US20060149244A1

US20060149244A1 - Device for connecting a longitudinal bar to a pedicle screw

Info

Publication number: US20060149244A1
Application number: US11/347,548
Authority: US
Inventors: Thomas Amrein; Martin Hess
Original assignee: Synthes USA LLC
Current assignee: DePuy Spine LLC; DePuy Synthes Products Inc
Priority date: 1997-01-22
Filing date: 2006-02-02
Publication date: 2006-07-06
Also published as: JP3766108B2; EP0954247A1; WO1998032386A1; ATE310455T1; DE59712497D1; US20030023240A1; JP2001508343A; AU1364397A; US6371957B1; EP0954247B1; US7022122B2; AU725487B2

Abstract

A device for connecting a longitudinal bar to a pedicle screw for fixation of the spine includes a body having an axis, an upper end, a lower end, a hole coaxial with the axis, and a through hole positioned perpendicular to the axis. The device also includes a collet chuck slidably disposed within the hole. The collet chuck includes a through hole substantially aligned with the through hole of the body for receiving the longitudinal bar. The collet chuck also includes a chamber defined by elastic tongues for receiving the head of the pedicle screw.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

This is a division of U.S. patent application Ser. No. 10/122,405, filed Apr. 16, 2002, now U.S. Pat. No. ______, which is a continuation of U.S. patent application Ser. No. 09/341,963, now U.S. Pat. No. 6,371,957, which is a national stage of PCT International Application No. PCT/CH97/00019, filed Jan. 22, 1997, all of which are hereby incorporated by reference in their entireties.

FIELD OF THE INVENTION

The invention concerns a device for connecting a longitudinal bar to a pedicle screw.

BACKGROUND OF THE INVENTION

From the related art, a large number of pedicle screws for fixation of the spinal column are already known; these known pedicle screws have the advantage that the individual pedicle screw can be attached to or removed from the longitudinal bar at any time without having to dismantle the entire fixation system. Such a pedicle screw is known from European Patent No. 330,881 B, for example.
The disadvantage of this and similar pedicle screws is the relatively complicated locking mechanisms for securing the longitudinal bar inserted into the open pedicle screw head. Furthermore, in most cases the head of the screw can be aligned with the position of the longitudinal bar only to a limited extent, necessitating complicated bending of the longitudinal bar to correct the angle.

SUMMARY OF THE INVENTION

The invention will provide a remedy in this regard and is based on the problem of creating a device for connecting a longitudinal bar to a pedicle screw, the device being easy to handle and permitting bending of the pedicle screw within a certain range.
The invention relates to a spinal fixation system including a longitudinal member positionable along the spinal column, a fastener for engaging a vertebra, and a connector for connecting the fastener and the longitudinal member. One part of the connector is a body having a through hole for receiving the longitudinal member and an opening in the bottom surface leading to the interior of the body. Another part of the connector is a collet chuck configured and dimensioned to be slidably received in the interior of the body. The collet chuck has a through hole alignable with the body's through hole for insertion of the longitudinal member in the connector. The collet chuck also has a plurality of resilient tongues and a chamber defined by inner surfaces of the tongues. The chamber is configured and dimensioned to receive the fastener head. The tongues flex outward for receiving the fastener head in the chamber and flex back inward for retaining the fastener head in the chamber. The connector also includes a locking element for securing the longitudinal member in the body and collet chuck through holes. Engagement of the locking element causes inward movement of the tongue and thereby secures the fastener at a surgeon selected angle.
In one embodiment, the desired number of devices according to the invention can be aligned on a longitudinal bar and can be simply snapped onto the pedicle screw with a spherical head already implanted in the vertebrae, so that a primary connection between the longitudinal bar and the pedicle screw is established. Other embodiments of the device according to the invention permit subsequent insertion of the longitudinal bar from the side or from above. By screwing the set screw into the fixation device, the longitudinal bar is locked axially and rotationally in the device at the same time, and the device is secured in a stable angular position. The set screw presses on the longitudinal bar inserted into the device, and the longitudinal bar presses on the bushing of the fixation device, and the bushing braces the collet chuck on the preferably spherical head of the pedicle screw by way of corresponding, preferably conical inside surfaces of the bushing and outside surfaces of the collet chuck.
Other embodiments permit sequential and independent locking of the longitudinal bar and rotation of the device with respect to the pedicle screw.
Thus, in comparison with known devices, the device according to the invention offers the advantage that the pedicle screws cannot only be secured exactly perpendicular to the longitudinal bar, but also permit an angle bend of up to ±25°. This is especially important when the longitudinal bar has not been bent accurately, which leads to major problems in assembly with traditional systems.
A preferred refinement of the device according to the invention also includes a pedicle screw with a preferably spherical head. The head of the pedicle screw is preferably provided with structuring in the form of transverse grooves or transverse ribs to achieve better fixation (bracing against the collet chuck). To be able to screw these pedicle screws into the bone, they are preferably provided with a hexagon socket in the spherical head.

