow a coupling device including a receiving portion and a compression member to be positioned in situ on an implanted bone anchor within the body.

[0006] SUMMARY OF THE PRESENT EMBODIMENT It is therefore an object of the present invention to provide an improved coupling device, and an instrument for use with such a coupling device, as compared to known devices. [Means for solving the problem]

[0007] This object is solved by a coupling device according to claim 1, by an appliance according to claim 10 and by a system of a coupling device and appliance according to claim 16. Further developments are given in the dependent claims.

[0008] The coupling device is of the type that applies pressure to the head using an outer locking ring as a compression member and can be placed in situ on a bone anchor inserted into a bone or vertebra. Such in situ placement must be performed with care to avoid damage caused by applying too much force. The instrument includes a handheld device that allows the coupling device to be placed in situ in vivo. This can be achieved with light force and does not require the application of excessive force that may cause damage. Such a procedure is advantageous, especially in spinal surgery.

[0009] Moreover, when the coupling device is placed on the head of the bone anchor, it can perform provisional locking without a rod or locking member. A rod can also be inserted, but it does not have to rest on the rod support, but can be placed at a higher position. Thus, by moving the locking ring from the locked position to the provisionally locked position and vice versa, the bone anchoring device can be locked and unlocked, allowing various adjustment steps to be performed. Only the presence of a rod and / or a locking member is required for the final locking at the end of the surgical procedure. Thus, the coupling device can be placed in situ in the body with the head provisionally and / or variably locked, which increases the variety of correction steps that can be performed during the procedure.

[0010] The locking ring can be moved to a provisionally locked position after placement on the head of the bone anchor using an instrument, which prevents the coupling device from disengaging from the head of the inserted bone anchor after it has been connected to the head of the bone anchor, and therefore allows the instrument to be safely removed.

[0011] According to one embodiment, the coupling device is configured to be engaged by the instrument at the inner wall of the leg of the rod channel. Since the receiver is not engaged by the instrument on the outer circumferential surface, less space may be required to place the coupling device on the head of the bone anchor already inserted in the bone. This allows access to the implantation site using a narrow path through the tissue of the body. Thus, the instrument and the coupling device are particularly applicable to minimally invasive surgery (MIS).

[0012] Furthermore, according to one embodiment, the arms of the instrument are resiliently flexible, which provides a tactile response when attaching the instrument to the coupling device, which facilitates attachment of the instrument to the coupling device.

[0013] Further features and advantages of the present invention will become apparent from the following detailed description of the embodiments taken in conjunction with the accompanying drawings. [Brief description of the drawings]

