Coupling device for coupling rod to bone anchor, and system of such coupling device and at least two bone anchors

Abstract

To provide a coupling device for coupling a rod to a bone anchor.SOLUTION: A coupling device (10) includes a receiving part (5) having a first end (5a), an opposite second end (5b) and a central axis (C) extending through the first end and the second end, and the receiving part includes a rod receiving portion (51) for receiving a rod (100), and a head receiving portion (52). A head receiving portion (52) includes the receiving part comprising an accommodation space for pivotably receiving a head (3) of a first bone anchor (1) or a second bone anchor (1') such that a shank (2) of the first bone anchor or the second bone anchor can assume a plurality of angular positions relative to the central axis, and a locking member (6) positionable at least partially around the head receiving portion (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 accommodation space.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a connecting device for connecting a rod to a bone anchor, a bone fixation device provided with such a connecting device, and a bone fixation system provided with such a connecting device and at least two bone anchors.

Background Art

[0002] The connecting device is used in orthopedic surgery, particularly spinal surgery, for connecting a rod to the head of a bone anchor fixed to a bone or vertebra. The head of the bone anchor may be pivotally received in a receiving portion of the connecting device that also houses the rod, such that the receiving portion can assume various angular positions relative to the bone anchor. Thus, an appropriate orientation of the bone anchor relative to the rod can be achieved.

[0003] To fix the inserted head in a specific angular position relative to the receiving portion, European Patent Application Publication No. 4074271 describes a receiving portion comprising a head receiving portion for receiving the head of a fixing element and a locking member attachable to the receiving portion so as to surround the head receiving portion. The locking member is designed as an outer ring and is movable between a first position and a second position. In the second position, the locking member compresses the head receiving portion to lock the inserted head. In addition, the head receiving portion has a locally reduced wall thickness to facilitate expansion of the head receiving portion for easy insertion of the head of the bone anchor, while the thicker wall portion of the head receiving portion provides sufficient strength and stability when clamping the inserted head.

[0004] The bone fixation device described in European Patent Application Publication No. 4074271 is a multi-axis bone fixation device configured such that the bone anchor can pivot relative to the receiving portion in multiple planes. Depending on the use or clinical application, it may be desirable to provide a bone fixation device configured to limit the pivoting of the bone anchor relative to the receiving portion to a single plane, i.e., a single-plane bone fixation device, or a uniaxial bone fixation device configured to prevent pivoting of the bone anchor relative to the receiving portion.

[0005] A variety of designs of single-plane bone fixation devices are known in which the shank of the bone anchor can pivot within the receiving portion only within a single plane. For example, U.S. Patent No. 7,749,258 describes a bone fixation device in the form of a single-plane bone fixation device that includes a receiving portion for receiving a rod, a pressure element, and a bone fixation element that is movable relative to the receiving portion within a limited angular range (the angle is within a single plane) about the longitudinal axis of the receiving portion. The movement of the bone fixation element relative to the receiving portion is restricted by a shape-conforming connection that includes a head of the bone fixation element and a guiding surface that cooperates with the pressure element.

[0006] There is still a need to provide a connecting device having a simple structure with only a few components that can enable the implementation of at least multi-axis bone fixation devices and single-plane bone fixation devices.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0008] Accordingly, an object underlying the present invention is to provide a connecting device that can be used in a modular bone fixation device that enables selectable functions with respect to multi-axis and single-plane designs. It is also an object to provide a bone fixation system that includes such a connecting device and at least two bone anchors that provide different functions to the bone fixation device.

[0009] This object is solved by the connecting device according to claim 1, the bone fixation device according to claim 13, and the bone fixation system according to claim 16. Further developments are described in the dependent claims.

Means for Solving the Problem

[0010] According to one embodiment, a connecting device is provided for selectively connecting a rod to a first bone anchor of a first type or a second bone anchor of a second type. The connecting device includes a receiving portion having a first end, an opposite second end, and a central axis extending through the first end and the second end. The receiving portion includes a rod receiving portion for receiving the rod and a head receiving portion. The head receiving portion includes an accommodation space for pivotally receiving the head of the first bone anchor or the second bone anchor such that the shank of the first or second bone anchor can take a plurality of angular positions with respect to the central axis. The connecting device further includes a locking member that is at least partially positionable around the head receiving portion and is movable between at least a first position where the head is pivotable and a second position where the head is locked within the accommodation space. The head receiving portion includes a restraint structure, whereby the connecting device is configured to cooperate with the first bone anchor such that the first bone anchor pivots with respect to the central axis in a single plane, or with the second bone anchor such that the second bone anchor pivots with respect to a pivot axis in a plurality of planes when the locking member is in the first position.

[0011] By selecting the first bone anchor and assembling it with the connecting device, the connecting device can be used as a single-plane bone fixation device. By selecting the second bone anchor and assembling it with the connecting device, the connecting device can be used as a multi-axis bone fixation device. Since the same connecting device can be used with different bone anchors, the surgeon can more flexibly and versatilely select the implant combination, and the number of parts per set is reduced.

[0012] Accordingly, using a connecting device, a modular bone fixation device can be implemented that can be assembled from a small number of interchangeable parts for different uses according to the user's selection.

[0013] The bone fixation device having a connecting device as described above is bottom-loading, i.e., a bone anchor can be inserted from the lower end of the connecting device. This enables in-situ assembly before or during surgery when the bone anchor is already inserted into the bone.

[0014] Furthermore, since the connecting device can be more expensive and / or more difficult to manufacture compared to the bone anchor, if the same connecting device can be used for two or more clinical applications, the manufacturing cost and / or the cost of inventory holding can be reduced.

