`
`WORLD INTELLECTUAL PROPERTY ORGANIZATION
`International Bureau
`
`
`
`INTERNATIONAL APPLICATION PUBLISHED UNDER THE PATENT COOPERATION TREATY (PCT)
`(51) International Patent Classification 5 :
`(11) International Publication Number:
`WO 91/06261
`AGIF 2/44
`(43) International Publication Date:
`16 May 1991 (16.05.91)
`
`(21) International Application Number: PCT/US90/05318|(81) Designated States: AT (European patent), AU, BE (Euro-
`
`pean patent), CA, CH (European patent), DE (Euro-
`(22) International Filing Date:
`18 September 1990 (18.09.90)
`pean patent)*, DK (Europeanpatent), ES (European pa-
`tent), FI, FR (European patent), GB (European patent),
`IT (European patent), JP, KR, LU (European patent),
`NL (European patent), NO, SE (Europeanpatent).
`
`(30) Priority data:
`432,088
`
`6 November 1989 (06.11.89) US
`
`the two bony structures (94, 95).
`
`A fusion cage (10) having an external thread (12) can be surgically inserted into a threaded bore extendinglaterally be-
`tween the adjacent bony structures such as two vertebrae (94, 95) with the thread (12) penetrating into cancellous bone of each of
`the vertebrae (94, 95). The fusion cage (10) is easily screwed into place by hand without damageto the bonystructures (94, 95).
`Cage (10) is then packed with a bone-growth-inducing substance such as cancellous bone. When a pair of such cages (10) are im-
`planted between adjacent vertebrae (94, 95), patients have been able to sit without pain by the second orthird day, muchearlier
`than has been possible in prior spinal fusions except those involving steel plates and screws. Eventually, the ingrowth of bone
`through perforations(13) in the valley (14) of the thread (12) of the fusion cage (10) forms a permanentinterconnection between
`
`[US/US];
`INC.
`(71) Applicant: SURGICAL DYNAMICS,
`1240 South Loop Road, Alameda, CA 94501 (US).
`(72) Inventors: RAY, Charles, D.
`; 19550 Cedarhurst, Wayzata,
`MN 55391 (US). DICKHUDT, Eugene, A.
`; 801 Con-
`ntinental, New Brighton, MN 55112 (US).
`
`(74) Agent: MEYER, Sheldon, R.; Fliesler, Dubb, Meyer &
`Lovejoy, Four Embarcadero Center, Suite 400, San Fran-
`cisco, CA 94111-4156 (US).
`
`Published
`With international search report.
`Before the expiration of the time limit for amending the
`claims and to be republished in the event of the receipt of
`amendments.
`
`(54) Title: SURGICAL METHOD AND APPARATUS FOR FUSING ADJACENT BONE STRUCTURES
`
`(57) Abstract
`
`* See back of page
`
`
`
`DESIGNATIONS OF “DE”
`
`Until further notice, any designation of “DE” in any international application
`whoseinternationalfiling date is prior to October 3, 1990, shall have effect in the
`territory of the Federal Republic of Germany with the exception of the territory of the
`former Gerrnman Democratic Republic.
`
`FOR THE PURPOSES OF INFORMATION ONLY
`
`Codes used to identify States party to the PCT on the front pages of pamphlets publishing international
`applications under the PCT.
`
`United States of America
`
`Spain
`Finland
`France
`Gabon
`United Kingdom
`Greece
`Hungary
`{taly
`Japan
`Democratic People’s Republic
`of Korea
`Republic of Korea
`Liechtenstcin
`Sri Lanka
`Luxembourg
`Monaco
`
`Austria
`Australia
`Barbados
`Belgium
`Burkina Faso
`Bulgaria
`Benin
`Brazil
`Canada
`Central African Republic
`Congo
`Switzerland
`Céte d'ivoire
`Cameroon
`Germany
`Denmark
`
`Madagasear
`Mali
`Mauritania
`Malawi
`Netherlands
`Norway
`Poland
`Romania
`Sudan
`Sweden
`Senegal
`Soviet Union
`Chad
`Togo
`
`
`
`WO 91/06261
`
`-l1-
`
`PCT/US90/05318
`
`SURGICAL METHOD AND APPARATUS FOR FUSING
`
`ADJACENT BONE STRUCTURES
`
`10
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`15
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`20
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`25
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`30
`
`35
`
`CROSS~REFERENCE TO RELATED APPLICATION
`
`This is a division and continuation-in-part
`of our copending application S.N. 07/259,031, filed
`
`October 17, 1988.
