WO2018186887A1

WO2018186887A1 - Spinal fixation element and stabilization system

Info

Publication number: WO2018186887A1
Application number: PCT/US2017/026594
Authority: WO
Inventors: Nickolas G. KRISKA; Jay Jones
Original assignee: Facet-Link Inc.
Priority date: 2017-04-07
Filing date: 2017-04-07
Publication date: 2018-10-11

Abstract

A fixation element (6) for an implant comprises a fastening means (3), preferably a screw, and a holder, wherein the fastening means (3) comprises a ball head (34), and wherein the holder comprises a sleeve (60), a compression cage (62) and a pressing element (65), wherein the pressing element (65) is attached to an inner portion of the sleeve (60) by means of an internal thread, the pressing element (65) configured to bear on the compression cage (62) such that the compression cage (62) is squeezed for arresting an angular position of the ball head (34). Opposite lateral sides of the sleeve (60) are formed as complementing abutment faces (61) for attaching adjacent fixation elements (6) closely together. This allows a closer positioning of two neighbouring sleeves than without the inventive faces. Applicability is expanded to very space-constrained stabilization tasks.

Description

SPINAL FIXATION ELEMENT AND STABILIZATION SYSTEM

FIELD OF INVENTION

[0001] The invention relates to a spinal fixation element and stabilization system and implanting method. More specifically, the fixation element comprises a fastening means, prefer- ably a screw, and a holder, wherein the fastening means comprises a ball head, and wherein the holder comprises a sleeve, a compression cage and a pressing element, wherein the pressing element is attached to an inner portion of the sleeve by means of an internal thread, the pressing element configured to bear on the compression cage such that the compression cage is squeezed for arresting an angular position of the ball head. BACKGROUND OF THE INVENTION

[0002] A central structural element of the human skeleton is the spine. It comprises a plurality of vertebrae which are arranged one above another for the transfer of loads and are connected to one another with articulation to allow movements. For transfer of load between the vertebrae, an intervertebral disk is arranged between the vertebral bodies of neighbouring vertebrae, filling up an interspace between the relatively flat top and bottom surfaces of the vertebral bodies. For articulation, upper joint protrusions and lower joint protrusions are provided on the left and right side of the posterior aspect of each vertebra. These joint complexes in the posterior column of the spine are often referred to as "facet joints". [0003] Due to wear or disease, the facet joints may be damaged. This may lead to a restricted movement, pain or even loss of mobility. Various approaches have become known for treatment. One using a fixation apparatus for stabilizing implants is known from US

2012/0143262 Al.

[0004] However, a problem often encountered with regard to stabilizing elements to the vertebrae is that the bony structure of the vertebrae is not strong enough. In such a case further stabilization is required, necessitating extensive stabilization systems. Their implantation may require massively invasive surgery. [0005] Improved multi-level stabilization systems are the subject of pending application PCT/US2016/056290 and PCT/US2016/056242. These require less space, in particular with respect to multi-level stabilization. Yet, the system is still not ideal for smaller stabilization tasks. This limits its usability. SUMMARY OF THE INVENTION

[0006] It is thus an object of the invention to provide an improved implant which gives more flexibility in use.

[0007] The solution according to the invention resides in the features of the independent claims. Advantageous further embodiments are the subject of the dependent claims.

[0008] A fixation element for an implant comprises a fastening means, preferably a screw, and a holder, wherein the fastening means comprises a ball head. The holder comprises a sleeve, a compression cage and a pressing element, wherein the pressing element is attached to an inner portion of the sleeve by means of an internal thread. The pressing element is con- figured to bear on the compression cage such that the compression cage is squeezed for arresting an angular position of the ball head. According to the invention, opposite lateral sides of the sleeve being formed as complementing abutment faces for attaching two adjacent fixation elements closely together.