[0015] For example, the connecting device or its three-dimensional parts may be manufactured using printing, such as additive manufacturing methods like laser sintering or laser or electron beam melting. By such methods, complex shapes can be easily manufactured based on the CAD data of the object to be manufactured.

[0016] According to a further embodiment, a receiving part is provided which comprises a first end part, an opposite second end part, and a central axis extending through the first end part and the second end part. The receiving part comprises a rod receiving part for receiving a rod and a head receiving part defining a receiving space for receiving the head of a bone anchor. The head receiving part further comprises a number of slits opening at the second end part of the receiving part, the slits forming a number of wall parts of the head receiving part. The slits and the wall parts preferably render the head receiving part flexible, in particular compressible and / or expandable. Further, at least one notch is provided in the head receiving part by removing, preferably cutting off, at least a part of one of the wall parts. Preferably, the notch is configured to receive at least a part of the shank of the bone anchor therein and to provide an enlarged pivotal angle of the bone anchor in a predetermined direction with respect to the central axis, or at least a limited angular range in the circumferential direction of the receiving part.

[0017] As used herein and in the appended claims, the term "rod" should be understood to include any elongated member regardless of its cross-sectional shape. Specifically, the spinal stabilization rods used herein may have a substantially circular, elliptical, or angled cross-section. Such cross-sections may vary along the length of the rod.

Brief Description of the Drawings

[0018]

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DETAILED DESCRIPTION OF THE INVENTION

[0019] Referring to FIG. 1, a system of a connecting device and two bone anchors according to one embodiment includes a first bone anchor 1 of a first type, a second bone anchor 1' of a second type, and a connecting device 10 connectable to the first bone anchor 1 or the second bone anchor 1'. When the connecting device 10 is assembled with the first bone anchor 1, the resulting bone fixation device is a single-plane bone fixation device in which the first bone anchor 1 can pivot only in a single plane. When the connecting device is assembled with the second bone anchor 1', the resulting bone fixation device is a multi-axis bone fixation device in which the bone anchor 1' can pivot in multiple planes. Thus, the first bone anchor 1 and the second bone anchor 1' can be used interchangeably with the same connecting device 10.

[0020] The connecting device 10 includes a receiving part 5 and a locking member 6. The receiving part 5 includes a rod receiving portion 51 for receiving the rod 100 and a head receiving portion 52 for receiving 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 monolithic component. The locking member 6 can be positioned around the head receiving portion 52 of the receiving part 5 and is movable along the outer surface of the receiving part 5 at least between a first position and a second position. The locking member 6 is configured to apply pressure to the head receiving portion 52 and the inserted head when the locking member 6 is at least in the second position, so as to lock the head to the receiving part 5 at a specific angular position of the shank 2. Preferably, the locking member 6 is a closed ring.

[0021] The connecting device 10 further includes a fixing member, for example, in the form of a fixing screw 7, to firmly fix the rod 100 to the receiving part 5. The fixing member 7 includes an engaging structure, for example, a male thread 71, and a tool engaging recess 72 on its outer surface. The fixing member 7 may be, for example, a set screw that can be screwed into the receiving part 5. FIGS. 2 and 3 show the first bone anchor 1 assembled to the connecting device 10 and the rod 100 inserted and fixed by the fixing member 7.

[0022] As shown in more detail in FIGS. 4 to 8, the receiving part 5 may be substantially cylindrical and includes a first end or upper end 5a, a second end or lower end 5b, and a passage or hole 53 that extends from the first end 5a toward the second end 5b and defines a longitudinal central axis C that extends through the first end 5a and the second end 5b. The rod receiving portion 51 is formed adjacent to the first end 5a, and the head receiving portion 52 is formed at the second end 5b.

[0023] The passage 53 extends away from the first end 5a and merges into a reduced-diameter intermediate portion 53a. The intermediate portion 53a may be, for example, cylindrical. Adjacent to the intermediate portion 53a, a receiving space 54 is formed with a shape and size such that the head 3 of the first bone anchor 1 or the head 3' of the second bone anchor 1' can be received therein. The receiving space 54 has an opening 54a at the second end 5b of the receiving part 5.

[0024] A substantially U-shaped recess 55 extends away from the first end portion 5a of the receiving portion 5. The substantially U-shaped recess 55 divides the receiving portion 5 into two leg portions 56 and forms a channel having a longitudinal axis L for receiving the rod 100. The bottom 55a of the channel may have a substantially V-shaped upper contour that provides a rod support surface for the inserted rod 100. Thereby, rods having different diameters may be inserted into the channel and supported on the rod support surface. In order to cooperate with the male thread 71 of the fixing member 7, a female thread 57, such as a flat thread or a square thread, is formed in the passage 53 on the leg portion 56 adjacent to the first end portion 5a. The U-shaped recess 55 defines an upper rod receiving portion 51 of the receiving portion.

[0025] The lower portion of the receiving portion 5 from approximately the middle portion 53a of the passage 53 to the second end portion 5b having the receiving space 54 defines a head receiving portion 52 of the receiving portion 5. The receiving space 54 has a substantially 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 in the direction of the central axis C of the receiving space 54 is adapted to cover the region having the maximum outer diameter E of the head 3 or 3' when the head is inserted into the receiving space 54. More specifically, the size of the receiving space 54 may be such that the head 3 of the first bone anchor 1 or the head 3' of the second bone anchor 1' can be held by friction. In order to facilitate the insertion of the head, a small chamfered portion 54b may be provided. As can be seen particularly from FIGS. 7 and 8, the receiving space 54 is divided into an upper portion 54c that covers the heads 3, 3' from above and a lower portion that includes a seat portion 54d for the heads 3, 3' that are pivotable.

