CA2242645A1

CA2242645A1 - Anterior stabilization device

Info

Publication number: CA2242645A1
Application number: CA002242645A
Authority: CA
Inventors: Robert S. Bray, Jr.
Original assignee: Individual
Current assignee: Individual
Priority date: 1995-12-08
Filing date: 1996-12-06
Publication date: 1997-06-12
Also published as: US5888223A; WO1997020526A1; EP0915687A4; AU1330197A; AU705598B2; EP0915687A1

Abstract

An anterior fixation device (12) comprises an oval-shaped intervertebral spacer (13) and a retaining plate (17). The spacer (13) has a sidewall (11) and superior (25) and inferior walls (26). The superior (25) and inferior (26) walls are dome-shaped and porous to allow bone to grow through the device to achieve fusion of two adjacent vertebral bodies. Extending from the anterior side of the spacer are superior and inferior lips (14, 15) through which bone screws (16) extend. The bone screws (16) are non-weight bearing and screw into the strongest areas of bone within the vertebral bodies. The intervertebral spacer (13) is hollow inside to allow for bone grafts, bone morphogenic protein, or other bone stimulating substances to be inserted therein. The retaining plate (17) is attachable to the anterior surface of the spacer (13) to prevent the bone screws from backing out once the device is installed.

Description

CA 0224264~ 1998-07-09 WO 97/20526 PCT/US96/194~6 ANTERl:OR STABILIZATION DEVICE

Field of the Invenffon The present invention relates to a device for stabilizing and/or fusing at least two adjacent vertebrae of a spine. More specifically, the present invention relates to a device that is placed on the anterior surface and in the intervertebral space of two adjacent vertebral bodies to thereby fix the spacial relationship of the vertebral bodies to achieve stabilization and/or bone fusion.

