CA2127130A1

CA2127130A1 - Spinal hook

Info

Publication number: CA2127130A1
Application number: CA002127130A
Authority: CA
Inventors: Richard B. Ashman; Michael C. Sherman
Original assignee: Individual
Current assignee: SDGI Holdings Inc
Priority date: 1991-12-31
Filing date: 1992-12-10
Publication date: 1993-07-08
Also published as: NZ246429A; JPH06510466A; JP2566375B2; CN1076606A; AU3275093A; ATE176146T1; US5246442A; KR970009552B1; BR9207001A; FI943112A; HK1005685A1; NO942453D0; WO1993012737A1; NO942453L; DE69228319D1; DE69228319T2; EP0619725B1; FI943112A0; AU668535B2; EP0619725A4

Abstract

A new spinal hook (10) of the present invention which comprises a hook-configured shoe (11) with an integral top portion (15). The top portion (15) includes a pair of central posts (17) which are displaced to form a slot (19) therebetween. Each central post includes a groove (22) colinearly formed to receive a spinal rod within. The slot between the two posts is oriented with respect to the grooves so that an eyebolt assembly (E) may be used to engage the hook to the fixation rod. In another aspect of the invention, a slot (25) is formed in the end faces (28) of the hook. The slot forms one part of a tongue and slot instrumentation engagement arrangement, with a hook-holding instrument including a correspondingly configured tongue. In another aspect of the invention, each of the pair of central posts (17) include grooves (22) on both lateral faces (27) of the posts so that the spinal rod (29) can be situated on either side of the spinal hook (10).

Description

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~ BACKGROUND OF THE INVENTION
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;i The present invention concerns spinal fixation systems, and particularly spinal hooks ~or engaging portions o a vertebra. More specifically, the present invention concerrls improvements in the manner of connecting the spinal ~look to a rod used in the spinal fixation system.
~A Several techniques arld systems have been developed for corref~ting and stabilizing spinal curYes and facilitatillg ~i, 10 spinal fusion. In one system, a bendable rod is longitudinally disposed adjacent tbe vertebral column and is fixed to various vertebra along the length of the column by ~, way of a number of fixation elements. A variety of fixation ;s elements can be provided which are configured to engage ~;, 15 specific portions of the vertebra.
The present invention specifically concerns one type of ixation element, that is a spinal compression/distraction hook o~ the type used in connection with the bendable rod.
The spinal hooks are used to anchor the rod relati~e to the spinal column~, as well as to provide a path for com~ression ;~ or distrac~ion loading of the vertebra.
An example of one such systeln is the TSRHTM spinal system o~ Danek Medical, Inc. In this system, a spinal hook, ; SUCII as ~ook H shown in FIG. l, is enyaged to the fixation rod R by way of a eyebolt assembly E. As is ~nown in tlle art, the eyebolt~E is threaded onto the spinal rod and captured within yokes on the spinal llook. A nut is t~lreaded onto th~ threaded post of the eyebolt to clamp the yoke between the nut and the f ixatio]l rod R . The eyebolt E and ~ ~ ~ 30 hook yokes provide tllree degrees of ~ixal:ion as represente~
5, ~ by the arrows in FIG. l. Details of th~ TSRHTM spinal implant system are disclosed in tlle "TSR~iTM Surgical .

:3WO93/12737 PCT/US92/1065~

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Techllique Manual" provided by Da~lek Medical, Inc. publislle~
in 1990 which disclosure is incorporated herein by reerence.
It is the goal of the surgeon using such spinal implant ;5 systems as the Danek TSRI~TM system to apply the verte~ral ~ixatioIl elernents, such as ~he spinal llook, ~o the spille in the appropriate anatomic pOSitiOII, and then to engage each f~ ~ fixation element to the spinal rod. lt has been found that in spite of the great beneits provided by the double-yoke 10 spinal hooks, such as hook H in FIG. 1, certain problems arise which have heretofore not been adequately addressed.
One problem with the spinal hooks H of the prior art is ,,that the hooks are rather bulky and wide since the fixation yokes of the hook are configured to surround the spinal rod 15 R. The size or~bulkiness oE the spinal hook is an especially important problem since a significant portion of the patient population for spinal implant systems of this type (namely the TSRHl~ system) is made up of pediatric patients. Bulky implants are not easily implanted into small, t~lirî people ; 20 because the space around thé vertebra is not great.
In patients~with~severe deformities of the spinal column, the rod must be~contoured to nleet the deformity. Prior art hooks, such as~hook H, only allow the rod to be implanted in one~position relative to the spinal~column as dictated by the required position~of the blade of the spinal hook. There is ~,, ~ ~ ~
the~refore~a need~for~a spinal hook~that can be fi~ed in more than one position on~the rod, thereby allowing the rod to be implanted in more t}lan one position relative to the spinal ~colunln.
;~ ~; 30 ~Another problem with the spinal hooks ~ o the prior art is that the instrumentation used to engage the hook and hold it for insertion is often difficult to engage to the hook and can be suscepti~le to a fragile engagement between the instrurneIltation an~ the hook. For exalnple, in one prior art . . ~
35 embodiment of the spinal hook H, pin holes P are situated in ~ .