[0026] The wall of the receiving part 5 around the accommodation space 54 is radially expandable and contractible with respect to the central axis C. This is achieved by a plurality of axially extending slits 58 that open at the second end 5b and extend to a certain distance from the second end 5b, preferably to the middle part 53a of the passage 53. The ends 58a of the slits 58 are enlarged, for example, with a diamond-shaped contour, a circular contour, or a triangular contour, or any other suitable shape. The slits 58 form some flexible wall portions 58b of the head receiving part 52. The size and number of the slits 58 can be selected to obtain the desired flexibility of the head receiving part 52.

[0027] A cavity 59 is formed in the wall of the head receiving part 52, and the cavity 59 extends circumferentially around the accommodation space 54. The cavity 59 can extend axially along the central axis C from a position below the region that accommodates the maximum diameter E of the head to the ends 58a of the slits 58. Thus, the cavity 59 surrounds the inserted head circumferentially and extends along a substantial region in the direction of the central axis C along the heads 3, 3'. Also, the cavity 59 communicates with the accommodation space 54 through an opening 59a that is narrower in the axial direction of the central axis C than the radially outer part of the cavity 59. More specifically, the opening 59a has the shape of an annular slit, as can be seen particularly from FIGS. 4, 7, and 8. The outward-facing wall portion 59b that defines the cavity 59 may be slightly convex and may be formed at a radially outward position away from the central axis C, whereby the radially outermost wall portion 50a of the head receiving part 52 is thinner than the lowermost wall portion 50b below the second end 5b or adjacent to the cavity 59. Also, the ends 58a of the slits 58 communicate with the cavity 59. Thus, the virtual connection line between two adjacent ends 58a of the slits 58, together with the radially thin wall portion 50a of the head receiving part 52, can define a predetermined breaking point or breaking line for removing a part of each wall portion 58b, as will be described in more detail below.

[0028] The upper wall portion 59c of the wall defining the cavity 59 may be tapered and narrowed toward the opening 59a toward the second end portion 5b. The lower wall portion 59d of the wall defining the cavity 59 may be substantially flat in a direction substantially perpendicular to the central axis C, or may curve or incline upward toward the opening 59a. It should be noted that the detailed shape of the cavity is not limited to the illustrated embodiment and may vary.

[0029] By the opening 59a of the cavity 59, the accommodation space 54 is divided into an upper portion 54c and a seat portion 54d that can be pressed against the heads 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.

[0030] The wall portion 50a is thinner than the wall portion 50b when viewed in the radial direction. Due to the cavity 59, the flexible wall portion 58b of the wall portion 50b can be easily expanded despite being relatively thick at the second end portion 5b of the receiving portion 5. When the head receiving portion 52 is compressed by the locking member 6, as will be described later, the lowermost wall portion 50b is configured to apply pressure to the heads 3, 3' from the axial position in the region having the maximum diameter E of the head or in the vicinity thereof as shown in FIG. 3 and from below this region. Therefore, by making the wall portion 58b of the wall portion 50b thick, a sufficiently strong clamping force can be obtained. Also, with this design, the strength against loosening can be increased. In other words, the wall portion provides a stable seat portion 54d for the heads 3, 3' that can securely clamp the heads.

[0031] The outer surface of the wall of the head receiving portion 52 expands toward the second end portion 5b at the tapered portion 50c near the second end portion 5b. Thereby, when the locking member 6 moves along the head receiving portion 52 in the direction toward the second end portion 5b, the compression force increases. Between the tapered portion 50c and the second end portion 5b, the outer surface portion 105 may be convex and rounded.

[0032] As best shown in FIGS. 4 and 6 - 8, two opposing recesses or slots 150 are formed at the lower end 5b of the head receiving portion 52. The recesses 150 are offset from each other by 180° and are aligned with the longitudinal axis L defined by the channel when viewed in top view as shown in FIG. 6. More specifically, the recesses 150 extend from the lower end 5b through the seat 54d and the upper portion 54c of the receiving space 54 to the middle portion 53a of the passage 53. The inner contour of the recesses 150 may be substantially rectangular. The recesses 150 may be provided at the circumferential position of the receiving portion 5 where the slit 58 is formed, i.e., may include the slit 58 as shown in FIG. 4. In the radial direction, the recesses 150 extend from the inner surface 154a of the wall of the head receiving portion 52 towards the outer surface 154b of the wall and terminate at a distance from the outer surface 154b. Thus, the recesses 150 open towards the receiving space 54 and do not completely penetrate the wall of the receiving portion 5 in the radial direction. Further, the recesses 150 do not substantially extend into the cavity 59.

[0033] As further described below, the recesses 150 enable the insertion of the head 3 of the first bone anchor 1 from the lower end 5b. Specifically, the recesses 150 define a restraint structure or a part of such a restraint structure that restrains the pivotal movement of the inserted head 3 of the first type of bone anchor 1 to a single plane including the central axis C.

[0034] The receiving portion 5 further includes cutout portions 151 formed adjacent to both sides of one of the recesses 150 configured to receive a part of the shank 2 of the bone anchor. The cutout portions 151 are formed at the inner edge portion 152 around the lower opening 54a of the receiving portion 5. The axial and radial extensions of the cutout portions 151 are shorter than the axial and radial extensions of the recesses 150. The cutout portions 151 may have a substantially triangular shape and may form a chamfered surface that gradually enters the recesses 150 from the edge portion 152. Thus, the cutout portions 151 provide an enlarged pivoting angle that allows the shank axis S of the first bone anchor 1 or the second bone anchor 1' to form with the central axis C when pivoting at the position of the cutout portions 151. Note that the cutout portions 151 may be formed on both sides of each recess 150.