[0009] By virtue of the abutment faces, two neighbouring fixation elements could be placed very close to each other, up to including being that close that they contact with their abutment faces. The complementary shaping of the abutment faces allows for contact between the two neighbouring fixation elements if the fixation elements are in close proximity with one another. This allows for a safe close positioning of the fixation elements at a distance (measured as distance of their center axis) which is smaller than the general width (diameter) of the sleeve of the fixation element. Thereby, a maximum compact arrangement of a pair of neighbouring fixation elements could be achieved. A maximum of space saving is achievable thereby. The invention thus expands its applicability to even small stabilization tasks that require a close positioning of the fixation elements. Usability and flexibility of use are thereby much enhanced. [0010] Preferably, the abutment faces are essentially flat, wherein the sleeve is preferably of a generally round shape. This allows a closer positioning of two neighbouring sleeves (wherein "closer" refers to a distance between centres of the neighbouring sleeves). Preferably, the abutment faces on either lateral side of the sleeve of the fixation elements preferably have the same width. Further, a large and plane contact area (as opposed to a mere line-like contact area in case of two round sleeves) is provided, thus minimizing contact friction. Thereby, any risk of unwanted interlock between neighbouring fixation elements is avoided.

[0011] Preferably, the abutment faces are provided with a non-abrasive surface. Thereby, friction between neighbouring fixation elements is reduced. Further, there is no risk of abrad- ed particles getting into surrounding tissue.

[0012] The sleeve preferably comprises at least one slot in its rear portion, the slot being configured for reception of an elongated carrier element, the elongated carrier element being preferably arrested by the second pressing element. By fixating of the elongated carrier element, a creation of a multi-level stabilization which may jump an intermediate vertebra and leaves it untouched is feasible, or the creation of a very compact stabilization for adjacent vertebrae, namely by placing the fixation elements so close as to abut against each other. For achieving a minimum distance it is preferable that the abutment faces are configured such as to be wider than the slot, so as to frame the slot on either side. Thereby, the advantageous effects of the abutment faces are maintained even in the region of the slot. [0013] Generally, the fixation element provides a locking polyaxial joint that is enabled to lock orientation of the fastening means with respect to the sleeve. It is activated by a pressing force exerted by the pressing element, thereby forcing the compression cage which encloses the head to press against said head. As a result, a press-fit is achieved which ensures a fixation at a stable angle. [0014] The range of motion for polyaxial movement of the fastening means is preferably limited by a skirt surrounding the head portion. This gives a general range of motion of preferably about 30°. However, in order to provide a sufficient range of angular motion to the upward direction, the rim is preferably slanted in respect to a center axis of the sleeve. Thereby, the range of angular motion is increased in a direction facing away from the elongated carrier element, to an angle of more than 45°, preferably about 50° (at the expense of the range of motion in the opposite direction which is of no interest in such a configuration). As a result, the slanted orientation of the rim gives a favourable bias for the angular range of motion of said polyaxial attachment. It is preferred that the slanted rim is combined with a configuration of the two abutment faces, wherein one reaches farther down than the other one on the other lateral side. [0015] Preferably, the head of the screw used as fastening means features a grit-blasted surface. Thereby, an improved friction fit in the polyaxial joint with the sleeve can be established.

[0016] In a preferred embodiment, the compression cage is provided with elastic tongues. Each of the tongues can expediently be formed by two parallel slot- like cuts, thereby creating a tongue between the cuts. The tongue is preferable elastic. By virtue of its elasticity, it exerts additional friction force on the head of the screw. To this end, the tongue preferably is offset such as to be bent inwards. Surprisingly, it was further found that the elasticity of the tongues provides for a smoother movement (rotation) of the head in the compression cage when the angle of the screw is to be adjusted. As a result, the elastic tongues improve both, smooth ad- justment of the angle and final fixation of said angle. A preferred material of which the compression cage is made is Titanium, in particular pure Titanium.

[0017] In another preferred embodiment, the shaft of the screw which forms the fastening means is threaded in its tipward portion only.

