Coupling device and bone anchoring device and bone anchoring system

Abstract

A coupling device for coupling a rod to a first bone anchor (1) of a first type or a second bone anchor (1 ') of a second type is provided, the coupling device (10) comprising: a receiving part (5), a locking member (6), the head being pivotable in a first position, the head being locked in the accommodation space (54) in a second position; wherein the head receiving portion (52) comprises a constraining structure (150) by means of which the coupling device is configured to cooperate with the first bone anchor (1) such that the first bone anchor (1) is configured to pivot in a single plane relative to the central axis (C), or to cooperate with the second bone anchor (1 ') such that the second bone anchor (1') is configured to pivot in a single plane relative to the central axis (C). The second bone anchor (1 ') is configured such that when the locking member (6) is in the first position, the second bone anchor (1') is configured to pivot in a plurality of planes relative to the pivot axis (C).

Description

Technical Field

[0001] The invention relates to a coupling device for coupling a rod to a bone anchor, a bone anchoring device having such a coupling device and a bone anchoring system comprising such a coupling device and at least two bone anchors. Background Art

[0002] A coupling device is used in orthopedic surgery, in particular spinal surgery, for coupling a rod to a head of a bone anchor anchored in a bone or vertebra. The head of the bone anchor can be pivotally received in a receiving part of the coupling device that also accommodates the rod, so that the receiving part can assume various angular positions relative to the bone anchor. Thus, a suitable orientation of the bone anchor relative to the rod can be achieved.

[0003] In order to lock the insertion head in a specific angular position relative to the receiving part, EP 4 074 271 A1 describes a receiving part, which includes a head receiving part for accommodating the head of the anchoring element, and a locking member, which can be mounted to the receiving part so that it surrounds the head receiving part. The locking member is designed as an outer ring and can be moved between a first position and a second position. In the second position, the locking member compresses the head receiving part to lock the insertion head. In addition, the head receiving part has a locally reduced wall thickness to facilitate the expansion of the head receiving part, thereby easily inserting the head of the bone anchor, while the thicker wall part of the head receiving part provides sufficient strength and stability when clamping the insertion head.

[0004] The bone anchoring device described in EP 4 074 271 A1 is a polyaxial bone anchoring device, which is configured such that the bone anchor can pivot relative to the receiving part in multiple planes. Depending on the use or clinical application, it may be desirable to provide a bone anchoring device that is configured to limit the pivoting of the bone anchor relative to the receiving part to a single plane, i.e., a monoplanar bone anchoring device, or a monoaxial bone anchoring device that is configured to prevent the bone anchor from pivoting relative to the receiving part.

[0005] Various designs of uniplanar bone anchoring devices are known, in which the shank of the bone anchor can be pivoted in the receiving part only in a single plane. For example, US 7,749,258 B2 describes a bone anchoring device in the form of a uniplanar bone anchoring device, which comprises a receiving part for receiving a rod, a pressure element and a bone anchoring element movable relative to the receiving part within a limited angular range around the longitudinal axis of the receiving part, the angle being located in a single plane. The movement of the bone anchoring element relative to the receiving part is limited by a form-fit connection, which comprises cooperating guide surfaces at the head of the bone anchoring element and at the pressure element.

[0006] There remains a need to provide a coupling device having a simple structure with only a few parts, which may allow for at least a polyaxial and a uniplanar bone anchoring arrangement. Summary of the invention

[0007] Therefore, it is an object of the present invention to provide a coupling device that can be used in a modular bone anchoring device that can have selectable functionality in terms of multiaxial and uniplanar design. Another object is to provide a bone anchoring system comprising such a coupling device and at least two bone anchors that provide different functionalities to the bone anchoring device.

[0008] This object is solved by a coupling device, a bone anchoring device and a bone anchoring system according to the present application.

[0009] According to an embodiment, a coupling device for selectively coupling a rod to a first bone anchor of a first type or a second bone anchor of a second type is provided. The coupling device includes a receiving component having a first end, an opposite second end, and a central axis extending through the first end and the second end, the receiving component including a rod receiving portion for receiving the rod and a head receiving portion, wherein the head receiving portion includes a receiving space for pivotally receiving a head of the first bone anchor or the second bone anchor, so that the handle of the first bone anchor or the second bone anchor can assume a plurality of angular positions relative to the central axis. The coupling device further comprises a locking member which is positionable at least partially around the head receiving portion and which is movable between at least a first position and a second position, in which the head is pivotable in the first position and in which the head is locked in the accommodation space; wherein the head receiving portion comprises a constraint structure, by means of which the coupling device is configured to cooperate with the first bone anchor such that the first bone anchor is configured to pivot relative to the central axis in a single plane, or to cooperate with the second bone anchor such that when the locking member is in the first position, the second bone anchor is configured to pivot relative to the pivot axis in multiple planes.

[0010] By selecting a first bone anchor and assembling it with the coupling device, the coupling device can be used as a monoplanar bone anchoring device. By selecting a second bone anchor and assembling it with the coupling device, the coupling device can be used as a polyaxial bone anchoring device. Since the same coupling device can be used with different bone anchors, the surgeon has a more flexible and versatile choice of implant combinations while reducing the number of components per set.

[0011] Thus, with the coupling device a modular bone anchoring device can be realized which can be assembled from several interchangeable parts according to the user's choice to allow use in different applications.

[0012] The bone anchoring device with coupling means as described above is bottom loading type, ie the bone anchor can be inserted from the bottom end of the coupling means. This enables the assembly to be in place before or during surgery when the bone anchor has been inserted into the bone.

[0013] Additionally, because coupling devices may be more expensive and / or difficult to manufacture compared to bone anchors, manufacturing and / or inventory costs may be reduced if the same coupling device can be used for more than one clinical application.

[0014] For example, the coupling device or its three-dimensional components can be manufactured using an additive manufacturing method such as printing (eg laser sintering or laser or electron beam melting). With this method, complex shapes can be easily manufactured based on the CAD data of the object to be manufactured.

[0015] According to another embodiment, a receiving part is provided, which comprises a first end, an opposite second end and a central axis extending through the first end and the second end. The receiving part comprises a rod receiving portion for receiving a rod and a head receiving portion defining a receiving space for receiving a head of a bone anchor. The head receiving portion further comprises a plurality of slits leading to the second end of the receiving part, the slits forming a plurality of wall segments of the head receiving portion. The slits and the wall segments preferably make the head receiving part flexible, in particular compressible and / or expandable. Furthermore, at least one cut-out portion is provided at the head receiving portion by removing (preferably cutting off) at least a portion of one of the wall segments. Preferably, the cut-out portion is configured to receive at least a portion of the shank of the bone anchor therein to provide an enlarged pivot angle of the bone anchor in a predetermined direction relative to the central axis or at least a limited angular range in a circumferential direction of the receiving part.