`
`BACKGROUND OF THE INVENTION
`Field of the Invention
`
`The invention concerns method and apparatus
`for fusing two adjacent bony structures such as a bone
`joint, especially adjacent vertebrae of the spine.
`
`Description of Related Art
`
`Subsequent to injury, diseases or other
`degenerative disorder,
`the disc, a ligamentous cushion
`between vertebrae, may undergo a painful
`deterioration.
`The disc shrinks and flattens out, and
`the distance between the vertebral bodies begins to
`collapse.
`Subsequently,
`there may be a progressive
`degeneration leading to mechanical instability, where
`painful translocations occur between adjacent
`vertebrae.
`The movement-induced pain may be so
`disabling that in many such cases,
`the vertebral
`
`motion must be eliminated. Thus, rigid fusions may be
`the only present means to stop the translocations and
`
`relieve the pain.
`
`It is generally held that successful fusions
`
`demand a contiguous growth of bone to create a solid
`
`mass that will unite the movable elements into one
`
`unit. Otherwise,
`
`the fusion cannot achieve the tasks
`
`
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`WO 91/06261
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`PCT/US90/05318
`
`of pain reduction, maintenance of intervertebral
`height, and immobility of the vertebrae. When fusion
`bone is first placed, it is soft and moveable, having
`no cohesive strength. Therefore a variety of
`appliances have been developed that attempt to hold
`the vertebrae quite still under conditions of normal
`spinal activity and daily stress. Bone graft material
`is placed between the vertebrae,
`the outer or cortical
`surfaces of which have been removed or deeply
`
`10
`
`scarified so as to promote the ingrowth of the graft
`
`into these recipient sites.
`
`Thus positioned,
`
`the bone
`
`Such an appliance
`graft slowly unites the vertebrae.
`is not meant to permanently secure immobility of the
`
`15
`
`segments. Bone ingrowth is required for this.
`Dependency upon such an appliance as the sole
`
`stabilizer is ultimately unsuccessful due to the
`
`development of a mechanical gap or transition between
`
`the bone and the appliance,
`
`leading to structural
`
`failure of the bone and adjacent connective tissue.
`
`20
`
`Such failure is seen in fractures, erosion and
`
`absorption of bone with potential further collapse.
`
`The pain may also become progressively disabling.
`Approximately 150,000 lumbar spinal fusions
`
`were performed in the USA during 1987, as reported by
`
`the American Hospital Association. There are may
`methods for intervertebral fusion.
`The most
`successful have achieved a success rate of about 90%
`
`in random cases. However, several of these
`
`techniques, especially those requiring complex
`appliances, are difficult to master and are hazardous
`to nerve and vessel structures normally lying close to
`
`the involved bones.
`
`25
`
`30
`
`
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`WO 91/06261
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`PCT/US90/05318
`
`From a biomechanical point of view,
`
`the most
`
`important location of a spinal fusion is at the
`
`mechanical center of rotation between the vertebrae.
`
`This point is centered within the dise space.
`
`Therefore, an interbody fusion is the most rigid and
`
`thus the most sought after method among surgeons.
`
`Current methods of interbody fusions are, however,
`
`the
`
`most hazardous of all spinal fusion methods.
`
`Both anterior (transabdominal) and posterior
`
`surgical approaches are used for interbody fusions.
`Typically, a plug, dowel or segment of bone is driven
`tightly into a cavity carved inside the interbody,
`intradiscal space.
`Since there must be a bone-to-
`
`bone bridge created during the fusion process,
`connective tissue and discal tissue must be removed.
`
`Deep cuts within the bone must penetrate into the
`
`softer, cancellous region to promote bone growth
`
`across the space.
`
`Intervertebral fusions using circular bone
`grafts have been reported in the orthopedic and
`neurosurgical literature for some years. B.R.