[0014] [Figure 1] FIG. 1 is a perspective view of a portion of a spinal column with bone anchors implanted therein and an instrument according to an embodiment attached to a coupling device according to an embodiment. [Diagram 2] FIG. 2 shows an enlarged portion of FIG. [Diagram 3] FIG. 13 is a cross-sectional view of an embodiment of a coupling device and tool disposed on the head of a bone anchor along a plane that includes the central longitudinal axis of the tool and is perpendicular to the centers of the legs of the receiver. [Figure 4] FIG. 4 is a perspective view of a receiving portion of the connecting device of FIGS. 1 to 3, as viewed from above. [Diagram 5] FIG. 5 is a bottom perspective view of the receiving part of FIG. 4. [Figure 6] FIG. 6 is a top view of the receiving part of FIGS. 4 and 5; [Figure 7] 7 is a cross-sectional view showing the receiving portion of FIGS. 4 to 6 taken along the line AA of FIG. [Figure 8]FIG. 4 is a perspective view from above of a locking ring of the coupling device of FIGS. 1 to 3; [Figure 9] FIG. 9 is a bottom perspective view of the lock ring of FIG. 8. [Figure 10] FIG. 10 is a top view of the lock ring of FIGS. 8 and 9. [Figure 11] 11 is a cross-sectional view showing the lock ring of FIGS. 8 to 10 taken along line BB in FIG. [Figure 12] FIG. 4 is a perspective view showing a front portion of the device of FIGS. 1 to 3. [Figure 13] 13 is a cross-sectional view of the front portion of the instrument shown in FIG. 12 taken along a plane that includes the central longitudinal axis of the instrument and extends through the centers of the arms of the instrument. [Figure 14] FIG. 14 is a top perspective view of the end of the retaining member of the device shown in FIGS. 12 and 13. [Figure 15] FIG. 15 is a bottom perspective view of the retaining member of the device of FIGS. 12 to 14. [Figure 16] FIG. 16 is a side view showing a retaining member of the device of FIGS. 12 to 15. [Figure 17] 17 is a cross-sectional view of the front portion of the retaining member of the device shown in FIG. 16 taken along a plane that includes the central longitudinal axis of the device and extends through the center of the arm. FIG. [Figure 18] FIG. 14 is a top perspective view of the front portion of the pusher member of the device of FIGS. 12 and 13; [Figure 19] FIG. 19 is a bottom perspective view of the pressing member of FIG. 18. [Figure 20] 20 is a side view showing a front portion of the pressing member shown in FIGS. 18 and 19. FIG. [Figure 21a] FIG. 13 is a side view showing the step of attaching the tool to the coupling device. [Figure 21b] FIG. 13 is a side view showing the step of attaching the tool to the coupling device. [Figure 21c] FIG. 13 is a side view showing the step of attaching the tool to the coupling device. [Figure 21d] FIG. 13 is a side view showing the step of attaching the tool to the coupling device. [Figure 22]FIG. 13 is a perspective view showing the step of fixing the front part of the instrument to the coupling device. [Figure 23] 13 is a perspective view showing a step of adjusting the provisional lock position of the lock ring relative to the receiving portion with a tool. FIG. [Figure 24a] 13A-13D show a step of placing an instrumented coupling device onto the head of a bone anchor inserted into bone. [Figure 24b] 13A-13D show a step of placing an instrumented coupling device onto the head of a bone anchor inserted into bone. [Figure 24c] 13A-13D show a step of placing an instrumented coupling device onto the head of a bone anchor inserted into bone. [Diagram 25] FIG. 13 is a perspective view of a portion of a spine with a bone anchor and a connecting device inserted therein and the attachment of another device for locking the connecting device to the bone anchor. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] 1-3 show a first embodiment of a coupling device 10 engaged by a tool 100 for placing the coupling device on the head of the bone anchor. According to one embodiment, the bone anchor 1 can already be inserted into the bone (e.g., the pedicle of the vertebral bone 500) before mounting the coupling device thereon. The bone anchor 1 comprises a shank 2 adapted to be anchored to the bone, and a head 3. The shank 2 may comprise, at least in a portion thereof, a bone anchoring structure, such as, for example, a bone screw or a barb, or any other suitable structure for anchoring. The head 3 may have a spherical outer surface portion. For example, the head 3 may have dimensions such that it includes the maximum outer diameter of a sphere. At the free end of the head 3, an engagement recess 4 may be provided for engagement with a screwdriver. The coupling device 10 is adapted to couple the bone anchor 1 to a rod (not shown) adapted to be inserted and fixed in the coupling device. As can be seen in particular from FIG. 3, the coupling device 10 comprises a receiving part 20 and a locking ring 40. The receiving part serves to accommodate the head 3 and to receive the rod (not shown). The locking ring 40 is configured to clamp and / or lock the head 3 to the receiving part 20. The bone anchor 1 and the coupling device 10 form a polyaxial bone fixation device configured to allow coupling of a rod to the bone anchor at various angular positions of the bone anchor.

[0016] With additional reference to Figures 4-7, the receiving portion has a first or upper end 2a and a second or lower end 2b. A longitudinal central axis C extends from the upper end 2a to the lower end 2b. The receiving portion includes a rod receiving portion 21 adjacent the upper end 2a and a head receiving portion 22 adjacent the lower end 2b. The rod receiving portion 21 is substantially cylindrical and defines a central axis C and has a passageway 23 extending from the upper end 2a into the head receiving portion 22. The passageway 23 may have regions with different diameters and / or shapes. In this embodiment, the first region 23a may be a coaxial bore with a first diameter and extends from the upper end 2a to a distance away from the head receiving portion (22). The first region 23a may be followed by a narrower second region 23b, which may be followed by a third region 23c with an even narrower diameter, which opens into the head receiving part 22. A step 23d may be provided between the first region 23a and the second region 23b. Similarly, a step 23e may be provided between the second region 23b and the third region 23c. In addition, the second region 23b may have two cylindrical segment shaped recesses 39 extending axially opposite to each other, as best shown in FIG. 4. The recesses 39 serve as a guide structure for a portion of the instrument 100. It should be noted that the detailed shape of the passage may differ from the illustrated embodiment.

