SPINAL MULTI-LEVEL INTERSEGMENTAL STABILIZATION SYSTEM AND METHOD FOR IMPLANTING

Abstract

A multi-level intersegmental stabilization implant for a facet joint of a first vertebra includes a lower retainer module having a transfacetal fastener and an upper retainer module having a second fastener configured for fastening through the pedicle of an upper vertebra. The lower and upper retainer modules are connected by an elongated carrier element dimensioned such as to span across at least two vertebrae. The transfacetal fastener is configured as a screw having a head and a shaft ending with a tip, the shaft being provided with a thread at least in a region near its tip such that it engages exclusively the lower section of the facet joint, wherein a washer is provided co-operatively connected with the transfacetal fastener, the washer being configured for bearing on an outer surface of the upper section of the facet joint.

Claims

1. A multi-level intersegmental stabilization implant for a facet joint of a first vertebra, the implant comprising a lower retainer module having a transfacetal fastener, the transfacetal fastener having a head and a shaft configured for traversing upper and lower sections of the facet joint, and an upper retainer module comprising a second fastener configured for fastening through a pedicle of a second vertebra, the lower and upper retainer modules being connected by an elongated carrier element dimensioned such as to span across at least two vertebrae, wherein the transfacetal fastener is configured as a screw having a head and a shaft ending with a tip, the shaft having a thread at least in a region near the tip such that the thread engages exclusively the lower section of the facet joint, and wherein a washer is connected with the transfacetal fastener, the washer having a hole for the transfacetal fastener, a pressure side, and an opposing seating side, the hole being configured for receiving the shaft of the screw, the pressure side being configured for bearing on an outer surface of the upper section of the facet joint, and the seating side being configured to abut the screw such that a compression force exerted by the screw is transferred through the washer onto the facet joint, wherein the washer provides a polyaxial seat for the screw.

2. The implant of claim 1, wherein at least one of the upper and lower retainer modules is configured as a polyaxial joint configured to hold at an adjustable angle.

3. The implant of claim 1, wherein the transfacetal fastener and the second fastener are angled such that trajectories of the fasteners are converging in a direction away from the vertebrae when the implant is implanted.

4. The implant of claim 1, wherein the shaft of the transfacetal fastener is threaded in a tipward portion only.

5. The implant of claim 1, wherein the shaft of the transfacetal fastener is threaded in both tipward and headward portions.

6. The implant of claim 1, wherein the elongated carrier element is dimensioned such as to bridge an intermediate vertebra between the first and second vertebrae preferably being shorter than a distance between the first and second vertebrae.

7. The implant of claim 6, wherein the elongated carrier element is shaped rodlike and a non-circular cross-section.

8. The implant of claim 1, wherein the retainer module comprises a lockable polyaxial joint.

9. The implant of claim 8, wherein the lockable polyaxial joint comprises a sleeve, a tension cage in an interior, and a pressing element, wherein the tension cage is configured to tiltably engage the head and the pressing element is configured to squeeze the tension cage for arresting of the head.

10. The implant of claim 9, wherein the sleeve has a skirt surrounding a head portion, wherein a rim of the skirt (67) limits a tilting angle of the elongated carrier element.

11. The implant of claim 10, wherein the rim is slanted to a center axis of the sleeve thereby allowing a greater tilt angle in a direction facing away from the elongated carrier element.

12. The implant of claim 9, wherein the sleeve comprises at least one slot in a rear portion, the at least one slot being configured for reception of the elongated carrier element.

13. The implant claim 1, wherein the upper and lower retainer modules are identical.

14. The implant of claim 1, further comprising a second washer for the upper retainer module.

15. The implant of claim 1, wherein the second fastener has a threaded portion configured for an oblique fastening to a cortical structure.

16. The implant of claim 1, wherein the transfacetal fastener further comprises a super-head that together with the head forms a stacked double-head arrangement.

17. The implant of claim 16, wherein the super-head is ball shaped and the head is conically shaped.

18. The implant of claim 16, wherein the super-head is polyaxially held in the sleeve.

19. A set of implants comprising the implant of claim 1, and a second implant is configured as a mirror image for bilateral application on either side of a spine.

20. The set of claim 19, wherein the second implant is arranged configured for implanting in a slanted position such that fasteners of the second implant converge with respect to fasteners of an implant implanted on the other side of the spine.