k~round of the Invenffon The spinal colurnn of hllm~n~ provides support to the body and protection to thedelicate spinal cord and nerves. The spinal column comprises a series of vertebrae stacked on top of each other. Each vertebra has a relatively large vertebral body that is located in the anterior portion of the spine and provides the majority of the weight bearing support of the vertebral column. Each ~.LelJ.dl body has relatively strong bone compri~ing the outside surface of the body and weak bone comprising the center of the body. Situated between each vertebral body is an illk;l ~ l disc that provides for cushioning and ~i~mrening of c~ ;ve forces to the sinal column. Located just posterior to the vertebral body and intervertebral disc is the velLeL.ldl canal cont~inin~ the delicate sinal cord and nerves.
Posterior to the spinal canal are the di~~ lL artic~ ting processes ofthe vertebra.
Various types of spinal colurnn disorders are known and include scoliosis (abnormal lateral ~;Ul ~/~Lulc; of the spine), kyphosis (abnormal forward curvature of the spine, usually in the thoracic spine), excess lordosis (abnorrnal backward curvature of the spine, usually in the lumbar spine), spondyloli cth~sic (~1 ~v~-l displ~c~ment of one vertebra over another, usually in the lumbar or cervical spine) and other disorders, such as ruptured or slipped discs, cle~n~rative disc ~i~e~cf fractured vertebra, and the like. Patients who suffer from such conditions usually experience extreme and debilitating pain and often neurologic deficit in nerve function.
A technique known as spinal fixation uses surgical implants which mechanically immobilize areas of the spine a~ tinp in the eventual fusion of the treated adjacent vertebrae. Such techniques have been used effectively to treat the above described conditions and, in most cases, to relieve pain suffered by the patient. ~Iowever, there are some disadvantages to the present fixation devices.
One technique for spinal fixation includes the imrnobilization of the spine by the use of spine rods that run generally parallel to the spine. In practicing this technique, the posterior surface of the spine is isolated and bone screws are first fastened to the pedicles of ~WO 97/20526 PCT/~S96/19456 - the al)p.u~liate ~,.,,l~l,-de or to the sacrum and act as anchor points for the spine rods. The bone screws are gener~lly placed two per ~ ~ld, one at each pedicle on either side of the spinous process. Clamp assemblies join the spine rods to the screws. The spine rods are ~çnPr~lly bent to achieve the desired curvature ofthe spinal column. These types of systems ~ are very stable but require implanting screws into each v~lebld over the area to be treated.
: Also, since the pedicles of vertebrae above the second lumbar vertebra (L2) are very small, = only small bone screws can be used which sometimes do not give the needed support to stabilize the spine. To stabilize the implanted system sufflciently, one vertebra above and ~~ one ~ lJld below the area to be treated are often used for impl~nt;n~ pedicle screws. The rods and clamps are surgically fixed to the spine from a posterior approach.
Anterior fixation devices have also been used such as anterior plate systems. One type ~ of anterior plate system involves a lil~liulll plate with unicortical lil~Jiulll bone screws that ~ lock to the plate and are placed over the anterior surface of a vertebral body. Another type of anterior plate system used less frequently nowadays involves the use of bicortical screws that do not lock to the plate. The bone screws have to be long enough to bite into both sides of - the vertebral body (cortex) to gain enough strength to obtain the needed stability. These - devices are difficult to place due to the length of the screws and damage occurs when the screws are misplaced.
A third type of anterior fixation device comprises a hollow cylinder, usually a hollow - cylinclric~l lil~iulll cage, that is extçrn~lly threaded. The ext~rn~lly threaded cage is screwed into place bc;lweell to adjacent vertebrae. Bone grafts from cadavers or the pelvis ~- are then packed into the hollow center of the device. Bone morrhog~nic protein ~which is not yet comrnercially available) or other substances that promote bone growth can also be placed in the hollow center of the device. The cage is porous such that bone can grow through the device and fuse the two adjacent vertebrae. The are many disadvantages to this =~ device. First, it is very difficult to align. Second, it requires drilling a large hole between two ~ c~nt vertebral bodies and then threading the device into the hole. The large hole can colll~r~ .ise the integrity ofthe vertebral bodies, and if drilled too posteriorly, can injure the spinal cord. ~hird, the end plates of the vertebral bodies are usually destroyed during the flril l ing The end plates comprise very hard bone and help to give the v~ I tt;~ l bodies needed - strength. With the end plates destroyed, the cylindrical device is now harder than the bone of ~ the vertebral bodies and the vertebral bodies tend to collapse, "telescope," together. The 3 5 telescoping causes the length of the vertebral column to shorten and can cause damage to the : spinal cord and nerves that pass between the two adjacent vertebrae.
It is desirable to have a fixation device which not only elimin~tes the need to implant pedicle screws into the v~ l,lde but also which connects to the strong anterior vertebral CA 0224264~ 1998-07-09 WO 97nos26 PCT/IJS96/19456 bodies. The device should be easy to place and should prevent potentially ~l~m~gin~;
telescoping of adjacent v~leb~de~
s S~ ry of the Invention The present invention provides an anterior stabilizdtion device which provides fixation and stabilizdtion at both the anterior margin of the vertebral body and in the anterior column.
The device comprises a hollow, g~ner~lly oval shaped spacer and a ret~ining plate. The spacer comprises a side wall and porous superior and inferior walls, which are preferably dome-shaped. Along the anterior side of the spacer there are provided at least one superior lip which extends upwardly, i.e.7 in a superior direction, from the side wall and at least one inferior lip extt~nflinp d~wllw~dly, i.e. in an inferior direction from the side wall, each lip CO~ g a screw hole for rec~lrring a non-weight bearing bone screw. Preferably there are three lips, i.e., two inferior lips and one superior lip or two superior lips and a single inferior lip. In a "l~,Ç~ d embodiment of the invention, the spacer comprises an anterior extension from which the superior and inferior lips extend.
Access means are provided for loading the interior of the spacer with bone graft, bone morphogenic protein or the like. One pl~relled access means compri~es one or more openings in the side wall on the anterior side of the spacer. Another pl~r~ d access means compri~es a removably ~ rh~hle superior and/or inferior wall.
The ret~ining plate is fixedly attachable to the anterior side of the spacer by means of a set screw or the like. The ret~ining plate is configured such that, when ~ r.1~ , it covers at least a portion of the head of any bone screw which is positioned in the screw holes of the superior and inferior lips to thereby prevent the screw from backing out. The ref~inin~ plate may also cover some or all of any access opening in the side wall.
The device of the present invention may be used to stabilize any portion of the spine, e.g., cervical, thoracic or lumbar. The device is sized according to the particular intervertebral disk which it replaces. Generally the spacer will have a height of from about 7 to about 14 rnm, a lateral width of from about 10 to about 32 mm and an anterior-posterior width of from about 10 to about 30 mm. Spacers designed for cervical and thoracic use will typically have a height of from about 7 to about 10 mm, a lateral width of from about 13 to about 17 mm and an anterior-posterior width of from about 10 to about 14 mm. Spacers f1e~ n~1 for lumbar use typically have a height of from about 8 to about 14 mm, a lateral width of from about 26 to about 32 mm and an anterior-posterior width of from about 22 to about 30 mm.