[0017] A substantially U-shaped recess 24 with a bottom 24a extends from the upper end 2a to a distance away from the head receiving part 22. The substantially U-shaped recess 24 forms two free legs 25. The recess 24 provides a passage for receiving a rod. An internal thread 26 is provided on the legs 25 and extends from substantially the upper end 2a to a distance away from the bottom 24a of the recess 24. In other words, the internal thread 26 is provided substantially along the first area 23a of the passage. The internal thread 26 may be, for example, a square thread, which may be advantageous in preventing the legs 25 from spreading. An undercut 26a may be formed at the lower end of the internal thread 26 facing the head receiving part 22. Away from the upper end 2a, a groove or weakened area 27 is provided. The groove or weakened area 27 has a thin wall and allows the upper part of the leg 25 to be broken off. The circumferential edge of the weakened area 27 may be formed with a circumferentially extending recess or cutout 27a, which further weakens the weakened area 27 and may facilitate breaking off the upper part of the leg 25. The internal thread 26 may also be interrupted inside the passage 23 at an axial position corresponding to the lower edge of the weakened area 27. The upper leg of the weakened area 27 may thus act as an enlarged tab. This allows the polyaxial bone anchoring device to be operated with an inserted rod that may be higher compared to the bottom 24a of the recess 24. This allows, for example, to draw the vertebrae towards the rod.

[0018] The outer surface of the rod receiving part 21 may be provided with an engagement structure for engaging with an instrument (e.g., an instrument 300 as shown in FIG. 25). The engagement structure may include circumferentially extending ribs 28. The ribs 28 may be arranged asymmetrically with respect to a plane containing the central axis C of the receiving part 20 and the path axis L of the substantially U-shaped recess 24. This means that a first rib starts away from the edge of the U-shaped recess 24 on one side and extends around the receiving part 20 to a certain distance. A second rib starts on the opposite side to the U-shaped recess and extends around the rod receiving part to a certain distance from there. This forms a ribless surface 29 on both sides of the U-shaped recess 24. Below each rib 28, a substantially flat outer surface portion 30 may be formed. The outer surface portion 30 may have a rectangular or square profile and may serve to engage with a portion of the locking ring 40. Two latch grooves or steps 31a, 31b may be provided axially alternating between the rib 28 and the substantially flat surface portion 30. The latch grooves 31a and 31b are configured to cooperate with a portion of the lock ring 40 to temporarily hold the lock ring 40 in a position. The upper latch groove 31a may serve to prevent the lock ring from moving further upwards in the insertion position. The lower latch groove 31b may serve to latch the lock ring 31b in the temporary lock position.

[0019] Between the weakened area 27 and the bottom 24a of the substantially U-shaped recess 24, an engagement structure 32 for engaging with the instrument 100 may be provided. The engagement structure 32 may be formed as a shallow circular groove, preferably substantially cylindrical, and may be located at the edge of the leg 25. There may be four such grooves, two on each leg 25 and one on each side of each leg 25. The axial position of the engagement structure 32 may be slightly below the weakened area 27. Preferably, the engagement structure 32 is shaped to allow a corresponding engagement portion of the instrument 100 to be fitted thereto to slide in and out of the engagement structure 32. More specifically, the engagement portion of the instrument may snap resiliently into the engagement structure 32.

[0020] Furthermore, cut-outs 33 may be provided on either side of the substantially U-shaped recess 24 which may serve to receive the protrusions of the locking ring 40, thereby fixing the locking ring 40 against rotation relative to the receiving part 20. The outer diameter or narrowing of the rod receiving part 21 forms a step 34 from a position above the cut-outs 33 to the lower end 2b. The step 34 serves as a further abutment for the locking ring.

[0021] The head receiving part 22 has a substantially cap-shaped shape and includes a substantially spherical hollow interior 35 forming a seat for pivotally receiving the head 3. A number of slits 36a, 36b provide flexibility to the head receiving part 22, which allows it to expand when the head 3 is inserted into the hollow interior 35. When pressure is applied by the locking ring 40 against the inserted head 3, the head receiving part 22 is compressed. The slits open towards the lower end 2b and extend along the spherical section. The slit 36a terminates at the end of the spherical section. The other slits 36b may extend into a region of the rod receiving part that includes the third region 23c of the passage 23. The outer surface of the head receiving part 22 may be radially recessed with respect to the lower end of the rod receiving part 21. The outer surface may include a bottom section 37a that may be cylindrical or may taper slightly outwardly. The base section 37a forms an annular protrusion that is configured to cooperate with a corresponding portion of the lock ring 40. The base section 37a is followed by a circumferential groove, which is followed by a radially outwardly bulging raised portion 37b that is configured to cooperate with another portion of the lock ring 40. The raised portion 37b narrows towards the rod receiving portion, which provides the head receiving portion 22 with a concave shape.

