CA2569778C - Interbody spinal fusion implants - Google Patents

Abstract

The present invention discloses a spinal fusion implant that is at least partially cylindrical, made of material appropriate for human implantation and having preferably, but not necessarily, one closed end and one end capable of being closed, such that an internal chamber can be filled and hold any natural or artificial osteoconductive, osteoinductive, osteogenic, or other fusion enhancing material, The partially cylindrical implant directly participates and is incorporated in the ensuing fusion. In the preferred embodiment, the implant of the present invention relies on surface roughenings of the outer surface to enhance its stability and resist dislodgement from within the disc space between two adjacent vertebrae. The implant of the present invention incorporates at its rear end, an engagement means to facilitate insertion or extraction of the implant. The implant may be filled with, coated with, and/or composed of, fusion promoting substances. Finally, the implant of the present invention does not require rotation for its insertion and can be seated by linear advancement.

Description

INTERBODY SPINAL FUSION IMPLANTS
Field of the Invention The present invention relates to artificial spinal fusion implants to be placed across the intervertebral space left after the removal of a damaged spinal disc, and in particular to an improved, at least partially cylindrical, spinal fusion implant for implantation where two threaded cylindrical implants of requisite height would not fit within the transverse width of the spine.

Description of the Related Art In the past, Cloward, Wilterberger, Crock, Viche, Bagby, Brantigan, Michelson and others have taught various methods involving the drilling of holes across the disc space between two adjacent vertebrae of the spine for the purpose of causing an interbody spinal fusion. Cloward taught placing a dowel of bone within that drilled hole for the purpose of bridging the defect and to be incorporated into the fusion. Viche taught the threading of that bone dowel. Bagby taught the placing of tl'le bone graft l.nto a metal 1)L1Cket otherwise siTlooth on its surface, except for rows of radially placed holes communicative to the interior of the basket and to the bone graft. The Bagby device was disclosed as capable of being used in a horse.
Brantigan taught the use of inert blocks preferably inade of metal and having that metal at its external surface iniitate L-lie porosity of bone. Brantigari tlieorized that the bone dowel could be replaced entirely with a metal plug, that, wliile not itself active in the flisiorl, would nevertheless serve Lo support the vertebrae frorn within the disc space while allowiiig fusion to occur around it.
U.S. Patent No. 3,844,601 issued to Ma et al. on November 19, 1974, teaclies a nlethod arid instrumeritation for preparing rectangular spaces across the disc space into i:tie adjacent vertebrae and for preparing a rectangular graft of Lhe uone itself that is inserted in the rectangular spaces.
U.S. Pateilt No. 4,743,256 issued to Brantigan on May 10, 1988 teaches the use of an inert artificial spacer in the sliape of a recLangle in place of us'ing a rectangular borie graft as taught by Ma et al.
U.S. Patent No. 4,878,915 issued to BranLigan on Noveniber 7, 1989, teacl-ies tlie use of fully cylindrical inert implaiiLs for use in inLerbody spinal fusion. Such irnplarits do riot participate in tlie bone fusion process but act as inert spacers a-id allow for the growtl-i of bone to the outer surfaces of the implants.
U.S. Paterit No. 4,834,757 issued Lo Braiitigan on May 30, 1989, teaches a rectaiigular shaped, liollow spinal fusion irnplant for use in lieu of a recLarlgular bone graft or Brantigan's earlier artificial irlert spacer.
U.S. PaLent No. 5,015,247 issued to Miclie'lson on May 14, 1991, teact-es the use of a thin-walled, lligllly perforated, threaded, hollow cylindrical iinplac-t closed or closable at botll eiids, so as Lo be compressably loaded wiL-li uone or otlier fusion promoLing niaterials. AdcliLionally, the Michelson device may tlien be coated with a bone productiori inducirig cheinical sucli as hydroxyapatite. The Miclrelson patent also discloses an improved method of drillirig lioles across the disc space and into the two adjacent vertebrae and safely installing cylindrical iinplants sucli that the entire surgical procedure may be conducted through a hollow cylindrical tube. The hollow cylindrical tube may be left in place throughout the surgical procedure and serves to hold LYie adjacent vertebrae in place relative to each other, permits the guarded drilling of the holes across the disc space, and permits the insertion of the iinpl.arit through that same tube into the hole drilled across the disc space and into the adjacent vertebrae.
As regards this metllod of perforrning interbody spinal fusion using essentially cylindrical threaded implants, a special problem arises (see Figure 1) when an aLtempt is nlade to place two cylindrical irnplanta (considered to be the preferred nurnber as it is a rnuch more stable constr.uct and lias more surface area than a siugle implant placed ceiiLrally) side-by-side across a disc space and into the two adjacent vertebrae where the lieight of the disc space is such that it requires an iinplanL- of a dianleter so large to penetrate into arid significaritly engage eacli of the adjacerrt vertebrae that it is no longer possible to place two such implarlts side-by-side and Lo sL-ill have thern coriLained wiLhin the t.ransverse widLl- of tlie spine. If an attenipt is niade to remedy tlie problem by us:iiig smaller diameter implants placed side-by-side sucli that both would theri be able Lo fit wit-hin the transverse widLh of the spine, then Llie implanL-s would be of insufficient heigIiL Lo adequately erigage the bone. If an attempt is inade to remedy tl'ie problem by abandoning the side-by-side dol.iule implant construct in favor of a single, centrally placed implant, tlieli where Llie implant is sufficient=ly large enougli to occupy a sufficient portion of Lhe lransverse widtll of tl-ze disc space to promute firin stability, iLs vertical heigl-zt and excursion iriL-o tlie vertebrae would be so severe that if ariy two consecutive disc spaces were to be operated upon, the vertebrae in betweerl .
would be cut in Yralf.
U.S. Paterrt No, 5,055,104 issuea to Ray ori October 8, 1991 ("Ray Patent") discloses an implant comprising a helical coil without- wall meinbers that is assembled afLer Llie coils are placed in the disc space between the vertebrae, which supposedly can ttien be removed afLer the vertebrae 11ave become fused togetller. The Ray implant is defective and unworkable in that it is irrcapaule of being used in the manrrer in wliich it is described as it is rrot possible to insert into hard bone an isolated helical coil wittrout any wall mernbers to support sucli a coil, which could would be analogous structurally to a slinky, (See Ray Patent, Figures 1 and 7). Furtlrer, the Ray implant is unduly complex, because it would require Llie difficult, if not impossible, task of assembly wiLliin Llie disc space. Figure 3 of the Ray PaLent clearly reveals that Ray does not teach the use of a truncated cylindrical iinplant, but rnerely teaclies tl--e use of a truncated, helical coil appearing as a sl-rarpened spring totally lacking ariy wall meinber wliich could be considered cylindrical. Tlierefore, Ray teaches o-rly Llie use of an isolated tlireaa wlriclr can only be inserLed by rot.ation aria carirrot be linearly advarrced.
If the overwi-ielrning obstacles of the iinpossibility of inserting an isolated thread witliouL wall menibers arid Llie problem of the assembly withiri tlre clisc space could be overcome, tlien the Ray ii-nplant woul.d still be unsafe for its irrLerraed purpose as it would be at liigh risk of spontaneous disasseinbly and niechariical failure. Further, there would be irrsuEficient roorn to safely rotate such a device for inserL-ion as it is i:lre very lack of sucli room that requires Llie use of a device liaving a decreased transverse widLh.
1'here is therefore, tiie need for a spinal fusion implant that is capable of beinq iriserted into a hole drilled across Llie disc space Uet,weeri two adjacer-t vertebrae and partially into the two adjacerit verLebrae sucii that Llie spinal fusiorr itnplanL is capable of fiLLing wiLllin the transverse widLh of-the spine when placed side-by-side next to a second of its kind.

