CA2240656C - Spinal fixation device with laterally attachable connectors - Google Patents

Abstract

A spinal fixation device (10) includes a threaded stud (24) having an open- ended axial slot (30) to straddle a rod (14) of a vertebral support (12), an d a bracket (22) which is rotatable on the stud (24). A vertebra bone screw (5 0) passes through an opening (48) in a distal end of the bracket (22). The stud (24) and bracket (22) are locked in position relative to the rod (14) by a n ut (34). An insert (32) within the slot (30) bears against the rod (14) and prevents the stud (24) from being deformed by the force of the nut (34) on t he stud segments. The bracket (22) can be be rotated around the stud (24); and the stud (24) can be rotated around and slid along the rod (14), to afford great adjustability and ease of attachment.

Description

WO 9712317(~ PCTIUS96/20680 SPINAL FIXATION DEVICE WITH LATERALLY ATTA~ARr~
~C~NN ~:~;l'U~CS
Field of the Invention This invention relates to a "spinal fixation device", that is, a device for securing vertebrae of the upper spine of a patient in desired positions in rela-tion to one another and/or to the skull.
Back~Lou~.~ of the Invention Fixation devices are used in many surgical procedures, for example to secure vertebral fra~Lu~e_ during h~Al;ng, and to fuse damaged vertebrae against mo~ement. Such devices typically include a longit~l~in~
~U~G~L such as a rod or U-shaped member which is ~h~ro~
to fit along the SDinal colllmn; a hook, clamp or screw type ~astener which engages a vertebra; and a bracket or cnnn~ctor which int~L ~o ~ ts the fastener to the longi~ ;n~l ~u~pOL~ All three types of fasteners --hook, clamp, and screw -- are widely used for fixation of the thoracic and lumbar regions (i.e., below the ~ervical vertebrae) where there are relatively large vertebral bone stru~L~es to carry the load. In those CA 022406~6 1998-06-l~
WO97/23170 PCT~S96/20680 regions, fasteners of the hook and clamp types can be h~kP~ over or engaged with posterior elements of the vertebrae or lateral projections. Large so-called "pedicle screws," which have coarse threads and are S roughly si ;1~r to a lag screw are also used in the lumbar and thoracic regions. They extend from a bracket down the pedicle of the vertebra and into the vertebral body.
However, it is more difficult to attach hooks, ~-l~nr~ and screws in upper spine areas, that is, in the thoracic and cervical areas, because there the bone anatomy becomes ~oyLessively smaller. There is not ade~uate space or bone mass to secure pedicle screws, which are too large; and hooks sometimes tend to wor~
loose in this area h~c~ of the hypermobility of the spine.
To achieve fixation in the cervical spine, the most common posteriorly used fixation devices are what are known as lateral mass plates. Screws are used to SQcure these but are much smaller than the p~Aicle screws used in lower thoracic and lumbar spine fixa-tions. The screws are driven into the lateral masses o~ the vertebral body through holes in a plate which vertically bridges sequential vertebral segments. The locations in which these screws can be placed are li~it-ed so that each screw must be placed in a closely de-fined ideal position. ~he device must accommodate the requirements of mounting each screw in a precisely se-wo s7n3l70 PcT~usg6~0680 lected location, because the screws cannot be forced into any other position.
To date, however, there has been no practical way of coupling these types of screw fixations, that is, to couple a device of the type suitable for cervical spine fixation with a support that allows either a rod type o~ construct for posterior cervical fusion or extension of a thoracic fusion across the cervicotho-racic junction. The same lack of inter-changeability between these two different types of constructs has also limi.ted their application superiorly, that is, zcross the upper end o~ the spine, between the occipital bone of the skull and the cervical spine.
Thus there has been a need ~or a fixation dev}ce which will allow mating both lateral mass fixa-tion screws and cl-C2 fixation screws with a rod-type ~u~ L that can be combined with other types of fixa-tion device at lower positions on the spine, for exam-ple, across the cervicothroracic junction.
In f~xation devices of the screw type, the scr~w usually extends t~OUy}l a first opening in a bracket while the longi~ ; n~ 1 ~o~ L extends through a ~econ~ op~n; n~ in the bracket. U.S. Patent Nos.
t 5,403,314 and 5,312,404 both disclose such apparatus.
In those patents, once the bracket has been placed on the rod, it can be rotated about one axis only, i.e., circum~erentia~ly around the rod. The bracket cannot be rotated about an axis perpendicular to the rod. Thus CA 022406~6 1998-06-1~
WO97/23170 PCT~S96/20680 the angulation of the axis of the bracket is fixed with respect to the axis of the support rod. This makes it difficult to "aim" a screw if it is to be secured into a small area of a cervical vertebra.
S Another disadvantage of the fixation devices of those patents is that the physician has to determine in advance the number of fasteners and connectors to be used for a particular surgical procedure, before the rod or rods are fixed in position along the spinal column, because connectors could be attached to a rod only by sliding them in sequence along the length of the rod.
After the rod was secured to the spinal column, an additional or intermediate connector could not be slid onto the rod without first removing at least one end lS of the rod from ~o~nPction to the spine of the patient.
If some fasteners were already secured to vertebrae and more were n~e~, they could be added only by removing the secured fasteners or the entire device from the pa-tient, so that they could be slid along the rod to the desired location.
It has been an objective of this invention to provide a system which mates a screw fixation t~hnique for the cervical spine with a rod-type ~u~OL L which allows fixation to be ext~n~ either superiorly or interior-y on the spine.
Tt has been a further object of this invention to provide a fixation device for cervical spine use, having a bracket that is rotatable a~out multiple axes, WO 97123170 PCT/lJS96/20680 so that the opening through which the fastener extends can be positioned in a wider range of orientations in ~ relation to the rod, ~or precise screw orientation.
Another object of this invention has been to provide a bracket that may be mounted to a rod which has itself already ~een secured to the spinal column.