[0018] According to a further aspect of the invention, which may deserve independent pro- tection, a stabilization implant for a first vertebra is provided. It comprises a lower fixation element being provided with a lockable polyaxial joint for a fastening means, the fastening means having a head and a shaft configured for fixation to a cortical portion of said first vertebra, and an upper fixation element being connected by an elongated carrier element, wherein at least one of the upper and lower fixation elements is configured with complementing abut- ment faces at opposite lateral sides of the sleeve, which are formed as complementing abutment faces for attaching two adjacent fixation elements closely together.

[0019] By virtue of this, a rather small access hole will be sufficient for implantation, as opposed to conventional implants which lack the claimed configuration of the abutment faces and consequently require more space for mounting, i.e. a much bigger access hole and consequently wound to the patient. This is a considerable advantage in terms of surgery success.

[0020] The term "elongated carrier element" relates to an extension element that is reaching predominantly in an upward direction, but may also be usable in horizontal direction. The direction indications refer to an implanted state of the implant.

[0021] Preferably, the fixation element with its lockable polyaxial joint comprises a sleeve, a compression cage in its interior and a pressing element, wherein the compression cage is configured to tiltably engage the head and the pressing element is configured to squeeze the compression cage for arresting of the head, preferably the sleeve having a skirt surrounding the head portion, wherein a rim of the skirt limits a tilting angle (a) of the fastening means. Further preferably, the rim is slanted to a center axis of the sleeve, thereby allowing a greater tilt angle (a) in a direction facing away from the elongated carrier element. For further details and the advantageous effects, please see the above explanation of the fixation element.

[0022] This advantage is further increased by an angled configuration of the fastening means, those of the lower and upper fixation element. The fastening means are angled such that their trajectories are diverging, preferably at an angle of at least 80°, preferably at least 90°. Thereby, even a very small access hole will be sufficient for mounting and tightening. By virtue of such a high angle arrangement of the fastening means, space requirements for the implantation are minimized. It was found that space savings and robust anchoring is best bal- anced for a converging angle of preferably at least 90°.

[0023] In a preferred embodiment of the stabilization implant, only one of the fixation elements features the slanted rim and the other of the fixation elements does not. This enables a rather direct mounting of one of the fixation elements namely the one without the slanted rim at the vertebra at a selected height which gives strong positional control for the surgeon (largely independent of the strength of fixation), whereas the other fixation element with the slanted rim provides for a high diverging angle and, therefore, saves a lot of space (and size of the surgery wound).

[0024] However, it may also be envisaged that both of the fixation elements feature the slanted rim. In this case, preferably a back-to-back configuration is selected as it provides the greatest angle of divergence and, therefore, maximizes compactness of both, the implant and the surgery wound for its implantation.

[0025] In a preferred variant of the invention, the fastening means of the upper fixation element is configured to engage an upper vertebra, preferably a pars of said upper vertebra. Thereby, a robust and compact fixation can be achieved.

[0026] In another preferred variant, the fastening means have differently pitched threads. Thereby, the fastening means can be adapted to different strength/softness of various regions of the vertebra. Screws configured for being placed at a stronger region of the vertebra will receive a finer pitch than those screws configured for being affixed at a softer region of the vertebra. Preferably, the upper fastening means features a smaller pitch (for affixing to a cortical region) than the lower fastening means (for affixing to a more cancellous region of the vertebra).

[0027] Preferably, the upper and lower fixation element are arranged such at the elongated carrier element that they contact each other at their abutment faces. Thereby, a zero distance is realized which provides maximum compactness. However, due to the large contact area provided by the abutment faces both fixation elements could move relatively to each other, thereby avoiding any risk of jamming which could create undue stress on the fastening means and could do their ultimate fail.