[0016] As used in this specification and the appended claims, the term "rod" should be understood to include any elongated member, regardless of the cross-sectional shape. Specifically, a spinal stabilization rod as used herein can have a generally circular, oval, or angled cross-section. Such a cross-section can vary along the length of the rod. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 A perspective exploded view of a system including a coupling device having two bone anchors that can be used in an interchangeable manner is shown according to an embodiment.

[0018] Figure 2Shown is the assembled Figure 1 A perspective view of an embodiment of a bone anchoring device assembled with components of a system.

[0019] Figure 3 Shows Figure 2 A cross-sectional view of the bone anchoring device in a plane including the central axis of the receiving part and the longitudinal axis of the rod.

[0020] Figure 4 Shows from Figures 1 to 3 A perspective view of the receiving part of the coupling device viewed from the bottom.

[0021] Figure 5 Shows from Figures 1 to 3 A perspective view of the receiving component viewed from the top.

[0022] Figure 6 Shows Figure 4 and 5 A top view of the receiving component.

[0023] Figure 7 Shows Figures 4 to 6 A cross-sectional view of a receiving component, the cross section being along Figure 6 The line AA in the figure is intercepted.

[0024] Figure 8 Shows Figures 4 to 7 A cross-sectional view of a receiving part of the Figure 6 The line AA in the figure is intercepted.

[0025] Fig. 9 Shows from Figures 1 to 3 A perspective view of a locking member of a coupling device viewed from the top.

[0026] Fig.10 Shows Fig. 9 A cross-sectional view of a locking member, the cross section being taken perpendicular to the central axis of the locking member.

[0027] Fig.11 Shows Figure 1 A perspective view of an embodiment of a first bone anchor of a system.

[0028] Fig.12 Shows Fig.11 A perspective view of a portion of a first bone anchor.

[0029] Fig.13 Shows Fig.11 and 12 A side view of a portion of a first bone anchor.

[0030] Fig.14 Shows Figures 11 to 13A top view of a first bone anchor.

[0031] Fig.15 Shown in assembled state Figures 1 to 14 A perspective view of a modified embodiment of a bone anchoring device.

[0032] Fig.16 A perspective exploded view of a bone anchoring device is shown, which comprises a coupling device and a bone anchor according to a further embodiment.

[0033] Fig.17 Shows Fig.16 A perspective view of an enlarged portion of the lower part of the receiving part of the bone anchoring device.

[0034] Fig.18 Shown from below in assembled state Fig.16 and 17 Perspective view of a bone anchoring device.

[0035] Fig.19 Shows Figures 16 to 18 A cross-sectional view of the bone anchoring device in a plane including the central axis of the receiving part and the longitudinal axis of the rod.

[0036] Fig. 20 Shows Figures 16 to 19 A perspective exploded view of a modified embodiment of a bone anchoring device.

[0037] Fig.21 Shows Fig. 20 A perspective view of an enlarged portion of the lower part of the receiving part of the bone anchoring device.

[0038] Fig. 22 Shows Fig. 20 and 21 A cross-sectional view of the assembled bone anchoring device in a plane including the central axis of the receiving part and the longitudinal axis of the rod.

[0039] Fig.23 Shows from Figures 20 to 22 A perspective view of a top view of the pressure member of the bone anchoring device.

[0040] Fig.24 Shows from Figures 20 to 22 A perspective view of the pressure member viewed from the bottom.

[0041] Fig.25 Shows Fig.23 and 24 Top view of the pressure member.

[0042] Fig.26 Shows Figures 23 to 25 A cross-sectional view of a pressure member, the cross section being along Fig.25 The line BB in is intercepted. DETAILED DESCRIPTION

[0043] refer to Figure 1 , a system of a coupling device and two bone anchors according to an embodiment comprises a first bone anchor 1 of a first type and a second bone anchor 1' of a second type and a coupling device 10 connectable to the first bone anchor 1 or the second bone anchor 1'. When the coupling device 10 is assembled with the first bone anchor 1, the resulting bone anchoring device is a monoplanar bone anchoring device, in which the first bone anchor 1 can only pivot in a single plane. When the coupling device is assembled with the second bone anchor 1', the resulting bone anchoring device is a polyaxial bone anchoring device, in which the bone anchor 1' can pivot in multiple planes. Therefore, the first bone anchor 1 and the second bone anchor 1' can be used interchangeably with the same coupling device 10.

[0044] The coupling device 10 comprises a receiving part 5 and a locking member 6. The receiving part 5 comprises a rod receiving portion 51 for receiving the rod 100 and a head receiving portion 52 for accommodating the head 3 of the first bone anchor 1 or the head 3' of the second bone anchor 1'. Preferably, the receiving part is a one-piece piece. The locking member 6 can be positioned around the head receiving portion 52 of the receiving part 5 and can be moved along the outer surface of the receiving part 5 between at least a first position and a second position. The locking member 6 is configured to apply pressure to the head receiving portion 52 and the insertion head at least when the locking member 6 is in the second position to lock the head in the receiving part 5 at a specific angular position of the handle 2. Preferably, the locking member 6 is a closed ring.

[0045] The coupling device 10 further comprises a fixing member, for example in the form of a fixing screw 7, for fastening and fixing the rod 100 in the receiving part 5. The fixing member 7 comprises an engagement structure at its outer surface, for example an outer thread 71, and a tool engagement recess 72. The fixing member 7 may be, for example, a fixing screw that can be screwed into the receiving part 5. Figure 2 and 3 The first bone anchor 1 assembled with the coupling device 10 and the rod 100 inserted and fixed by the fixing member 7 are shown.

[0046] like Figures 4 to 8 , the receiving member 5 may be generally cylindrical and include a first or top end 5a, a second or bottom end 5b, and a passage or hole 53 extending from the first end 5a toward the second end 5b and defining a longitudinal center axis C extending through the first end 5a and the second end 5b. A rod receiving portion 51 is formed near the first end 5a, and a head receiving portion 52 is formed at the second end 5b.