BRIEF DESCRIPTION OF THE DRAWINGS

The detailed description will be better understood in conjunction with the accompanying drawings, in which like reference characters represent like elements, as follows:
FIG. 1 is an exploded perspective view of the device with a longitudinal bar, a pedicle screw with a spherical head, and a set screw;
FIG. 2 shows a slotted longitudinal section through the device as shown in the plane of FIG. 1;
FIG. 3 is a perspective view of the device of FIG. 1 in the mounted state after locking the longitudinal bar and the pedicle screw by means of the set screw;
FIG. 4 is an exploded perspective view of another embodiment of the device shown in FIG. 1 with an adjusting nut and a divided bushing;
FIG. 5 is an exploded perspective view of another embodiment of the device shown in FIG. 4 with a channel on the collet chuck that is open at the top and with a securing pin;
FIG. 6 is an exploded perspective view of another embodiment of the device shown in FIG. 1 with an adjusting nut for securing the spherical head of the pedicle screw and a set screw for locking the longitudinal bar;
FIG. 7 shows a longitudinal section through another embodiment of the device illustrated in FIG. 6 with a set screw integrated into a locking screw;
FIG. 8 is an exploded perspective view of another embodiment of the device shown in FIG. 5 with a collet chuck that is open at the side to accommodate the longitudinal bar and an adjusting nut as a chucking means for locking the longitudinal bar while at the same time securing the spherical head of the pedicle screw;
FIG. 9 is an exploded perspective view of the device shown in FIG. 5 without a securing pin;
FIG. 10 is an exploded perspective view of another embodiment of the device shown in FIG. 5 with a set screw and an inside thread in the collet chuck;
FIG. 11 is an exploded perspective view of another embodiment of the device shown in FIG. 8 with an adjusting nut for securing the spherical head of the pedicle screw and with a set screw for locking the longitudinal bar;
FIG. 12 is an exploded perspective view of another embodiment of the device shown in FIG. 11 with a collet chuck that is open at the top;
FIG. 13 is an exploded perspective view of another embodiment of the device shown in FIG. 11 with a through hole in the bushing which is open at the side; and
FIG. 14 is an exploded perspective view of another embodiment of the device shown in FIG. 12 with a through hole in the bushing which is open at the top.