I Brief D~ )n of the D. ~
Embo~1im~nt~ of the invention will now be described with reference to the following S drawings which:
FIG. 1 is an anterior view of the lumbar spine with the present invention inserted between hvo z~ rent vertebral bodies;
FIG. 1 a is a superior view of a lumbar vertebra with the present invention placed over -~ the vertebral body, FIG. lb is a superior view of a vertebral body;
FIG. 1 c is a lateral view of the lumbar spine with the present invention placed between t~,vo adjacent VG1~G~1~1 bodies;
FIG. 2 is an anterior view of a pl~fc.lGd anterior stabilization device made in = accordance with the present invention;
FIG. 3 is an exploded anterior view of the device of FIG. 2;
~: FIG. 4 is a lateral anterior view of an hll~ Gl lebral spacer of the device of ~G. l;
FIG. S is a posterior view of an hll~" ~/el Lebldl spacer of the device of FIG. 1;
- FIG. 6 is a superior view of the h~ . l~lal spacer of the device of FIG. l;
FIG. 7 is an inferior view of the illl~,. v.,. LGbral spacer of the device of FIG. l;
FIG. 8 is a superior view of a ret~inin~ plate of the device of FIG. 1, FIG. 9 is an inferior view of a ret~ining plate of the device of FIG. 1;
~G. 10 is a lateral view of a lordotic vertebral spacer made in accordance with the - present invention;
FIG. 1 1 is a lateral view of a k,vphotic VG1 lGI; lal spacer made in accold~lce with the present invention;
FlG. 12 is a posterior view of a scoliotic spacer with a left to right angle;
FIG. 13 is a posterior view of a scoliotic spacer with a right to left angle;
FIG. 14 is an exploded perspective view of another ~le~llGd anterior stabilization device made in accordance with the present invention;
= F~G. 15isananteriorsideviewofthedeviceofFIG. 14;
~~ FIG. 16 is an exploded p~or.~pective view of yet another plGr~.lGd anterior stabilization , device made in accordance with the present invention;
FIG. 17 is a lateral view of an intervertebral spacer connected to a stem and a handle;
~ and FIG. 18 is a superior view of an hllc~Gllebral spacer connPcted to a stem and a ~ handle.

