A connecting device for linking a rod to a bone fixation element.

Abstract

The present invention provides a connecting device for linking a rod to a bone fixation element. [Solution] A coupling device for connecting a rod 100 to a bone fixation element 1 having a head 3 and a shaft 2 comprises a receiving part 5, the receiving part having a recess for receiving a rod and a receiving space for accommodating the head of the bone fixation element, and comprising a pressure element 6 having a first part including a rod support surface 62a and a second part 66 having a hollow interior, the receiving part includes a first fixing part, the pressure element includes a second fixing part 63a configured to engage with the first fixing part, the pressure element is insertable into the receiving part from the second end in a first rotational direction in which the first fixing part and the second fixing part are not engaged with the receiving part, and the pressure element is rotatable within the receiving part to take a second rotational direction in which the first fixing part and the second fixing part engage with the receiving part to prevent the pressure element from moving toward the first end.

Description

Technical Field

[0001] The present invention relates to a connecting device for connecting a rod to a bone fixation element. In particular, the present invention relates to a connecting device forming part of a multi-axis bone fixation device.

Background Art

[0002] In the art, various types of multi-axis bone fixation devices are known. Generally, a multi-axis bone fixation device includes a connecting device and a bone fixation element, the bone fixation element having a head that is pivotally received within the connecting device and can be locked at a desired angle with respect to the connecting device. The connecting device also receives a rod configured to connect the multi-axis bone fixation device to a further bone fixture.

[0003] For example, US9,486,246 B2 (Patent Document 1) describes a bone fixation device including a fixation element including a shaft and a head, a receiving component having a first end and a second end and a channel for receiving a rod near the first end, a receiving space for receiving the head near the second end, and a pressure element configured to be at least partially located within the receiving space and including a flexible portion for clamping the head. The connecting device can be assembled by inserting the pressure element from the first end into the receiving component in a first rotational direction, and then rotating the pressure element 90° such that a protrusion engages a recess within the receiving component. In this position, the pressure element is prevented from escaping through the first end. The bone fixation device can be used as a bottom-loading multi-axis bone fixation device, and the bone fixation element is inserted into the receiving component from the second end, i.e., the bottom end. In an alternative aspect of assembly, the pressure element is first assembled with the bone fixation element. Then, the bone fixation element with the pressure element attached is inserted into the receiving component from the first end, i.e., the top end, in the first rotational direction, and then the protrusion of the pressure element is rotated until it engages the recessed section of the receiving component in a second rotational direction.

Prior Art Documents

Patent Documents

[0004] [Patent Document 1] US9,486,246 B2 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] The object of the present invention is to provide an improved coupling device that can be used with a bone fixation element having an enlarged head, and a bone fixation device including such a bone fixation element. This object is solved by the coupling device described in claim 1 and a method for assembling the coupling device described in claim 17. Further developments are given in the dependent claims. [Means for solving the problem]

[0006] According to one embodiment, a coupling device for connecting a rod to a bone fixation element having a head and a shaft comprises a receiving component having a first end, a second end, a central axis extending between the first and second ends and a passage extending from the first end to the second end, and a recess for receiving a rod, the recess extending from the first end to the second end and forming two free legs, and the receiving component further has a accommodating space for accommodating the head of the bone fixation element, the accommodating space having an opening at the second end. The coupling device further comprises a pressure element configured to be at least partially located within the accommodating space and including a first portion including a rod support surface and a second portion having a hollow interior with an opening that defines a flexible portion configured to accommodate and tighten the head. The receiving component further includes a first fixing portion, and the pressure element includes a second fixing portion configured to engage with the first fixing portion, the pressure element being insertable into the receiving component from the second end in a first rotational direction in which the first and second fixing portions are not engaged, and the pressure element being rotatable within the receiving component to take a second rotational direction in which the first and second fixing portions engage with the receiving component, preventing the pressure element from moving toward the first end.