DETAILED DESCRIPTION OF THE INVENTION

The device according to the invention illustrated in FIGS. 1 and 2 generally includes a body 3 in the form of a hollow cylindrical bushing with an axis 4 (axis of the hollow cylinder) and a hollow cylindrical collet chuck 7 arranged coaxially so it can slide in the interior of body 3.
Body 3 has a through hole 6 running across axis 4 that intersects the cylindrical surface of the hollow cylinder at two points symmetrically with axis 4. Collet chuck 7 also has a through hole 17 running across axis 4. Insertion of a longitudinal bar 1 running across axis 4 is made possible by the aligned arrangement of through holes 6 and 17 as illustrated in FIG. 2.
In its upper part, collet chuck 7 is secured within (hollow cylindrical) body 3 by a press fit and can be displaced axially with respect to body 3 when the relatively high force of the press fit is overcome.
Hollow cylindrical body 3 and collet chuck 7 are preferably in a rotationally locked arrangement relative to one another, e.g., by means of suitable groove/channel guides running axially. Collet chuck 7 is designed with tongues 8 that are spring mounted against cylinder axis 4 and point downward. The spherical head 9 of a pedicle screw 2 can be snapped from below with a spring action into the chamber formed by these tongues.
A hole 10 with an inside thread 11 is provided in the upper part of collet chuck 7 to accommodate a set screw 12 with a hexagonal socket head 20 which can exert a force on a longitudinal bar 1 inserted into the device, so the longitudinal bar 1 is locked axially and rotationally with respect to body 3, as indicated in FIG. 3. Collet chuck 7 is designed at its lower end such that screw shaft 13 of pedicle screw 2 connected to spherical head 9 can be locked at an angle α of −25° to +25° with respect to axis 4.
At its lower end 24, body 3 has a conical inside surface 14 which becomes wider toward the lower end and can come into sliding contact with a suitably designed conical outside surface 18 of the free ends of tongues 8 of collet chuck 7. As soon as set screw 12 abuts against longitudinal bar 1 inserted into the device, collet chuck 7 begins to push upward against body 3. This process is illustrated in FIG. 2, where the left half of the FIG. shows the condition before pushing collet chuck 7 upward, and the right half shows the conical surfaces 14 and 18 slipping past one another as collet chuck 7 is pushed upward with tongues 8. Tongues 8 are designed with a spring action due to slot 22 being pushed toward cylinder axis 4 such that hollow spherical cavity 19 is reduced in size and head 9 of pedicle screw 2 inserted into it is gripped securely. To optimize the locking of head 9, it is provided with a structuring 15, preferably in the form of transverse grooves or transverse ribs. Otherwise, pedicle screw 2 corresponds to known screw designs and is expediently provided with a hexagonal socket head 16.
Hollow spherical cavity 19 may in turn be provided with a structuring 21, preferably in the form of transverse grooves or transverse ribs. A combination of structuring 21 and structuring 15 is possible to further improve the fixation effect of head 9 in hollow spherical cavity 19.
Hollow spherical cavity 19 is preferably designed with a shape complementary to that of head 9 of pedicle screw 2 so the head can be accommodated in the cavity.
The embodiment of the device shown in FIG. 4 illustrates the use of a body 3, which is divided into a bottom part 52 and a top part 53 across axis 4 in the middle of through hole 6, in combination with an adjusting nut 26. The bottom part 52 of body 3 should be tall enough that longitudinal bar 1 is always in contact with bottom part 52.
Collet chuck 71 differs from collet chuck 7 shown in FIG. 1 only in that the inside thread 11 on the upper end has been replaced by an outside thread 27 for use by an adjusting nut 26. When tightened, adjusting nut 26 presses on top part 53 of body 3, which subsequently presses directly on longitudinal bar 1. Longitudinal bar 1 is subsequently pressed against bottom part 52 of body 3, and then locks spherical head 9, as shown in FIG. 2.
The embodiment of the device shown in FIG. 5 differs from the embodiment illustrated in FIG. 9 only in that a peg 55 prevents collet chuck 72, which has been weakened by channel 54, from collapsing when adjusting nut 26 is tightened. To prevent this peg 55 from falling out, it is advantageously provided with an outside thread and screwed in.
The embodiment of the device shown in FIG. 6 differs from the embodiment illustrated in FIG. 4 only in that:
a) collet chuck 73 has an inside thread 11 in addition to outside thread 27, and