[0022] Now, with reference to Figures 8 to 11, the locking ring 40 will be described. The locking ring 40 is designed to surround the head receiving portion 22. The locking ring 40 further has an inner surface structure that allows the inserted head 3 to be fully locked in the head receiving portion 22 in cooperation with the head receiving portion 22 when the locking ring is in its lowest position. This further allows a provisional lock to be achieved when the locking ring is in a position slightly above the lowest position. This provisional lock allows the head 3 to rotate in the head receiving portion 22, while preventing the head 3 from being removed from the head receiving portion 22. Finally, the locking ring is configured to allow the head 3 to be inserted into the hollow interior 35 when the locking ring is in its uppermost position relative to the receiving portion.

[0023] More specifically, the lock ring 40 has a lower surface 4b and an opposite upper surface 4a, and is substantially ring-shaped. Adjacent to the lower surface 4a, a first radial projection 41 is provided toward the inside. The first radial projection 41 is configured to cooperate with the outer portion 37a of the head receiving part. The annular projection 41 is followed by a widened area 42. The widened area 42 is followed by a second annular projection 43 on the side of the upper surface 4a. The second annular projection 43 protrudes toward the inside. As shown in FIG. 3, when the lock ring 40 is fitted around the head receiving part 22, the first annular projection 41 is configured to press against the first portion 37a of the head receiving part, and the second annular projection 43 is configured to press against the raised portion 37b.

[0024] Two projections 44 protrude from the upper surface 4a of the ring-shaped part of the locking ring 40. The two projections 44 have free end faces forming rod support surfaces 44a for the stabilization rods. The projections 44 are diametrically opposed (i.e. offset by 180°). The rod support surfaces may have a substantially V-shaped cross section to allow safe support of rods of different diameters. When the locking ring 40 is mounted on the receiving part 20 with the upper surface 4a facing the upper end 2a of the receiving part, the projections 44 extend through the cutouts 33, so that the rotational orientation of the locking ring 40 relative to the receiving part 20 is fixed. The locking ring 40 also includes two upstanding arms 45. The two upstanding arms 45 are asymmetrically positioned with respect to a plane extending through the central axis C and through the center of the rod support surface 44a, in the same manner as the ribs 28 of the rod receiving part 21 of the receiving part 20. At the upper end of the arm 45, an engagement portion in the form of a circumferential rib 46 defining a groove 46a is provided for engagement with an instrument. Such an instrument may be, for example, the instrument 300 as shown in FIG. 25. The arm 45 may have an inwardly facing upper edge 45a. The upper edge 45a is configured to engage with the latch grooves 31a, 31b in the receiver 20. In the assembled state, the engagement structure in the form of the rib 46 with the groove 46a is aligned with the engagement structure 28 in the receiver 20, leaving the non-ribbed surface 29 of the receiver 20 exposed. Furthermore, the arm 45 has a substantially flat inner wall configured to engage with the flat portion 30 in the rod receiver 21. This provides a more form-fitting connection between the lock ring 40 and the receiver 20. Between the projection 44 and the arm 45 there is an upstanding flexible portion 47. The upstanding flexible portion 47 is configured slightly higher than the projection 44 and includes a ledge 47a on its inner wall which is configured to abut against the step 34 on the receiving part 20.

[0025] The bone fixation device according to one embodiment may further include a rod configured to be inserted into the substantially U-shaped recess 24 and a locking member (e.g., a set screw, etc.) configured to be screwed between the legs 25.

[0026] With reference to Figures 12 to 20, an embodiment of the tool 100 for placing the coupling device 10 on the head 3 of the bone anchor 1 will be described in more detail. As additionally shown in Figure 1, the tool 100 includes a substantially tubular holding member 101 and a shaft-like pressing member 120 arranged inside the holding member 101. The holding member 101 includes a rear portion connected to or comprising a handle 102 and a front portion. The front portion is bifurcated via a slot 104 to include two arms 105. The two arms 105 are configured to be flexibly compressible and expandable in a transverse direction to the longitudinal tube axis T of the holding member. The slot 104 extends from the free end 101a of the holding member 101 in a substantially U-shaped manner, with a bottom facing the rear end of the holding member. A substantially straight portion 104b continues from the bottom of the slot and opens into an elongated portion 104c. It should be noted that the slots may have different shapes to provide varying degrees of flexibility.