[0007] By using this coupling device, bone fixation elements having enlarged heads that cannot be inserted through the first end, i.e., the apex end, of the coupling device can be used. Instead, the bone fixation device is designed as a bottom-loaded bone fixation device in which the head of the bone fixation element is inserted into the receiving component from its bottom.

[0008] This coupling device design allows for a smaller overall lateral dimension. Simultaneously, the increased retention force between the head of the bone fixation element within the pressure element and the receiving component provides a robust bone fixation device.

[0009] In addition, it is possible to increase the maximum pivot angle of the bone fixation element relative to the receiving component. Connecting devices and bone fixation devices including such connecting devices provide modular bone fixation devices in which components can be selected and assembled in a simple manner at the surgical site or at any other location after the components have been manufactured. Such modular bone fixation devices allow for various combinations of fixation elements and receiving components as required, depending on the actual clinical requirements and circumstances. This reduces the cost of bone fixation devices, reduces inventory, and gives surgeons substantial choices of implants.

[0010] Further features and advantages of the present invention will become apparent from the description of the embodiments and the accompanying drawings. [Brief explanation of the drawing]

[0011] [Figure 1.2] Figure 1 is an exploded perspective view of a multi-axis bone fixation device having a connecting device and rod according to the first embodiment. Figure 2 is a perspective view of the assembled multi-axis bone fixation device of Figure 1. [Figure 3] Figure 3 is a cross-sectional view of the multiaxial bone fixation device shown in Figure 2, taken in a plane perpendicular to the rod axis of the inserted rods. [Figure 4.5.6.7]Figure 4 is a perspective view from the top of the receiving part of the coupling device shown in Figures 1 to 3. Figure 5 is a perspective view from the bottom of the receiving part of Figure 4. Figure 6 is a top view of the receiving part of Figures 4 and 5. Figure 7 is a cross-sectional view of the receiving part of Figures 4 to 6, and is a cross-sectional view along line AA in Figure 6. [Figure 8.9.10.11a] Figure 8 is a top-view perspective of the pressure element of the coupling device shown in Figures 1 to 3. Figure 9 is a bottom-view perspective of the pressure element of Figure 8. Figure 10 is a top view of the pressure element of Figures 8 and 9. Figure 11a is a cross-sectional view of the pressure element of Figures 8 to 10, and is a cross-sectional view along line BB in Figure 10. [Figure 11b] Figure 11b is a magnified view of Figure 11a. [Figures 12, 13, 14, 15] Figures 12-15 are perspective views of the steps involved in assembling the receiving components and pressure elements of the coupling device shown in Figures 1-3. [Figures 16, 17, 18, 19] Figures 16-19 are cross-sectional views of the steps for assembling a multiaxial bone fixation device, taken in a plane perpendicular to the axis of the channel for the rods. [Modes for carrying out the invention]

[0012] Referring to Figures 1 to 3, the bone fixation device includes a bone fixation element 1 having a shaft portion 2 for fixation within bone or vertebral space, and a head portion 3. The shaft portion 2 has bone engagement features such as threads. The head portion 3 is formed as a segment of a sphere and therefore includes a spherical outer surface portion. The spherical outer surface portion may include a region having the maximum outer diameter of the head portion 3. Furthermore, the head portion 3 includes an engagement portion 4 at its free end for engaging with a tool such as a screwdriver. Furthermore, the bone fixation device includes a receiving component 5 for receiving the head portion 3 of the bone fixation element 1 and for receiving a rod 100 configured to connect several bone fixation devices. The receiving component 5 is provided with a pressure element 6 for applying pressure to the head portion 3 of the bone fixation element 1 and for supporting the rod 100. The pressure element 6 may be secured by a pin 7. A locking element 8 in the form of an internal thread or set screw is provided to lock the head and rod 100 within the receiving component 5.