[0047] The passage 53 extends from the first end 5a to a certain distance therefrom and merges into an intermediate portion 53a having a reduced diameter. The intermediate portion 53a may be, for example, cylindrical. Adjacent to the intermediate portion 53a, a receiving space 54 is formed, which is shaped and dimensioned to receive the head 3 of the first bone anchor 1 or the head 3' of the second bone anchor 1' therein. The receiving space 54 has an opening 54a at the second end 5b of the receiving part 5.

[0048] A generally U-shaped recess 55 extends from the first end 5a of the receiving part 5 to a certain distance therefrom. The generally U-shaped recess 55 divides the receiving part 5 into two legs 56 and forms a channel with a longitudinal axis L for receiving the rod 100. The bottom 55a of the channel can have a generally V-shaped upper profile, which provides a rod support surface for inserting the rod 100. By means of this, rods with different diameters can be inserted into the channel and can be supported on the rod support surface. An internal thread 57, such as a flat thread or a square thread, is formed in the channel 53 on the leg 56, adjacent to the first end 5a, for cooperating with the external thread 71 of the fixing member 7. By means of the U-shaped recess 55, the upper part of the receiving part defines the rod receiving portion 51.

[0049] The lower portion of the receiving part 5 (approximately from the middle portion 53a of the channel 53 to the second end 5b, which includes the accommodation space 54) defines the head receiving portion 52 of the receiving part 5. The accommodation space 54 has a generally spherical inner contour that matches the outer contour of the head 3 of the first bone anchor 1 and the head 3' of the second bone anchor 1'. The axial extension of the accommodation space 54 in the direction of the central axis C is such that when the head is inserted into the accommodation space 54, it covers the area of ​​the head 3 or 3' having the maximum outer diameter E. More specifically, the size of the accommodation space 54 can be such that the head 3 of the first bone anchor 1 or the head 3' of the second bone anchor 1' can be retained therein by friction. A small chamfered portion 54b can be provided to facilitate the insertion of the head. As particularly in Figure 7 and 8 As can be seen in FIG. 5 , the accommodation space 54 is divided into an upper portion 54 c configured to cover the head 3 , 3 ′ from the top and a lower portion comprising a seat 54 d for the head 3 , 3 ′ in which the head can pivot.

[0050] The wall of the receiving part 5 surrounding the accommodation space 54 is expandable and compressible in the radial direction relative to the central axis C. This is achieved by a plurality of axially extending slits 58, which lead to the second end 5b and can extend a distance from the second end 5b, preferably to the middle part 53a of the channel 53. The end portion 58a of the slit 58 is enlarged, for example with a diamond profile, a circular profile or a triangular profile or any other suitable shape. The slits 58 form a plurality of flexible wall sections 58b of the head receiving part 52. The size and number of the slits 58 can be selected so as to obtain the desired flexibility of the head receiving part 52.

[0051] A cavity 59 is formed in the wall of the head receiving portion 52, the cavity 59 extending circumferentially around the accommodation space 54. The cavity 59 may extend in the axial direction of the central axis C from a position below the region of the maximum diameter E of the accommodation head to the end portion 58a of the slit 58. Thus, the cavity 59 circumferentially surrounds the insertion head and extends along a considerable area along the head 3, 3' in the direction of the central axis C. Furthermore, the cavity 59 communicates with the accommodation space 54 through an opening 59a having a width in the direction of the central axis C that is smaller than the radially outer portion of the cavity 59. More specifically, the opening 59a has the shape of an annular slit, as particularly in Figure 4 , 7 8. The outwardly directed wall portion 59b defining the cavity 59 may be slightly convex and may be formed at a radial position away from the central axis C, so that the radially outermost wall portion 50a of the head receiving portion 52 is thinner than the lowermost wall portion 50b below the cavity 59 at or near the second end 5b. In addition, the end portion 58a of the slit 58 communicates with the cavity 59. Therefore, the virtual connecting line between two adjacent end portions 58a of the slit 58 can define a predetermined breaking point or breaking line together with the radially thinner wall portion 50a of the head receiving portion 52 for removing a portion of the corresponding wall segment 58b, as explained in more detail below.

[0052] An upper wall portion 59c of the wall defining the cavity 59 may be inclined toward the second end 5b and taper to the opening 59a. A lower wall portion 59d of the wall defining the cavity 59 may be generally flat in a direction generally perpendicular to the central axis C and may rise toward the opening 59a in a curved or inclined manner. It should be noted that the detailed shape of the cavity is not limited to the embodiment shown but may vary.

[0053] By the opening 59a of the cavity 59, the accommodation space 54 is divided into an upper portion 54c and a seat 54d which can be pressed against the head 3, 3' by the locking member 6. The upper portion 54c of the accommodation space is at least partially delimited by an inner wall portion 59e located above the opening 59a.

[0054] When viewed in the radial direction, the wall portion 50a is thinner than the wall portion 50b. Due to the cavity 59, the flexible wall sections 58b of the wall portion 50b can be easily expanded, although they are relatively thick at the second end 5b of the receiving part 5. When the head receiving portion 52 is compressed by the locking member 6, as described below, the lowermost wall portion 50b is configured to apply pressure to the head 3, 3' from an axial position at or near the area of ​​the head having the largest diameter E and from below this area, as shown in FIG. Figure 3 As shown in . Since the wall section 58b of the wall part 50b is thicker there, a sufficiently strong clamping force can be achieved. In addition, the strength against loosening can be increased by this design. In other words, the wall section provides a stable seat 54d for the head 3, 3', in which the head can be safely clamped.

[0055] The outer surface of the wall of the head receiving portion 52 widens toward the second end 5b in the tapered portion 50c near the second end 5b. Therefore, when the locking member 6 moves along the head receiving portion 52 in the direction toward the second end 5b, the compressive force increases. Between the tapered portion 50c and the second end 5b, the outer surface portion 105 may be convexly rounded.

[0056] like Figure 4 and 6 As best shown in FIG. 8, two opposing recesses or slots 150 are formed at the bottom end 5b of the head receiving portion 52. Figure 6 When viewed in the top view shown, the recesses 150 are offset from each other by 180° and are aligned with the longitudinal axis L defined by the channel. In more detail, the recess 150 extends from the bottom end 5b through the seat 54d and the upper part 54c of the accommodating space 54 to the middle part 53a of the channel 53. The inner contour of the recess 150 can be generally rectangular. The recess 150 can be arranged at a circumferential position of the receiving part 5 where the slit 58 is formed, that is, the recess 150 can include a Figure 4 In the radial direction, the recess 150 extends from the inner surface 154a of the wall of the head receiving portion 52 toward the outer surface 154b of the wall and ends at a distance from the outer surface 154b, such as Figure 4 As shown in . Therefore, the recess 150 is open toward the accommodation space 54 and does not extend completely through the wall of the receiving part 5 in the radial direction. In addition, the recess 150 does not extend substantially into the cavity 59.