b) body 3 (which is one piece) and through hole 6 are positioned with respect to through hole 17 so that only spherical head 9 is locked when adjusting nut 26 is tightened. This permits distraction or compression with a stable angular position. Adjusting nut 26 presses on body 3, and the resulting bracing of body 3 with collet chuck 73 ensures fixation of spherical head 9 of pedicle screw 2 without locking longitudinal bar 1. Longitudinal bar 1 is pressed separately with the help of set screw 12 against the lower edge of through hole 6 of body 3. Therefore, body 3 is further wedged with collet chuck 73, which leads to a greater clamping effect on spherical head 9. Through hole 6 should be positioned in body 3 so that longitudinal bar 1 also rests on the lower edge of through hole 6 after tightening adjusting nut 26.
The embodiment of the device illustrated in FIG. 7 differs from the device illustrated in FIGS. 1-3 only in the design of locking screw 91 and the positioning of through hole 6 with respect to through hole 17. Collet chuck 7 is provided with an inside thread 11. A locking screw 91, which is screwed into inside thread 11, and a set screw 12, which is integrated into locking screw 91, serve to lock spherical head 9 and longitudinal bar 1. Body 3, which is designed in one piece by analogy with FIGS. 1-3, is provided with a turning 94 at the top, accommodating the shoulder 93 of locking screw 91. Through hole 6 is positioned in body 3 with respect to through hole 17 in collet chuck 7 in such a way that only spherical head 9 is locked when locking screw 91 is tightened. Longitudinal bar 1 is secured afterwards by means of set screw 12. As long as this set screw 12 is screwed completely into locking screw 91, and locking screw 91 has been screwed back to the extent that longitudinal bar 1 touches the lower edge of through hole 6 in body 3, spherical head 9 can be secured or removed. Furthermore, collet chuck 7 is released again from the tightened state when locking screw 91 is screwed back. To accommodate longitudinal bar 1, collet chuck 7 may be provided with a through hole 17 according to FIG. 4, with a channel 54 that is open at the top according to FIG. 9, or with a channel 42 which is open at the side according to FIG. 8. In these latter two cases, either a two-piece design of body 3 or a design according to FIGS. 11 and 12 is advantageous to facilitate insertion of the longitudinal bar. However, with the two-piece design, the two parts of body 3 must be designed so that top part 53 presses directly on bottom part 52 and not on longitudinal bar 1 even after bracing.
The embodiment of the device shown in FIG. 8 differs from the embodiment illustrated in FIG. 4 only in that, in contrast with collet chuck 71, collet chuck 74 has a channel 42 that is open at the side instead of having a through hole 17 to accommodate longitudinal bar 1, but slot 22 does not extend into this open channel.
The embodiment of the device shown in FIG. 9 differs from the embodiment illustrated in FIG. 4 only in that, in contrast with collet chuck 71, collet chuck 72 has a channel 54 that is open at the top instead of having a through hole 17 to accommodate longitudinal bar 1, and slot 22 does not extend into this open channel. To prevent collet chuck 72 from collapsing when adjusting nut 26 is tightened, the thread should be designed so that negligible radial forces occur in tightening. A sawtooth thread, for example, would meet this requirement.
The embodiment of the device shown in FIG. 10 illustrates the use of a collet chuck 75, which is provided with an inside thread 11 instead of an outside thread 27, in contrast with collet chuck 72 illustrated in FIGS. 5 and 9. A set screw 56 with an outside thread 57 and a flange 58 serves as the clamping means. When tightened, set screw 56 presses against longitudinal bar 1, which in turn presses on bottom part 52 of body 3. This bracing of bottom part 52 and collet chuck 75 locks spherical head 9 of pedicle screw 2, as illustrated in FIG. 2. Top part 53 of body 3 prevents widening of collet chuck 75 when set screw 56 is tightened. Top part 53 rests on shoulder 63.
The embodiment of the device shown in FIG. 11 differs from the embodiment illustrated in FIG. 6 only in that collet chuck 76, in contrast with collet chuck 73, has a channel 42 that is open at the side instead of having a through hole 17, and slots 22 do not extend into the channel.
According to FIG. 13, through hole 6 in body 3 is preferably open at side 80 to permit unhindered insertion of longitudinal bar 1.
The embodiment of the device shown in FIG. 12 differs from the embodiment illustrated in FIG. 11 only in that, in contrast with collet chuck 76, collet chuck 77 has a channel 54 that is open at the top to accommodate longitudinal bar 1. According to FIG. 14, through hole 6 in body 3 is open toward top 81 for unhindered insertion of longitudinal bar 1.
The embodiment of the device shown in FIG. 13 differs from the embodiment illustrated in FIG. 11 only in that a through hole 80 which is open at the side is provided in body 3.
The embodiment of the device shown in FIG. 14 differs from the embodiment illustrated in FIG. 12 only in that a through hole 81 which is open at the top is provided in body 3.