[0013] In addition, the receiving component will be described in more detail with reference to Figures 4 to 7. The receiving component 5 has a first end, i.e., a top end 5a, and a second end, i.e., a bottom end 5b, opposite the top end 5a. Generally, the receiving component 5 may have a substantially cylindrical shape with a central longitudinal axis C extending through the top end 5a and the bottom end 5b. Coaxial with the central axis C, a passage 51 is provided, extending from the top end 5a to the bottom end 5b and forming an opening 52 at the bottom end 5b. At a distance from the top end 5a, the passage 51 widens into a dwelling space 53 configured to receive the head 3 and at least a portion of the pressure element 6. The receiving component 5 further has a substantially U-shaped recess 54, starting from the top end 5a and extending toward the bottom end 5b. The U-shaped recess 54 forms two free legs 55, defining a channel that opens toward the first end 5a for receiving the rod 100. An internal thread 56 is formed on the inner surface of the leg portion 55, which in the exemplary embodiment is a square thread or another flat thread.

[0014] In particular, as shown in Figure 7, the portion of the passage 51 beginning from the apex 5a is formed by a substantially cylindrical lumen 51a having an inner diameter smaller than the maximum outer diameter of the head 3. In particular, the maximum outer diameter of the head 3 may be the same as or larger than the root diameter of the female thread 56. The lumen 51a of the passage 51 may extend axially below the bottom 54a of the U-shaped recess 54. Following the lumen 51a, the passage widens in a widened portion 51b into a substantially cylindrical portion 51c having an inner diameter larger than the maximum outer diameter of the head 3 and larger than the outer diameter of the pressure element 6 into which the head 3 is inserted. Following the cylindrical section 51c, the passage 51 narrows toward the bottom 5b in a constricted portion 51d, for example, a conical constriction. The width of the opening 52 may be larger than the maximum outer diameter of the head 3 so that the head 3 can be inserted into the housing space 53 from the bottom 5b. In order to allow the head 3 to be inserted from the bottom end 5b while the pressure element 6 is inside the receiving part 5, the width of the portion of the housing space 53 is such that the pressure element 6 can expand within it to allow the insertion of the head 3.

[0015] Two opposing notches 57 are formed in the inner wall of the passage 51 in the direction of the longitudinal axis L of the channel formed by the U-shaped recess 54. The notches 57 may have width in the circumferential direction so that a portion of a pressure element can extend therein and be guided by the notches 57. In the axial direction, the notches 57 extend into the widened section 51b of the passage 51 from a distance above the bottom 54a of the U-shaped recess 54. The inner contour may conform to the outer contour of a portion of a pressure element, as will be described in more detail below. The depth of the notches 57 in the radial direction is at least the same to accommodate a portion of a pressure element therein. Thus, the notches 57 form a radially widened section which helps to allow insertion of the pressure element 6 from the bottom end 5b in a first rotational direction relative to the receiving part 5.

[0016] A first circumferential groove 58a may be provided on the inner wall of the leg portion 55 at a distance from the bottom 54a of the U-shaped recess 54. The first inner groove 58a can provide a stopper to restrict the upward movement of the pressure element 6 toward the top portion 5a when the pressure element 6 is assembled with the receiving component 5 and in the insertion position. In the axial direction, between the first circumferential groove 58a and the bottom of the U-shaped recess 54a, there may be a second circumferential groove 58b for engaging with a portion of the pressure element 6 to secure the pre-locked position of the pressure element 6.

[0017] The receiving part 5 may further include two transverse holes 59 that completely penetrate each leg 55, perpendicular to the central axis C and located approximately in the center of each leg 55 in the circumferential direction. The transverse holes 59 may serve to accommodate pins 7, as shown in Figures 1 to 3. The pins 7 are configured to engage with the pressure element to form a fixing device for securing the pressure element 6 against rotation. Furthermore, the pins 7 may restrict the upward movement of the pressure element 6.