CA 0224264~ 1998-07-09 Detailed Ds- ;~,lion The following is a list of definitions that apply to this application:
S Anterior -- situated in front of or in the fol ~v~d part of an organ or structure;
Ldil~illg to the front surface.
Inferior -- situated below; directly dowllw~d, p~Laillillg to the bottom surface; closest to the tail.
Lateral -- denoting a position farther from the median plane or mirlline of the body or of a structure; pertaining to a side surface.
Posterior -- ~ ted in back of or in the bac~w~.l part of an organ or structure;
p~l Ldillillg to the back surface.
Superior -- situated above; directly upward; pc. lahlillg to the top surface, closest to the head.
Turning in detail to the dldwillg.7 where like reference mlmer~ lç~i ,n~te identical or corresponding parts throughout the several views and different embo~iment~, FIG. 1 illu~,lld~es an anterior view of two lumbar vertebrae with a ~,-er~lled anterior fixation device 12 made in accol-lal~ce with the present invention installed. The intervertebral disc that normally is bc;lw~;~ll the two vertebrae has been replaced with the anterior fixation device.
Besides the lumbar spine, the anterior fixation device can also be used in the cervical spine and the thoracic spine.
FIG. la is a superior view of the anterior fixation device 12 located on the superior surface of a lumbar ~/e~ d. As illustrated in FIG. la, the anterior fixation device is primarily centered within the vertebral body, V.B., of the lurnbar vertebra. The spinal cord, S.C., is located posteriorly from the anterior fixation device. The spinous process, S.P., is the most posterior pat of the vertebra. The mzlmmill~ry processes, M.P., are lateral to the spinous process and the transverse processes, T.P., are located on the lateral sides of the vertebra.
FIG. 1 b is a cross section of a vertebral body illu~ the relative strengths of the bone within the vertebral body. The vertebral body is e~enti~lly oval shaped. The anterior surface, A, and the posterior sl-rf~ c, P, are in~lic~te~ In the center of the vertebral body is a gener~lly weak area of bone that comprises mostly cancellous bone. A ring shaped area surrounding the weakest area of the bone comprises stronger cortical bone. The o~ltPrmost ring ofthe vertebral body compri~es annular apophyses, the strongest bone. As will be detailed below, the anterior fixation device is shaped to utilize the stronger areas of the vt;ll~bldl body for support. Additionally, relatively short bone screws are placed through the device and into the bone of the annular apophyses and the cortical bone to secure the device in place to fix the relative position of the two adjacent vertebrae.
FIG. lc is a lateral view of the lumbar spine with the anterior fixation device 12 - inserted in a vertebral disc space. The anterior fixation device is anchored into place by relatively short bone screws 16 on the anterior surface of two ~dj~c~?nt vertebral bodies. The length of the bone screws being from 1/4 to 1/2 of the anterior-posterior dimension of the ve.lebldl body. The bone screws 16 are placed at an angle relative to the h(,liGolllal midline --- plane of the anterior fixation device. The angle of pl~em~nt iS about l 5o to about 200 from - the ho~ plane. As will be described later, the angled pl~c~m~nt ofthe bone screws : provides the surgeon placing the device in a patient one access point from which to screw the bone screws in place.
The complete anterior fixation device 12 is better illustrated in FIGS. 2 and 3. The anterior fix~tinrl device comprises an intervertebral spacer 13 (also referred to herein simply as a spacer)having a gen~lly vertical side wall 11 which has a generally oval cross sectional shape, a generally dome-shaped porous superior wall 25 with tapered sections 27 about its periphery, a generally dome-shaped inferiorporous wall 26 with tapered sections 28 around - its periphery, a superior lip 14 and two inferior lips 15. Each lip 14 and 15 has a screw hole 19 through which a bone screw 16 may pass. A ret~inin~ plate 17 is attached to the spacer 13 by a set screw 18.
The hlt~ Lebldl spacer 13 can be made out of any suitable m~t~ l that is well known in the art. Preferably, the spacer will be made out of ~ .", or an alloy of l ;~
~ The spacer is a hollow ~L..~ k with walls that are preferably about 1 to 2 mrn thick. As can be seen in FIG. 3, the side wall of the spacer 13 has access openings 20 on both sides of a - - threaded set screw ~ . IU~t; 21. The openings 20 allow access into the interior of the hollow ~ spacer.
_ On the superior lip 14 and inferior lips 15 are screw holes 19 that bone screws 16 can be inserted through and into the annular apophysis and cortical bone of a vertebral body. The bone screws can be made out of any suitable m~ter~l that is well known in the art.
- Preferably, the bone screws will be made out of the same m~t~ l as the spacer, which in the pl~L,led embodiment is Lila~ or an alloy of Li~ . In the preferred embodiment, the ~ bone screws are round head screws that may be screwed into ~e bone of the vertebral bodies with a flat head S~ ;W~ivt;L. Other types of bone screws can also be used.
Referring to FIGS. 6 and 7, the intervertebral spacer 13 is ecs~nti~lly oval in shape with the anterior portion of the oval having an extension 39 to allow for the spacer to be ~: anchored over anterior annular apophyses of two ~(~ nt vertebral bodies. The anterior edge of the extension 39 has a curved superior lip 14 that has a screw hole 19 sized such that a bone screw can be inserted Ll~ ;Lhl~ugh. As illustrated in FIGS. 4 and 6, the superior - lip 14 is curved posteriorly for placement over an annular apophysis of a vertebral body. The superior wall is preferably porous, i.e., compri~Ps pores or holes, to allow for bone to grow WO 97/ZOS26 PCT/US96/}9456 through the pores or holes to fuse the two vertebra together. As illll~tr~t~-1, the superior surface could be made porous by drilling a plurality of holes 40 through the surface.
Additionally, a porous material such as Hydracell supplied by Danek Medical, Inc. can be used.