[0057] By means of the recess 150, the head 3 of the first bone anchor 1 can be inserted from the bottom end 5b, as explained further below. Specifically, the recess 150 defines a constraint structure or a part of such a constraint structure, which constrains the pivoting movement of the insertion head 3 of the first type of bone anchor 1 to a single plane including the central axis C.

[0058] The receiving part 5 further includes a cutout portion 151 formed near both sides in one of the recesses 150, which is configured to receive a portion of the shank 2 of the bone anchor therein. The cutout portion 151 is formed in an inner edge 152 around the lower opening 54a of the receiving part 5. The axial and radial extensions of the cutout portion 151 are smaller than the axial and radial extensions of the recess 150. The cutout portion 151 may have a generally triangular shape and form a chamfered surface that gradually merges from the edge 152 into the recess 150. Therefore, when pivoted to the position of the cutout portion 151, the cutout portion 151 provides an expanded pivot angle that the shank axis S of the first bone anchor 1 or the second bone anchor 1' can form with the central axis C. It should be noted that the cutout portion 151 may be formed on both sides of each recess 150.

[0059] At the center of each leg 56 in the circumferential direction, a through hole 500 or another engagement structure may be provided for engagement with an instrument. In addition, an inclined cut-out portion 501 may be formed at either end of the passage of the rod near the bottom 55a of the generally U-shaped recess. Additional chamfered portions 502 may extend to some extent from the cut-out portion 501 toward the edge of each of the legs 56 on either side of the passage. The cut-out portion 501 and the chamfered portion 502 may facilitate mounting the locking member 6 from the first end 5a of the receiving part 5 and / or reduce the size of the receiving part 5.

[0060] Additional references Fig. 9 and 10 , the locking member 6 will be described in more detail. The locking member 6 is formed as a closed loop having a first end or upper end 6a and a second end or lower end 6b. The inner surface 61 of the locking member 6 is generally cylindrical, and its inner diameter size is determined so that the locking member 6 fits around the receiving part 5 and is configured to slide along the outer surface of the receiving part 5. Adjacent to the second end 6b, the locking member 6 may include a tapered inner surface portion 62, which tapers toward the first end 6a and is configured to cooperate with the tapered outer surface portion 50c of the receiving part 5. The angles of the tapered portions of the locking member 6 and the receiving part 5 preferably correspond to each other. Preferably, the angle is selected so that self-locking occurs when the surfaces engage with each other. Therefore, once the locking member 6 is installed and the tapered surfaces engage with each other, the locking member 6 is prevented from accidentally moving upward and the lock is released. However, the cooperating surfaces can be disengaged, for example, using an instrument.

[0061] The outer surface of the locking member 6 can be cylindrical and can include an engagement structure for engaging with an instrument (not shown in the figure). Adjacent to the second end 6b, the outer surface can be tapered toward the second end 6b. However, the shape is not limited to this design. The axial length of the locking member 6 between the first end 6a and the second end 6b can be at least the axial extension of the cavity 59 of the receiving part 5, preferably greater than the axial length of the cavity 59. Therefore, the locking member 6 is configured to apply a radial compressive force to the main part of the head receiving part 52 of the receiving part. The locking member 6 can be installed to the receiving part 5 from the second end of the receiving part 5 or from its first end 5a.

[0062] Further references Figures 11 to 14 , the first bone anchor 1 will be described in more detail. The bone anchor 1 comprises a shank 2 having a shank axis S and a head 3 having a free end 3a, wherein the shank is preferably fully or partially threaded. A neck 2a may be present between the head 3 and the shank 2. The head 3 has a spherical outer surface portion, which includes a region having a maximum diameter E of the sphere. Preferably, the spherical outer surface portion is substantially symmetrical in the axial direction relative to a plane including a plane of the maximum outer diameter E. Furthermore, the head 3 comprises two opposite wings 4, which protrude from the spherical surface of the head away from the shank axis S. Each wing 4 extends parallel to the shank axis S along the spherical surface of the head 3. The wings may extend from the free end 3a of the head 3 up to the neck 2a, or may be arranged at a distance from the free end 3a of the head and / or at a distance from the neck 2a.

[0063] The wings 4 are offset by 180° along the circumferential direction of the head 3 and are symmetrical with respect to a mid-plane including the handle axis S. Each wing 4 has the shape of a spherical shell segment. The upper end 4a of the wing 4 may be flat and slightly inclined toward the handle 2. However, the upper end 4a may also be curved. The width of the wing 4 is such that when the head 3 is received in the head receiving portion 52 of the receiving part 5, the wing 4 can extend into the recess 150 and pivot therein. Thus, the wing 4 forms a restraining structure or part of a restraining structure that cooperates with a corresponding restraining structure in the form of a recess 150 provided at the receiving part 5 to limit or constrain the pivoting movement of the head 3 in the head accommodating space 54 to a single plane. It should be noted that the width of the wing 4 is such that when the head 3 passes through the lower opening 54a of the receiving part 5 during insertion, the wing 4 passes through the recess 150 at the bottom end 5b of the receiving part 5.

[0064] Furthermore, at the free end 3a of the bone anchor 1, a tool engagement recess 31 is formed which may have a polygonal shape or any other engagement structure such as, for example, a plum or star shape or other axial groove-shaped structure suitable for screwing the bone anchor 1 into the bone.

[0065] refer to Figure 1 , the second bone anchor 1 ' will be described in more detail. The same components and parts as the first bone anchor 1 are marked with the same reference numerals, and their description will not be repeated. The second bone anchor 1 ' differs from the first bone anchor 1 in that the head 3' of the second bone anchor lacks the wing 4. Therefore, the outer surface of the head 3' is uniformly spherical between the neck 2a and the free end surface 3a. As a result, when the second bone anchor 1 ' is inserted into the coupling device 10, the head 3' can freely pivot in the accommodation space 54 of the receiving part 5 without constraint. This means that the second bone anchor 1 ' can pivot in multiple planes relative to the central axis C, or even in an unlimited number of planes.