[0027] The arms 105 have a front portion 105a adjacent the free end 101a. The front portion 105a is recessed from the overall cylindrical shape of the retainer to fit into the rod receiving portion of the receiver 20. The recessed configuration of the front portion 105a of the arms 105 provides an abutment surface 106 at the end of the front portion 105a. The abutment surface 106 may abut against the upper end 2a of the receiver when the front portion 105a of the arms is inserted into the rod receiving portion. The front portions 105a of the arms each have a recess 107 adjacent the free end 101a. The recesses 107 may be substantially rectangular. The recesses 107 form two short legs 107a in each of the front portions 105a of the arms 105. This design allows the front portions 105a of the arms to extend downwardly into the lowermost region of the substantially U-shaped recess 24. The outer surface of the front portion 105a includes an axially extending, substantially cylindrical segment shaped rib or protrusion 108 configured to engage a cylindrical recess 39 in the second section 23b of the rod receiving portion 21.

[0028] Furthermore, each arm 105 includes an engagement portion 109 away from the abutment surface 106. The engagement portion 109 is configured to engage with the engagement structure 32 in the rod receiving part 21. More specifically, the engagement portion 109 may be formed as a cylindrical protrusion along a cylindrical axis extending transversely to the longitudinal axis T of the holding part and may be arranged and configured to engage with the groove 32. As can be particularly seen from Figures 12, 14 and 15, each front part 105 includes two engagement portions 109. The two engagement portions 109 are located to the right and left of the axial cylindrical protrusion 108. The arms 105 may be substantially flat on their outer surface except in the area of ​​the axial protrusion 108 and the engagement portions 109. The inner wall of the front part 105a is formed with cylindrical recesses 110 extending coaxially therein in the area adjacent to the recess 107. These recesses 110 guide the pressing member 120. The front portions 105a of the arms may include an expanded diameter section 111 on their inner side adjacent the recess 110. The expanded diameter section 111 is for providing sufficient space to allow the push member 120 to slide therethrough. A stepped portion 111a may be formed between the recess 110 and the expanded diameter section 111 to form an abutment for a stepped portion on the outer surface of the push member, as described below.

[0029] Here, the pressing member 120 will be described with particular reference to Figs. 18 to 20. As shown diagrammatically in Fig. 1, the pressing member 120 may be connected at its rear side to a knob 121. The knob 121 is adapted to displace the pressing member 120 within the holding member 101. The handle 102 may additionally accommodate a mechanism (not shown) that transmits the rotational movement of the knob 121 to an axial displacement of the pressing member 120 relative to the holding member 101. Various mechanisms for displacing the pressing member 120 relative to the holding member may be contemplated. For example, the mechanism may be designed to be capable of axially pressing the pressing member to a maximum position relative to the holding member by rotating the knob 121, and to retract the pressing member from the maximum axial position when the knob 121 is further rotated.

[0030] The front part of the pressing member 120 is shown in detail in Figs. 18-20. The pressing member 120 comprises a first substantially cylindrical section 122 adjacent to the free end 120a. The first substantially cylindrical section 122 comprises an outer diameter adapted to fit into an axially cylindrical recess 110 in the inner wall of the front part 105a of the holding member (see further Fig. 13). Next to or close to the free end 120a, an elongated engagement portion 123 is provided. The elongated engagement portion 123 extends transversely to the longitudinal axis T (in particular perpendicularly to the longitudinal axis). The elongated engagement portion 123 has a rod shape in the illustrated embodiment and may be realised by a pin extending through a transverse hole in the front part 122. The length of the elongated engagement portion 123 is at least longer than the distance between the projections 44 on the locking ring 40, so that the rod support surface 44a of the projections 44 can be engaged by the elongated engagement portion 123. In other words, the elongated engagement portion 123 forms a kind of dummy rod that is configured to press against the rod support surface 44a. Next to the first cylindrical section 122, a second section 124 with a slightly larger outer diameter may be provided, so that a shoulder 122a is formed between the second section 124 and the first section 122. The shoulder is configured to abut against the step portion 111a on the inside of the retaining member 101. The second section may have a length such that it extends further into the retaining member than the length of the front portion 105a of the arm. To provide further stability, a third section 125 with an even larger diameter may be provided.

[0031] The front portion 105a of the arm is configured for insertion into the rod receiving part 21 and is sized so that when the abutment surface 106 abuts the upper end 2a of the receiving part 20, the leg 107a extends a short distance from the bottom 24a of the substantially U-shaped recess 24 in the receiving part 20. In this position, the engagement portion 109 is at an axial height to allow engagement with the engagement structure 32 in the receiving part.