21-24. (canceled)

25. A method for stabilizing a facet joint, the method comprising: opening an access hole providing access to a vertebra having a facet joint to be stabilized, forming a hole through the facet joint, the hole crossing an upper section of the facet joint and reaching into a lower section of the facet joint, positioning a washer on top of the hole, inserting a transfacetal fastener through the washer into the hole, tightening the transfacetal fastener such that the facet joint is immobilized, wherein a shaft of the transfacetal fastener is polyaxially orientable with respect to the washer, forming a second hole in a pars portion of a superior vertebra, inserting a second fastener, and closing the access hole, wherein the transfacetal fastener and the second fasteners are each held in a retainer module, and the retainer modules are connected by a rigid, axially adjustable connection member, the transfacetal fastener being polyaxially adjustable in the retainer module for the transfacetal fastener.

26. The method of claim 25, wherein the connection member spans over at least one intermediate vertebra such that the intermediate vertebra is untouched apart from having an inferior facet fastened.

27. The method of claim 25, wherein the transfacetal fastener and the second fastener are angled such that respective tips of the fasteners diverge by an angle of at least 30.

28. The method of claim 27, wherein a spacing between the retainer modules of the transfacetal fastener and the second fastener is a distance of between 0.85 and 1.25 of a body height of one vertebra.

29. The method of claim 25, wherein the access hole is at most two times a vertebrae height for a multi-stage implant involving three vertebrae.

30. The method of claim 25, wherein the transfacetal fastener is a screw having a lag thread.

31. The method of claim 25, wherein the transfacetal fastener is a screw having a full thread.

32. The method of claim 31, wherein a bore in the upper section is made wider than a diameter of the full thread.

33. The implant of claim 3, wherein the trajectories converge at an angle of at least 60.

34. The implant of claim 6, wherein the elongated carrier element is shorter than a distance between the first and second vertebrae.

35. The implant of claim 34, wherein the elongated carrier element is shorter by at least half of a height of a vertebra.

36. The implant of claim 2, wherein the adjustable angle is oblique with respect to the elongated carrier element.

37. The implant of claim 12, wherein the pressing element is configured for arresting the elongated carrier element.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The invention will now be explained in reference to the enclosed drawing, which shows an advantageous sample embodiment. There are shown:

[0032] FIG. 1 is a side view of the implant position at the vertebrae of the spine;

[0033] FIG. 2a-c are lateral, rear and bottom view of the implant of FIG. 1;

[0034] FIG. 3a-b are embodiments of a washer;

[0035] FIG. 4a-b are side view and cross-section of the washer of FIG. 3b;

[0036] FIG. 5 is an exploded view of a retainer with a transfacetal screw;

[0037] FIG. 6 is a detail view of a slanted rim on the sleeve;

[0038] FIG. 7a-c are detail views of retainers with different screws;

[0039] FIG. 8a-e are views showing assembly of retainer and transfacetal screw, and

[0040] FIG. 9a-e are some steps showing implantation.

DETAILED DESCRIPTION OF THE INVENTION

[0041] An embodiment of a fusion implant 1 comprises a lower and upper retainer module 6, 6 and an elongated carrier element 5. In the lower retainer module 6, a transfacetal fastening means 3 is held. In the upper retainer module 6, a second fastening means 4 is held. Further, a washer 2 is provided through which the screw 30 is routed. As it can be readily appreciated in the drawing of FIG. 1, the transfacetal fastening means 3 and second fastening means 4 are diverging at an angle (the retainer modules 6, 6 and the elongated carrier element 5 are omitted in FIG. 1 for clarity). Thereby, the heads of the transfacetal fastening means 3 and second fastening means 4 are located in close proximity (much closer than the positioning of the transfacetal fastening means 3 and second fastening means 4 at the vertebrae themselves), so that a rather small access hole will suffice. A small access hole means a small surgery wound and therefore lesser stress for the patient.

[0042] The transfacetal fastening means 3 comprise a screw having a shaft 30 with a thread 34, a head 31, and a tip 35. The shaft 30 is of sufficient length to traverse both, a lower and an upper section 96, 97 of a facet joint 95 of the two adjacent vertebrae 90 and 91. It comprises a thread 34 which may be cortical or cancellous thread, i.e. optimized for engaging cortical or cancellous bone structure, respectively. The thread may be configured as a full thread 34 as shown in FIG. 6 or a lag thread 34 as shown in FIG. 7a), b). In the latter case, the thread 34 is present in a tip-ward portion of the shaft 30 only, whereas the headward portion of the shaft 30 is threadless.