[0035] A through hole 500 or another engagement structure for engaging with the instrument may be provided at the circumferential center of each leg portion 56. Further, inclined cutout portions 501 may be formed at both ends of the rod channel close to the bottom 55a of the substantially U-shaped recess. An additional chamfered portion 502 may extend to some extent from the cutout portions 501 toward the edges of each leg portion 56 on both sides of the channel. The cutout portions 501 and the chamfered portions 502 may facilitate the attachment of the locking member 6 from the first end portion 5a of the receiving portion 5 and / or may reduce the size of the receiving portion 5.

[0036] Referring further to FIGS. 9 and 10, the lock member 6 will be described in more detail. The lock member 6 is formed as a closed ring having a first end or upper end 6a and a second end or lower end 6b. The inner surface 61 of the lock member 6 is substantially cylindrical with an inner diameter sized such that the lock member 6 fits around the receiving portion 5 and is configured to slide along the outer surface of the receiving portion 5. The lock member 6 may include a tapered inner surface portion 62 adjacent to the second end 6b, the tapered inner surface portion tapering towards the first end 6a and being configured to cooperate with the tapered outer surface portion 50c of the receiving portion 5. The angles of the tapered portions of the lock member 6 and the receiving portion 5 are preferably corresponding to each other. Preferably, the angles are selected such that self-locking occurs when the surfaces engage with each other. Thereby, when the lock member 6 is attached and the tapered surfaces engage, it is prevented that the lock member 6 inadvertently moves upward and the lock is loosened. However, for example, it may be possible to disengage the cooperating surfaces using an instrument.

[0037] The outer surface of the lock member 6 may be cylindrical and may be provided with an engagement structure for engaging with an instrument (not shown). Adjacent to the second end 6b, the outer surface may taper towards the second end 6b. However, the shape is not limited to such a design. The axial length of the lock 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 portion 5 and is preferably longer than the axial length of the cavity 59. Thus, the lock member 6 is configured to apply a radially compressive force to most of the head receiving portion 52 of the receiving portion. The lock member 6 can be attached to the receiving portion 5 from the second end of the receiving portion 5 or its first end 5a.

[0038] Further referring to FIGS. 11 to 14, the first bone anchor 1 will be described in more detail. The bone anchor 1 includes a shank 2 having a shank axis S, which is preferably fully or partially threaded on the shank, and a head 3 having a free end 3a. There may be a neck portion 2a between the head 3 and the shank 2. The head 3 has a spherical outer surface portion, and the spherical outer surface portion includes a region having a maximum diameter E of the sphere. Preferably, the spherical outer surface portion is substantially axially symmetric with respect to a plane including the plane of the maximum outer diameter E. Further, the head 3 includes two opposing wings 4 that project from the spherical surface of the head away from the shank axis S. Each wing 4 extends along the spherical surface of the head 3 parallel to the shank axis S. The wings may extend from the free end 3a of the head 3 to the neck portion 2a, or may be provided at a distance from the free end 3a of the head and / or at a distance from the neck portion 2a.

[0039] The wings 4 are offset 180° along the circumferential direction of the head 3 and are symmetric with respect to a central plane including the shank 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 may be slightly inclined toward the shank 2. However, the upper end 4a may 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 portion 5, the wing 4 can extend into and pivot within the recess 150. Thus, the wing 4 forms a restraint structure or a part of a restraint structure that cooperates with a corresponding restraint structure in the form of the recess 150 provided in the receiving portion 5 to limit or restrain the pivoting movement of the head 3 within the head receiving 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 portion 5 during insertion, the wing 4 passes through the recess 150 at the lower end 5b of the receiving portion 5.

[0040] Furthermore, a tool engagement recess 31 is formed at the free end 3a of the bone anchor 1, which may have a polygonal or any other engagement structure suitable for screwing the bone anchor 1 into the bone, for example, a Torx (registered trademark) shape or a star shape or other axially grooved shape structure.

[0041] Referring to FIG. 1, the second bone anchor 1' will be described in more detail. The same components and parts as those of the first bone anchor 1 are denoted by the same reference numerals and the description thereof will be omitted. The second bone anchor 1' is different from the first bone anchor 1 in that the head 3' of the second bone anchor has no wing portion 4. For this reason, the outer surface of the head 3' is uniformly spherical between the neck portion 2a and the free end surface 3a. Thereby, when the second bone anchor 1' is inserted into the connecting device 10, the head 3' can pivot freely within the accommodation space 54 of the receiving portion 5 without being restricted. This means that the second bone anchor 1' can pivot with respect to the central axis C in a plurality of planes even in an unlimited number of planes.

[0042] The components and parts of the multi-axis bone fixation device can be made of any material, preferably a biocompatible material such as titanium or stainless steel, or any other biocompatible metal or metal alloy, or a plastic material. As the biocompatible alloy, a NiTi alloy such as nitinol may be used. Other materials can be magnesium or magnesium alloys, and the biocompatible plastic materials for use may be, for example, polyether ether ketone (PEEK) or poly-L-lactic acid (PLLA). The components can be made of the same or different materials from each other.