E~eferrin~ now to FIGS. 4, 5 and 7, the inferior wall 26 is i~ tr~tecl with inferior lips 15 and screw holes l 9 therethrough. As with the superior lip 14, the inferior lips 15 are curved posteriorly such that the inferior lips 15 can be anchored to a vertebral body armular 10 apophysis. The inferior wall is a mirror image of the superior wall and is preferably also made porous. In the ~l~r~ d embodiment, holes 40 are drilled through the s~lrf~eIn the ~l~r~ .d embodiment there are three lips, one superior and two inferior, that form a triangle shape and provide three points of fixation to the vertebral bodies. The tri~n~ tion provides an additional benefit in that the spacers can easily stack on top of each other such that a series of ~ c~nt ~e leblae can be fixed together using the spacers of the present invention. As would be appreciated by a person skilled in the art, four or more points of fixation to the vertebral bodies could also be used.
In FIG. 4, the mi~lline 29 of the larger ~ m~t~r of the oval part of the spacer 13 is tr~te-l In use, the midline 29 is along the midline of the larger diameter of two ~ Cf~nt oval shaped vertebral bodies. As can be seen in FIGS. 4 and 5, the superior wall 25 has tapered surfaces 27 about its outer pt;li~ and the inferior wall 26 has tapered surfaces 28 about its outer p~ h~lr. As will be ~ cuC~e(1 below, the tapered superior and inferior surfaces allows the surgeon easier pl~f em~?nt during a surgical procedure. Additionally, the tapered sl~ çs provide greater stability of the device once installed.
In an ~It~rn~t~ embodiment, the superior and inferior walls have lateral ridges (not shown) sp~nning across the anterior half of the oval shaped spacer. The lateral ridges provide re~i~ct~n~e against the device slipping forward after the surgical inct~ tion of the spacer.
Referring now to FIGS. 3, 8 and 9, a ret~ining plate 17 is ill--~tr~te(l The ret~inin~
plate can be made from any suitable m~t~ri~l well known in the art. Preferably, the retaining plate will be made out of the same m~teri~l as the intervertebral spacer, which in the pl~r~lled embodiment is LikL~ or a lil~~ alloy. The retaining plate is curved to fit the curvature of the anterior surface of the intervertebral spacer 13 . In the center of the ret~ining plate is a tapered ~ ; 39 that is sized to allow a set screw 18 to be inserted therethrough with the head of the set screw retained in the tapered a~ . The lelailling plate has a superior retaining lip 22 and two inferior ret~inin~ lips 23. When the retaining plate 17 is in place on the intervertebral disc spacer 13, the superior retaining lip 22 partially covers the head of a bone screw e~t~n~1ing through the superior lip of the intervertebral spacer and the CA 02242645 l99X-07-09 WO 97/;!0526 PCT/US96/19456 inferior lc~ g lips 23 partially cover the heads of bone screws extenclin~~ through the inferior lips of the intervertebral spacer.
As illustrated in FIGS. 8 and 9, the posterior surface of the retaining plate has two ~- rect~n~ll~r shaped flanges 24. The flanges are located laterally with respect to the tapered set screw aperture 38. The flanges extend outward from the posterior surface of the ret~inin~
~- plate 1 to 2 mm. The rect~n~ll~r shaped flanges are sized to m~tinF~ly fiit into the rect~n~ll~r access openings 20 of the intervertebral spacer when the ret~inin~ plate is in place. Thus, as 10 ~ illustrated in FIG. 2, when the l~ainillg plate 17 is secured to the spacer with the set screw 18 screwed into the threaded aperture 21 ofthe spacer, the bone screws 16 cannot back out from the spacer. The set screw 18 is secured to the spacer and is ti~ht~ned accordingly to prevent ~- loosening. The set screw is preferably any suitable m~t~ri-ql well known in the art, preferably titanium or a liLaniulll alloy. In the ~.er~ ,d embodirnent, the set screw is an hexagonal set screw that is placed with an hexagonal driver. Other types of set screws can be used.
As would be appreciated by a person skilled in the art, the shape and size of the opening 20 in the spacer may vary. If other shapes or sizes are used, then varying sized and - shaped ret~inin~ plates would also be used.
The flim~n~ions of the intervertebral spacer vary depending on the int~n~lPc~ use of the spi~cPrs, having small spacers for the cervical spine, medium spacer for the thoracic spine, and large spacers for the lumbar spine. I~or ~e cervical and thoracic spine, spacers having a range of heights of about 7, 8, 9, or 10 mm are ~l~;f~ d. The lateral side to side dimen~ions of the largest lateral diameter of the spacers are preferably about 13, 15 and 17 mm. The anterior-posterior ~limen~ion ofthe cervical and thoracic spacers are preferably about 10, 12 and 14 mm. The spacers in the lumbar spine also have varying ~iimen~ionS. The heights of the lumbar spacers are preferably about 8, 10, 12, and 14 mm. The lateral dimensions of the ~lumbar spacers are preferably about 26, 28, 30, and 32 mm. The anterior-posterior - flimen~ions of the lurnbar spacers are preferably about 22, 24, 26, 28, and 30 mm. The ret~inin~ plates would be sized a~lupl;ately to fit the varying heights and lateral dimen~ions of the varying sized spacers.
FIG. 10 illustrates an ~ltPrn~tive embodiment to the present invention. A spacer 30 =-with a lordotic angle, a, is ill-l~tr~t~l The lordotic angle extends from a smaller posterior -:sllrf~re7 p~ to a larger anterior surface, A. The angle, a, can range from about 1~ to about 45 ~. Similar reference numerals are used to inclir~te the superior wall 25 with tapered 35 ~sections 27, the inferior wall 26 wi~ tapered sections 28, the superior lip 14 and inferior lip ~15.
~ FIG. 1 1 illustrates a kyphotic spacer 31. In this embodiment the kyphotic spacer has a ~superior wall 25, and inferior wall 26, a superior tapered section 27 and inferior tapered CA 0224264~ 1998-07-09 WO 97no526 PCT/US96/19456 section 28, an ~-ltliti~m~l superio} tapered section 34 and inferior tapered section 35 on the anterior surface of the spacer. The kyphotic spacer has a kyphotic angle, b, from a smaller anterior surface, A, to a larger posterior surface, P, the kyphotic angle r~ngin~ from about 1 ~