Summarv of the Inven~ion This inventlon provides a fastener having a bracket or ~o~P~tor which is adjustable about multiple axes with respect to a longit~ l support, so that a screw through it can be precisely positioned to engage a cervical or other vertebra. The ~racket is movable on a connector which can be inserted laterally onto a rod o~ a vertebral support in situ, that is, directly onto the middle of an already mounted rod, as distin-guished from being slid axially from an end of a rod before mounting to the spine.
In accordance with the invention the device inc7udes a fastener bracket having first and ~co~

2 0 or~n i n~s through it, one for a fastener such as a small bone screw to be secured to a vertebrae, the other orDn;~g for a stud (i.e., a post) by which the bracket can be connected to the rod of a vertebral u~LL. The stud has an enlarged head and a threaded shank which ex-tends through the C~con~ opening in the bracket so that the brac~et is rotatable around the longi~ ; n~ 1 axis o~ the stud. me shank of the stud is threaded but has CA 022406~6 1998-06-l~
W097/23l70 PCT~S96/20680 a longit~l~in~l (axial) slot which extends from the end of the stud partway toward the head. The slot lies between two threaded shank segments on opposite sides of the shank, like a tl~i ng f ork.
The vertebral ~u~OL L includes at least one rod or leg and is preferably U-Ch~r~, having two spaced apart parallel rods connected by a generally semicircu-lar middle section. The c~ctor assemblies can be mounted on one or two rods; o~ten connectors will be mounted on both rods. The stud slot straddles the rod;
that is, the rod extends crosswise through the slot.
A clamping and spacing insert is seated in the slot of the stud for clamping the rod to the connector. The insert is preferably T-shaped, having a flange project-ing from a stem. The stem of the insert fits ~Yi~lly in the slot between the shank segments, projecting away from the stud head. The flange of the insert extends laterally across the slot between the segments o~ the stud, parallel to the rod, and in use is held against 2Q the rod to clamp it against the slot end. A nut i5 threaded onto the two segments of the stud, and in use bears against the r~iAlly projecting ends of the flange of the insert to clamp it against the ~u~vLL rod in the slot. The stem of the insert holds the stud segments spaced apart as the nut is tightened, and has been found to prevent inward deformation or h~n~ of the segments which otherwise could render it considerably more diffi-cult to remove or adjust the ~ ctor.