[0043] A preferred method for manufacturing the receiving portion and optionally the locking member and / or the bone fixation element is an additive manufacturing method, more preferably a layer manufacturing method such as three-dimensional printing. More specifically, the preferred method is laser sintering or laser melting or electron beam melting. In such a method, subsequent layers of a powder material such as metal powder are solidified with an energy beam, particularly a laser or an electron beam, at positions corresponding to the cross-sections of the components within each layer.

[0044] In use, the connecting device 10 may be pre-assembled. The locking member 6 can be attached to the receiving portion 5 from the first end portion 5a or from the second end portion 5b. At the insertion position of the locking member 6, the second end portion 6b of the locking member 6 can be in an axial position above the end portion 58a of the slit 58 of the head receiving portion 52 (see FIG. 15). When the heads 3, 3' of the bone anchors are inserted, the receiving space 54 of the receiving portion 5 can expand radially. The pre-assembled connecting device 10 can be connected to the bone anchors 1, 1' before the bone anchors are inserted into the bone or after the bone anchors have been inserted into the bone. In either case, the head of the bone anchor is inserted into the receiving portion 5 through the lower opening 54a and further moved into the receiving space 54 of the receiving portion 5. The receiving portion 5 is snap-fastened to the head by the slit 58 of the head receiving portion 52. Thereafter, the locking member 6 is moved downward in the direction of the central axis C to compress the head receiving portion 52 by the tapered inner surface portion 62 of the cooperating locking member 6 and the tapered outer surface portion 50c of the receiving portion 5. In this position, the inner surface 61 of the locking member 6 is disposed around the head receiving portion 52 and completely surrounds the head receiving portion 52. Compression of the head receiving portion 52 can lock the angular position of the bone anchor relative to the receiving portion. When the locking member 6 is attached to the receiving portion 5 from the first end, the receiving portion 5 may first be connected to the bone anchor, and then the locking member 6 may be attached.

[0045] A system of at least two bone anchors comprising a connecting device and a first bone anchor 1 and a second bone anchor 1' enables the connecting device 10 to be selectively combined with either the first bone anchor 1 or the second bone anchor 1'. Thus, the same connecting device 10 can be used to create either a single-plane bone fixation device or a multi-axis bone fixation device. Specifically, when the second bone anchor 1' is inserted into the connecting device, the second bone anchor 1' is configured to pivot about a central axis C in multiple planes. The restraint structure in the form of the recess 150 provided in the receiving portion 5 does not limit, i.e., does not affect, the pivoting movement of the second bone anchor 1'. At the position where the cutout portion 151 is formed, the second bone anchor 1' is configured to take an enlarged pivoting angle of its shank axis S with respect to the central axis C. For example, in the absence of the cutout portion 151, the maximum pivoting angle of the shank axis S with respect to the central axis C can be about 32°, and in the presence of the cutout portion 151, the enlarged pivoting angle can be about 42°. After inserting the rod 100, the fixing member 7 is screwed between the legs 57 of the receiving portion to fix the rod 100 to the receiving portion.

[0046] When the first bone anchor 1 is inserted into the connecting device 10, the head 3 is oriented with respect to the connecting device such that the wing portion 4 can engage with the recess 150 of the receiving portion. Thereby, the pivoting movement of the first bone anchor 1 is restricted to a single plane. In an embodiment, due to the position of the restraint structure, the single plane is a plane defined by the central axis C and the longitudinal axis L of the rod channel. The cutout portion 151 provides an enlarged pivoting angle of the second bone anchor 1' with respect to the central axis C. After inserting the rod 100, the fixing member 7 is screwed between the legs 57 of the receiving portion to fix the rod 100 to the receiving portion. FIG. 3 shows the locked position of the locking member 6, and the fixing member 7 presses the rod 100 against the first end 6a of the locking member 6 to maintain the locking member 6 in the lowermost position. In the locked position, the second end 6b of the locking member 6 is close to the second end 5b of the receiving portion 5 and completely surrounds the head receiving portion 52.

[0047] When the locking member 6 is in a pre-lock position slightly above the lowest position, which still allows the heads 3, 3' to pivot within the head receiving portion 52 but prevents removal of the heads 3, 3' from the head receiving portion 52, pre-locking of the inserted heads 3, 3' can be provided.

[0048] FIG. 15 shows a modification of the embodiment of the connecting device described above with reference to FIGS. 1 - 14. In FIG. 15, elements that are the same as or identical to those in FIGS. 1 - 14 are denoted with the same reference numerals and description thereof is omitted.

[0049] The receiving portion 5' of the connecting device in FIG. 15 is different from the receiving portion 5 of the embodiment in FIGS. 1 - 14 in a configuration that provides an enlarged pivoting angle. Specifically, instead of or in addition to the cutout portion 151, in the modified receiving portion 5', as shown in FIG. 15, at least one of the wall portions 58b of the head receiving portion 52 is at least partially removed. The wall portion 58b may be partially removed by breaking it along a virtual connection line between two end portions 58a of the slit 58 that demarcates the flexible wall portion 58b such that only the inner wall portion 59e located above the opening 59a remains. The gap formed by removing a part of the wall portion 58b is provided at a circumferential position of the receiving portion 5' that is different from the circumferential positions of the two recesses 150. The gap provides a notch configured to receive a part of the shank of the bone anchor therein, and thus provides an enlarged pivoting 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 portion 58b, as well as the head 3' of the inserted bone anchor, can be seen through the gap formed by removing a part of the wall portion 58b. Note that the position of the enlarged pivoting angle can be selected by breaking an appropriate one of the wall portions 58b.