SUMMARY OF THF PFtES1;N'i INVLNI'IUN

The presenL- invention is an improved iriLerbody spirial fusion iniplant that is capable of being inserLed into a hole drilled across the disc space between two adjacent vertebrae and irito the two adjacetit vertebrae such that tlle spinal fusion iinplant is capable of fitting within the transverse width of ttie spine when placed side-by-side next to a second of its kind. The spinal fusion imp'lant of the preserrt iriveriLion comprises a thin-wall, multi-perforate, cylinder or partial cylinder, made of material appropriate for human implanLation and Y-aving preferably, but not necessarily, orie closed end and one erid capable of being closed, such than an ilrL-ernal chamber can be filled and liold any natural or artificial osLeoconducL-ive, osL-eoiriductive, osLeogenic, or oLlier fusion enhancing material. The spinal fusion implant of the present irivention relies on rouglienings of the outer surface to enhance its stability. Dependinq on the dimension of the trarisverse widLh of the spiiie iri whicli the spinal fusioir implar-t is being inserL-ed, the spiiial fusion implarit of the present invention may liave one or more flat sides to reduce the widtli of the spinal fusion implant. The spinal fusion implaiit of tlie present invention incorporates at iLs rear enc7, an engageinent ineans to facilitate insertion or extraction of the implant, preferably at its rear erid. The implant of Lhe presetit ir-vention may be made of, filled with and/or coated with fusion 1?romoting substances. Furl.her, Llle spirial fusion irnplarit of Lhe present inventiori does not require rotation for iL-s insertior- and can be seaLed by l.inear advancement.
Tl-ie spinal fusion implarit of Llie present invenLion is generally effective, arid is safer and more effective tllan tlie cylindrical implants of the prior arL for tlie special instance when it is desirable to insert two implants side-by-side into cylindrically prepared cliaiinels, and where the height of the disc space between two adjacent vertebrae is so great relative to the transverse width of the spine, that two implants of ttie requisite height will not fit within the transverse width of the spine. Prior art has taught those knowledgeable in the art of spinal surgery, that the likelihood of obtaining a spinal fusion is proportionate to three factors: 1) the surface area of the implant 2) the quality and quantity of the graft material and 3) the stability of the fusion construct. The spinal fusion iinplant of the preserit inverition increases each of these three factors by making it possible to use two implants side-by-side across a disc space that would otherwise lack sufficient width to accept more than orie.
The spinal fusion implant of the present invention is more efficacious than the prior art on an individual implant basis for the following reasons:

1. Increased surface area. The spinal fusion implarit of the present invention, because of its surface roughenings lias greater surface area for engaging the adjacent vertebrae than an iniplant with smooth external surfaces. The presence or absence of holes does not materially affect this, so far as the holes are filled with material effectively contributing to the area of contact at the surface. The arced portions of the partially cylindrical implant of the present invention are in coiitact wiLli L:he adjacent vertebrae and provide a greater surface area than is possible with a flat portion from a non-cylindrical implant.

2. The auarititv and quality of graft material presented. As the spinal fusion implant of the present invention is not screwed in, it need not be constructed to resist the torquing tlierewith associaLed. Tlius, the implant of the present invention may be thinner walled and thereby, for a given diameter, liave greater internal volume. The spinal fusion implant of tlie present invention llas arced portions making the implanL- sLroriger irl compression tlian an iinplarit lacking upper and loiaer curved supporting surfaces such tliat tl-ie wall of Llie implarit can be relatively tliinner tlian sucli iniplants. A
thinner wall is easier for bone to grow througli. Also, the interpore bridges may be smaller allowing for greater porosity and thereby greater exposure to the internal graft material.
Furtlier, the spinal fusion implant of the present inventiori may be constructed of arid/or coated with, and/or loaded with a variety of rnaterials and/or cheniical subsLrates knowti to actively participate in ttie bone fusion process. As the spinal fusion implant of the present invention offers greater surface area, and greater internal volume for its outside diameter, it offers tl-ie opportunity for presenting a greater surface area and volume of these fusion nlaterials.

3. The implant o_E tlte present invention of fers greater staility tlian the prior ait inlPlarl_ts. The least staule iinplants are the iinplarits lacking surface roughenings. Surface i--oles increase implant stability by increasing the interference of tlie iniplant to the opposed surfaces. The spinal fusion implant of the present invention is a furLlier improvemerit over the prior art in that the surface roughenings of the spinal fusion implant of tlle present invenLion resist motion in all directions. Furtlier, all implants are subject to ttie possibility of backing ouL, by retracing the path by wliich they were inserLed. flowever, the spinal fusion implant of Lile present irivention can have a surface corifigured to urge tlle spinal fusioii implant forward as to offer increased resistance against such undesirable backward migration. P'urtlier, Llie arcec7 portions of the iinplant of tlie preseiit invention provide a greater support area to betLer distribute the compression forces tl-irougl- tlie verLebrae.
1'lie spinal fusion implant of tl-ie preserit invention is easier to use as it occupies less space, does not require pre-tapping, and can be inserted witliout tl-ie need to rotate an instrument within the closed confines of the spinal wound.
Further, the spinal fusion implant of the present invention is easier to insert than implants lacking upper and lower curved supporting surfaces that are arcs of the same circle and which implants are to be inserted across the disc space and into the adjacent vertebrae as it is easier to prepare a round hole than a square hole, as a round hole can be drilled in a single step.

In accordance with the present invention, there is provided a spinal fusion implant made of a material appropriate for human implantation at least in part between two adjacent vertebral bodies, said spinal fusion implant comprising a partially cylindrical non-threaded body portion having an exterior surface formed by opposite cylindrical portions defining a maximum diameter and intermediate opposite non-cylindrical portions defining a width therebetween configured to be placed in close proximity to a second partially cylindrical non-threaded spinal fusion implant, whereby said implant and said second implant when placed together with said non-cylindrical portions in proximity to one another have a combined overall width less than the sum of the individual maximum diameters of each of said implant and second implant, each of said opposed cylindrical portions having at least one opening passing therethrough to allow bone growth from adjacent vertebral body to adjacent vertebral body through said implant.

In accordance with the present invention, there is further provided a spinal fusion implant made of a material appropriate for human implantation at least in part between two adjacent vertebral bodies, said spinal fusion implant comprising: a first implant having a longitudinal central axis, a non-threaded cylindrical portion having a diameter and at least one non-cylindrical portion with an exterior surface oriented at a distance transverse from the longitudinal central axis that is less than the distance of said non-threaded cylindrical portion from the longitudinal central axis, said non-threaded cylindrical portion having at least one opening passing therethrough to allow bone growth from adjacent vertebral body to adjacent vertebral body through said first implant; and a second implant having a cylindrical portion with a diameter, said cylindrical portion of said second implant having at least one opening passing therethrough to allow bone growth from adjacent vertebral body to adjacent vertebral body through said second implant; wherein said second implant is configured to be placed in close proximity to said non-cylindrical portion of said first implant to produce a combined overall width that is less than the sum of the diameters of said first and second implants.