[0066] The components and parts of the polyaxial bone anchoring device can be made of any material, however, preferably, of a biocompatible material, such as titanium or stainless steel or any other biocompatible metal or metal alloy, or a plastic material. As a biocompatible alloy, a NiTi alloy can be used, for example Nitinol. Other materials can be magnesium or magnesium alloys, and the biocompatible plastic material used can be, for example, polyetheretherketone (PEEK) or poly-L-lactide acid (PLLA). The components can be made of the same or different materials from each other.

[0067] A preferred method for manufacturing the receiving part and optionally also the locking member and / or the bone anchoring element is an additive manufacturing method, more preferably an additive layer manufacturing method, such as three-dimensional printing. More particularly, a preferred method is laser sintering or laser melting or electron beam melting. In this method, subsequent layers of powder material, such as metal powder, are solidified with an energy beam, in particular a laser or an electron beam, at locations corresponding to the cross section of the part in the respective layer.

[0068] In use, the coupling device 10 may be preassembled. For assembly, the locking member 6 may be mounted to the receiving part 5 from the first end 5a or from the second end 5b. In the inserted position of the locking member 6, the second end 6b of the locking member 6 may be located in an axial position above the end portion 58a of the slit 58 of the head receiving portion 52 (see Fig.15), when the head 3, 3' of the bone anchor is inserted, the accommodation space 54 of the receiving part 5 can expand in the radial direction. The preassembled coupling device 10 can be connected to the bone anchor 1, 1' before the bone anchor is inserted into the bone or after the bone anchor has been inserted into the bone. In both cases, the head of the bone anchor is inserted into the receiving part 5 through the lower opening 54a and further moved into the accommodation space 54 of the receiving part 5. Due to the slit 58 of the head receiving portion 52, the receiving part 5 snaps onto the head. Thereafter, the locking member 6 moves downward in the direction of the center axis C to compress the head receiving portion 52 by means of the cooperation of the tapered inner surface portion 62 of the locking member 6 and the tapered outer surface portion 50c of the receiving part 5. In this position, the inner surface 61 of the locking member 6 is positioned around the head receiving portion 52 and completely surrounds the head receiving portion 52. The compression of the head receiving portion 52 can lock the angular position of the bone anchor relative to the receiving part. If the locking member 6 is mounted to the receiving part 5 from a first end, the receiving part 5 may first be connected to the bone anchor and then the locking member 6 may be mounted.

[0069] The coupling device and the system of at least two bone anchors including the first bone anchor 1 and the second bone anchor 1' allow the coupling device 10 to be selectively combined with the first bone anchor 1 or the second bone anchor 1'. Therefore, using the same coupling device 10, a uniplanar bone anchoring device or a polyaxial bone anchoring device can be produced. Specifically, when the second bone anchor 1' is inserted into the coupling device, the second bone anchor 1' is configured to pivot around the central axis C in multiple planes. The constraint structure in the form of the recess 150 provided at the receiving part 5 does not limit the pivoting movement of the second bone anchor 1', that is, it has no effect on the pivoting movement of the second bone anchor 1'. At the location where the cutout portion 151 is formed, the second bone anchor 1' is configured to present an expanded pivot angle of its shank axis S relative to the central axis C. For example, in the absence of the cutout portion 151, the maximum pivot angle of the shank axis S to the central axis C can be about 32°, and in the presence of the cutout portion 151, the expanded pivot angle can be about 42°. After the rod 100 has been inserted, the fixing member 7 is screwed between the legs 57 of the receiving part to fix the rod 100 in the receiving part.

[0070] When the first bone anchor 1 is inserted into the coupling device 10, the head 3 is oriented relative to the coupling device in such a way that the wings 4 can engage the recesses 150 of the receiving part. By means of this, the pivoting movement of the first bone anchor 1 is restricted to a single plane. In an embodiment, due to the position of the restraining structure, the single plane is the plane defined by the central axis C and the longitudinal axis L of the rod passage. The cutout 151 provides an enlarged pivot angle of the second bone anchor 1 'relative to the central axis C. After the rod 100 is inserted, the fixing member 7 is screwed between the legs 57 of the receiving part to fix the rod 100 in the receiving part. Figure 3 The locking position of the locking member 6 is shown, wherein the fixing member 7 presses the rod 100 onto the first end 6a of the locking member 6 to hold the locking member 6 in its lowest position. In the locking position, the second end 6b of the locking member 6 is close to the second end 5b of the receiving part 5 and completely surrounds the head receiving portion 52.

[0071] Pre-locking of the insertion head 3 , 3 ′ may be provided when the locking member 6 is in a pre-locking position slightly above the lowermost position, which still allows the head 3 , 3 ′ to pivot in the head receiving portion 52 , but prevents the head 3 , 3 ′ from being removed from the head receiving portion 52 .

[0072] Fig.15 The above reference Figures 1 to 14 A modification of the coupling device of the described embodiment. Fig.15 In, with Figures 1 to 14 Similar or identical elements are denoted by the same reference numerals, and description thereof will not be repeated.

[0073] Fig.15 The receiving part 5' of the coupling device is connected to Figures 1 to 14 The difference between the receiving part 5 of the embodiment of the present invention lies in the configuration of the structure that provides the enlarged pivot angle. Specifically, instead of the cutout portion 151 or in addition to the cutout portion 151, at the modified receiving part 5', one of the wall sections 58b of the head receiving portion 52 is at least partially removed, such as Fig.15. The wall segment 58b can be partially removed by being disconnected at an imaginary connecting line between the two end portions 58a of the slit 58 defining the flexible wall portion 58b, so that only the inner wall portion 59e located above the opening 59a remains. The gap formed by removing a portion of the wall segment 58b is provided at a circumferential position of the receiving part 5' that is different from the circumferential positions of the two recesses 150. The gap provides a cutout portion configured to receive a portion of the shank of the bone anchor therein, thereby providing an enlarged pivot angle that the shank axis S of the bone anchor can form with the central axis C. The lowermost wall portion 50b and the radially thinner wall portion 50a of the adjacent wall segment 58b and the head 3' of the inserted bone anchor are visible through the gap formed by removing a portion of the wall segment 58b. It should be noted that the position of the enlarged pivot angle can be selected by disconnecting a suitable one of the wall segments 58b.

[0074] Fig.15 A coupling device comprising a modified receiving part 5' with an inserted second bone anchor 1' is depicted. However, the modified receiving part 5' can also be connected to the first bone anchor 1. In addition, Fig.15 , the locking member 6 is depicted in an inserted position, wherein the second end 6b of the locking member 6 may be in an axial position above the end portion 58a of the slot 58 of the head receiving portion 52, and without the insertion rod.