[0043] The washer 2 features a center bore 20 which receives the shaft 30 of the transfacetal fastening means 3. The washer 2 has a lower side acting as a pressure face 21 configured to bear on an outer surface of the vertebra 91, and an upper side acting as a seating 22 for the transfacetal fastening means 3. The seating is configured as a polyaxial seat 23 for the screw of the transfacetal fastening means 3. The length of the lag thread 34 is dimensioned such as it will be placed completely in the lower section 96 of the facet joint 95.

[0044] For an improved transmission of force via the washer 2 to the facet joint 95, the seating is configured as a polyaxial seat 23. It comprises a spheroid ring 24 which is tiltably mounted in a complementary shaped receptable formed by a collar 25. The spheroid ring 24 and/or the collar 25 may be slotted. In an embodiment of the washer 2 as shown in FIG. 3a the spheroid ring 24 features a single slot 26, whereas in the embodiment of the washer 2 as shown in FIG. 3b the spheroid ring 24 is unslotted and the collar 25 features six slots 26 around its perimeter. The spheroid ring 24 is placed such in the collar 25 that it is recessed referenced to the pressure face 21, thereby forming a free space 26 underneath of the spheroid ring 24. The free space 27 is dimensioned such as to allow a range of movement of at least 45 tilting angle for the spheroid ring 24. In a mounted state, the transfacetal fastening means 3 abuts with its head 31 on the spheroid ring 24 which will be tilted under the tensioning force of the transfacetal fastening means 3 such as to provide circumferential support for the head 31. By further tightening of the transfacetal fastening means 3, the head 31 will assisted by an optional slightly conical shapearrest the angular position of the spheroid ring 24, thereby fixating the tilt angle. As a result, the facet joint is immobilized and secured.

[0045] By tightening of the transfacetal fastening means 3, the i lower section 96 of the facet joint 95 is pulled upward by the lag thread 34 of the transfacetal fastening means 3, against the upper section 97 of the facet joint which is forced downwards under the pressure exerted by the washer 2 which acts as a counter support for the transfacetal fastening means 3 held in the retainer module 6. Thereby, both sections 96, 97 of the facet joint 95 are tightened against each other, thereby reliably immobilizing the facet joint 95. Alternatively, in the case of a full thread 34 a bore for in the upper section 97 of the facet joint 95 is made wider than an outer diameter of the thread 34, thereby it is also ensured that the full thread 34 will engage the lower section 96 of the facet joint 95 only.

[0046] The head 31 may have an additional thread 36 on its outer circumference which is configured to wedge against the spheroid ring 24 in its collar 25 in order to lock a desired angular position. Thereby, the tilt angle for the transfacetal fastening means 3 could be adjusted and securely fixed for a secure immobilization of the facet joint between the vertebrae 90 and 91.

[0047] The head 31 of the transfacetal fastening means 3 is part of a stacked double head arrangement which features at its end an additional head superimposed on the head 31, this additional head being termed a ball-shaped super-head 32.

[0048] On the super head 32, an elongated carrier element 5 is affixed. Said elongated carrier element 5 is linked to the transfacetal fastening means 3 by means of the retainer module 6 having a lockable polyaxial joint. At a far end of the elongated carrier element 5, a cortical bone screw acting as a second fastening means 4 is located which is configured for an oblique fastening to a cortical structure of an upper vertebra 93. It features a pointed tip configured for breaking the surface of upper vertebra 93 in order to gain access for better stabilization. At the other end opposite to the tip, a ball shaped head similar to the super-head 32 is provided. It is to be retained by a retainer module 6 configured similar to the retainer module 6 which will be described below.