It is an object of embodiments of the present invention to provide an improved interbody spinal fusion implant such that it is possible to place two such implants side-by-side across a disc space and into two adjacent vertebrae in close approximation to each other and within the transverse width of the spine, where the transverse width of the spine would have otherwise been insufficient relative to the required implant height to have allowed for the accommodation of two prior art cylindrical threaded implants.

It is another object of embodiments of the present invention to provide a spinal fusion implant that is easier to insert, and does not require tapping prior to implantation.

It is yet another object of embodiments of the present invention to provide a spinal fusion implant that is - l0a -safer, in which there is no need to run sharp threads near delicate structures.

It is still another object of embodiments of the present invention to provide a spinal fusion implant that is faster to implant between adjacent vertebrae via linear advancement as opposed to rotational advancement.

It is yet another object of embodiments of the present invention to provide a method for implanting partially cylindrical implants having at least one flat side.

These and other objects of embodiments of the present invention will be apparent from a review of the accompanying drawings and the following detailed description of the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is diagrammatic representation of a segment of the human spinal column comprising several vertebrae with various cylindrical threaded implants inserted across the disc space and into the two adjacent vertebrae to illustrate the problems encountered by those implants.

Figure 2 is a top plan view along lines 2--2 of Figure 1 with the top vertebrae removed, of two cylindrical threaded implants illustrating the minimum distance possible between the two threaded implants when placed beside each other across the disc space.

Figure 3 is a perspective side view of an embodiment of the spinal fusion implant of an embodiment of the present invention having surface roughenings in the form of ratchetings.

Figure 4 is a first side elevational view of the spinal fusion implant of Figure 3.

Figure 5 is a top plan view of two spinal fusion implants of Figure 3 illustrating the minimum distance possible between the two implants when placed beside each other across the disc space.

- 11a -Figure 6 is a second side elevational view of the spinal fusion implant of Figure 3.

Figure 7 is a cross sectional view along lines 7--7 of the spinal fusion implant of Figure 6.
Figure 8 is a cross sectional view along lines 8--8 of the spinal fusion implant of Figure 6.
Figure 9 is a top end view of the spinal fusion implant of Figure 3.

Figure 10 is a bottom end view of the spinal fusion implant of Figure 3.

Figure 11 is a side perspective view of an alternative embodiment of the spinal fusion implant of the present invention.

Figure 12 is a first side elevational view of the spinal fusion implant of Figure 11.

Figure 13 is a second side elevational view of the spinal fusion implant of Figure 11.

Figure 14 is a cross sectional view along lines 14--14 of Llie spinal fusion implanL of Figure 13.
Fic~ure 15 is a perspective side view of an alLerriative embodimerit of the spinal fusion itnplant of the present invention havirrg surface roughenings in the forrn of 1.nurlirrg.
Figure 16 is a first side elevational view of the spinal fusiorr implant of Figure 15.
Figure 17 is a top plan view of two spinal fusion implarrts of Figure 15 illustrating the mini-num distance possible between the two iiuplant wl-ien placed beside each other across the disc space.
P'igure 18 is an enlarged fraginentary view alorig line 18 of Figure 16 slrowing Llie surface corifiguration of Llie implant of Figure 15.
Figtrre 19 is a second side elevaLional view of the spirial fusiori implant of Figrire 15.
Figure 20 is a cross sectional view alorig lines 20--20 of the spinal fusion irnplant of P'igure 16.
Figrire 21 is a top end view of tlie spinal fusiorr iinplant of Figure 15.
Figure 22 is a boL-tom eiid view of the spinal fusion irnplant of Figure 15.
Figure 23 is a perspective sicle view of an alternative embodinient of Llie spinal fusiori irnplant of the preserit invenLion 1-aving flat sides and surface roughenirrgs in tiie forin of ratclreLings.
I'igure 24 is a first side elevational view of Llie spinal fitsion implant of Figure 23.
Figure 25 is a diagraminatic representation of a segment of the human spinal colurnn showinc7 two implants of F'igure 23 the present invention inserted witlrin Llie spine.
Figur.e 26 is a top plarl view along lines 26--26 of Figure 25 witli the top vertebrae removed, illustrat:ing the minimum distance possible between two spinal fusion irnplants of Figure 23 placed beside eacli oLher across Llie disc space.
Figure 27 is a top end view of the spinal fusiori irnplarit of Figure 23.

Figure 28 is a uottom erra view of the spinal fusion implarit of Fi_gure 23.
Figure 29 is a second sicle elevaLional view of the spinal fusion implant of Figure 23.
Figure 30 is a cross sectional view along lirres 30--30 of the spinal fusion implant of Figure 29.
Figure 30A is a cross sectional view of an a'lterrraLive eniuoditnent of the spinal fusion implant of the present irrvention havirrg only one flat side.
Figure 31 is a perspective side view of an alL=ernative etrtuoainient of the spinal fusion implant of the present invention lraving flat sides arid surface roughenings in the forln of ratcheLings.
Figure 32 is a first side elevational view of the spinal fusion irnplant of Figure 31.
Figure 33 is a second side elevaLiorral view of Lhe spinal fusion implant of L'igure 31.
Figur.e 34 is a cross secLional view along lines 34--34 of L-lie spinal fusion implarit of Figure 33.
I'igure 35 is a cross sectional view along lines 35--35 of Llre spinal fusion itnplant of Figure 33.
Figure 36 is a perspective side view of ari alLernal-ive ernbodimerrt of tile spinal fusion implant of tlre presertt invenL-ion having flat sides artd having surface rouglienirrgs in the form of kntrrliny.
Figure 37 is a first side elevational view of the spinal fusion implant of Figure 36.
Figure 38 is a seconcl side elevatiolial view of tlle spirral fusion implant of Figure 36.
F'igure 39 is a cross sectional view along lines 39--39 of tlre spinal fusion implarrL of Figure 38.
Figure 40 is an errlarged fragrnentary view alorig line 40 of Figure 37 slrowing l:lie surface configuration of tl-re spirial fusiorr ituplant of Figure 36.
Figure 41 is a perspective side view of an alternative embodiment of the spinal fusion implant of the present inverition having surface roughenings coinprising of a blasted extertial surface.
Figure 42 is a perspective side view of an alternative embodiment of the spinal fusion implant of the present inve2ition liaving flat sides and openings iri the forin of vertical and horizontal slots.
Figure 43 is an elevational side view of a segmerit of the spiiial column witli an alternaLive embodimeiit of two spinal fusion implants of the present invention having corresponding concave and convex sides inserted across one disc space and aii alLernative embodiment of a single spinal fusion iaiplant of tlie pr.esezit inveiition liaving a two cylindrical portioi-is inserted across one disc space.