one or more preassembled connectors can be ~lid along the rod to desired position, or they can be inserted laterally on the rod intermediate to other points of attachment. To do so the stem, with the insert and the nut removed, is placed so that the seg-ments on either side of the slot straddle the rod. The insert is then placed in the slot, and the nut applied and tightened. This affords a substantial advantage in comparison to previous screw connectors of the type 1~ which had to be slid in longitl7~;n~l sequence onto the rod of the vertebral support.
Until the nut is tightened, the connector can ~e adjusted on three axes with respect to the rod: (1) it can be slid lengthwise along the rod to a desired lS vertical position; (2) it can be rotated around the axis of the rod; and (3) the brac~et or tab can be rotated around the axis of the stud. ~Io~eo~aL, the angulation of the bone screw or other fastener through the bracket can be adjusted with respect to the bracket tl~o~h which it extends. Also, the tab can be bent to closQly conform to the bony anatomy.
The present invention thus allows ~or great ~lexibility in placing the st~d which attaches to the ~'~L~vrL rods. Ihis is a substantial advantage over systems in which one has to place pedicle screws (for example in the lumbar spine) and then try to contour the rod 50 that it will line up with the op~ni ngS in each of the ~o~ ctors. With this invention each screw can be placed in the ideal position for that vertebra, the bracket can then be pivoted in such a way that the re-ceiving studs along the spine are in alignment. The rod, contoured only for anterior/posterior variations or desired anatomy, can be "dlG~d'l into the slots and the screws secured, to achieve a fast and very good alig~nt.
In short, the invention is ~acile to use and results in an easy ~ut secure cn~ection to the rod, with much less practical difficulty.

D~scri~tion of the ~rawinqs The invention can best be ~urther descri~ed ~y reference to the ac~n~nying drawings in which, Figure 1 is a fr~r?ntary, enlarged and ex-ploded perspective view of a preferred form of fixation device in accordance with the invention, showing one cequence in which its.components can be ACC~ hled;
Figure 2 is a side elevation o~ the assembled connector of Figure l;
Figure 3 is a top plan view of the ~onn~tor;
Figure 4 is a vertical cross-section taken on line 4-4 of Figure 2; and Figure S is a perspective view, diagrammatic in nature, showing the invention being used to fixate the cervical spine and occipital bone of the skull of a patient.