[0050] FIG. 15 shows a connecting device including a modified receiving portion 5' into which the second bone anchor 1' is inserted. However, the modified receiving portion 5' can also be connected to the first bone anchor 1. Further, in FIG. 15, the locking member 6 is shown in the inserted position, and the second end portion 6b of the locking member 6 can be in an axial position above the end portion 58a of the slit 58 of the head receiving portion 52, and the rod is not inserted.

[0051] The receiving portions 5, 5' can be provided with both a cutout portion 151 and a gap formed by partially removing one of the wall portions 58b, both of which provide an enlarged pivotal angle of the inserted shank with respect to the central axis C, or only one of the cutout portion 151 and the partially removed wall portion 58b can be provided. The receiving portion may also include a plurality of cutout portions 151 and / or a plurality of partially removed wall portions 58b. However, the receiving portion may be provided without the cutout portion 151 and the partially removed wall portion 58b, i.e., without a structure providing an enlarged pivotal angle. Here, it should be noted that the "enlarged pivotal angle" does not necessarily mean a single enlarged pivotal angle that the shank can take with respect to the central axis C. Rather, the term "enlarged pivotal angle" can also refer to a limited circumferential portion of the receiving portion where the shank can take a larger pivotal angle with respect to the central axis C than other circumferential portions of the receiving portion.

[0052] Next, with reference to FIGS. 16 to 19, an embodiment of a multi-axis bone fixation device including a connecting device 10' of a further embodiment and a first bone anchor 1 will be described. The connecting device 10' includes a receiving portion 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 to the receiving portion 5''. Preferably, the receiving portion 5'' is a monolithic part. The connecting device 10 further includes a fixing member, for example in the form of a fixing screw 7, to firmly fix the rod 100 to the receiving portion 5''. The fixing member 7 and the bone anchor 1 may be the same as the fixing member 7 and the first bone anchor 1 of the system described above with reference to FIGS. 1 to 15.

[0053] The receiving portion 5'' has a first end or upper end 5a and a second end 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 substantially cylindrical and defines a longitudinal central axis C that extends from the upper end 5a into the head receiving portion 52' and extends through the first end 5a and the second end 5b, and includes a passage or coaxial hole 53'. The passage 53' includes an internal thread 57' at least in that region for receiving the fixing member 7. A substantially U-shaped recess 55' that forms a channel having a longitudinal axis L for receiving the rod 100 extends from the first end 5a of the receiving portion 5'' to approximately the very beginning of the head receiving portion 52'. A groove or other weakened portion 93 may be provided at a distance from the upper end 5a, enabling the upper portion of the receiving portion 5'' formed by the U-shaped recess that functions as an extended tab to be broken. The extended tab enables the multi-axis bone fixation device to be manipulated with the inserted rod 100 in a higher position compared to the final position, for example, to pull the vertebra against the rod.

[0054] An engagement structure for engaging an instrument (not shown) may be provided on the outer surface of the rod receiving portion 51'. The engagement structure may include circumferentially extending ribs 94. At a position below the ribs 94, the rod receiving portion 51' is provided with a flat outer surface portion 95, which may help facilitate the assembly of the locking member 6' and / or prevent rotational movement of the locking member 6' around the central axis C.

[0055] As shown in more detail in FIG. 17, the head receiving portion 52' formed adjacent to the second end portion 5b of the receiving portion 5'' has a substantially cap-shaped configuration having a hollow substantially spherical inner portion 101 that defines an accommodation space 54' for pivotally receiving the head 3 therein. A plurality of axially extending slits 102 that open at the second end portion 5b and may extend a distance from the second end portion 5b render the head receiving portion flexible, whereby the head 3 can be clamped and locked when pressure is applied to the head receiving portion by the locking member 6'.

[0056] At the lower end 5b of the head receiving portion 52', two opposing recesses or slots 150' are formed. The recesses 150' are offset 180° from each other and may be aligned with the longitudinal axis L defined by the U-shaped recess 55'. Each recess 150' opens toward the lower end 5b and extends completely through the wall of the head receiving portion 52' from the inner surface of the wall defining the accommodation space 54' to the outer surface of the wall. In the figure, only one of the recesses 150' is visible, and the other is hidden from view by the head receiving portion 52'. The inner contour of the recess 150' may be substantially rectangular. The width of the recess 150' in the circumferential direction of the receiving portion 5'' may be narrower than the distance between the two slits 102 or wider than the width of the slit 102.

[0057] With the head 3 oriented such that the wing portion 4 can engage the recess 150' of the receiving portion 5'' by the recess 150', it is possible to insert the head 3 of the first type of first bone anchor 1 from the lower end 5b. The recess 150' defines a restraining structure or a part of such a restraining structure that restrains 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 restraining structure 150', the single plane is the plane defined by the central axis C and the longitudinal axis L of the rod channel.

[0058] The locking member 6' is formed as a closed ring that is arranged around and designed to surround the head receiving portion 52'. The inner diameter of the locking member 6' is sized such that the locking member 6' fits around the receiving portion 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 enables, when the locking member 6' is in its lowest or locked position, for example, when the second end or lower end 6b of the locking member 6' is close to or adjacent to the second end 5b of the receiving portion 5'', the locking of the head 3 in the head receiving portion 52' in cooperation with the head receiving portion 52'. When the locking member 6' is in a pre-lock position slightly above the lowest position, which still allows the head 3 to pivot within the head receiving portion 52' but prevents the removal of the head 3 from the head receiving portion 52', a pre-lock of the inserted head 3 can be provided.