DETAILED DESCRIPTION OF TIIE DRAWINGS
The_Previous Devices Referring to Figure 1, a diagrammatic represeriLation oF a seclrneiit of the human spinal colurnn generally referred to by the letter S is slzown. The segrnent of ti-re spinal colunrn S
cornprises several vertebrae V arld a disc space D betweerr two acljacent vertebrae V. Various cylindrical threaded spinal fusion inmplants, each liaving different diameters, are shown inserted across the disc space D.
Wlren tl-ie lieiglrt lls of the disc space D is so large that two cylindrical iniplanL-s, such as spinal fusion irnplants l0a and 10b, each having a sufficient diameter to cross tl-le disc space D and sufficieriLly engage iirLo tlre bone of adjacent vertebrae V, are placed across ttre disc space D, the coiubined overall width of Llie two sp:i nal implanLs l0a arld lOb exceeds Llie transverse width WS of the spinal column S. As a result, a portion of each iinplant l0a and 10b protrudes froin i.tre sides oC the spinal column S and could cause severe and perllaps rnortal damage to Llie patierit as delicate arrc] vital structures lie adjacent to tliat area of the spinal column S such tliat tlre use of two cylindrical spinal fusion implants l0a arid lOb woulcl uot be desirable.
If instead of two spinal fusion implants 10a arrd lOb, a single iinplarrt, sucl'i as spinal fusion irriplant 12a were to be used lraving a sufficienL diauleL-er to provide for sLability aria fusion, then the iruplant would perretrate deeply inLo the adjacent vertebrae V. 1'lie spinal fusion implant 12a would have a diameter that is sigriificarii_l.y greater tlian Llie heiglit HS
of tlre disc space L), sucli tlrat the vertebrae V would lrave to be substantially bored out to accommodaL-e Llie large diameter of Llie spinal fusiori iinplar-t 12a. As a result, a large part oC
the vertebrae V would ue reniovec7, and thus the overall strucLural inLegriLy of the vertebrae V would be substantially weakened. This is especially a Proulern wlrerr a second spinal fusion irnplartt 12b iderttical i:o spirtal fusion implant 12a is placed across disc space D on the other side of the sarne vertebrae V suctt that two spinal fusion iinplartL-s 12a and 12b are placed across the disc spaces D ort eitlrer sicae of tlte vertebrae V. As a result, tlre vertebra V is cleaved ittto a "butterfly" cortfigitration as shown in Fiiure 1, and the sLructural irtteyriLy atta strengtll of the vertebrae V is furLlter diminished such that the effectiveness of Llie spinal fusiort process is substantially reduced, and the vertebrae V are at ltigh risk of devascularizaLiort attd fracture.
Conversely, if two cylindrical irnplartts such as spirial fusion irnplants 14 a arid 14b, each Ytaving a sufficierrtly sized diatneter such that when placed side-by-side in Llie disc space C), the combined overall wiclth of the spinal fusion implants 14a and 14b just fills the transverse widtli Ws of the spinal colurnn S, the diameLer of eaclt of Llie spinal fusion irnplartLs 14a artd 14b will not be sufficient to cross tlte disc space ll to engage the vertebrae V. Tlrerefore, wirile Ll-te spinal fusion implants 14a and 14b will not proLrude from Llie sicles of the spinal colurnn S, tite spinal fusion i-nplants 14a and 14b carrnot reach and engage the bone of Llte vertebrae V and Ll-us cannoL
function to stabilize the adjacent vertebrae V.
Referring to Figure 2, a top plarr view, taken alorig line 2--2 of Figure 1 wi Lli Llie upper vertebrae V removed, of two cylindrical tlrreacled implarits 10a ancl l0U placea across tl-te disc space D is shown. The i,lireac]ea iinplants l0a arra lOb ]rave an external tlzread ll.a and llb wlzich must have a minirnum height-tltat is proportional to the size of the Lhread.ed irnplarit to be effective. Tlte tltreaa lla and llb of tl-te tlrreaded iniplants l0a and lOb converts torque to linear inotiorr, such L1tat the threads lla arid lib need to be of a suf f iciertt l-teigl-t t:o overcome Llie resistance of Llie maLerial, suclt as bone, irt whiclr Llie Lhreaded iruplants 10a and lOb are being inserted, such resistartce beittg proportional to tl-re surface area arrd diainei.er of each of tlrreaded implarit l0a aiid 10u. Thus, the differeirce ueLween Llie major diameter (including the threads) and the root diameter (rninus tlie tl-rreads) of eacl-r t-hreaded implant 10a and lOb is suclr tl-rat when two tl-rreaded implants l0a and 10b are implanted across the disc space D and into the adjacerrt vertebrae V, there rnust be a mini.mum dislance between the two Lhreaded iniplants l0a and lOb to allow for the height of the threads lla and llb. This would be true even if the threads lla and llb were interdigitated the threaded implants 10a and 10b would still be offset by at least the height of the ttrread of at least one of the threaded irnplants l0a and lOb. Such a minimum distance betweerr l.lre two l.-lrreaded implants 10a arrd 10b increases the cornbiried overall widtlr of tlie two tlrreaded implants l0a and lOb wlren i.nserted.
Tlreref-ore, in order for a cylindrical spinal fusion implairt-to be used in tlie spirral fusion process wtrere tlre heiglrt Hs of the disc space ll between two adjacent vertebrae V is larqe relative to its widtll WS, it is necessary to lrave an inrplarit tlrat can be implanted adjacent to a secorrd of its kind in closer coiltact than is possible with threaded implants, while sLill providing for an iniplant surface that will provide niechanical stabiliLy irr errgagernerrL to tlre adjacent vertebrae V. 1.'he use of a cylindrical irnplaiit is desirable as it is easy to prepare tl-ie recipient site by drilling a cylindrical llole across Llre disc space D arrd into Llre adjacerrL verLeurae V. Tlre curved surface of the cylindrical lioles drilled into the vertebrae V lrave increased .:.urface area comparecl to a flat surface and also provides for tlre possibility of tigrrt congruency when the cylindrical Irole is fitted witlr an implarrt liaving corresponding cylindrical portiorrs of matched diameter.
Vt(a--Aresent lnverition.
Ileferring to Figures 3-10, an enrbodirnerrt of tl-re spinal fusion implant oE the presenL- irrvenL-ion, is s[iown an(l generally referred to by tlre numeral 100. Tlre spinal fusion implant 100 lras a substarrtially cylindrical conf-iguration lravirrg a thin outer wall 112 surrounding ari internal chamber 114 and a longitudinal central axis L. The exLerior of tlie spinal fusiori implant 100 comprises surface rouglrerrings Lhat provide a surface suitable for engaging the vertebrae V Lo sLauilize the spirial fusion implant 100 across the disc space D and irito Ltie adjacent vertebrae v orice surgically implarrtec7. In one enibodiment of the spinal fusion imp].ant 1.00, the surface roughenings comprise a plurality of ral.cl-retirigs 120 alorrg Lhe circumference of said spinal fusion irtrplant. Eacli of the plurality of ratclieLi.ngs 120 l-ras a bone engaging edge 122 and an angled segnrent 124.