[0018] Furthermore, circumferential tool engagement grooves 500 for engagement with tools and instruments may be formed on the outer surface of each leg at a certain distance from the top end 5a.

[0019] On the outer surface of the receiving component 5 aligned with the U-shaped recess, two opposing flat regions 501 that reduce the overall width of the receiving component may be provided.

[0020] Referring further to FIGS. 8 to 11a and 11b, the pressure element 6 will be described. Preferably, the pressure element 6 is a single-piece structure that is disposed within the passage 51 and is configured to apply pressure to the head 3 in a lateral direction and surrounding the head from the free end of the head such that when the head 3 and the pressure element 6 are within the receiving component 5, the head 3 is pivotable relative to the receiving component 5 and can be locked at an angle relative to the receiving component. More specifically, the pressure element 6 has a first end, i.e., a top end 6a, and a second end, i.e., a bottom end 6b. Adjacent to the top end, the receiving component includes a first portion 61 having a substantially cylindrical outer surface with an outer diameter that allows the pressure element 6 to move axially within the inner cavity 51a of the passage 51 of the receiving component 5. A rod receiving recess 62 including a rod support surface 62a is formed in the top end 6a. The rod support surface 62a may have a substantially V-shaped cross-section having a longitudinal axis l that extends substantially perpendicular to the cylindrical axis of the first portion 61 that coincides with the central axis C of the receiving component 5 when the pressure element 6 is within the receiving component 5. The depth of the rod receiving recess 62 may be smaller than the diameter of the rod 100. Thus, when the rod 100 rests on the rod support surface 62a, the rod 100 projects beyond the top end 6a of the pressure element, as shown, for example, in FIG. 3. The V-shape of the rod support surface 62a facilitates the use of rods having different diameters.

[0021] The rod receiving recess 62 is shaped such that it forms two free upright legs 63 on each side, which can be separated from the rod support surface 62a by grooves 64. This makes the legs 63 slightly flexible in the direction transverse to the longitudinal axis l of the rod support surface 62a. The free end of each leg 63 may have a radially outward projecting edge 63a, the upper surface of which forms the apex 6a of the pressure element 6. The outward projecting edge 63a is configured to engage with and be guided within each notch 57 of the receiving component 5. To secure the insertion position of the pressure element, the radially outward projecting edge 63a is configured to engage with a first groove 58a provided on the inner surface of the leg 55 of the receiving component 5. Therefore, the first groove 58a of the receiving component forms a first fixing portion, and the radially outward projecting edge 63a of the pressure element forms a second fixing portion configured to cooperate with the first fixing portion, as will be described in more detail below. To ensure a pre-locked position of the pressure element 6 within the receiving component 5, the radially outward projecting edge 63a is configured to engage with a second groove 58b provided on the inner surface of the leg portion 55.

[0022] Each leg portion 63 is provided with an elongated through-hole 65 extending in the axial direction at its circumferential center, as shown in Figure 3, for receiving a pin 7.

[0023] The second portion 66 of the pressure element 6 has a substantially cap-like shape configured to receive the head 3 of the bone fixation element 1. The second portion 66 of the pressure element includes a hollow head-receiving portion 67 having an opening at the bottom end 6b for inserting the head 3. The head-receiving portion 67 may have a lower substantially spherical section 67a and an upper substantially spherical section 67b, which are molded to receive and fit the spherical head 3. The intermediate section 67c may have a larger inner diameter to facilitate the insertion of the head 3. In addition, a plurality of axial slits 68 are formed, which open at the second end 6b and may have enlarged, preferably rounded, ends 68a. The slits 68 extend along the axial length, at least to the intermediate section 67c having the largest inner diameter. Generally, the number, shape, and size of the slits are selected so as to achieve the desired flexibility, allowing expansion of the head-receiving portion 63 when the head 3 is inserted through the bottom end 6b, and compression around the inserted head 3. The size of the head receiving portion 67 may also be such that friction can hold the head 3 within the head receiving portion 67 before finally locking the head 3 into place within the receiving component 5.