[0075] The receiving part 5, 5' can be provided with both a cutout 151 and a gap formed by partially removing one of the wall segments 58b, both of which provide an expanded pivot angle of the insertion handle relative to the central axis C, or only one of the cutout 151 and the partially removed wall segment 58b is provided. The receiving part can also include more than one cutout 151 and / or more than one partially removed wall segment 58b. However, the receiving part can also be provided without a cutout 151 and a partially removed wall segment 58b, that is, without any structure providing an expanded pivot angle. It should be noted here that "expanded pivot angle" does not necessarily mean a single expanded pivot angle that the handle can present relative to the central axis C. Instead, the term "expanded pivot angle" can also refer to a limited circumferential section of the receiving part, in which the handle can present a larger pivot angle relative to the central axis C than other circumferential portions of the receiving part.

[0076] Next, we will refer to Figures 16 to 19An embodiment of a polyaxial bone anchoring device comprising a coupling device 10' and a first bone anchor 1 of another embodiment is described. The coupling device 10' comprises a receiving part 5'' for receiving the head 3 of the bone anchor 1 and connecting the bone anchor 1 to the rod 100, and a locking member 6' for locking the head 3 in the receiving part 5''. Preferably, the receiving part 5'' is a one-piece piece. The coupling device 10 further comprises a fixing member, for example in the form of a fixing screw 7, for fastening and fixing the rod 100 in the receiving part 5''. The fixing member 7 and the bone anchor 1 can be similar to those described above with reference to Figures 1 to 15 A fixation member 7 and a first bone anchor 1 of the system are described.

[0077] The receiving part 5 ″ has a first or upper end 5a and a second or lower end 5b. A rod receiving portion 51 ′ is provided adjacent to the first end 5a and a head receiving portion 52 ′ is provided adjacent to the second end 5b. The rod receiving portion 51 ′ is generally cylindrical and comprises a passage or coaxial bore 53 ′ extending from the upper end 5a into the head receiving portion 52 ′ and defining a longitudinal center axis C extending through the first end 5a and the second end 5b. The passage 53 ′ comprises an internal thread 57 ′ at least in its area for receiving the fixing member 7. A generally U-shaped recess 55 ′ forming a passage with a longitudinal axis L for receiving the rod 100 extends from the first end 5a of the receiving part 5 ″ to almost the beginning of the head receiving portion 52 ′. At a distance from the upper end 5a, a groove or other weakened section 93 may be provided which allows disconnection of the upper part of the receiving part 5 ″ formed by the U-shaped recess acting as an extension tab. By means of the extension tab, the polyaxial bone anchoring device with the inserted rod 100 can be manipulated in a higher position compared to the final position so that, for example, a vertebra can be pulled against the rod.

[0078] An engagement structure for engaging with an instrument (not shown) may be provided at the outer surface of the rod receiving portion 51 '. The engagement structure may include a circumferentially extending rib 94. At a position below the rib 94, a flat outer surface portion 95 is provided at the rod receiving portion 51 ', which may be used to facilitate assembly of the locking member 6' and / or prevent rotational movement of the locking member 6' around the central axis C.

[0079] like Fig.17 As shown in more detail in FIG. 5 , the head receiving portion 52′ formed adjacent the second end 5b of the receiving part 5″ has a generally cap-like shape with a hollow, generally spherical inner portion 101 defining a receiving space 54′ for pivotably receiving the head 3 therein. A plurality of axially extending slits 102 lead to the second end 5b and may extend a certain distance from the second end 5b, so that the head receiving portion is flexible so that the head 3 may be clamped and locked when pressure is applied to the head receiving portion by the locking member 6′.

[0080] Two opposite recesses or slots 150' are formed at the bottom end 5b of the head receiving part 52'. The recesses 150' are offset 180° from each other and can be aligned with the longitudinal axis L defined by the U-shaped recess 55'. Each recess 150' is open toward the bottom end 5b and extends completely through the wall of the head receiving part 52' from the inner surface of the wall defining the accommodating space 54' to the outer surface of the wall. In the figure, only one of the recesses 150' can be seen, while the other is hidden and invisible by the head receiving part 52'. The inner contour of the recess 150' can be roughly rectangular. The width of the recess 150' in the circumferential direction of the receiving part 5'' can be less than the distance between the two slits 102, and can be greater than the width of the slit 102.

[0081] By means of the recess 150', the head 3 of the first bone anchor 1 of the first type can be inserted from the bottom end 5b, wherein the head 3 is oriented in such a way that the wings 4 can engage the recess 150' of the receiving part 5". The recess 150' defines a constraint structure or a part of such a constraint structure, which limits the pivotal movement of the inserted head 3 of the bone anchor 1 to a single plane including the central axis C. In the present embodiment, due to the position of the constraint structure 150', the single plane is the plane defined by the central axis C and the longitudinal axis L of the rod channel.

[0082] The locking member 6' is formed as a closed loop designed to be positioned around and surround the head receiving portion 52'. The inner diameter of the locking member 6' is sized so that the locking member 6' fits around the receiving part 5'' and is configured to slide along the outer surface of the head receiving portion 52'. The locking member 6' has an inner surface structure that allows the head 3 to be locked in the head receiving portion 52' in cooperation with the head receiving portion 52' when the locking member 6' is in its lowest position or locked position, for example, when the second or lower end 6b of the locking member 6' is close to or adjacent to the second end 5b of the receiving part 5''. When the locking member 6' is in a pre-locking position slightly above the lowest position, a pre-locking of the inserted head 3 can be provided, which still allows the head 3 to pivot in the head receiving portion 52', but prevents the head 3 from being removed from the head receiving portion 52'.

[0083] Figures 16 to 19The locking member 6' also includes a plurality of upright flexible sections 63, which can be used to engage with the receiving part 5' to initially maintain the locking member 6' in a pre-locking position (not shown in the figure). In addition, two opposing protrusions 64 are provided on the upper side of the locking member 6', which are used to support the rod 100 at an upper surface 64a provided at the protrusions 64. In the illustrated embodiment, the locking member 6' also includes two opposing upright arms 65. At the upper end of the arm 65, an engagement structure in the form of a groove 65a can be provided, which is configured to be engaged by an instrument (not shown in the figure). The inner surface 65b of the arm 65 can be flat and configured to cooperate with the flat outer surface portion 95 of the rod receiving part 51'. The cooperating flat outer surface portion 95 at the receiving part 5' and the inner surface 65b at the locking member 6' can prevent unintentional rotation of the locking member 6'. In the mounted state, the locking member 6' can assume different axial positions relative to the receiving part 5'', such as an insertion position, in which the head 3 of the bone anchor 1 can be inserted, a pre-locking position, in which the head can still be pivoted relative to the receiving part 5'' but is prevented from being removed therefrom, and a locking position, in which the head 3 is locked in its angular position.