Each of the plurality of raLclretirrgs 120 has a lreicllrt t1raL
is substantially less than the heiglrt of a requisite tliread [or a cylindrical tlrreaded irnplant of Llie sarne size. As a Lhreaa is a simple device for converting torque to linear advancement, Llie requisite lreiglrt of the Lliread is proportional to the surface area and dianieter of ttre irnplaut and rnust be sufficierrt Lo pull a cylindrical irnplant lraving a diarneter sufficient to cross Llie disc space D Llrrough a uiaterial as dense as bone. In contrast, tlre raL-clretings 120 liave a lieight tllat is significantly less than the requisiLe lieiglrt of a thread of a same sized threaded irnplant since the spirial fusion iuiplant 100 is irnplanted across Llie disc space D ancl into Llie acljacent vertebrae V by lirrear advancenienL. Tl-ie spinal fuslon implant 100 may be puslred into tl-ie cylindrical disc space U by direct, linear aclvancerueii.t since iL requires no Lliread Lo pull iL
forwara Lhrough tl-re spine. As no torque is required Lo advance Llie spinal fusion irnplant 100 there is rio niinirnurn requisite lieiglrt of Llie surface rouglrenings. '1'lre only surface feaLure necessary is that wlricli gives the spinal fusion irnplant 100 stability once implantea.
Moreover, the ratcheLings 120 nray face in one direcLion, Llie direction iri wlricti the spinal fusion implarit 100 is inserted, and functioii to prevent the spinal fusiorr implant 100 from backing out of the disc space D in a direction opposite to the direction of irrsertion once iriserted between Llie two adjacerit vertebrae V. 1'lie ratchetings 120 urge Llie spinal fusion implant 100 forward against Llie unrernoved bone of the vertebrae V. Sirice iinplants gerrerally warrt to Uack out alorig tf-e sarne patli in which they are inserted, stich as repeated rnovement of the patieriL's body over Lime ar-d wllich would cause some oL-her design of implant L-o come loose (e.g. cause a threaded cylindrical i-nplant to possibly unscrew), the ratchetings 120 tend to urge Llie spinal fusion implarit 100 forward against the solid unremoved bone furLlrer resisting dislodgernerit and coritrolling motion resulting in ari exceedirrgly sLable irnplantation.
Tlie bone engaging edges 122 of tlre ratcl-elirrgs 120 thaL
llave a heiglit at a highest point ineasured frorn the root diameLer of the spinal fusion implant 100 thaL- is approxiniaLely 0.35 nun. In Llris manner the spirial fusion ilnplanL 100 -nay be placed beside a second of its kind at a distance of approximately 0.7 mm apart or if offset even closer, substantially reaucing Llie combiiled overall wiclth of tlre two spirial fusion implants 100 orice' surgicall.y implariLec]. The ratclietirigs 120 may have a heiglit in the range of 0.25 - 1.5 rnm, wiLh tlre preferred lleiglit rarige beirig 0.35 - 0.75 in-u.
Referring to Figure 5, two spinal fusion implants 100a arrd 100b are stlown inserted across the disc space U having Llle same diinensioris of Llie disc space D sYrown in Fiyure 2. T'lie two spinal fusiorr implanLs 100a ancl 100b Irave a decreased overall conibined widLh when compared to two threadecl spinal fusion iml~lallL-s placed side by siae previously described anc]
illustrated in Figure 2. The decreased coinbiiied overall widLll of the two spinal fusi.on irnp].arits 100a and lOUb is L1--e difference between the root and major dianieters of Llie spiiia1 fusion itnplarits 100a and 100b and is acliievecl by uLilizirig surface rouglieniric~s such as raLclieL-ings 120 for stability. 'i'he suLface rougherrings allow Llie Lwo spinal. fusion iinplanLs 100a ailcl lOUb to come irrLo considerably closer approxiination to one another and require less total transverse widtlr for tlreir irrserl-ion than is possib].e for two threaded cylindrical irnplants liaving iderrLical root diameters because of the requisite thread lreiglrL of such tlireaded irnplarrts. Reducirrg the offset between implants allows for the uses of larger diameter implants which can tlren still fit wii:hin the trarlsverse width Ws of ttre spinal column and acliieve rnore substantial engagenient into the adjacent vertebrae V.
Referring to Figure 7, a cross section of Ll-re spinal fusion irnplant 100 is shown whereirr the wall 112 lras opeirings 128 passing therethrouglr to communicate witli the irrterrral chamber 114. The internal chainber 114 may be filled witll bone material or any natural or artificial bone growtli material or fusion promoting material such tlrat bone growth occurs from the vertebrae V tlrrouglr Llie operrings 128 to tlie tnaterial witliirr irrternal cliamber 114. Wlrile the openirrgs 128 rrave been shown in the drawirigs as being circular, it is appreciated Lhat the openings 128 may have any shape, size, or form suitable for use in a spinal fusion i-nplarrt without departing fronr the scope of Llie present invention. Also, the nunlber of openings rnay be varied or no openirrgs rnay be preserrt ori the spinal fusion iinplarrt.
Referring to Figures 8 and 9, the spinal fusiorr iinplant 100 lras a cap 130 willl a thread 132 ttrat threac]ably attaclres to one end of the spinal fusion iinplant 100. Once the cap 130 is aLLached to the spirral fusion implarrt 100, the edge 136 acts as an additional ratcheting 120 to furtlzer stabilize Llie spinal fusiorr iinplant 100 once it is implarrtecl across the disc space U.
The cap 130 is removable to provide access to the irrterrlal chaniber 114, sucl-r tliaL Llie iriterrral cliamber 114 can be fillec]
ancl lrolcl arry natural or arLificial osteoconductive, osteoirrductive, osteogenic, or other fusion enhancing niaLerial. Some examples of sucli materials are bone llarvested from the patient, or bone growLrr irrducirrg rnaLerial such as, but not limited to, lrydroxyapaLite, hydroxyapaLite tricalciu-n phosphate; or one morphogenic protein. The cap 130 and/or the spinal fusion implant 100 itself is made of material appropriate for human implantation such as titanium and/or may be made of, and/or filled and/or coated with a bone ingrowth inducing material such as, but not limited to, hydroxyapatite or hydroxyapatite tricalcium phosphate or any other osteoconductive, osteoinductive, osteogenic, or other fusion enhancing material.