[0024] The outer surface 69 of the second portion 66 of the pressure element 6 may be rounded and may have an outer diameter larger than the outer diameter of the cylindrical first section 61. Adjacent to the bottom end 6b, the outer surface 69 includes a constricted portion 69a, which is a portion that narrows, for example, in a conical shape, and is configured to engage with the constricted portion 51d in the bottom region of the housing space 53 of the receiving component 5. When the pressure element 6 and the head 3 of the bone fixation element 1 are inside the receiving component 5 and the constricted portion 69a engages with the constricted portion 51d of the housing space, the head 3 is prevented from coming out through the lower opening 52 of the receiving component.

[0025] In addition, the pressure element 6 includes a coaxial opening, or lumen 600, which allows a tool such as a screwdriver to access the tool engagement recess 4 of the inserted head 3.

[0026] As can be seen from the enlarged views in Figures 11a and 11b, the second portion 66 of the pressure element includes a groove 601 on its outer surface, preferably extending entirely circumferentially between the outer surface 69 and the cylindrical first section 61. The groove 601 forms a transition between the outer surface 69 of the first section 61 and the second section 66 of the pressure element 6. The circumferential groove 601 has a minimum diameter in the direction perpendicular to the central axis C that is smaller than the outer diameter of the cylindrical first section 61 and smaller than the outer diameter of the outer surface 69. The profile of the groove 601 may be spherical in the cross-sectional view shown in Figures 11a and 11b. The outer surface 69 may have a first outer surface portion 602 adjacent to the groove 601, preferably a spherical portion having a first radius, which protrudes further outward than the cylindrical first section 61. The outer surface 69 extends from the first outer surface portion 602 to the second outer surface portion 603, preferably a spherical portion having a second radius greater than the first radius, up to the edge 604 between the second outer surface portion 603 and the constricted portion 69a. The edge 604 may form the maximum outer diameter of the second portion 66 of the pressure element.

[0027] The intermediate section 67c on the inner surface of the head receiving portion 67, located between the upper spherical section 67b and the lower spherical section 67a, includes a first portion 607 that extends from the upper spherical section 67b toward the bottom end 6b to a position 608 having the maximum inner diameter of the head receiving portion 67. Adjacent to this, the intermediate section 67c has a second portion 609, preferably conical in shape, that narrows toward the lower spherical section 67a. This results in a gap 610 between the inserted head 3 and the inner wall of the head receiving portion 67 in the region of the intermediate section 67c, as shown, for example, in Figure 3. It should be noted that the pressure element 6 has a wall portion 611 adjacent to the bottom end 6b, which has increased radial thickness due to the narrowing second portion 609 of the intermediate section 67c. This can result in an increased clamping force for tightening the head 3.

[0028] If the bone fixation element has an enlarged head 3 that can only be inserted into the receiving component from the bottom end 5b, the head receiving portion 67 of the pressure element must be large and flexible enough to allow for the insertion and accommodation of such an enlarged head. The shape of the groove 601 of the pressure element and the inner and outer surfaces of the second portion 66 can achieve sufficient flexibility to allow the second portion 66 of the pressure element to expand when the head 3 is inserted. Furthermore, the mounting of the pressure element 6 in the receiving component 5 can be facilitated.

[0029] The components and parts of the bone fixation device may be made from any material, but preferably from titanium or stainless steel, or from biocompatible metals or metal alloys or plastic materials. For biocompatible alloys, NiTi alloy, such as Nitinol, may be used. Other usable materials include, for example, magnesium or magnesium alloys. Examples of biocompatible plastic materials include polyetheretherketone (PEEK) or poly-L-lactic acid (PLLA). The components may be made from the same or different materials.