[0028] In a particularly preferred embodiment, the implant is provided as a pair wherein the other, second implant is preferably a mirror image. Such a pair is particularly useful for implantation on either side of the spine, thereby providing a bilateral stabilization. The mirror image configuration ensures an optimum fit on either side. However, the mirror image configuration is not a must. The pair may comprise identical implants, too. Preferably, the two implants are arranged in an inverted V-configuration in their implanted state, preferably at a dorsal side of the vertebra. By virtue of the inverted V-configuration, an improved stabilization against lateral forces can be achieved, thereby improving stabilization of the affected vertebrae in a lateral direction, while maintaining simplicity of the design and ease of implantation. [0029] The invention further relates to a method for stabilizing a vertebra comprising the steps of opening an access hole providing access to the vertebra; forming a hole into a first vertebra; inserting a fastening means into the hole, the fastening means being a part of a fixation element; tightening the fastening means, whereby a shaft of the fastening means is poly- axially orientable in respect to a sleeve of the fixation element; forming a second hole at a superior vertebral position; inserting a second fastening means, whereby a shaft of the second fastening means is polyaxially orientable in respect to a sleeve of a second fixation element; tightening of the fastening means; adjusting a distance between the fixation element and the second fixation element with a minimum distance of zero and locking the polyaxial orienta- tion of the fastening means; and closing the access hole, wherein the fixation element and the second fixation element are connected by an elongated carrier element, at least one of the upper and lower fixation elements is configured with complementing abutment faces at opposite lateral sides of the sleeve, which are formed as complementing abutment faces for attaching two adjacent fixation elements closely together. [0030] By this method, the implant as described above can be implanted. Additionally, this method requires just a minimum size for the access hole, thereby keeping the surgery wound small and aiding in fast recovery of the patient. It is to be noted that the superior vertebral position can be at the same or an upper vertebra. The minimum size access hole according to the invention is particularly advantageous if the connecting member is configured such as to span over at least one intermediate vertebra.

[0031] For further explanations, reference is made to the above description of the fixation element and implant.

BRIEF DESCRIPTION OF THE DRAWINGS [0032] The invention will now be explained in reference to the enclosed drawing which shows advantageous sample embodiments. There are shown:

[0033] Fig. 1 is a side view of the implant position at the vertebrae of the spine;

[0034] Fig. 2a-c are lateral, rear and bottom view of the implant of Fig. 1;

[0035] Fig. 3 is an embodiment of a fixation element having a skirt with a slanted rim; [0036] Fig. 4 is an explosive view of the fixation element of Fig. 3;

[0037] Fig. 5 is an implant having two fixation elements;

[0038] Fig. 6 is an axial view of the fixation element;

[0039] Fig. 7a-c are detail views of the implant with two fixation elements in an implanted state;

[0040] Fig. 8a-b are views of a compression cage and a sleeve;

[0041] Fig. 9 is a variant of the implant having two fixation elements arranged back-to- back; and

[0042] Fig. lOa-e are some steps showing implantation. DETAILED DESCRIPTION OF THE INVENTION

[0043] An example for an implant set according to an embodiment of the invention is shown in Fig. 1 and 2. The set comprises an implant according to the invention as well as a second implant which is a mirror image thereof. For the sake of brevity the following expla- nations would be given to one of these implants only; they apply to the mirror image implant, accordingly.

[0044] The implant comprises two fixation elements 6, 6' which are connected by a rod serving as an elongated carrier element 5.

[0045] Each of the fixation elements 6, 6' comprise a sleeve 60 and a screw 3, 3' having a head 34 and a shaft with a thread. The thread of screw 3' is finer pitched than the thread of screw 3. The head 34 features a grit-blasted surface. In a mounted state that head 34 is located at a forward position within the sleeve 60, and is being held in the sleeve 60 by means of the skirt 67 and a rim 66 defining an opening which is smaller than the width of the head 34.