Claims

1. A spinal fixation system comprising:

a longitudinal member;

a fastener having a head, the fastener being configured and dimensioned for engaging vertebrae; and

a connector for coupling the fastener and longitudinal member comprising:

a body having a through hole extending from a top surface to a bottom surface, and a first opening in a side surface for receiving the longitudinal member;

a collet chuck with at least a portion slidably received in the through hole of the body, the collet chuck having external threads and having a second opening for receiving the longitudinal member, the second opening being alignable with the first opening, and a plurality of resilient tongues defining a chamber for receiving the fastener head therein; and

a locking element threadably associated with the external threads of the collet chuck for releasably locking movement of the longitudinal member with respect to the collet chuck;

wherein engagement of the body with the tongues of the collet chuck moves the tongues inward to secure the fastener at a surgeon selected angle.

2. The spinal fixation system of claim 1 wherein the body comprises top and bottom portions, the bottom portion having a sufficient height so that the longitudinal member is in contact with the bottom portion when secured in the first and second openings.

3. The spinal fixation system of claim 1 wherein the second opening comprises a U-shaped portion.

4. The spinal fixation system of claim 3 wherein the second opening communicates with the chamber.

5. The spinal fixation system of claim 1 wherein the body and collet chuck are disposed about a central axis.

6. The spinal fixation system of claim 5 wherein the collet chuck has upper and lower ends and an outside surface defined there between, with the second opening extending through the outside surface transverse to the central axis.

7. The spinal fixation system of claim 6 wherein the second opening is remote from the upper and lower ends.

8. The spinal fixation system of claim 5 wherein the collet chuck has upper and lower ends, and the second opening extends along the central axis through the upper end.

9. A spinal fixation system comprising:

a longitudinal member;

a fastener having a head and a threaded end for engaging a vertebra; and

a connector for connecting the fastener and the longitudinal member comprising:

a body having top, bottom, and side surfaces, a first opening in the side surface for receiving the longitudinal member, and a second opening extending from the top surface to the bottom surface;

a collet chuck configured and dimensioned to be slidably received in the second opening of the body and having upper and lower ends, a third opening in the upper end with threading, a fourth opening alignable with the first opening of the body for receiving the longitudinal member, a plurality of resilient tongues, and a chamber defined by the tongues configured and dimensioned to receive the fastener head; and

a threaded locking element for releasably fixing movement of the longitudinal member with respect to the first and fourth openings,

wherein flexing of the tongues permits the fastener head to be received and retained in the chamber, and threading of the locking element with the threading of the collet chuck causes translation of the collet chuck and body with respect to each other.

10. The spinal fixation system of claim 9 wherein a portion of the locking element abuts the body when the locking element is threadably associated with the threads of the collet chuck.

11. The spinal fixation system of claim 9 wherein the fourth opening comprises a U-shaped portion.

12. A spinal fixation element system comprising:

a spinal rod;

a bone fastener having a head and an end portion for engaging a vertebra; and

a connector for coupling the bone fastener to the spinal rod, the connector including:

a first member having a first end, a second end, a through hole extending therebetween, and a first rod receiving channel;

a second member at least partially slidably received in the through hole of the first member, the second member includes a top end, a second rod receiving channel substantially aligned with the first rod receiving channel when the second member is partially disposed within the first member, and a resilient bottom end defining a chamber for receiving the head of the bone fastener; and

clamping securing means associated with the top end of the second member for releasably fixing the position of the spinal rod with respect to the second member and for moving the second member with respect to the first member without the securing means directly engaging the first member;

wherein movement of the second member with respect to the first member causes the inward movement of the bottom end of the second member so that the position of the bone fastener is fixed with respect to the second member.

13. The system of claim 12 wherein the first member includes a bottom portion and a top portion, the bottom portion having a sufficient height so that the spinal rod is in contact with the bottom portion when secured in the first and second rod receiving channels.

14. The system of claim 12 wherein the clamping means includes an externally threaded surface formed adjacent the top end of the second member for threadably engaging an internally threaded nut.

15. The system of claim 12 wherein the clamping means includes an inner threaded surface and an external threaded surface formed adjacent the top end of the second member for threadably engaging an externally threaded set screw and an internally threaded nut, respectively.

16. The system of claim 15 wherein rotation of the internally threaded nut fixes the position of the bone fastener with respect to the second member while rotation of the externally threaded set screw fixes the position of the spinal rod with respect to the second member.

17. The system of claim 12 wherein the clamping means includes an inner threaded surface formed adjacent the top end of the second member for engaging an externally threaded locking screw, the locking screw further including an internally threaded surface for engaging an externally threaded set screw.

18. The system of claim 17 wherein rotation of the externally threaded locking screw fixes the position of the bone fastener with respect to the second member while rotation of the externally threaded set screw fixes the position of the spinal rod with respect to the second member.

19. The system of claim 12 wherein the rod receiving channel of the second member is opened towards a side thereof so that the spinal rod is side-loading.

20. The system of claim 19 wherein the rod receiving channel of the first member is opened towards a side thereof.

21. The system of claim 12 wherein the rod receiving channel of the second member is opened towards the top end so that the second rod receiving channel is U-shaped.

22. The system of claim 21 wherein the rod receiving channel of the first member is opened towards the top end so that the first rod receiving channel is U-shaped.