[0049] The lockable polyaxial joint in the retainer module 6 comprises a tensioning cage 62 in a sleeve 60. Slots 63 are provided at a forward facing portion of the tension cage 62 being configured to engage the ball shaped head 32 in a pivotally manner. At its front end, the sleeve 60 comprises a skirt 67 having a rim 66 at its free end. The tension cage 62 is at a forward position in the interior of the skirt 67, and the ball shaped head 32 is moved into engagement by the tension cage 62 through an opening defined by the rim 66. Further, a saddle like cutout 68 is formed at a rear end of the tension cage 62, that saddle like cutout being configured as a receptable for the elongated carrier element 5. From the back end of the sleeve 60, a pressing element 65 is to be mounted. To this end, the sleeve 60 is provided with an inner thread lining the nearly cylindrical wall of the interior of the sleeve 60. The pressing element 65 features a corresponding outer thread on its circumference which engages the inner thread. Thereby, the pressing element 65 moves forward by screwing it in and bears on the tension cage 62 which exerts a clamping force on the ball shaped head 32 of the transfacetal fastening means 3 and on the elongated carrier element 5. Thereby, the transfacetal fastening means 3 is affixed in its angular position relative to the retainer module 6 and provides additional stability by forming a rigid connection to the second fastening means 4 held in the retainer module 6 farther upward.

[0050] For a proper attachment of the elongated carrier element 5 to the sleeve 60, the latter is provided with two opposing slots 63 in a wall of the sleeve. The slots 63 are of such a width to allow a passage of an end portion of the elongated carrier element 5. Thereby, the jump bar 40 passes transversely through the interior of the sleeve 60, between the pressing element 65 and the tension cage 62. In order to give a more rigid fixation, a rear face of the tension cage 62 features a concave portion forming a saddle 68. It is dimensioned such as to provide a form fit for the elongated carrier element 5. The pressure force exerted by the pressing element 65 is thus transmitted via the elongated carrier element 5 to the tension cage 62. Thereby both, the elongated carrier element 5 as well as the tension cage 62 are receiving said pressure force and are locked in their respective positions.

[0051] The second fastening means 4 is affixed similarly, although usually to a pars section of the upper vertebra 93. The retainer module 6 for the second fastening means 4 is configured and employed similar to the retainer module 6.

[0052] The length of the elongated carrier element 5 is equivalent to the height of a vertebra 92. As a result, an effect of inserting the elongated carrier element 5 is that the retainer module 6 is positioned so far upwards that it engages the over next vertebra 93, leaping one intermediate vertebra 92. Thereby, a truly multi-level stabilization is achieved, wherein the stabilizing upward extension attaches to a vertebra 93 which is two levels above that vertebra 91 to which the retainer module 6 is attached.

[0053] On a front end of the sleeve 60, the circumferential skirt 67 is provided. It delimits with its rim 66 angular movement of the cortical screw of elongated carrier element 5. A variant 6 as exemplary shown in FIG. 5a features a slanted rim 66. The length of the skirt 67 is not uniform, rather it is shortest or zero toward a top position and longest toward a bottom position. As a result, the rim 66 is slanted against a center axis 69 of the sleeve 60. By virtue of this, the upward fixation element can reach a rather steep upward pointing position, up to an angle of 50 degrees or even more, as opposed to a much limited movement in a downward direction.

[0054] For improved stabilization of the spine, a mirror-shaped implant 1 is provided. It is configured to be mounted on a side contralateral to the implant 1, as best seen in FIGS. 2b) and c). As it can be readily appreciated from these drawings, the implant 1 is arranged slanted in relation to implant 1 such that the transfacetal fastening means 3 of both implants 1, 1 converge at an angle .

[0055] Steps for implanting the implant according to the invention are (i) opening an access hole by cutting and spreading (FIG. 9a, b), then using a template to determine the position (as indicated by the dashed lines in FIG. 9c). A hole is formed through the facet joint 95, the hole passing through the upper section 97 and ending in the lower section 96. The portion of the hole in the upper section may be formed with a bigger drill, thereby providing a width of the hole bigger than an outer diameter of the full thread 34 in the upper section 96 (FIG. 9d, part view on the right hand side shown only). The transfacetal fastening means 3 will be tightened by using a screwdriver of another appropriate tool, thereby pressing the washer 2 down, leading to an immobilization of the facet joint and to a fixation of the polyaxial position of the transfacetal fastening means 3. Similar steps of drilling a hole in a pars section of an upper vertebra and placing the second fastening means 4 therein are performed, using the same compact access hole (see FIG. 1). After completing the implant 1 (see FIG. 2), the access hole is finally closed.