[0046] As it is shown in more detail in Fig. 3 to 5, the sleeve 60 forms with the head 34 of the screw 3, 3' a poly axial joint, thereby allowing the shaft of the screw 3, 3' to be oriented at a variable angle to a center axis 69 of the sleeve 60. To this end, the head 34 is ball-shaped and held in a front portion of the sleeve 60 by means of a compression cage 62. At a forward facing portion of the compression cage 62 slots are provided which define a tongue 64 being configured to engage the ball-shaped head 34 in an elastic manner. In a neutral state the tongue 64 is bent inwardly and, therefore, preloaded for tighter fit on the ball head 34.

[0047] The compression cage 62 is located in its mounted state at the forward position in the interior of the sleeve 60 and engages the ball-shaped head 34. It presses the head 34 against the rim 66 located at the forward end of the skirt 67 arranged at a lower portion of the sleeve 60. A rear portion of the sleeve 60 is provided with an inner thread lining the nearly cylindrical wall of the interior of the sleeve 60. Further, a circular pressing element 65 is provided having an outer thread on its circumference, said outer thread being configured to engage the inner thread of the sleeve 60. Thereby, by screwing in of the pressing element 65 it moves forward and bears on the compression cage 62 which exerts a clamping force on the ball-shaped head 34 of the screw 3. Thereby, the angular position of the screw 3 with respect to the sleeve 60 is affixed.

[0048] The compression cage 62 features in the depicted embodiment a concave saddle-like recess 68. It is shaped and dimensioned such as to accept the elongate carrier element 5. If the elongated carrier element 5 is present in the saddle-like recess 68 then the pressing element 65 does not bear directly on the compression cage 62, but does so via the elongated carrier element 5 as an intermediate. Thereby, the pressing element 65 also locks the positioning of the sleeve 60 with respect to the elevated carrier element 5. However, if the elongated carrier element 5 were not to be present, then the pressing element 65 would be enabled to bear directly on the compression cage 62 by contacting on the end horns 68' at either end of the saddlelike recess 68.

[0049] Further, for accepting of the elongated carrier element 5 the sleeve 60 is provided with two slots 63 on opposing lateral sides. The slots 63 are open to the rear of the sleeve 60 and are of such a width to allow a passage of the elongated carrier element 5. Thereby, the elongated carrier element 5 passes transversely through the interior of the sleeve 60, between the pressing element 65 and the compression cage 62.

[0050] As already mentioned above, at the front end of the sleeve 60 a circumferential skirt 67 is provided. It delimits with its rim 66 the angular movement of the screw 3, 3' of the fixation element 6. As it can be readily seen in Fig. 3 and 4, the length of the skirt 67 is not uniform, rather it is shortest or zero at one lateral side and longest at the other lateral side (left respectively right as shown in Fig. 3 and 4; or top and respectively bottom as shown in Fig. 2b). As a result, the rim 66 is slanted against the center axis 69 of the sleeve 60. By virtue of this, the screw 3 can reach a rather steep angle (which can be used for a rather steep upward pointing position as shown in Fig. 1 and 2), up to an angle a of 50° or more, as opposed to a much limited movement in the opposite downward direction, and with respect to a restricted movement in a transversal direction of about an angle β of 30°.

[0051] The sleeve 60 is provided at its two opposing lateral sides which already feature the slots 63 with abutment faces 61. These abutment faces 61 are generally flat depressions on the otherwise essentially circular sleeves 60. The abutment faces 61 have such a width that they are wider than the slots 63. As a result, the abutment faces 61 frame the slots 63 at both sides of the slot 63. The flat configuration of the abutment faces 61 allows for a very close positioning of two adjacent fixation elements 6, 6' down to and including a distance d of zero (see arrow in Fig. 5), that means the two adjacent fixation elements 6, 6' are contacting each other at the flat abutment faces 61. By selecting a distance of zero, the spacing of two fixation ele- ments 6, 6' and their screws 3, 3' can get smaller than it normally could be due to the width of the sleeves 60. This allows for a more compact configuration of the implant, thus requiring just a smaller access opening for surgery.