[0059] The locking member 6' of FIGS. 16 - 19 further comprises several upright flexible portions 63 that can serve to engage with the receiving portion 5'' and pre-hold the locking member 6' in a pre-lock position (not shown). Also, on the upper side of the locking member 6', two opposing protrusions 64 are provided, and the upper surface 64a provided on the protrusion 64 serves to support the rod 100. In the illustrated embodiment, the locking member 6' also comprises two opposing upright arms 65. At the upper end of the arm 65, an engagement structure in the form of a groove 65a configured to be engaged by an instrument (not shown) may be provided. The inner surface 65b of the arm 65 can be flat and may be configured to cooperate with the flat outer surface portion 95 of the rod receiving portion 51'. The cooperating flat outer surface portion 95 of the receiving portion 5'' and the inner surface 65b of the locking member 6' can prevent inadvertent rotation of the locking member 6'. In the installed state, the locking member 6' can take different axial positions relative to the receiving portion 5'', such as an insertion position where the head 3 of the bone anchor 1 can be inserted, a pre-lock position where the head is still pivotable relative to the receiving portion 5'' but is prevented from coming off, and a locked position where the head 3 is locked in its angular position.

[0060] By attaching the locking member 6' to the receiving portion 5 from the second end portion 5b of the receiving portion 5, the locking member 6' and the receiving portion 5'' may be pre-assembled. When assembling the single-plane bone fixation device, the first bone anchor 1 is used. The head 3 of the first bone anchor 1 can be inserted into the receiving space 54' of the receiving portion 5'' from its second end portion 5b when the locking member 6' is in the insertion position. The wing portion 4 extends into the recess 150'. Due to the slit 102, the head receiving portion 52' is flexible and snap-fastened to the head. Thereafter, the locking member 6' can be moved downward, for example, using an instrument (not shown), thereby compressing the head receiving portion 52' and applying pressure to the head. If necessary, the locking member 6' can be moved upward, for example, using an instrument, to loosen the lock of the head. The rod 100 may already be inserted into the substantially U-shaped recess 55', and the fixing member 7 is screwed into the passage 53' of the receiving portion 5''. Due to the extended tab of the receiving portion 5'', the rod 100 is still movable, and the head can be locked independently of the rod. For final locking, the fixing member 7 is tightened so that the rod 100 presses against the surface 64a of the locking member 6', further moving the locking member 6' to the locked position.

[0061] In the modification of the receiving portion 5'' shown in FIGS. 16 to 19, a cutout portion 151 described above with reference to FIGS. 1 to 15 may be provided in the receiving portion 5'' to provide an enlarged pivotal angle of the bone anchor with respect to the central axis C.

[0062] The connecting device 10' of the present embodiment may be connected to the second bone anchor 1' described above with reference to FIGS. 1 to 15. When the connecting device 10' is assembled with the second bone anchor 1', the resulting bone fixation device is a multi-axis bone fixation 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 connecting device 10'. Alternatively or additionally, at least one wall portion separated by two adjacent slits 102 of the head receiving portion 52' may be at least partially removed to provide an enlarged pivotal angle of the bone anchor with respect to the central axis C.

[0063] Next, a further modified example of the connecting device will be described with reference to FIGS. 20 to 26. In FIGS. 20 to 26, elements similar or identical to those in FIGS. 16 to 19 are denoted by the same reference numerals, and the description thereof will be omitted.

[0064] The connecting device 10'' in FIGS. 16 to 19 is different from the connecting device 10' in FIGS. 16 to 19 in that a pressure member 8 is provided in addition to the receiving portion 5'' and the locking member 6'. The pressure member 8 is configured to be disposed in the passage 53' of the receiving portion 5'', and to contact the inserted head 3 from above to further apply pressure to the inserted head. Preferably, the pressure member 8 is configured to apply pressure to the inserted head only from above.

[0065] As can be best seen from FIGS. 23 to 26, the pressure member 8 extends from the first end or upper end 8a to the second end or lower end 8b, and includes a central passage 81 extending from the first end 8a to the second end 8b. The first portion 81a of the passage 81 adjacent to the first end 81a is substantially cylindrical and provides a substantially cylindrical inner surface of the pressure member 8. Adjacent to the second end 8b, the second portion 81b of the passage 81 has a substantially spherical inner surface configured to contact the spherical outer surface portion of the head 3 from above.

[0066] At its first end 8a, the pressure member 8 includes a rod support surface 82 for supporting the inserted rod 100. The rod support surface 82 defines the 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.

[0067] At the second end portion 8b of the pressure member 8, two opposing recesses or slots 83 that open to the second end portion 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. The upper portion 83a that delimits the recess 83 toward the first end portion 8a of the pressure member 8 may have a curved shape corresponding to the shape of the upper end 4a of the wing portion 4 provided on the head 3 of the first bone anchor 1.

[0068] The recess 83 is configured to receive a part of the wing portion 4 of the head 3 of the first bone anchor 1 therein. Specifically, the recess 83 of the pressure member 8, together with the recess 150' provided in the receiving portion 5'', defines a restraining structure or a part of such a restraining structure that restrains the pivotal movement of the inserted head of the bone anchor in a single plane including the central axis C.

[0069] The pressure member 8 is attached to the receiving portion 5'' in such an orientation of the pressure member 8 that the recess 83 of the pressure member 8 is circumferentially aligned with the recess 150' of the receiving portion 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 portion 5''.

[0070] In use, depending on the selection of the bone anchor, the connecting device 10'' can be assembled to a single-plane bone fixation device using the first bone anchor or to a multi-axis bone fixation device using the second bone anchor. The final locking of the head is achieved by applying pressure to the pressure member 8 with a rod, thereby locking the head to the head receiving portion.