[0032] The parts and portions of the bone anchors, coupling devices and instruments may be made of any material, but preferably biocompatible materials, such as titanium or stainless steel, or any other biocompatible metal or metal alloy, or plastic materials. As biocompatible alloys, NiTi alloys (for example Nitinol) may be used. Other materials may be magnesium or magnesium alloys. Biocompatible plastic materials used may be, for example, polyether ether ketone (PEEK) or poly-L-lactide acid (PLLA). The parts may be made of the same or different materials.

[0033] The use state of the coupling device 10 and the tool 100 will be described with reference to Figs. 21a to 24c. First, the steps of assembling the coupling device 10 and the tool 100 will be described. The coupling device includes the receiving part 20 and the locking ring 40 in the pre-assembled state. As shown in Fig. 21a, the pressing member 120 is in a storage position further away from the free end portion 101a of the holding member than the engagement portion 109. The locking ring 40 is mounted on the receiving part so that the projection 44 engages with the cutout 33 of the receiving part. To engage with the tool 100, the locking ring 40 is in an insertion position. In this insertion position, the end edge 45a of the arm 45 abuts against the latch step 31a arranged axially higher. In this insertion position, the head 3 can enter the hollow interior 35 of the head receiving part 22. The distance between the front portions 105a of the arms 105 is such that when the front portions of the arms are inserted between the legs 25, the front portions 105 are compressed towards each other.

[0034] When the front portions 105a of the arms are compressed towards each other by the inner walls of the legs 25, as shown in Fig. 21b, the front portions 105 can penetrate deeper into the passage 23. When the engagement portion 109 on the outer wall of the front portions 105a of the arms reaches the engagement structure 32 on the receiver 20, the engagement portion 109 snaps into the engagement structure 32, as shown in Fig. 21c. The retaining member 101 is fixedly connected to the receiver 20 because the front portions 105a of the arms 105 are prevented from being compressed inwards. As a result, the coupling device 10 is fixedly connected to the instrument. Fig. 21d shows the fixed connection between the retaining member 101, the receiver 20 and the pressing member 120 in the forward pushing position, where the elongated engagement portion 123 is in contact with the rod support surface 44a.

[0035] 22 and 23 show the position of the pressing member 120 relative to the holding member 101 in a more detailed perspective view. In FIG. 22, the pressing member is in a position above the engagement portion 109 and the engagement structure 32 and starts to expand the front portion 105a of the arm. In FIG. 23, the pressing member is pushed downwards until the elongated engagement portion 123 is in a position slightly above the rod support surface 44a of the projection 44. The elongated engagement portion 123 is not yet in contact with the rod support surface 44. From this position, a small axial movement of the pressing member downwards allows the elongated engagement portion 123 to press against the rod support surface 44a. This causes the locking ring 40 to move downwards, allowing the annular projection 41 of the locking ring to engage with the bottom portion 37a at the outer surface of the head receiving part 22. This narrows the lower opening of the hollow interior 35 so that the inserted head 3 cannot be removed.

[0036] 24a-c, the positioning and use of the coupling device 10 and the tool 100 are shown together with the bone anchor 1. In FIG. 24a, the shank 2 has already been inserted into the bone (e.g. into the vertebrae 500) before the coupling device is fitted onto the head. The tool is fixedly connected to the coupling device and the locking ring is in the insertion position. In this insertion position, the head receiving part is expandable to allow the head 3 to enter therein. The engagement portion 123 does not yet press against the rod support surface 44a. As shown in FIG. 24b, the coupling device is placed onto the head 3 by the tool 100. In this way, the head 3 can fit into the hollow interior 35 of the head receiving part 22 and be held there by friction. In the next step, shown in FIG. 24c, the pressing member 120 is moved towards the locking ring 40. The pressing member is moved further downwards to press the locking ring 40 downwards until the engagement portion 123 contacts the rod support surface 44a of the projection 44 as shown in FIG. 24c. This causes the arms 45 to engage with their edges 45a in the lower latch recesses 31b in the receiver. The locking ring 40 is then in the pre-locked position and is latched there. In addition, the ledge 47b of the projection 47 can fit under the step 34 on the outer surface of the rod receiver, further securing the pre-locked position. After reaching the pre-locked position, the pressing member 120 is retracted. When the pressing member 120 is in a position such that it does not obstruct the engagement portion 109 and the engagement structure 32, the flexible front portions 105a of the arms can be compressed towards each other and the instrument can be removed from the head.

[0037] After placement of the coupling device, the polyaxial bone anchoring device is in a provisionally locked position: the head can be held in the seat by friction, allowing the coupling device to assume a certain angular position relative to the shank, which can be temporarily maintained before final locking.