[0052] In the embodiment as depicted in Fig. 5, the two fixation elements 6, 6' are both of the type having a skirt 67 with a slanted rim 66. However, in case of the fixation element 6' the angular tilt is not utilized, and the screw 3' basically follows the center line of the sleeve

60. A variant of this embodiment is depicted in Fig. 9. It differs from the embodiment depicted in Fig. 5 by the orientation of the sleeve 60 of the fixation element 6' . It is turned around by 180° such as to form a back-to-back configuration with the fixation element 6. This arrangement allows for an increased angle γ of the screw 3", thereby increasing the total angle of divergence α+γ between screw 3 and screw 3 ' to values in the range of 80° to 90° or more, without requiring more space for the sleeve 60 of the fixation elements 6, 6".

[0053] In Fig. 7, examples for mounting the implant at a vertebra are shown. The implant shown is mounted at one (left) side of the spine and features a slightly slanted configuration; this allows for the provisioning of a second implant which act as a mirror image for maximum stabilization and is placed on the other side of the spine such as to form an inverted V- configuration. [0054] Steps for placing an implant comprising the fixation elements according to the invention are shown in Fig. 10. As a first step, an access hole is formed by cutting and spreading covering tissue (Fig. 10a, b), then using a template to determine a correct positioning (as indicated by dashed lines in Fig. 10c). In the specific depicted embodiment, a first fixation hole for the fastening means (screw 3) of the fixation element 6 is created and the fastening means 3 will be placed therein (Fig. lOd, e show a placement through a facet joint 95 having two sections 96, 97 such that a tip 34 of the fastening means 3 extends into section 96, but placement in other parts of the vertebra 91 are possible and within the scope of the present invention). Next, the fastening means will be tightened by using a screwdriver. A similar step of drilling a hole, in this case preferably in a pars section of the upper vertebra, and placing the second fastening means would be performed using the same compact access hole. As a result, after tightening of the fastening means the adjacent vertebrae are immobilized with respect to each other. Finally, the access hole would be closed.

Claims

1. A fixation element (6) for an implant comprising a fastening means (3), preferably a screw, and a holder, wherein the fastening means (3) comprises a ball head (34), and wherein the holder comprises a sleeve (60), a compression cage (62) and a pressing element (65), wherein the pressing element (65) is attached to an inner portion of the sleeve (60) by means of an internal thread, the pressing element (65) configured to bear on the compression cage (62) such that the compression cage (62) is squeezed for arresting an angular position of the ball head (34), characterized in that opposite lateral sides of the sleeve (60) being formed as complementing abutment faces (61) for attaching adjacent fixation elements (6) closely together.

2. The fixation element of claim 1, wherein the complementing abutment faces (61) are essentially flat, the sleeve (60) being preferably of a generally round shape.

3. The fixation element of claim 1 or 2, wherein both of the abutment faces have the same width.

4. The fixation element of any of the preceding claims, characterized in that the sleeve (60) comprises at least one slot (63) in its rear portion, the slot (63) being configured for reception of an elongated carrier element (5), the elongated carrier element (5) being preferably arrested by the pressing element (65).

5. The fixation element of claim 4, wherein the abutment faces are wider than the slot (63) so as to frame the slot (63) on either side.

6. The fixation element of any of the preceding claims, wherein a surrounding skirt is provided on the front end of the sleeve and a rim of the sleeve forms a limit for a range of angular motion of the screw.

7. The fixation element of claim 6, wherein the rim (66) is slanted to a center axis (69) of the sleeve (60).

8. The fixation element of claim 7, wherein a range of motion in direction of the slanting is bigger than transversal to it, preferably it is more than 45° versus 35° or less in the transversal direction.

9. The fixation element of claim 7 or 8, wherein the attachment face at one of the lateral sides extends farther down than at the other lateral side.

10. The fixation element of any of the preceding claims, wherein the head (34) has a grit-blasted surface.

11. The fixation element of any of the preceding claims, wherein the compression cage (62) is provided with elastic tongues (64) which are preferably bent inwards.

12. The fixation element of any of the preceding claims, wherein the compression cage (62) is made of Titanium, preferably pure Titanium.