to about 45 ~ . Additionally illu~tr~te~l on the anterior surface is an optional smaller kyphotic angle, b'. The angle b' le"l~;st;llL~ the kyphotic angle ofthe anterior extension 39 ofthe spacer. The kyphotic angle b' will be from about 1 ~ to about 10 ~ less than the kyphotic angle b.
FIG. 12 isaposteriorviewofascoliotic inte.velLebl~l spacer32. Inthisparticular embodiment the scoliotic angle, c, is from a smaller left lateral side to a larger right lateral side. Angle c range from about 1 ~ to about 45 ~. The ret~inin~ plate would also be al)plv~liately angled.
FIG.13 is a posterior view of a scoliotic spacer with a scoliotic angle, d, from a smaller right lateral surface to a larger left lateral surface. Angle d ranges from about 1 ~ to about 45 ~ . The ret~ining plate would also be a~.~ p,;ately angled.
FIGS.14 and 15 show an ~lt~rn~tç embodiment ofthe invention wherein the screw holes 19 in the superior and inferior lips 14 and 15 are located in recesses 40. The ret~ining plate 17 comprises superior and inferior ret~ining lips 22 and 23 which have the same shape as and nest in the recesses of the lips 14 and 15 when the ret~ining plate is in~t~lle-l FIG.16 shows yet another embodiment of the invention. In this embodiment, the superior wall 25 is removable. This allows the hollow interior of the spacer to be packed with bone grafts, bone morphogenic protein or the like before insertion of the spacer into the inteLvc~Leb.dl disk space. The top plate is fixedly ~tt~rh~kle to the rest ofthe spacer by means of a set screw (now shown) which extends through the superior wall 25 through screw hole 42 into a threaded post 43. It is lmtler,stood that the inferior wall may be removable instead of or in addition to the top wall. ~It(~ iv~:;ly~ only a portion of the superior and/or inferior wall may be removable. Further, a removable superior and/or inferior wall may replace access openings 20 or may be present in addition to access openings 20.
The present invention is designed to be m~mlf~rtured as a kit with multiple sized spacers and ret~ining plates present in the kit as well as multiple lordotic, kyphotic and scoliotic spacers. Thus, a surgeon who is performing an anterior fixation surgery can isolate the anterior spine using well known surgical techniques and place an ~ ,-;ate sized and shaped spacer from the kit into the intervertebral space of two adjacent vertebrae. If the spacer used is too large, too small, or the wrong shape that spacer can be removed and replaced with a spacer of a more ~L,I.~l;ate size and shape.
FIGS.17 and 18 illll~tr~te a specialized tool, a "spacer sizer," used for a~lop.ial~
sizing of the intervertebral spacer. An intervertebral spacer 38 is fixedly attached to a stem 36 which is attached to a handle 37 of the spacer sizer. The stem extends from the center of the anterior surface of the spacer. ~ltPrn~Ttively, a placement tool with a handle 37 and a threaded end P~tencTing from the stem 36 that can be threaded into the threaded set screw aperture 21 of the interv~ . kbldl spacer is provided. The stem 36 would be of sllfficient length to allow the surgeon easy pkTc PmPnt into the illlcl ~/cl~ebral disk space of the spine. In the surgical kit described above, there would be included a set of spacer sizers co~ ondirlg to the difrer-clll shaped and sized sp~çers .Al~ ;vcly, the kit would include the threaded placement tool to be threaded into different sized and shaped spacers for surgical placement.
The following is a des~ Lion of the use of the anterior fixation device of the present invention. A patient nPeAing spinal fixation or fusion would be prepped a~ ,pl;ately for -- anterior spine surgery. The surgeon would then use standard anterior surgical approaches to isolate two or more ve-l~-dl bodies to be treated. The intervertebral disc would then be removed and a curette or similar surgical instrument would prepare the vertebral body end plates for receiving the anterior fixation device. The end plates would be lightly scraped or - drilled, with the majority of the scraping oCcllrrin~ in the center of the vertebral body end plate. The end plate scrapings generate a tapered pocket for placement of the tapered anterior fixation device. The t~perTng helps to ensure proper pl~PmPnt of the anterior fixation device and helps to m~Tint~in the device in place.
-~ Once a tapered pocket has been created, the surgeon then selects a spacer sizer as illlTctr~Tte-l in FIGS. 14 and 15 to size the pocket and to select the ~ o~l;ately sized spacer.
With the spacer sizer in place in the pocket between two ~ C Pnt vertebrae, the surgeon would take a~.ol~;ate X-rays to check the size of the spacer and the pocket and its location.
_ If a larger, smaller or di~Cl~ shaped spacer is nPPc~le~i the surgeon would remove the spacer sizer and replace it with a more a~pl~-iate spacer sizer until a proper size is confirmed by X-ray. In the zllternsltive~ the surgeon would thread a spacer onto the threaded stem of the placement tool and ~en place that spacer into the pocket with the tool attached. The shape and size of the spacer would then be confinnec~l with X-ray. If a difr~,.e.l~ spacer is nPeclef1 the tool is removed with the spacer :ltt~che~l, the spacer is then unscrewed fro~n the handle and replaced with a different spacer. Once confirm~tic n of the shape and size occurs using X-ray, the surgeon then UllS~;Ic~ the tool from the spacer leaving the spacer in the pocket between the adjacent vertebrae.
~ The ~ ,eon next secures the spacer to the ~f1jslct-nt vertebrae using the bone screws.
35 ~ As indicated above, the bone screws are preferably angled away from the horizontal plane of the spacer. Thus, all three bone screws can be driven into the annular al,u~hy:jes and cortical bone of the vertebral bodies using one axial access point. The use of only one access point is advantages, especially in the cervical spine, where there is limited maneuvering room.