WO 97/23170 PCT~TJS96/20680 Detailed Descri~tion Referring first to Figure 5 o~ the drawings, there is shown the upper portion of a ~ ~ spinal col-umn comprising cervical vertebrae Cl-C7 and the occip-ital bone S of the skull. A fixation device in accor-dance with this invention i5 designated generally by 10 and comprises a vertebral ~u~L 12, preferably having two spaced parallel rods in the form of legs 14, 16, ro~n~ted at the top by a middle section 18. In the embodiment shown, vertebral support 12 is generally in the shape of an inverted "U" with its legs 14, 16 ex-t~ ng downwardly from a semicircular middle section 18 located adjacent the base of skull 5. Rods or legs 14, 16 preferably have shallow spiral ~-ooves 19 along them, which ~acilitate securing vertebral attachment wires (not shown) to them so that the wire cannot slip longit~ lly. (Use of such wires is well known and does not comprise part of the invention.) Several con-nector assemblies 20, each in accordance with the inven-tion, are mounted on the respective legs or rods 14, 16 of ~U~OL L 12. Although not shown in Figure 5 for simplicity, a connector will usually be provided for and sec~red to each vertebra between the uppermost and lo~ermost vertebrae to be secured.
fi As best shown in Figures 1-4, each connector assembly 20 comprises a bracket 22 which is rot~table around the axis o~ a stud 2~. The stud has a longitu-dinal (axial) slot 30 wh~ch str~ ~e a rod or leg 14 WO 97/23170 PCT/US96t20680 --~0--or 16 of vertebral support 12. The leg can be clamped in slot 30 by a clamping and spacing insert 32 and a nut 34 screwed onto shank 26.
More specifically, stud 24 has a stopped axial bore 27 which extends from stud end 36 toward the en-larged or flanged head 25 of the stud. Slot 30 inter-sects and extends across bore 27, leaving only shallow longi~A; n~ 1 bore portions or rh~nnel ~ 40, 40 which run longit~t~ lly on the o~roc~ faces of stud shank seg-ments or sectors 42, 42 on each side of slot 30.
Bracket 22 has two op~ gs through it, a larger diameter first opening 46 sized to rotatably receive the shank 26 of stud 24, and a second op~n;~g 48 which provides a seat for the head of a screw fasten-er 50. Screw 50 has a slot or socket 61 for tigh~ni n~
with an Allen wrench or a screwdriver, and is adapted to be driven into bone. The head may ~e flared as shown or rounded to seat in the r~c~ss~ opening 48 of bracket 22. Bracket 22 may be an essentially flat tab as shown in Figure 1, or it may be canted or angulated along a transverse axis S4, 56, or 58 (shown in dashed lin~s in Fig. 1), to better orient or direct screw 50 in a de-sired direction toward the ideal vertebrae area into which it is to be driven. If bracket 22 is bent along either axis 54 or 58, the axes of openings 46 and 48 will not intersect. One face of bracket 22 (the lower face in the drawings) may be counte.~o~ed tr~c~sse~) to receive the enl~rged head 25 of stud 24. The opposite WO 97/2317l) PCT/lJS9612~68l) (upper) face of the bracket may be recessed to receive the head of fastener 50~ Thus, as viewed in Figs. 1-4, the shank 26 of stud 24 extends upwardly above the upper face of bracket 22 while fastener 50 extends downwardly below the lower face.
Insert 32 is generally T-shaped, having a flange 66 and a generally cylindrical stem 64. The stem 64 is seated and axially slidable in stud slot ch~nn~ls 40, 40. The flange is sized to project laterally out-wardly o~ slot 30 in stud 24. In use, one face of flange 66 (the lower face in Figure 1) bears on the surface of rod 14 or 16 which pAcc~ through slot 30.
When nut 34 is tightened on stud segments 42, 42, its face bears on projecting ends 68 of flange 66, urging flange 66 against leg 14 to clamp the leg between the flange and slot end 38. Stem 64 extends upwardly (Fig.
1) and acts as a radial spacer to prevent shank segments 42, 42 from being squeezed or deformed inwardly toward one another by the force exerted on them as nut 34 i8 tightened. This has been found desirable to prevent the con~ector from possibly "freezing" so that it cannot thereafter easily be moved to a desired position.
In use, conn~ctor assembly 20, including stud 24, bracket 22, stud slot insert 32, and nut 34 can be slid longit~; n~ 1 1 y along rod 14 to a desired position ~ (note arrow 70 in Fig. 5). Until nut 34 is tightened the ~n~ector can ~e rotated circumferentially around the rod (arrow 71) and the bracket can be rotated tarrow CA 022406~6 l998-06-l~
WO97/23170 PCT~S96/20680 72) about the central axis of the stud, which extends perpendicularly to the rod. At a desired vertebral position, fastener SO can be driven precisely into the spine where desired, through second or~nin~ 48. As previously noted, bracket 22 may be a flat bracket as shown, or it can be supplied with bends along various axes 54, 56, 58, so that the axis of op~ 48 lies in a desired direction. The connector ZO can be used on a support in the ~or~ of a single rod 14; it is not limited to use with the double legged or U-ch~pD~ sup-port shown, although that is preferred. The middle section 18 of support 12 (if a U-shaped support is used) can ~e screwed or otherwise secured to the skull. Wire attAc onts can also be used.
lS As previously noted, it is alternatively possible to insert a cn~n~tor assembly 20 onto a rod 14 which has a}ready been partially secured in place.
For that purpose the slot insert 32 and nut 34 are re-moved, and the stud with the bracket on its ch~nk is 51 ~p~ laterally onto the leg 14. The spacer 32 is then seated on top of the rod, and the nut is se~ul~l.
The stud can be slipped on the leg from the side and then rotated so that the nut is facing outward. Alter-natively, the rod can be d~v~ed into the slots o~ one or more connector studs with the brac~ets already ~e-cured to vertebrae.
T~is invention provides a significant i~v~-ment in vertebral fixation because it allows a physician CA 02240656 l998-06-l5 to add one or more connectors on either or both legs of support ~2, even after an operative procedure has start-ed and the support has been mounted to the spine, if the physician determines that others are desirable. This can save substantial time and reduces the need for a highly prescribed mounting plan in advance. Although not shown in the drawings, the 5~0L L rods 14, 16 may optionally extend downward across the cervicothoracic junction and may accept other connectors to secure it to lower spinal portions. Cross connectors be~ween the rods can be used to ; , L ~e the -- h~n; cal rigidity of the device. One or more lateral mass plates can also be positioned and secured to the same rods, in conjunc-tion with this device, in order to secure cervical vertebrae.
Having described the invention, what i 5 claimed is:

Claims (13)

1. A spinal fixation device, comprising:
a vertebral support comprising a rod;
a bracket having first and second openings;
a stud having a head and a threaded shank, said shank extending through said first opening of said bracket and having a longitudinal cross slot which extends toward said head, said slot separating shank segments on opposite sides of said slot, said rod of said support extending laterally through said slot in said stud;
a nut threaded onto said shank segments of said stud;
an insert seated within said slot of said stud, said insert having a flange and a stem, said flange projecting laterally outwardly of said slot between said segments and bearing against said rod, said nut bearing against said flange to clamp said rod in said slot, said stem extending in said slot between said segments and holding said segments apart when said nut is tightened thereon; and a fastener extending through said second opening of said bracket for securing said bracket and rod to a vertebra.

2. The fixation device of Claim 1 wherein said bracket is rotatable about said shank.

3. The fixation device of Claim 1 wherein said bracket further includes a first portion having said first opening and a second portion having said second opening, said second portion being angulated with respect to said first portion.

4. The fixation device of Claim 3 wherein said second portion is canted so that central axes of said fastener and said stud do not intersect.

5. The fixation device of Claim 1, wherein said bracket is a flat tab.

6. The fixation device of Claim 1 wherein said insert is T-shaped, said flange extending outwardly beyond said shank to be engaged by said nut, said stem extending axially in said slot.

7. The fixation device of Claim 1 wherein said fastener is loosely received in said second opening, so that the axial direction of said fastener with respect to said stud can be adjusted.

8. The fixation device of Claim 1 wherein said fastener is a bone screw.

9. The fixation device of Claim 1 wherein said support is U-shaped with a middle section for securing to the occipital bone of a patient and has two parallel rods for securing to the spinal column.

10. The fixation device of Claim 1 wherein said slot extends to a slot end adjacent said head, and said slot end is contoured to facially engage said rod.

11. The fixation device of Claim 1 wherein said bracket is recessed to receive said enlarged head of said stud.

12. The fixation device of Claim 1 wherein said rod of said support has a wire-receiving groove around it, along its length.

13. The fixation device of Claim 12 wherein said groove is a spiral groove.