[0030] Referring to Figures 12 to 15, the steps for assembling the coupling device, i.e., the receiving component 5, with the pressure element 6 are shown. As shown in Figure 12, first, the pressure element 6 is oriented such that its top end 6a faces the bottom end 5b of the receiving component 5, so that the pressure element 6 can be inserted from the bottom end 5b of the receiving component 5. The pressure element 6 takes a first rotational orientation relative to the receiving component 5, in which the longitudinal axis of the rod support surface 62a of the pressure element 6 is perpendicular to the longitudinal axis of the U-shaped recess 54 for receiving the rod.

[0031] Next, as shown in Figure 13, the pressure element 6 is inserted into the receiving part 5 through the bottom end 5b in a first rotational direction. During insertion, the outer edge 63a extends into the notch 57 which guides the pressure element 6 during insertion. The pressure element 6 is inserted to an axial position where the edges 63a on each leg 63 of the pressure element 6 emerge from the notch 57 and are at the axial height of the first groove 58a. The elongated recess 65 may protrude from the bottom 54a of the U-shaped recess to such an extent that the elongated recess 65 can be engaged by the pin 7. Once the pressure element 6 is fully inserted, the outer edge 63a extends axially out of the notch 57, allowing the pressure element to be rotated.

[0032] Subsequently, as shown in Figure 14, the pressure element 6 is rotated to take a second rotational orientation in which the longitudinal axis of the rod support surface 62a is aligned with the channel provided by the U-shaped recess 54. In the second rotational orientation, the pressure element 6 engages with the upper wall of the first groove 58a at its outer edge 63a, preventing the pressure element from moving further toward the top end 5a of the receiving component 5 when the head 3 is inserted into the head receiving portion 67 of the pressure element 6. Thus, the upper groove 58a forms a first fixing portion, and the outer edge 63a forms a second fixing portion that fixes the pressure element 6 to the receiving component 5 at the insertion position of the head 3. As also shown in Figure 14, the rod support surface 62a protrudes above the bottom 54a of the U-shaped recess 54.

[0033] Next, as shown in Figure 15, the pressure element 6 is fixed against unintended rotation by a pin 7 inserted into a pin hole 59. The pin 7 has a length such that it extends into the elongated recess 65. However, the pin 7 may be omitted if the first portion 61 of the pressure element 6 is sized to be fixed in portion 51a of the passage 51 by friction.

[0034] Typically, the coupling device is pre-assembled. In clinical use, the bone fixation device can be used in a first embodiment in which the bone fixation element 1 is pre-assembled with a coupling device including a receiving component 5 and a pressure element 6 outside the patient's body, or in a second embodiment in which the bone fixation element 1 is already inserted into the bone or vertebra and the coupling device is attached in situ to the head 3 of the bone fixation element.

[0035] The attachment of the coupling device to the bone fixation element will be described with reference to Figures 17 to 19. As shown in Figure 16, the pressure element 6 is in the insertion position, with its edge 63a in the first groove 58a, and the flexible second portion 66 of the pressure element is located in the widened sections 51b and 51c of the housing space 53.

[0036] As shown in Figure 17, the coupling device is positioned on the head 3 of the bone fixation element such that the head 3 enters the receiving space 53 through the lower opening 52 of the receiving part 5 and enters the head receiving portion 67 of the pressure element 6. The pressure element 6 is prevented from moving toward the top end 5a of the receiving part because the top end 6a of the outer edge 63a abuts against the upper wall of the first groove 58a. Thus, the pressure element 6 is fixed in the insertion position.

[0037] Next, as shown in Figure 18, the pressure element 6 is pressed downward. As shown in Figure 19, the legs 63 of the pressure element 6 are slightly flexible, so the outer edge 63 can disengage from the first groove 58a when the pressure element 6 is pushed down and engages with the second groove 58b. By pulling the receiving part 5, the pressure element is moved further downward relative to the receiving part 5 until the constricted outer portion 69 engages with the constricted inner portion 51d of the receiving part 5. Thus, as shown in Figure 19, the pressure element 6 is in the pre-locked position, the lower opening 52 is constricted by the pressure element 6, and the head 3 is prevented from coming out through the lower opening 52.