CA 0224264~ 1998-07-09 The interior of the spacer is then filled with bone grafts, bone morphogenic protein, or the like, using the anterior openings to the spacer. The ret~ininP plate is then placed over the anterior spacer openings and the set screw is then driven into place to secure the ret~inin~
plate to the spacer. Alternatively, if the superior and/or inferior wall is removable, the spacer is filled with bone grafts, bone morphogenic protein or the like before pl~me~nt of the spacer in the intervertebral disk space.
If three or more ~dj~ nt ~ e~lel,l~e are to be treated, the surgeon would remove the next intervertebral disc and then repeat the above procedure to surgically place another anterior fixation device. As can be appreciated, the spacers are desi~e(l to stack one on top of the other such that the entire spine could be fixed. The .ein~ r superior lip of a spacer iqttz-r~?d to the inferior annular ~L)oplIy~is of a vertebral body fits between the two inferior lips of another spacer attached to the superior annular apophysis of the same ~,~.Lel,ldl body.
Once the spinal column has been ~pr~pliately treated, the surgeon then finiches the anterior surgery using well known surgical techniques.
The anterior stabilization device of the present invention provides a number of unique adv~nt~ges. The device provides stability by fixation both in the anterior column by means of the bone screws at the anterior margin of the v ~,lteblcll body and in the inte~ L~ldl disk space by means of the spacer and subsequently by means of fusion. Conventional anterior plates fix only at the anterior portion of the vertebral body. Conventional cages provide only stabilization in the hlL~I ~elLebral disk area.
In conventional anterior plates, rigidity is derived either from biocortical purchase of bone or by locking the screw head to the plate. This creates a rigid box-like structure which can prevent desirable weight bearing on bone grafts in the intervertebral disk space which, in turn, may prevent fusion. The present invention overcomes this potential disadvantage. In the present design, the bone screws are non-weight bearing. Due to the presence of the ret~inin~ plate, the bone screws are allowed to toggle within the screw holes of the spacer without worry of backout. Hence, the present design allows non-weight bearing screws to m~int~in positional fixation at the anterior margin while at the same time allows weight bearing support onto the intradiscal portion of the device.
The presence and design of the retaining plate contributes to the unique advantages of the present invention. Conventional devices that lock screws in place are desiPn~d to be weight bearing and to provide a rigid structure. With such de~i~n~, there is a risk of screw breakage, screw backout and, as described above, bone fusion failure. By means of the design described herein, the bone screws do not create a rigid structure and are non-weight bearing, thereby elimin~ting the risk of breakage. Moreover, by use of a ret~inin~ plate as described herein, risk of screw backout is elimin~t~A