Referring to Figure 4, alternatively the cap 130a may be "bullet"-shaped to facilitate insertion. The cap 130a has at its greatest diameter a diameter equal to the root diameter of the spinal fusion implant 100 such that no additional ratchetings 120 are formed.

Referring to Figure 10, the spinal fusion implant 100 has an engagement means at one end in the form of a rectangular slot 140 for engaging a driver instrument having a removable engagement means for intimately engaging the rectangular slot 140. A threaded portion of the driver instrument, which in one embodiment extends as a rod through a hollow tubular member and can be rotationally controlled, screws into a threaded aperture 142 in the slot 140 and binds the implant 100 and the driver instrument together.
Once affixed to the implant driver instrument, the spinal fusion implant 100 may be then introduced through a hollow cylindrical tube and driven into the cylindrical hole that has been drilled across the disc space D. The implant driver instrument may then be impacted by a mallet, or similar device, to linearly advance the spinal fusion implant 100 across the disc space D. Once the spinal fusion implant 100 is inserted across the disc space D, the ratchetings 120, engage the bone of the vertebrae V and the implant driver instrument is detached from the spinal fusion implant 100. The procedure for drilling the holes across - 21a -the disc space D and instrumentation pertaining thereto are described in U.S. Patent No. 5,484,437.

Referririg to Figures 11-14, an alternative einbodinietit of the spinal fusion implant of the present invenLion, generally referred to by the numer.al 200 is sliown. The spinal fusiori irnplant 200 is similar to the spinal fusion iinplariL 100 except that the operiings 228 are bisected by the borie engagirig edge 222 of the plurality of raLclietings 220. In Lliis inanner, the bone engaging edges are inL-errupted by the operrings 228 to provide a "tooth-like" edge that engages the borie of the vertebrae V and creates an interference fit to prevent the uacking out of L1ie implarrt 200 orrce inserted. IL- is appreciated that tlre number of opeTiings 228 and the riurnber of bone engaging edges 222 may be varied and i:liat tlie opening 228 can be placed in ariy orientation relative to Llie raLclietings 220 or otlier surface roughening without departirig from the scope of the present invent-ion.
Re.ferring to Figui-es 15-19, an alLerrraLive eaiboclimeiit of-ti-re spinal fusion iniplarrt of the present invenL-ion get7erally referred to by the numeral 300 is showzl. The spinal fusion implant 300 lias a substanlially cylirtcJrical configuraLion Itaving surface rougitenings for stabilizing the implant 300 within the intervertebral space D. As sltown in Figure 18, Llie surface roughenings comprise a surface krnurling 320 suclr as, but riot limited to, the dian-onrl-shaped bone engaging patterr-sliown. The spinal fusion iniplant 300 may lrave surface knurling 320 tlirougliout the entire exLernal surface of Llie spirtal fusiorr iinplairt 300, ttirougliout only a portion of the external surface, or any conibination thereof, without deparLing froin tl-te scope of the present invention. In those circumstances wliere tl-rere is ito undrilled bone in L1-re disc space D forward of Llie spinal fusion implant 300 to resist further forward advancernerrt of tl-ie implant, surf_ace kriurling 320 is preferred as it produces aii exceeding ly liigli inter. f-ererice f i t wi Lli Llie bone of Llie vertebrae V and resists inotion eqtially in all directions arid witliout the tendency to urge itself forwarc7.
Referrirtg Lo Figure 17, two spiital fusion implants 300a and 300b uiay be placed side-by-side across Llie disc space D lraviiig L1-re same dimensions of the disc space D shown in F'igure 2, such that the two spinal fusiorl implants 300a arrd 300b are touchind eaclr oLher and tllus reducirig the overall cornbinea widLlr of Llie two spinal implants 300a and 300b to the minimi_im distance possiule witli a subsLantially cylindrical irnplant l-raving a rouglrerred surface. In this rnanner, two cylindrical spinal fusion implants 300a and 300b lraving a sufficient diaineter to cross the lreight Iis of the disc space D cari be placed across the disc space D wiLlrout exceedirrg tlre transverse widLli Ws of the spinal column S. T11e spinal fusion implants 300a and 3001) are inserted by linear advancenlent as described above for spinal fusion iniplaut 100. Tlierefore, as rio tlrreaaing is required for the inserLion of spinal fusi.on iniplants 300a and 300b, liLLle or rio space ireed be present hc,tweeil Llie spinal fusion implants 300a ana 300b, as cornpared to Llie space tliaL
would be reqi..iired for a tlireacl wlien using tlir.eacled iinplants.
7'rrus, the spinal fusion iniplants 300a and 300b may be placed closer togeLlrer to substarrtially reauce tlre overall combinea widtlr of two such implants.
Referring to Figures 23-30, an all-ernat.ive eiuUodi.rnerit oL-tl-ie spinal fusion implant of the present invention is shown and is generally referred to by the numeral 400. Tlie spinal fusion iniplaiit 400 lras a similar corrfiguratiori to tilat of Llie spinal fusion iniplarit 200, except that it cornprises a parLially cylindrical me[riber Yraving arcuate portiorrs 402 and 404 whiclr are arcs of tl-re saine circle witl-i portions of its ouLer wall 405 Llrat are flattenecl so as to present a first f1aL- side 406 aiid a second flat side 408.
Referring to L igure 28, Llie spinal fusion implant 400 has a rnajor diameter M equal Lo Llie distance ueLween two diameLrically opposite rion-flaLtened segmeiiLs, suclr as arcuate portions 402 arid 404 wi-rich are arcs of the saine circle. 1'lie widtli W. of the spinal fusion irnp7.ajrL 400 is ec1ual Lo Llie d.isLarrce between a flatL-ened segmerit and a point diarnetrically opposite the flattened segmerit, such as the distance betweeri Llie first and secorid flat sides 406 and 408.
Referring to Figure 25, a diagrammatic representation of a segment of a spinal colurnil S comprising several vertebrae V is sliown 1-aving two spinal fcision implaiits 400a and 400b inserted across tlie disc space D between the two adjacent vertebrae V.
The spinal fusion implants 400a and 400b are identical and eacli lias a firsL arcuate porLion 402a arid 402u, respecLively; a secorid arcuaLe portion 404a and 404b, respectively; a first flat side 406a and 40Gb, respectively; aiid a seconcl f1aL side 408a ancl 408b, respectively. The spirial fusion implarlts 400a and 400b are implanLed across L-lie disc space D wi Ll- the secoiiQ
flat side 408a of spinal fusion implant 400a facinc~ ancl adjacent to the first flat side 408b of spinal fusion irnplarit 400u sucli that the corubined overall width of Llie two spinal ftision implants 400a aiid 400b is less than Lwice the maximum diameter M of the implants. The spinal fusion irnplanl.s 400a arid 400b are inserted by liriear advancement as described above for spinal fusion iinplant 100.
Prior to irnplantation, two partially overlappirrc~
cylindrical lioles are drilled across the disc space D and irito tl-ie adjacent vertebrae V. '1'he holes are drilled sufficiently overlapping to allow tlie L-wo spinal fusion implarits 400a aiid 400b Lo be implanL-ecl witli Llie flat sides perpeticlicular Lo Llie plane of tiie disc space U, Llie disc space L1 being in a plaiie perpenclicular to the longitud.inal vertical axis A of tiie spinal column S as sllown in Figure 25.
T'lie spinal fusioii icnplaiitJ 400a ancJ. 400b rnay be iirsertecl separaLely such that once a first splnal fusion implanL- 400a is inserted across Llie disc space U, a second spinal fusioli implant 400b is driven across tlie disc space D so tliat the flaL
side 402 or 404 of eacll spinal tLlslon implarit 400 are adjacer-t L-o eacli otlier and are toucliing. Ici Lhis manner, tlte Lwo spinal fL.rsion irnplants 400a aiid 400b are iinplanLecl across Llie disc space ll aiid engage tlie uone of LIIe adjacenL verLebrae V wiLhouL