[0038] Due to the large outer diameter of the head 3, the bone fixation element 1 can pivot to a larger maximum angle within the receiving component compared to bone fixation devices with smaller heads. For example, a bone fixation element with a head having a maximum outer diameter of 8 mm can be used instead of a head having a maximum outer diameter of 7 mm. The maximum pivot angle that the shaft 2 can form with the central axis C may be 35° or more. The large head provides a stable and robust implant with increased retention force.

[0039] When in use, once the desired angular position of the bone fixation element 1 relative to the receiving component 5 is achieved, the rod 100 is inserted, and the locking element 8 is inserted and tightened to lock the head and rod.

[0040] In clinical applications, multiple multiaxial bone fixation devices are inserted into the bone or vertebra, particularly the pedicle of the vertebra. The coupling devices are then aligned so that the rods can be received within the rod receiving portions of two or more bone fixation devices.

[0041] Modifications to the embodiments described above are possible. In particular, the shape of the parts is not limited to the detailed shapes shown in the figures. Modifications are possible and may be included in this disclosure. For example, the first and second fixing portions may be located at other positions on the receiving component and pressure element, and may have different shapes. It may be sufficient to have only one first fixing portion and one second fixing portion on the same side with respect to the rod receiving recess.

[0042] Instead of a set screw as the locking member, any other type of locking assembly known in the art may be used. For the bone fixation element, any type of bone fixation element suitable for fixation to bone or vertebrae, such as bone screws or bone nails, may be used. The rod can be any elongated device configured to connect two bone fixation devices. The rod may have various shapes and / or varying cross-sections along its length. The rod may be rigid or more flexible.

[0043] The spherical outer surface portion of the head may be only partially spherical when viewed circumferentially, and the seat within the head receiving portion may be adapted to the spherical outer surface portion of the head such that the pivot of the head is possible only within a predetermined plane. Other restricting structures that limit the pivot of the bone fixation element to one or more distinct planes may also be applied to provide such a single-plane bone fixation device.

[0044] Furthermore, the head receiving portion may be designed to allow the bone fixation element to pivot to a larger pivot angle on one side compared to the other side.

Claims

1. A connecting device for connecting a rod (100) to a bone fixation element (1) having a head (3) and a shaft (2), The coupling device is The receiving component (5) comprises a first end (5a), a second end (5b), a central axis (C) extending between the first end (5a) and the second end (5b), a passage (51) extending from the first end (5a) to the second end (5b), and a recess (54) for receiving the rod (100), the recess (54) extending from the first end (5a) to the second end (5b) forming two free leg portions (55), the receiving component (5) further comprises a receiving space (53) for accommodating the head (3) of the bone fixation element (1), the receiving space (53) having an opening (52) at the second end (5b), and the connecting device further comprises The pressure element (6) is configured to be at least partially located within the housing space (53) and comprises a first portion (61) including a rod support surface (62a) and a second portion (66) having a hollow interior (67) with an opening that defines a flexible portion configured to house and tighten the head (3), The receiving component (5) includes a first fixing portion (58a), and the pressure element (6) includes a second fixing portion (63a) configured to engage with the first fixing portion (58a). A coupling device wherein the pressure element (6) is insertable into the receiving component (5) from its second end (5b) in a first rotational direction in which the first fixing portion and the second fixing portion are not engaged with the receiving component (5), and the pressure element (6) is rotatable within the receiving component (5) in a second rotational direction in which the first fixing portion (58a) and the second fixing portion (63a) are engaged with the receiving component (5) to prevent the pressure element (6) from moving toward the first end (5a).

2. The coupling device according to claim 1, wherein the passage (51) includes a portion (51a) having a minimum width along the central axis (C), and the pressure element (6) is sized to clamp a head (3) having a maximum width greater than the minimum width of the passage (51).