[0084] The locking member 6' and the receiving part 5'' can be preassembled by mounting the locking member 6' from the second end 5b of the receiving part 5 to the receiving part 5. If a monoplanar bone anchoring device is to be assembled, the first bone anchor 1 is used. When the locking member 6' is in the insertion position, the head 3 of the first bone anchor 1 can be inserted into the receiving space 54' of the receiving part 5'' from the second end 5b of the receiving part 5''. The wing 4 extends into the recess 150'. Due to the slit 102, the head receiving part 52' is flexible and snaps onto the head. Thereafter, the locking member 6' can be moved downwards, for example with an instrument (not shown), whereby it compresses the head receiving part 52' so that pressure is exerted on the head. If necessary, the locking member 6' can be moved upwards, for example with an instrument, to release the locking of the head. The rod 100 can already be inserted into the substantially U-shaped recess 55' and the fixing member 7 screwed into the channel 53' of the receiving part 5''. Due to the extended tab of the receiving part 5'', the rod 100 is still movable so that the head can be locked independently of the rod. For final locking, the fixing member 7 is tightened so that the rod 100 presses on the surface 64a of the locking member 6', which further moves the locking member 6' into the locked position.

[0085] exist Figures 16 to 19 In the modification of the receiving part 5'', the receiving part 5'' can be provided with the above reference Figures 1 to 15 The cut-away portion 151 is depicted to provide an increased pivot angle of the bone anchor relative to the central axis C.

[0086] The coupling device 10' of this embodiment can also be coupled to the above reference Figures 1 to 15The second bone anchor 1 ' is described. When the coupling device 10' is assembled with the second bone anchor 1 ', the resulting bone anchor device is a polyaxial bone anchor device, in which the bone anchor can pivot in multiple planes. Therefore, the first bone anchor 1 and the second bone anchor 1 ' can be used interchangeably with the same coupling device 10'. Alternatively or additionally, at least one wall segment defined by two adjacent slits 102 of the head receiving portion 52' can be at least partially removed to provide an enlarged pivot angle of the bone anchor relative to the central axis C.

[0087] Next, we will refer to Figures 20 to 26 A further modification of the coupling arrangement is described. Figures 20 to 26 In, with Figures 16 to 19 Similar or identical elements are denoted by the same reference numerals, and description thereof will not be repeated.

[0088] Figures 16 to 19 The coupling device 10'' and Figures 16 to 19 The difference of the coupling device 10' is that a pressure member 8 is provided in addition to the receiving part 5'' and the locking member 6'. The pressure member 8 is configured to be arranged in the channel 53' of the receiving part 5'' and is configured to contact the insertion head 3 from above to additionally apply pressure to the insertion head. Preferably, the pressure member 8 is configured to apply pressure to the insertion head only from above.

[0089] As in Figures 23 to 26 As can be best seen in FIG. 1 , the pressure member 8 extends from a first or upper end 8a to a second or lower end 8b and includes a central passage 81 extending from the first end 8a to the second end 8b. A first portion 81a of the passage 81 adjacent to the first end 81a is generally cylindrical and provides a generally cylindrical inner surface of the pressure member 8. Adjacent to the second end 8b, a second portion 81b of the passage 81 has a generally spherical inner surface configured to contact a spherical outer surface portion of the head 3 from above.

[0090] At its first end 8a, the pressure member 8 includes a rod support surface 82 for supporting the insertion rod 100. The rod support surface 82 defines a channel axis K of the pressure member 8. Adjacent to the rod support surface 82, opposing flat surfaces 82a may be formed at the first end 8a of the pressure member 8.

[0091] At the second end 8b of the pressure member 8, two opposing recesses or slots 83 leading to the second end 8b are formed. The recesses 83 are offset from each other by 180° and are aligned with the axis K defined by the rod support surface 82. The inner contour of the recess 83 may be substantially rectangular. An upper portion 83a delimiting the recess 83 toward the first end 8a of the pressure member 8 may have a curved shape corresponding to the shape of the upper end 4a of the wing 4 provided at the head 3 of the first bone anchor 1.

[0092] The recess 83 is configured to receive therein a portion of the wing 4 of the head 3 of the first bone anchor 1. Specifically, the recess 83 of the pressure member 8 together with the recess 150' provided at the receiving part 5" defines a constraint structure or a portion of such a constraint structure, which constrains the pivoting movement of the insertion head of the bone anchor to a single plane including the central axis C.

[0093] The pressure member 8 is mounted to the receiving part 5'' in an orientation of the pressure member 8 such that the recess 83 of the pressure member 8 is aligned in the circumferential direction with the recess 150' of the receiving part 5'' and the axis K defined by the rod support surface 82 is aligned with the longitudinal axis L defined by the U-shaped recess 55' of the receiving part 5''.

[0094] In use, the coupling device 10 ″ can be assembled with a first bone anchor into a monoplanar bone anchoring device or with a second bone anchor into a polyaxial bone anchoring device, depending on the choice of bone anchor. Final locking of the head is achieved by applying pressure with the rod to the pressure member 8, which in turn locks the head in the head receiving portion.

[0095] Modifications of the above-described embodiments are conceivable. For example, the constraint structure in the receiving part 5, 5', 5" and / or the pressure member 8 may be in another position such that a single pivot plane may have an angle relative to the channel axis. It is also possible to provide more than one constraint structure at different positions such that several different pivot planes are provided, one of which may be selected when the first bone anchor is inserted. Furthermore, a further bone anchor of a third type may be provided, which cooperates with one or more constraint structures provided at the receiving part and / or the pressure member such that the bone anchor assumes a predetermined angular orientation relative to the central axis C and is prevented from pivoting, i.e. the further bone anchor and the coupling device form a uniaxial bone anchoring device.

[0096] The first bone anchor may have wings or any other constraining structure which is at a distance from the free end of the head.

[0097] It should be noted that specific shapes of the above-mentioned respective components and elements are not limited to the specific shapes shown in the drawings but may vary.

[0098] The bone anchor is not limited to having a threaded shank. All types of bone anchors suitable for anchoring in bones or vertebrae can be used.