exceedirig the trarrsverse widLli VIS of Llie spinal coluicui S.
Alternatively, the two spinal fusiori irnplarrts 400a and 400b inay be implanted across ttre disc space D sinrultaneously by placing them adjacent and facing eacll otlrer, irr the orierrtatiorr described above, prior to implantation. Tl-re two spirral fusiorr implarits 400a arrd 400b are tlien lirrearly advanced into the drilled holes across the disc space D.
Referring to Figure 28, the effect of liavirrc~ first and second flat sides 406 and 408 is tl-rat the overall widL-ll Wi of ttie spinal fusion iinplant 400 is substantially reduced while the lreigYrL of Llie spinal fusion implant 400 remairrs Llie maxiurum diameter M of the cylindrical portiori of the spinal fusion iinplant 400.
Referring to Figures 25 arrd 26, as tlie heiglrL of eacli spinal fusion implarlt 400a and 400b is sufficierrt to cross the disc space D and inl=o the two adjacent vertebrae V, eaclr spirial fusion implant 400a and 400b errgages Llie bone of Lhe adjaceriL
vertebrae V while the combined width of the two spinal fusion iinplarit 100 does not exceed the trarrsverse widtlr Ws of the spinal column S. As a result, tlre advarrLages oE placing two cylindrical implarrts side by side across the disc space D rnay be obtained without exceeding tlie widLh WS of the spinal colurnn S. Thus, as shown in Figure 26, Llie Lwo spinal fusion implants 400a and 400b can be inserL-ed across the disc space L), liaving the sanie di-nerrsions as tYre disc space D sllown in Figure 2, an(i can be placed much closer togeLher as a resulL- of tlie first flat side 408b placed adjacenl to the secorra flat side 408a while corrLirruing Lo engage tlle adjacerYt verLeb):ae V.
As shown in F'igure 30, Llie sp.inal fusion irnplallL 400 has a Yrollow internal central charnber 414 and has a series of openirigs 428 passing through tlre outer wall 405 and into the central charnber 414 of the spinal fusion iinplaiiL- 400. The openings 428 may also be preserrt on tlre first and seconc] flaL
sides 406 and 408. Said operrings 428 while sl-rown as round lroles for example, rnay be any oLher workable configuraL-ion consisterrt with their purpose and may iricluae, but is not lirnited to, ovals, slots, grooves and holes that are not rourrd as is true for any of the cylindrical irnplants disclosed above.
Referring to Figure 30A, it is appreciated that it is also within the scope of the preserrt invention that the spinal fusiori implant 400' could 1-rave or'rly one flat side so as to provide only a first flat side 406'. 1'his configuratiori is appropriate where the width W. of ttie spinal fusion implant 400 tieecl orily be sligl-Lly reduced wiLli respect to iLs maximuM
dianieter M, to prevent ttie combined overall width of two suclr implants from exceeding the transverse width W5 of tlle spinal coluinn S.
Referring to F'igures 23, 24 and 29, the spinal fusion irnplant 400 of the present inverition has a plurality of ratclreLings 420 facing one direction, as described above for spinal fusion iniplant 100, alorrg the outer surface of the cylindrical portion of ttie circumference of the spinal fusion implarit 400. The ratcl-etirigs 420 llave a bone engaging edges 422 arrd ttie arrgled configuratioil of the ratchetinys 420 provide for a "one-way" irrsertion of the spinal fusion iniplant 400 as the -novement of the spinal fusion implarit 400 in the opposiLe way is prevented by the eiicjageinerit or the engaging edges 422 witli Llic, vertebrae V. 1-lowever, the flat sides 402 arrd 404 are preferably smooLli and liave a flat surface so as to allow placement in Lhe closest possible proxiniity of the two spinal fusion implants 400a arrcl 400b. The bone engaging edge 422 of each ratcheting 420 bisects the lioles 428 to inerease the sLability of tlre spinal fLtslon implarit 400 once irnplariLecl.
Tl-re spinal fusion implants 100-600 eacli have an overall length in the range of 20nun to 30mm, witlz 25mm beirrg preferred, ancl a rnaxiinurn cliaiueLer M in Llie range of 141111u Lo 24mrri, witli 18nut1 being preferred wheii insertea in the lumbar spirre from Llie posterior approach, and 20nun being preferred when iriserted in Llre lu-nbar spine froin Llre anLerior approacli. The spinal fusion iiuplant 400 is quite appropriate for use in ti-e cervical ai-d tlroracic spirre as well. In the cervical spine sucli implants would lrave a lengLii irr the rarrge of 10-18inm preferred 12 mm arrc7 a inaxirnuul diameter M in the range of 12-20mm, witli the preferred diaineter being 16nu1i. In tkre thoracic spirre such implants would lrave a lerrgLl-r in the rarige of 16-26rnni and a greatest diaineter in the range of 14-20rnrn, with tlre preferred diameter being 16mrn. In addition to the foregoing dimensions, spinal fusion implanLs 400-600 lrave a width Wi for use in Llie cervical spine in the range of 8-161nm, wil-h the preferred wicltli Wi being 10-14inm; for use in the lurnbar spine in tlre range of 18-26mm, with the preferred widtll Ws ueiug 18-20rnm; and for use in Llie lu-nuar spine in the range of 18-26r11m, wiLlr tlre preferred widtlr W. Ueing 20-24mm.
Ref-er_ring to F'igures 27 ana 28, wherr viewed oir encl, the spirral fusion irnplarrt 400 of Llie preserrt 1r1ve11tlorl lras exterrrally the geometrical configuraLion of a circle with a portion of each side tangenLially amputated vertically to forrn the first and seconcl flat sides 406 and 408. The cap 430 extends beyorid the narrowest diameter of the wall 412 along the first and secorrd arcuate portions 402 and 404 at the errd of Lhe spinal fusion iinplarrt 400 and acts as arr additional ratcheting 420 witli an engagirrg edge 436. In this marrner, tt-re additional ratcheting 420 functlotls to further increase the stability of Llie spirral fusion implant 400 once irrserted uetween the adjacerrt vertebrae V arrcI to further prevent tlre dislodgemerit of the spinal fusiorr iinplarrL 400 frorn the disc space U. 'i'lre cap 430 is fl.usl-r wit1i Llie flat sides 406 and 408 Lo preserve tlie flat surfaces of flat sides 406 arid 408. The cap 430 furtlier }ras a sloping sides 438a and 438b corresporiding posiLion wiLli Llie flat sides 406 arid 408 Lo facilitaLe iriserLion of Llie spirral fusiorr implant 400 arrc7 to perinit for close side by sic]e placement of two spirral fusion implants 400. AlterrlaLively, Llie cap 430 can be flusli all the way aroi.rnd Wltl1 Llie root c]iaineter of Llie spirral fusion implant 400 to furLher facilitate irrsertiorr for a longer ramp lenc~th.
1'he spinal fusion implant 400 has surface rouglrenirrgs sucli as, but not limited to, ratchetirrgs 420 sucl-i that tlie outer surface of the spinal fusiori irnplarrt 400 may have a plurality of other surface roughenings to enhance to stability of the spinal fusion implant 400 and to resist dislodc~emerrt once irnplanted across the disc space D. For example, the spinal fusion implant 400 may have an irregular outer surface that may be created by blasting or rougli casting and Llie like. Sucl1 aii irregular surface may be used alone or in conibination with other surface roughenings such as ratchetings and/or knurling and as already discussed, Llie openings 428 niay be holes, grooves, slots or other.
Referring to Figures 32-35, an alternative enibodiment of Llie spinal fusion irnplant of the present invention is sl-own and generally referred to by the rrumeral 500. The spinal fusion irnplant 500 is substantially the same as the spinal fusion implant 400, except tl-rat Llie openings 528 are positioned oii Ll-ie ratclieting 520 sucli that the openirigs 528 are positioned between the bone engaging edges 522 and are not bisected by the bone engaging edges 522. In tllis manner the bone engaging edges 522 are corrtirruous and uriinterrupted to engage Llie borie of Llie vertebrae V and preverrt Llie backing out of the irnplant 500 once inserted.
Referrirrg to Figures 36-40, an alterrrative einbodiinerrt oC
the spinal fusion implant of the present invention is strown and generally referred to by the ririmeral 600. The spirial fusion irnplant 600 is substantially identical to the spinal fusion iniplarit 400 described above except that in place of ratchetings 420, it has surface knurling 620 such as, but not lirnited to, l.:lie diamond-shaped bone engaging pattern showri in Figiire 40.
Z=he surface knurling 620 assists in the retainiirg of the spirral fusion implant 600 once it is inserted across ttie disc space D
between two adjacerit vertebrae V. It is recognized that the surface knurling 620 of tlre iinplant 600 rnay be cornbirred witli arry of a number of other surface roughenings sucll as, but riot limiLed to, ratchetings to assist in retainirrg L1--e spinal fusion implant 600 across Lhe disc space D.