3. The coupling device according to claim 1 or 2, wherein the second portion (66) of the pressure element (6) extends around the inserted head (3) in a region including at least the maximum outer diameter of the head (3), and preferably the second portion (66) of the pressure element (6) is sized to cover the inserted head (3) from its free end and extend beyond the region including the maximum outer diameter of the head (3).

4. The coupling device according to any one of claims 1 to 3, wherein when the first fixing portion (58a) and the second fixing portion (63a) are engaged, the first fixing portion (58a) provides a stopper that prevents the pressure element (5a) from coming off the first end.

5. The coupling device according to any one of claims 1 to 3, wherein the first fixing portion (58a) is a groove and the second fixing portion (63a) is a projection.

6. The coupling device according to any one of claims 1 to 5, wherein the second fixing portion (63a) is provided on the outer surface of the first portion (61) of the pressure element (6), preferably the first portion (61) of the pressure element (6) includes two legs (63), and the second fixing portion (63a) is provided on at least one outer surface of the legs (63).

7. The coupling device according to any one of claims 1 to 6, wherein the passage (51) includes at least one radially expanded section (57) between the receiving space (53) and the first end (5a), and the at least one radially expanded section (57) allows the second fixed portion (63a) to extend in the at least one radially expanded section (57) when the pressure element (6) is inside the receiving part (5) in the first rotational direction.

8. The coupling device according to claim 7, wherein the radial width of the radially expanded section (57) is greater than the width of the passage (51) in a direction perpendicular thereto.

9. The coupling device according to claim 7 or 8, wherein the radially enlarged section (57) is aligned with the recess (54) for receiving the rod (100).

10. The coupling device according to any one of claims 7 to 9, wherein the radially enlarged section (57) extends at least from the bottom (54a) of the recess (54) for receiving the rod into the upper portion (51b) of the housing space (53).

11. The coupling device according to any one of claims 7 to 10, wherein the enlarged section (57) has a circumferential size so as to guide the second fixed portion (63) during axial movement of the pressure element (6).

12. In the first rotational direction of the pressure element, the longitudinal axis (l) of the rod support surface (62a) is substantially perpendicular, preferably perpendicular, to the longitudinal axis of the recess (54) for receiving the rod (100), and more preferably, in the second rotational direction, the rod support surface (62a) is aligned with the longitudinal axis of the recess (54), according to any one of claims 1 to 11.

13. The coupling device according to any one of claims 1 to 12, wherein the receiving component (5) has a constricted portion (51d) near the opening (52) that is configured to tighten the head in cooperation with the corresponding constricted portion (69a) of the pressure element (6).

14. The coupling device according to any one of claims 1 to 13, wherein a groove (601), preferably a circumferential groove (601), is formed between the first portion (61) and the second portion (66) of the pressure element (6).

15. The coupling device according to any one of claims 1 to 14, wherein the inner wall of the hollow interior (67) of the pressure element includes an upper portion (67b) and a lower portion (67a) that conform to the shape of the inserted head (3), and an intermediate portion (67c), and a gap (610) is located between the inserted head and the intermediate portion (67c).

16. A bone fixation device comprising a connecting device according to any one of claims 1 to 13, further comprising a fixing element (1) having a shaft portion (2) and a head portion (3), preferably the head portion (3) having a maximum outer diameter smaller than the opening (52) at the second end portion (5b) of the receiving component and larger than the minimum width of the passage (51).

17. A method for assembling a coupling device according to any one of claims 1 to 13, The steps include orienting the pressure element (6) with respect to the receiving component (5) such that the pressure element (6) has a first direction of rotation, The steps include inserting the pressure element (6) into the receiving part (5) from the second end (5b) of the receiving part (5) in the first direction of rotation, A method comprising the step of rotating the pressure element (6) to take the second direction of rotation and engaging the first fixing portion (58a) and the second fixing portion (63a).

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