:'i '1 ~ ~ g3/l2737 2 ~ ~ 7 ~ 3 0 Pcr/usg2/lo658 '!i' ._,, ;~ -3-each of the four posts of the double-yoke hook. Tlle pin ~ Itoles P are designed so that they receive the pins of a hook ,~ holder. Such hook-llolding ins~ruments incorporat~ our or eigtlt pins to correspond to the nwllber of pinholes in the hook (which in the case of the hook H in FIG. 1 is 8 pinholes). Engage~nent of tlle pins to tlle pinholes is oterl ¦ difficult as all tlle components must be aligned perfec~ly for , I tlle instrument to ~e locked into place. Moreover, as the j hook-llolding instrulllent is mal~ipulated to properly positiorl i~ 10 the spinal hook about a lamina L (as shown in FIG. 2), there is a risk that the pins will become disengaged with the pinholes P. It ~las been fourld that these frailties of the ;~, ' present hooks H as shown in FIGS. 1 and 2 can often lead to ~A significant amounts of manipulation in order to proper~y ;1l! ~ ~ 15 implant the hook.
; As shown in FIG. 2, the placement of the spinal hook H
and engage~ent of the hook to the rod R by way of the eyebolt .~A assemb~y E must~frequently occur in very tigllt quarters. In -~ one particular application shown in FIG. 2, the hook is oriented between the L2 and L3 lumbar vertebra so that the hook engages the lamina L of the L2 vertebra. It can certainly be~appreciated that in smaller patients, such as pediatric pat~ients,~the room to manipulate the spinal hook to engage it to the~rod is very ~limited.
There is~therefore a need for a new spinal hook ~ ;~ configuration which is less bulky and easier to engage than f~,' ~ the spinal hooks~previously known. There is also a need for such a spinal hook which can be more easily engaged to the spinal rod,~preferably on either side of the rod as required ;~; ~; 30 by the spinal~anatoiny.
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~ WO93/12737 PCT/US92f1065~
2 :1 2 7 1 ~.:3 0 --SUMMARY OF THE INVENTIO~

A new spinal hook is offere~l by ~he present i~vention which has a smaller profile and which includes means for more easily engaging a hook }lolder instrument for irnplarlting the 5 hook. More particularly, and in one aspect of the invention, the spinal hook comprises a hook-conigured shoe to which a central post top is engaged. Tlle top portion includes a pair of central posts which are displaced to form a slot therebetween. Each central post includes a groove colinearly ; 10 forrned to receive a spinal rod within. The slot between the two posts is oriented with respect to the grooves so that an eyebolt assembly may be used to engage the hook to t~e fixation rod.
~ ln another aspect of the invention, a slot is formed in ~ ~ 15 the end faces of the hook. The slot forms one part of a tongue and slot instrument engagement arrangement, with the hook-holding instrument including a correspondingly configured tongue. The tongue;o the hook-holder instrument engages within the slot on each central post of the hook to 20 provide a more~substantial engagemen~ as the hook is being impla~ted.
In anot~ler~ aspect of the inyention, sach of the pair of centr~al; posts include grooves on both lateral faces of the posts so that~the~spinal rod can be situated on either side 5 of the spinal~hook.~Tllus, the spinal hook of the presellt invention is~more~readily~adaptable to various spinal ~ ~ anatomies without r~quiring that the spinal rod be bent in ,~ ~ the saggital;plane~in~order to contact the spinal hook.
It is one obj~ect of the spinal hook of the present ~30 invention to ~reduce the overall profile of the spinal fixation system, and par~icularly the components used ~o engaye the vertebra of the patient.
It is another object to provide such a hook which incorporates a tongue and slot arrangement for a firm, solid ` :~

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.~ , '~-~ 93/12737 ~ 1. 2 7 13 (3 PC~/US92/10658 and easy engagement to a hook-holding instrument;.
Pcelated ob3ects and advantayes of the present invention wil'l be apparent from the following descripl:ion.-,,, :"~', .