[0071] Modifications of the above-described embodiments are conceivable. For example, the restraint structures of the receiving portions 5, 5', 5'' and / or the pressure member 8 may be in different positions such that the single pivoting plane can have an angle with respect to the channel axis. It may also be possible to provide two or more restraint structures in different positions such that several distinct pivoting planes can be provided, one of which can be selected when inserting the first bone anchor. Further, a third type of additional bone anchor may be provided that cooperates with one or more restraint structures provided in the receiving portion and / or the pressure member such that the bone anchor takes a predetermined angular direction with respect to the central axis C and pivoting is prevented, i.e., such that the additional bone anchor and the connecting device form a uniaxial bone fixation device.

[0072] The first bone anchor may have a wing portion or any other restraint structure having a distance from the free end of the head.

[0073] It should be noted that the specific shapes of the individual parts and elements described above are not limited to the specific shapes shown in the drawings and may vary.

[0074] The bone anchor is not limited to having a threaded shank. Any type of bone anchor suitable for fixing to bone or vertebrae may be used.

[0075] In a further modification, the bone anchor can be a two-piece bone anchor comprising a shank and a separate head connectable to the shank. Thus, different heads that can be selectively combined with the shank can be provided. For example, one of the heads can be a head 3 with a restraint structure such as a wing portion, and another head can be a head 3' having a spherical outer surface as described without a restraint structure. In other words, a single-plane head or a multi-axis head can be selectively combined with the shank. Thus, modularity is further expanded.

[0076] Note that, instead of the above-described fixing member, other fixing devices such as a bayonet fixing device or a two-component fixing device capable of independently fixing a rod and a head may be used.

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, said coupling device (10, 10', 10'') comprising: a receiving part (5, 5', 5'') having a first end (5a), an opposite second end (5b) and a central axis (C) extending through said first end and said second end, said receiving part comprising a rod receiving portion (51, 51') for receiving said rod (100) and a head receiving portion (52, 52'), said head receiving portion (52, 52') comprising an accommodation space (54, 54') for pivotally receiving a head (3, 3') of said first bone anchor (1) or said second bone anchor (1') such that a shank (2) of said first or said second bone anchor can assume a plurality of angular positions with respect to said 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 can pivot and a second position in which the head is locked in the receiving space (54, 54'); Equipped with a coupling device, wherein the head receiving portion (52, 52') comprises a restraining structure (150, 150') whereby the coupling device is configured to cooperate with the first bone anchor (1) such that the first bone anchor (1) is configured to pivot about the central axis (C) in a single plane, or with the second bone anchor (1') such that the second bone anchor (1') is configured to pivot about the pivot axis (C) in multiple planes when the locking member (6, 6') is in the first position.

2. 3. The connecting device according to claim 1 or 2, wherein the restraining structure comprises 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 restraining structure (4) of the first bone anchor (1) to allow pivoting of the first bone anchor (1) in the single plane.

3. 3. The coupling device of 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. A coupling device according to claim 2 or 3, characterized in that two recesses (150) are provided which are offset from each other by 180°.

5. Coupling device according to any one of claims 2 to 4, wherein the at least one recess (150) extends axially below, preferably also above, the portion of the receiving space having the greatest internal width.

6. 6. The connecting device according to any one of claims 1 to 5, wherein the head receiving portion (52, 52') further comprises a cut-out portion (151) provided at the second end (5b) of the receiving portion and 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 provided adjacent to the restraining structure (150) in a circumferential direction about the central axis (C).

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

9. 9. A coupling device according to claim 8, wherein at least one of said slits (58) comprises an end (58a) at a distance from said second end (5b) of said receiving part (5, 5'), said end (58a) preferably comprising a diamond-shaped contour, and preferably a connection line between two ends (58a) of adjacent slits (58) defines a predetermined breaking point or line for removing said part of said wall portion (58b).

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

11. 11. The coupling device according to claim 10, wherein the locally reduced thickness of the wall of the accommodating 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. 12. A connecting device according to any one of claims 1 to 11, wherein an outer surface of the head receiving portion (52, 52') and an inner surface of the locking member (6, 6') are configured to cooperate to increase the compressive force of the locking member on the head receiving portion upon moving the locking member (6, 6') from the first position to the second position, thereby clamping the inserted head (3, 3') of the bone anchor, preferably at least one of the cooperating surfaces being tapered.

13. The coupling device according to any one of the preceding claims, further comprising a pressure member (8) arranged in the receiving part (5'') and configured to apply pressure to the inserted head (3, 3') to clamp the head (3, 3') in a specific angular position.

14. A bone fixation device comprising a connecting 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) is provided with a corresponding restraining structure (4) such that the first bone anchor (1) is configured to pivot about the central axis (C) in a single plane, and the second bone anchor (1') is configured to pivot about the central axis (C) in multiple planes.

15. 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 and is provided with a constraining structure (4) on its outer surface configured to cooperate with the constraining structure of the connecting device, preferably the constraining structure (4) being a protrusion with at least one wing (4) extending away from the shank axis (S) and defining the single pivot plane together with the shank axis (S), said wing preferably extending parallel to the shank axis along the spherical outer surface of the head, and wherein the head (3') of the second bone anchor (1') preferably has a uniform spherical outer surface without a constraining structure.

16. A bone anchoring system comprising a bone anchoring device according to claims 13 and 14, comprising at least the first bone anchor (1) and the second bone anchor (2) which can be used interchangeably.

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