Another advantage of the present design is that the bone screws are anchored in the hardest portions of the vGllGbl~, thereby providing the greatest structural support.
Conventional anterior plates place long bone screws into the mid body area of the vertebra which provides less overall structural support.
- Thus, an anterior fixation device is disclosed which allows the surgeon to spatially fix two or more iqdj~ nt vertebral bodies together at both the anterior margin and the hl~ ,e~IGbral disk portions ofthe vertebral body. The device uses relatively small, non-weight bearing bone screws that cannot extend into the spinal canal. The device is easy to - place arld prevents potentially ~l~m~ing telescoping of the fixed vertebral bodies.
While embocliment~ and applications of this invention have been shown and described, it would be al~palG~IL to those skilled in the art that many more mo~1i1;c~tion~ are possible without departing from the inventive concepts herein. The invention, therefore, is not to be 15 restricted except in the spirit of the appended claims.

Claims

WHAT IS CLAIMED IS:

1. An anterior stabilization device comprising:
a generally hollow intervertebral spacer having anterior and posterior sides andcomprising:
a side wall having a generally oval cross-sectional shape;
a porous superior wall;
a porous inferior wall, at least one superior lip extending upwardly above the side wall at the anterior side of the spacer;
at least one inferior lip extending downwardly below the side wall at the inferior side of the spacer;
a screw hole in each superior and inferior lip; and access means for allowing insertion of bone graft material into the hollow interior of the spacer, and a retaining plate fixedly attachable to the anterior side of the spacer, said retaining plate being sized to cover at least a portion of the head of each bone screw which is inserted through screw holes of each superior and inferior lip.

2. An anterior stabilization device as claimed in claim 1 wherein the spacer further comprises an anterior extension and wherein the superior and inferior lips extend upwardly and downwardly from the anterior extension.

3. An anterior stabilization device as claimed in claim 1 wherein each of the superior and inferior walls are dome-shaped.

4. An anterior stabilization device as claimed in claim 1 wherein the spacer has a height of from about 7 to about 14 mm.

5. An anterior stabilization device as claimed in claim 1 wherein the spacer has a lateral width of from about 13 to about 32 mm.

6. An anterior stabilization device as claimed in claim 1 wherein the spacer has an anterior-posterior width of from about 10 to about 30 mm.

7. An anterior stabilization device as claimed in claim 1 wherein the spacer comprises two inferior lips and one superior lip.

8. An anterior stabilization device as claimed in claim 1 wherein the access means comprises at least one opening in the side wall at the anterior side of the spacer.

9. An anterior stabilization device as claimed in claim 1 wherein the access means comprises a removably attachable superior wall.

10. An anterior stabilization device as claimed in claim 1 wherein the access means comprises a removably attachable inferior wall.

11. An anterior stabilization device as claimed in claim 1 wherein the spacer issized to fit within the intervertebral disk space between two adjacent cervical vertebrae.

12. An anterior stabilization device as claimed in claim 1 wherein the spacer issized to fit within the intervertebral disk space between two adjacent thoracic vertebrae.

13. An anterior stabilization device as claimed in claim 1 wherein the spacer issized to fit with the intervertebral disk space between two adjacent lumbar vertebrae.