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~ ~7 ~ t : --6--.,, ;~ BRIEF DESCRIE'TION OF T~iE l)RAWI~7C;S
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FIG. 1 shows a spinal hook ellgaged ~o a fixation rod by way of an eyebo~t assemlly as conEigured in accordance Witll the prior art conEiguratiorl.
~i~s 5 FIG. 2 is a side view showirly the existing standard hook of FIG. 1 engaged about the lalnina of the lumbar vertebra.
FIG. 3 is a side elevational view of a spinal hook in accordance with the preserlt inv~ntion.
. FIG. 4 is an end elevation of the spinal hook shown in 10 FIG. 3.
~ FIG. 5 shows the spinal hook of FIGS. 3 and 4 engayed on S~r' a spinal rod by way of an eyebolt assembly.
.~; FIGS. 6-9 show alternative conigurations of the spinal ~,. hook of the present invention for engaging different portions .~;
of t~le vert~bra.
FIG. 10 is a top elevational view of hook-holding ~ instrurnent adapted to enga~e the spinal hook of the present ,.!, invention.

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~ DESCRIPTION OF THE PREFERREl:) EMBODIMENTS
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For the purposes of promoting an understandin~ of the ~3 principles of the illventioll, reference will now be made to the elnboaiments illustrated in the drawings and specific language will be u~ed to de~cribe the s~me. It will ~ nevertheless be understood tllat nv linlitation of the scope of .~ the invention is t~lereby intended, such alterations and further modifications in the illustrated device, and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention ~ rela~es.
t~ ~S discussed a~ove, FIG. 1 illustrates a spinal hook ~ of a known standard design whic~l is used as part of a spinal ~ ~ 15 fixation system, such as the TSRHTM system of Danek Medical, ,~ ~ Inc. The hook is fixed to a ~pinal rod R by way of an ,. eyebolt assembly E. The hook H also includes a number of pinholes for engaging a conventional hook hol~er, such as the ~!, hook holder part number 8~8-036 of Danek ~edical, Inc. The ; ~ 20 hook H depicted in FIG. 1 can be a hook such as the laminar hook part number 808-007 of Danek Medical, Inc. FIG. 2 shows the same hook H and spinal rod R engaged between the lumbar ver~ebra L2~and L3,~specifically with the hook engaging the : lamina ~ of the L2 Yertebra. Th~ spinal hook of the present 25 invention to be described hereill is intended as a substitute for this known~:hook H.
~ne embodiment of the spinal hook of the present ~,~, ~ invention is depicted in FIGS. 3 arld 4. In particular, the spinal hook lO in ludes a shoe ll having a bone-engaging ' ~ 30 surface l~. The bone-engaging surface 12 can be formed in a parti~ular shape ~o engage a lamina of a vertebra, ~or instance. Integral with the shoe ll of t~le hook lO is a top portion 15.
: In as::cordance with tl~e present invention, the toE) porl:ion '' ''i ~;~,`, ,.' ~.''` ' '. ,!