As shown in Figure 36, ttre cap 630 of tlre spinal fusion implarrt 600 has sloping sides 660 ar-d 662 corresponding wit:lr Ll-ie first and second flat sides 606 and 608 to facil.itate insertiori of the spirral fusion implarrt 600 anc:l to perinit for close side by side placemerit of two spinal fusion implants 600.
It is appreciated tlrat the implant invention may include arry and all surface rouglrening corrfiguration that eiLlrer increase the surface area or interference fit of the irnplant and the vertebrae V. It is appreciaLed that the raLclretings described above for the various einbodinients oE Llie spiiial fusion implants of the present invention may also comprise a knurled or otlrer surface rougl-renings in combination with the ratcheLirrgs to further errlrance the reterrtion of the spinal fusion implant across the disc space D once inserLed.
Referring to Figtire 41, an alternative embodiinerit of the spirial fusion implanL of Llie present invenLion generally referred to by the riumeral 700 is slrown. Tlre spinal firsion iniplant 700 has surface rougllenings comprising of a blasted exterrral surface 701 to provide an encJagemerit surface for the vertebrae V wlien irrserted across the clisc space D. The spinal fusion iinplarrt has a plurality of openings 728, a renlovable cap 730 wiL-h a l-rex slat 734 for engaging a hex tool.
Referrirrg to Figure 42, an alterrrative ernbodimerrt of the spinal fusion implant of the preserrt invention generally referred to by tl-re nurneral 800 is slrown. Tlre spinal fusion iinplanL 800 is sirnilar to splnal fusiori implant 400 described above except that iL- has openings in t.he form of liorizorrtal slots 828 on Llie flat side 806 and vertical s1oLs 829 on the cylindrical portion of Llie spinal fusion iinplarit 800.
It is appreciated ttiat Llie spinal iniplants of Llie present invenLiorr inay lrave arry corifiguration such Llrat the coinbined overall widLlr of the two sucll spinal fusiori implanLs is less than twice the rnaxirnurn diameLer M of those iniplants wi.Lliout departing from the scope of Llie present inveirLi.on.

Referring to Figure 43, a segcnerit of the spinal colurnn S is shown with an alternative embodiinenL of two spinal fusion implaiits 900a and 900b iziserLed across disc space D 1 is sllown. Spinal fusion irnplant 900a lias a concave surface 902 wl-iich is correspondingly shaped for receiving tlie convex surface 904 of spinal fusion implarit 900b. When tl-e two spirial fusion implants 900a and 900b are placed side by side, the concave surface 902 mates with the convex surface 904 sttCh i:llat tlie combined overall widtli of the two spinal fusion implanLs is less than twice the inaximutri diameter M of those implar-ts. As a result, the advantages of placing two iinplarits t:hat are partially cylirid.rical, wiLli respect to the portion en(jaging Lhe vertebrae V, side by side across tlle disc space I) may be obtained without exceeding the widtli WS of the spinal column S.
Referriiig still to FicJure 43, an alLerrlaL-ive einUocliineiit ot the spinal fusion implant of tl-ie present invention comprising a single spinal. fusion implant 1000 inserLed across Llie disc space D2 of the spinal colurnn S is shown. The spiiial fusioil implarit 1000 comprises a first cyliridrical porLior- 1010 and a second cylindrical portion 1012 and may liave arry of tlie surface roughenings described above in refererice to the e-uuodiinents seL-forth above. In the preferrer) ernbodiinent, the spinal fusiori iniplant 1000 is inserted by linear advancement iril:o two overlapping cylinarical l-ioles drilled across the disc space D2.
Wliile the preseiit iiiveiiLion lias been described in (letail with regard to the 1.)referred emboclimeriL-s, it is appreciated ttiat otl7er variatioils of the presei-t invention may be devised whicly do not depart from the inventive concept ar-a scope of Llre present invenLion.

Claims (23)

CLAIMS:

1. A spinal fusion implant made of a material appropriate for human implantation at least in part between two adjacent vertebral bodies, said spinal fusion implant comprising a partially cylindrical non-threaded body portion having an exterior surface formed by opposite cylindrical portions defining a maximum diameter and intermediate opposite non-cylindrical portions defining a width therebetween configured to be placed in close proximity to a second partially cylindrical non-threaded spinal fusion implant, whereby said implant and said second implant when placed together with said non-cylindrical portions in proximity to one another have a combined overall width less than the sum of the individual maximum diameters of each of said implant and second implant, each of said opposed cylindrical portions having at least one opening passing therethrough to allow bone growth from adjacent vertebral body to adjacent vertebral body through said implant.

2. A spinal fusion implant made of a material appropriate for human implantation at least in part between two adjacent vertebral bodies, said spinal fusion implant comprising:

a first implant having a longitudinal central axis, a non-threaded cylindrical portion having a diameter and at least one non-cylindrical portion with an exterior surface oriented at a distance transverse from the longitudinal central axis that is less than the distance of said non-threaded cylindrical portion from the longitudinal central axis, said non-threaded cylindrical portion having at least one opening passing therethrough to allow bone growth from adjacent vertebral body to adjacent vertebral body through said first implant; and a second implant having a cylindrical portion with a diameter, said cylindrical portion of said second implant having at least one opening passing therethrough to allow bone growth from adjacent vertebral body to adjacent vertebral body through said second implant;

wherein said second implant is configured to be placed in close proximity to said non-cylindrical portion of said first implant to produce a combined overall width that is less than the sum of the diameters of said first and second implants.

3. The spinal fusion implant of either claim 1 or 2, wherein at least one of said non-cylindrical portions has a substantially flat exterior.

4. The spinal fusion implant of either claim 1 or 2, wherein said exterior of at least one of said non-cylindrical portions is at least in part concave.

5. The spinal fusion implant of either claim 1 or 2, wherein said exterior surface includes a plurality of surface roughenings configured to resist expulsion of said implant from between the two adjacent vertebral bodies.

6. The spinal fusion implant of claim 5, wherein said surface roughenings include ratchetings.

7. The spinal fusion implant of claim 6, wherein said ratchetings face the same direction.

8. The spinal fusion implant of claim 5, wherein said surface roughenings include knurling.

9. The spinal fusion implant of any one of claims 1-8, further comprising a plurality of cells in said exterior for retaining a fusion promoting substance.

10. The spinal fusion implant of any one of claims 1-8, wherein said spinal fusion implant is porous.

11. The spinal fusion implant of any one of claims 1-8, wherein said exterior has a bone ingrowth surface.

12. The spinal fusion implant of any one of claims 1-11, wherein said spinal fusion implant is treated with a fusion promoting substance.

13. The spinal fusion implant of any one of claims 1-11, wherein said spinal fusion implant is coated with a fusion promoting substance.

14. The spinal fusion implant of any one of claims 1-13, wherein said spinal fusion implant is stronger than bone.

15. The spinal fusion implant of any one of claims 1-14, further comprising a hollow interior in communication with said at least one opening.

16. The spinal fusion implant of claim 15, wherein said implant includes an end along the longitudinal central axis of said implant that is open to allow access to said hollow interior.

17. The spinal fusion implant of claim 16, wherein said end is adapted to be closed by a cap.

18. The spinal fusion implant of claim 17, in combination with a cap adapted to close said hollow interior.

19. The spinal fusion implant of any one of claims 1-18, in combination with a fusion promoting substance.

20. The spinal fusion implant of claim 19, wherein said fusion promoting substance includes at least one of bone, hydroxyapatite, hydroxyapatite tricalcium phosphate, and bone morphogenic protein.

21. The spinal fusion implant of any one of claims 1-20, in combination with an implant driver configured to insert said spinal fusion implant into the spine.

22. The spinal fusion implant of any one of claims 1-21, in combination with a guard having an opening for providing protected access to the disc space and the adjacent vertebral bodies and for guiding the insertion of said spinal fusion implant into the spine.

23. The spinal fusion implant of any one of claims 1-22, in combination with a drill for preparing an implantation space to receive said spinal fusion implant.