[0038] In clinical applications, multiple polyaxial bone anchoring devices are inserted into bone portions or vertebrae, for example into the pedicles of a vertebra 500 as shown in FIG. 25. The coupling devices 10 are then aligned such that at least two or more of the bone anchoring devices can receive rods (not shown). In another instrument 300, as shown diagrammatically in FIG. 25, different from the above-mentioned instrument 100, the locking ring can be moved from a provisional locking position to a locked position to release the locked position. In the locked position, the locking ring 40 is moved further downward until the head receiving portion 22 is tightly compressed so that the head is locked. The instrument 300 can include an outer tube that engages the locking ring, for example at the engagement portion 28, and an inner tube that engages the rod receiving portion. The inner tube can be displaceable relative to the outer tube. Thus, the locking ring can be moved from a provisional locking position to a locked position or vice versa by displacing the outer tube relative to the inner tube. The adjustment of the coupling device to the bone anchor can be performed without placing the rod and / or the locking member in the rod receiving part or the rod can be placed at a higher position compared to the bottom 24a of the recess 24. It should be noted that the locking and unlocking can be performed any number of times. Once the correct position of the coupling device has been adjusted, it is locked to the bone anchor by means of the locking member screwed between the legs 25. Finally, the upper parts of the legs can be broken off.

[0039] Variations of the described embodiment may also be contemplated. The above-mentioned parts are not limited to the detailed shapes as shown in this embodiment. In particular, the specific shapes of the receiver and the locking ring may vary. The shape and structure of the engagement between the receiver and the instrument may differ from the illustrated embodiment. The design of the instrument, in particular for placing the coupling device on the head of the front part, is not limited to the specific design shown in this embodiment. Other shapes may also be suitable. For example, the instrument may engage the receiver on its outer surface.

[0040] A rod is intended to encompass any elongated device configured to connect two bone anchoring devices. As bone anchors all kinds of bone anchors can be used, such as bone screws, bone nails, etc.

[0041] Further provided is a method of assembling the coupling device 10 with the tool 100. The coupling device includes a receiving portion. The receiving portion includes a head receiving portion for pivotally receiving the head of the bone anchor and a rod receiving portion including a recess. The recess forms two open legs and a bottom and defines a passage for receiving the rod. The receiving portion further includes a locking ring configured to be disposed around the head receiving portion. The locking ring can be in an insertion position in which the head can be inserted into the head receiving portion and in a pre-locked position in which the head is prevented from being removed from the head receiving portion. The tool includes a retaining member configured to engage the receiving portion and a pressing member. The pressing member is displaceable relative to the retaining member and configured to engage the locking ring. The method includes the step of engaging the receiving portion with the retaining member when the locking ring is in the insertion position. The assembling step is performed prior to placing the coupling device on the head of the bone anchor. [Explanation of symbols]

[0042] 1 bone anchor, 3 head, 10 coupling device, 20 receiving portion, 21 rod receiving portion, 22 head receiving portion, 24 recess, 24a base, 25 foot, 32 first engagement structure, 40 locking ring, 44a second engagement structure, 100 instrument.

Claims

1. 1. A coupling device for coupling a rod to a bone anchor, comprising: The coupling device includes a receiving portion (20), the receiving portion comprising: a head receiving portion (22) including an inner seat (35) for pivotably receiving the head (3) of the bone anchor, said head receiving portion being expandable to allow insertion of said head and compressible to lock the inserted head in said seat, said receiving portion further comprising: a rod receiving portion (21) including a recess (24) forming two open legs (25) and a bottom (24a), said recess defining a passage for receiving said rod, said rod receiving portion including a first engagement structure (32) for engagement with an instrument (100), said receiving portion further comprising: a locking ring (40) configured to be disposed about the head receiving portion (22), the locking ring including a second engagement structure for the instrument (100); the locking ring (40) including a protrusion (44) having a free end surface forming a rod support surface (44a) for an inserted rod, the rod support surface (44a) forming the second engagement structure; When the locking ring (40) is around the head receiving portion (22), the locking ring can take an insertion position in which the head (3) of the bone anchor can be inserted into the head receiving portion, and a provisional locking position in which the inserted head (3) can rotate in the head receiving portion (22) but is prevented from coming out of the head receiving portion, the locking ring (40) is movable from the insertion position to the provisional locking position by an instrument engaging the first engagement structure (32) and the instrument pressing against the second engagement structure; a coupling device configured to be disposed on the head of the bone anchor when the first engagement structure is engaged with the instrument when the locking ring is in the insertion position.