~ WO93/1~737 PCT/US92/lU65~
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15 includes a pair of posts 17 disposed apart from each other to form a slot 1~ therebetween. The slot is wide enough to `! receive an eye~olt assembly, such as eye~ol~ asse~bly E sllown ir~ FIG. l. A pair of coaxial grooves 22 are forrned in eacll lateral surface 27 of botll central posts 17. Each groove 22 ~i is configured to receive a portion of a spirlal rod SUC~I as rod R shown in FIG. l. ~'he rod grooves 22 are present on ''t, each lateral surface 27 of tlle central post 17 so that the hook lO can be oriented on either side of a spinal rod.
In yet another feature of the invention, a slot 25 is ~ formed in the outwardly faciny end face 28 of each of the p., central posts 17. The slots 25 are preferably elongated and , generally elliptical in shape and are cut illtO the ~ost 17 to a sufficient depth for firm engagement by a hook-holding ,, 15 instrument, to be discussed h~rein.
; Referring now to FIG,. 5, the mallner of installing the hook lO o~ the present invention is depicted. In particular, ,, a spinal rod 29 is provided which extends through a rod bore x, 31 of an eyebolt assembly 30. The eyebolt assembly 30 s 20 projscts through the slot 19 between the central posts 17 of ~ the hvok lO. The threaded post 32 of the eyebolt assembly ,~ also projects through the slot 19 for engagement with a nut 33. The nut 33 is~ then threaded onto the post 32 until it contacts a lateral surface 27 of the two central posts 17, ~ ~ 25 tllere~y trapping the central posts between the rod 29 an~ the ;~ nut 33. The grooves 22 on the opposite lateral surfaces of the cent~al p~osts 17 pinch a portion o the rod 29 to clamp the hook lO to the rod. It should ~e apparent that tl~e hook lO could have been situated on the opposite side of the rod 30 29 with the rod engaged within the ~rooves 22 that are .~
exposed in FIG. S.
The hook of the present invention can be reconfigured for engaging different portions of the vertebral columns. For ,~ ~ instance, as shown in FI~. 6, a hook 40 includes a shoe 41 configured for engaging the lanlina of a t~loracic ~ertebra.
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;~ Similarly, the hook 45 of E'I~. 7 includes a shoe 4~ adapted to engaye a transverse process, while hook 50 in FIG.8 is a pedicle hook having a shoe 51 a~apted to engaye a-pedicle.
ln each case, the top portion of each of these hooks, namely top 42 of the laminar thoracic ~look, top 47 of the transverse ~ process iloak, and top 52 o~ the pedicle hook, are configured ;~ identically to the top portion 15 described above. While the central post hook of the present invention provides a narrower profile t~lan t11e four-post hooks of the prior art, the bone-engaging surfaci can be enlarged for engaging a ~articular vertebral componen~, such as shown in FIGS. 8 and ~ ~ 9 for the pedicle hook ~0. Specifically, t~le pedicle hook 50 `~ includes a shoe 51 which is enlarged with respect to the ~; shoes of the hooks previously described. A transition section 53 is provided between tlle central post top 52 and the shoe 51~ ~
Re~erring llOW to ~'IG. lO, a hook holder 60 is shown which includes a pair of pivoted arlns 61. Jaws 63 at tlie end of the arms 61 are configured for engaging the opposite end faces o~ a central post llook, such as hook lO of the present invention. Specif~ically, the~jaws include opposite inwardly ~acing tongues 65 which are configured to be received within ,~ the slots 25 in the~end ~aces 28 of the central posts 17.The use of the tongue and slot arrangement is an improvement over the prior~pin and pinhole arrangement for the hook-engaging~instrument. Tle elongated area of co`ntact ~ ~ between tllé tongues 65 and the slots 25 provides a irmer ''j~.;! engagement between the instrument 60 and the hook lO that is ~ ~ ~ not likely to be;jarred loose or require e~cessive J,i~i. ~ ~ 30 manipulation duri~ng implallta~ion of t~le hook during connection to a fixation rod, such as rod 29. In addition, the tongue and slot~configuratioll offers greater lateral and angular strength and restraint than does the prior art pillhole and pin designs.
In one specif~ic embodiment for the hook lU shown in FIGS.

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~ WO93/12737 PCT/~592/106~
2~ 13~ -lo-3-5, t11e grooves 22 ir1 t11e latelal ~aces of the cer1tral posts 17 }lave a diameter of 0.188 inches. It has been found t~1at t~liS groove diameter is sufficient to capture a larger rod, sucll as a rod having a diameter of 0.250 inches. In the specific embodiment, the slots 25 for engaging the hook-holder instrument have a lenc3th of .31~ inches, a width of .067 inches, and a depth of .04l inches. The tongues 65 of the hook-holding instrument 60 must be similarly configured but having a length, width and height sli~htly smaller than the corresponding dimensions of the slot 25 to allow a sliding insertion. Again, in the specific embodiment, the width o each central post 17 is approximately 0.188 inches. Eac}1 of the edges o~ the central posts 17 is rounded to avoid trauma to soft tissue surroundi~g the vertebra to w}lich the hook is engaged.
As is represented by FIGS. 6-9, the central post hook lO
of th present invention;can be easily configured to enyage a variety of vertebral portions. In fact, the range o~
available hook designs for thé central post hook lO of the 20 present invention is;the same as f~r the prior known . four-post hook de~signs. Thus, the central post hook lO of the~present invention has the flexibility of the prior hook de~igns coup~led with the additional flexibility of situating the hook on either~side of ~he spinal rod depending on the requirements o ~the specific~spinal anatomy. Moreover, the central ~ost~configuration offers a significantly reduced profile which reduces the risk of trauma to the patients, and ~ which facilitates the implantation of tlle hooks lO, 40, 45 ;~ and 50 of the present invention.
While~the inv~ention has been illustrated and described in detail in the drawings and foreyoing description, the same is to be considered a~s illustrative arld not restrictive in character, it beiny understood that only the preferred : ~ .
e1nbodiment has been shown and described and that all c11anges and~modificati;ons that come within the spirit of tlle invention are des~ired to be protected.
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Claims