[0099] In another modification, the bone anchor may be a two-part bone anchor comprising a handle and a separate head connectable to the handle. Thus, different heads may be provided that may be selectively combined with the handle. For example, one of the heads may be a head 3 comprising a constraining structure such as a wing, and the other head may be a head 3' having a spherical outer surface as described without the constraining structure. In other words, a single-plane head or a multi-axial head may be selectively combined with the handle. Thus, modularity is further expanded.

[0100] Instead of the above-mentioned fixing members, other fixing devices may be used, such as for example a bayonet fixing device or a two-part fixing device which allows independent fixing of the rod and the head.

Claims

1. A coupling device for coupling a rod to a first bone anchor (1) of a first type or to a second bone anchor (1') of a second type, the coupling device (10, 10', 10'') comprising: A receiving part (5, 5', 5''), the receiving part having a first end (5a), an opposite second end (5b) and a central axis (C) extending through the first end and the second end, the receiving part comprising a rod receiving portion (51, 51') for receiving the rod (100), and a head receiving portion (52, 52'), wherein the head receiving portion (52, 52') comprises a receiving space (54, 54') for pivotally receiving the head (3, 3') of the first bone anchor (1) or the second bone anchor (1'), so that the handle (2) of the first bone anchor or the second bone anchor can assume a plurality of angular positions relative to the central axis (C), a locking member (6, 6') positionable at least partially around the head receiving portion (52, 52') and movable between at least a first position, in which the head is pivotable, and a second position, in which the head is locked in the receiving space (54, 54'); The head receiving portion (52, 52') comprises a constraint structure (150, 150'), by means of which the coupling device is configured to cooperate with the first bone anchor (1) so that the first bone anchor (1) is configured to pivot relative to the central axis (C) in a single plane, or the coupling device is configured to cooperate with the second bone anchor (1') so that when the locking member (6, 6') is in the first position, the second bone anchor (1') is configured to pivot relative to the pivot axis (C) in multiple planes.

2. The coupling device according to claim 1, wherein the constraint structure includes at least one recess (150, 150') provided in the head receiving portion (52, 52'), the at least one recess being configured to cooperate with a matching constraint structure (4) of the first bone anchor (1) to allow the first bone anchor (1) to pivot in a single plane.

3. The coupling device according to claim 2, wherein the at least one recess (150) extends from an inner surface (154a) of the accommodating space (54) toward an outer surface (154b) of the head receiving portion and terminates at a distance from the outer surface (154b).

4. The coupling device according to claim 2 or 3, wherein two recesses (150) are provided which are offset by 180° from each other.

5. The coupling device according to any one of claims 2 to 4, wherein the at least one recess (150) extends axially below the portion of the accommodating space having the largest inner width, and preferably also extends axially above the portion of the accommodating space having the largest inner width.

6. A coupling device according to any one of claims 1 to 5, wherein the head receiving portion (52, 52') further comprises a cutout portion (151), which is arranged at the second end (5b) of the receiving part and is configured to receive at least a portion of the shank (2) of the bone anchor therein to provide an enlarged pivot angle of the bone anchor in at least one predetermined direction relative to the central axis (C).

7. The coupling device according to claim 6, wherein the cutout portion (151) is disposed adjacent to the restraining structure (150) in a circumferential direction around the central axis (C).

8. A coupling device according to claim 6 or 7, wherein the head receiving part (52, 52') comprises a plurality of slits (58, 102), which open into the second end (5b) of the receiving component (5, 5', 5'') and extend from the second end (5b) towards the first end (5a) of the receiving component, the slits forming a plurality of wall segments (58b) of the head receiving part, the plurality of wall segments making the head receiving part compressible and / or expandable, wherein the cut-out portion (151) is provided by removing, in particular cutting off, at least a portion of one of the wall segments (58b).

9. Coupling device according to claim 8, wherein at least one of the slits (58) comprises an end portion (58a) at a distance from the second end (5b) of the receiving part (5, 5'), wherein the end portion (58a) preferably comprises a diamond-shaped profile, wherein preferably a connecting line between two end portions (58a) of adjacent slits (58) defines a predetermined breaking point or breaking line for removing the at least part of the wall segment (58b).

10. A coupling device according to any one of claims 1 to 9, wherein the wall of the head receiving portion (52) comprises at least one cavity (59), the at least one cavity being configured such that the thickness of the wall in a radial direction relative to the center axis (C) between the accommodating space (54) and the locking member (6) is locally reduced by the cavity (59).

11. Coupling device according to claim 10, wherein a locally reduced thickness of the wall of the accommodation space (54, 54') provides a predetermined breaking point or breaking line for removing a portion of the wall of the head receiving portion (52).

12. A coupling device according to any one of claims 1 to 11, wherein an outer surface portion of the head receiving portion (52, 52') and an inner surface portion of the locking member (6, 6') are configured to cooperate in such a manner that moving the locking member (6, 6') from the first position to the second position increases the compression force of the locking member on the head receiving portion to clamp the insertion head (3, 3') of the bone anchor, preferably wherein at least one of the cooperating surfaces is tapered.

13. A coupling device according to any one of claims 1 to 12, further comprising a pressure member (8) arranged in the receiving part (5") and configured to exert pressure on the insertion head (3, 3') to clamp the head (3, 3') in a specific angular position.

14. A bone anchoring device comprising a coupling device according to any one of claims 1 to 12 and a first bone anchor (1) of a first type or a second bone anchor (1') of a second type, wherein the first bone anchor (1) comprises a matching constraint structure (4) so ​​that the first bone anchor (1) is configured to pivot relative to the central axis (C) in a single plane, and wherein the second bone anchor (1') is configured to pivot relative to the central axis (C) in multiple planes.

15. The bone anchoring device according to claim 14, wherein the head (3) of the first bone anchor (1) has a substantially spherical outer surface portion and comprises a constraint structure (4) at the outer surface, the constraint structure being configured to cooperate with a constraint structure of the coupling device, preferably wherein the constraint structure (4) is a protrusion comprising at least one wing (4), the at least one wing extending away from the handle axis (S) and defining a single pivot plane together with the handle axis (S), the wing preferably extending along the spherical outer surface portion of the head parallel to the handle axis, preferably wherein the head (3') of the second bone anchor (1') has a uniformly spherical outer surface portion without a constraint structure.

16. A bone anchoring system comprising the bone anchoring device according to claims 13 and 14, wherein at least the first bone anchor (1) and the second bone anchor (2) are interchangeable.

Images