2. 2. The connecting device according to claim 1, wherein the receiving part has an upper end (2a) adjacent to the rod receiving part (21) and a lower end (2b) adjacent to the head receiving part (22), and the bone anchor (1) can be inserted from the lower end (2b) of the receiving part into the head receiving part (22), and the bone anchor (1) is a bone anchor inserted into a bone.

3. 3. The coupling device of claim 1 or 2, wherein the locking ring (40) is configured to be moved from the insertion position to the pre-locked position by a downward movement of the locking ring (40).

4. 4. The coupling device of claim 3, wherein the locking ring (40) is movable from the insertion position to the pre-locked position by pressing the second engagement structure (44a) with the tool (100).

5. The coupling device of any one of claims 1 to 4, wherein the first engagement structure (32) comprises a recess or protrusion capable of engaging a corresponding protrusion (109) or recess on the instrument (100).

6. A coupling device according to claim 5, wherein the recesses (32) or protrusions are formed at opposite positions on each of the legs (25).

7. A coupling device according to any one of claims 1 to 6, wherein the first engagement structure (32) is located on a portion of an inner wall of at least one of the legs (25).

8. The coupling device of claim 7, wherein the first engagement structure (32) is located at or near an edge of the recess (24) for receiving the rod.

9. 9. A coupling device according to any one of claims 1 to 8, wherein the locking ring (40) comprises two of the projections (44) offset by 180°, each of the projections (44) having a free end face forming a rod support surface (44a) for an inserted rod, the rod support surface (44a) forming the second engagement structure.

10. 10. The coupling device of claim 1, wherein the receiving portion (20) includes a third engagement structure (31 a) configured to engage with the locking ring (40) such that the locking ring is prevented from moving beyond the insertion position in a direction away from the provisional locking position.

11. The coupling device according to claim 10, wherein the third engagement structure (31a) is located on an outer surface of the rod receiving portion (21).

12. The coupling device of any one of claims 1 to 11, wherein the receiving portion (20) includes a fourth engagement structure (31b), the fourth engagement structure (31b) configured to engage with the locking ring (40) such that the locking ring is latched in the provisional lock position relative to the instrument (100).

13. The coupling device according to claim 12, wherein the fourth engagement structure (31b) is located on an outer surface of the rod receiving portion (21).

14. 14. A coupling device according to any one of the preceding claims, wherein the locking ring (40) is capable of assuming a locking position relative to the head receiving portion (22) in which the head receiving portion is compressed such that the head (3) is locked.

15. 15. An instrument for placing a coupling device according to any one of claims 1 to 14 on a head of a bone anchor, comprising: The device (100) comprises: a retaining member (101) configured to engage with the receiving portion (20); and a pressing member (120) that is displaceable relative to the retaining member (101), wherein the instrument (100) is configured to position the connecting device (10) on the head (3) of the bone anchor (1) when the retaining member (101) engages with the receiving portion (20) and the locking ring (40) is in the insertion position.

16. 16. The instrument of claim 15, wherein when the connecting device (10) is placed on the head (3) of the bone anchor (1), the pressing member (120) is configured to engage the locking ring (40) to move the locking ring (40) to the provisionally locked position.

17. 17. The device of claim 15 or 16, wherein the retaining member (101) has a longitudinal axis and includes a front portion with two arms (105, 105a), the front portion configured to be inserted between the legs (25) and configured to engage the rod receiving portion (21).

18. 18. The device of claim 17, wherein the arms (105, 105a) are configured to be flexibly expanded and / or compressed in a direction transverse to the longitudinal axis and include an engagement portion (109) configured to engage an engagement structure (32) on an inner wall of the leg (25) of the rod receiving portion (21).

19. 19. The device according to claim 17 or 18, wherein the pressing member (120) is configured to be pressed between the arms (105, 105a) to expand the arms to secure the retaining member (101) to the receiving part (20).

20. 20. The device according to any one of claims 15 to 19, wherein the engagement portion (123) at the end portion of the pressing member (120) is substantially elongated along a longitudinal axis extending substantially transversely to the longitudinal axis of the retaining member (101).

21. 21. The instrument of claim 20, wherein the engagement portion (123) is configured to engage a rod support surface (44a) on the locking ring (40).

22. 22. A system of a coupling device for coupling a rod to a bone anchor and an instrument, said coupling device comprising a coupling device (10) according to any one of claims 1 to 14 and said instrument comprising an instrument (100) according to any one of claims 15 to 21.

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