IN THE CLAIMS
2. A spinal hook for interengaging a fixation rod with the human spine, comprising:
a shoe portion configured to engage a portion of a vertebra in the human spine; and a top portion integrally formed on said shoe portion, said top portion including only a plurality of posts projecting therefrom, each of said plurality of posts having mutually coplanar first lateral surfaces and each including a groove formed in said first lateral surface, each of said grooves being coaxial and adapted to engage the fixation rod, wherein each of said plurality of posts includes mutually coplanar second lateral surfaces opposite said first lateral surfaces, each of said second lateral surfaces including a second groove formed therein, each of said second grooves being coaxial and adapted to engage the fixation rod.
3. A spinal hook for interengaging a fixation rod with the human spine, comprising:
a shoe portion configured to engage a portion of a vertebra in the human spine; and a top portion integrally formed on said shoe portion, said top portion including only a plurality of posts projecting therefrom, each of said plurality of posts having mutually coplanar first lateral surfaces and each including a groove formed in said first lateral surface, each of said grooves being coaxial and adapted to engage the fixation rod, wherein a pair of said plurality of posts includes opposite outwardly facing end surfaces, each of said end surfaces having an elongated slot defined therein for engaging an insertion instrument.
PCT/US92/10658
5. The spinal hook of claim 2 wherein said top portion is symmetrical about a plane extending parallel to and between said first and second lateral surfaces.
6. The spinal hook of claim 5 wherein said shoe portion is symmetric about said plane.
7. A spinal hook for interengaging a fixation rod with the human spine, comprising:
a shoe portion configured to engage a portion of a vertebra in the human spine; and a top portion integrally formed on said shoe portion, said top portion including only a plurality of posts projecting therefrom, each of said plurality of posts having mutually coplanar first lateral surfaces and each including a groove formed in said first lateral surface, each of said grooves being coaxial and adapted to engage the fixation rod, wherein said groove of each of said plurality of posts is defined at a groove radius, said groove radius being less than the effective radius of the fixation rod.
8. The spinal hook of claim 2 wherein a pair of said plurality of posts includes opposite outwardly facing end surfaces, each of said end surfaces having an elongated slot defined therein for engaging an insertion instrument.
9. The spinal hook of claim 2 wherein said plurality of posts includes only two posts.
10. A spinal hook assembly for interengaging a fixation rod with the human spine comprising:
an eyebolt assembly having a body with a bore for receiving the fixation rod, a threaded post projecting from the body and a nut for engaging the threaded post; and a spinal hook including:
a shoe portion configured to engage a portion of a vertebra in the human spine; and a top portion integrally formed on said shoe portion, said top portion including only a plurality of posts projecting therefrom, said plurality of posts being displaced from each other to define a number of slots therebetween, at least one of said number of slots being sized to receive said body of said eyebolt assembly therethrough for fixing said spinal hook to the fixation rod, each of said plurality of posts having mutually coplanar first lateral surfaces and each including a groove formed in said first lateral surface, each of said grooves being coaxial and adapted to engage the fixation rod, each of said plurality of posts further having mutually coplanar second lateral surfaces opposite said first lateral surfaces, each of said second lateral surfaces including a second groove formed therein, each of said second grooves being coaxial and adapted to engage the fixation rod, whereby the spinal rod can be received in one of said first groove or second groove in the corresponding one of said first lateral surfaces or said second lateral surfaces, while said nut of said eyebolt assembly is threaded along said post extending through said one of said number of slots to clamp against the other of said first lateral surfaces or said second lateral surfaces.