13. A stabilization implant system for a first vertebra (91), comprising a lower fixation element (6) being provided with a lockable polyaxial joint for a fastening means (3), the fastening means (3) having a head (34) and a shaft (30) configured for fixation to a cortical portion of said first vertebra (91), and an upper fixation element (6') being connected by an elongated carrier element (5), characterized in that at least one of the upper and lower fixation elements (6, 6') is configured with complementing abutment faces (61) at opposite lateral sides of the sleeve (60), which are formed as complementing abutment faces (61) for attaching two adjacent fixation elements (6, 6') closely together.

14. The implant system of claim 13, characterized in that the fastening means (3, 3') are angled such that their trajectories are diverging, preferably at an angle of at least 80°, preferably at least 90°.

15. The implant system of claim 13 or 14, characterized in that the lockable polyax- ial joint comprises a sleeve (60), a compression cage (62) in its interior and a pressing element (65), wherein the compression cage (62) is configured to tiltably engage the head and the pressing element (65) is configured to squeeze the compression cage (62) for arresting of the head (34), preferably the sleeve (60) having a skirt (67) surrounding the head portion, wherein a rim (66) of the skirt (67) limits a tilting angle (a) of the fastening means (3, 3').

16. The implant system of claim 15, characterized in that the rim (66) is slanted to a center axis (69) of the sleeve (60), thereby allowing a greater tilt angle (a) in a direction facing away from the elongated carrier element (5).

17. The implant system of claim 16, characterized in that the fastening means (3, 3') are angled such that their trajectories are diverging, preferably at an angle of at least 80°, preferably at least 90°.

18. The implant system of claims 16 or 17, wherein only one of the fixation elements (6, 6') features the slanted rim (66) and the other does not.

19. The implant system of claims 16 or 17, wherein both of the fixation elements (6, 6') feature the slanted rim (66) and they are oriented in a back-to-back configuration.

20. The implant system of any of claims 13 to 19, wherein the fastening means (3') of the upper fixation element (6') is configured to engage an upper vertebra (92, 93), preferably a pars of said upper vertebra.

21. The implant system of any of claims 13 to 20, wherein the fastening means (3, 3') have differently pitched threads, wherein preferably the upper fastening means (3') features a finer pitch than the lower fastening means (3).

22. The implant system of any of claims 13 to 21, wherein the upper and lower fixation element (6, 6') are arranged such at the elongated carrier element (5) that they contact each other at their abutment faces.

23. The implant system of any of claims 13 to 22, characterized in that it comprises a second implant which is preferably configured as a mirror image for bilateral application on either side of the spine.

24. The implant system of claim 23, wherein the implant and the second implant are arranged in an inverted V-configuration at a dorsal side of the vertebra.

25. A method for stabilizing a vertebra comprising: opening an access hole providing access to the vertebra, forming a hole into a first vertebra, inserting a fastening means into the hole, the fastening means being a part of a fixation element, tightening the fastening means, whereby a shaft of the fastening means is polyaxially orientable in respect to a sleeve of the fixation element, forming a second hole at a superior vertebral position, inserting a second fastening means, whereby a shaft of the second fastening means is polyaxially orientable in respect to a sleeve of a second fixation element, tightening of the fastening means, adjusting a distance between the fixation element and the second fixation element with a minimum distance of zero and locking the polyaxial orientation of the fastening means, and closing the access hole, wherein the fixation element and the second fixation element are connected by an elongated carrier element, at least one of the upper and lower fixation elements is configured with complementing abutment faces at opposite lateral sides of the sleeve (60), which are formed as complementing abutment faces for attaching two adjacent fixation elements (6, 6') closely together.

26. Method of claim 25, wherein a second implant being a mirror image is implanted at the other side of the vertebra.

27. Method of claim 26, wherein the implant and the second implant are positioned such as to form an inverted V-configuration at a dorsal side of the vertebra.