`Wiltberger in a paper published in Clinical
`
`Orthopedics, Vol 35, pp 69-79, 1964, reviewed various
`
`methods of intervertebral body fusion using posterior
`bone dowels driven firmly into a suitably smaller hole
`
`_between the adjacent vertebrae. Upon doing so the
`dowel can split or crack or collapse.
`The stretched
`
`bone might also split and it can be compressed by the
`
`dowel to the point that it will not grow normally due
`
`to collapse of formerly open pores or vascular
`
`channels.
`
`If this occurs,
`
`there may be a late
`
`absorption of surrounding bone and the dowel might
`
`10
`
`15
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`20
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`25
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`30
`
`
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`WO 91/06261
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`PCT/US90/05318
`
`See also
`loosen, with a renewed danger of expulsion.
`a 2~page brochure from Neurological Survey Associates
`of Cincinnati,
`Inc. entitled "Posterior Lumbar
`Interbody Fusion Made Simple" which shows, after the
`bone dowel placement,
`the "(a)pplication of 5 mm
`dacron suture around spinous processes."
`
`U.S. Patent 4,501,269 (Bagby) describes a
`surgical procedure for stabilizing the cervical spine
`of a horse and says that the procedure:
`"is applicable to any human or animal joint formed
`by opposed contiguous bony surfaces which are
`covered and separated by intervening cartilage and
`are surraunded by ligaments which resist expansion
`of the joint. Specific examples of such joints
`are a spinal joint between adjacent vertebrae or
`the ankle joint.
`The process was developed to
`immediately stabilize the joint and to further
`promote ultimate bone-to-bone fusion....
`The
`implanted structure is in the form of a perforated
`cylindrical bone basket which can be filled with
`bone fragments produced during the preparation of
`the joint. These bone fragments provide
`autogenous tissue to promote bone growth through
`the basket, as well as around it.
`"The process involves the initial steps of
`surgically accessing the joint and removing
`intervening cartilage located between the
`
`A transverse
`contiguous bony surfaces.
`cylindrical opening is then bored across the
`contiguous bony surfaces.
`Immediate stabilization
`is achieved by driving into the cylindrical
`opening a hollow basket having a rigid perforated
`
`10
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`20
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`
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`WO 91/06261
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`PCT/US90/05318
`
`cylindrical wall whose outside diameter is
`slightly greater than the inside diameter of the
`cylindrical opening.
`The implanting of the basket
`
`spreads the bony surfaces apart in opposition to
`
`the resistance to expansion of the joint provided
`
`by the surrounding ligaments" (col. 2,
`
`lines 26-
`
`55).
`
`U.S. Pat. No. 2,537,070 (Longfellow)
`
`shows in
`
`10
`
`2 a "reinforce 7" that is much like Bagby’s
`Fig.
`fusion basket.
`
`Vich, J. Neurosurg., Vol 63, pp 750-753
`
`(1983) describes a means for cervical spine fusion,
`
`using an anterior approach, by surgically implanting a
`
`cylindrical bone graft.
`
`15
`
`"Screw threads are placed in the graft with a
`
`small, previously sterilized die.
`
`The grooves of
`
`the thread can be made as deep as required.
`
`The
`
`vertical cervical bodies are prepared according to
`
`‘Cloward’s technique. After a cylindrical bed has
`
`20
`
`been drilled in the appropriate intervertebral
`
`bodies,
`
`the graft is screwed into place with
`
`instruments especially developed for this purpose"
`
`(p. 750).
`
`Vich's Fig.
`
`2 legend points out that a threaded graft
`
`25
`
`dowel has a larger contact surface than a plain dowel
`
`and a greater resistance to pressure and sliding.
`
`Vich also says:
`
`"When grafts with a diameter of 14 mm were used,
`
`30
`
`we sometimes threaded the receiving bed with a
`die-stock of 13 mm to facilitate the insertion"
`
`(p. 751).
`
`
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`WO 91/06261
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`PCT/US90/05318
`
`An additional desirable effect of an
`
`intervertebral fusion is the restoration or
`
`maintenance of a normal intervertebral spacing.
`
`Spreading devices are generally required in order to
`
`restore all or a part of the normal intradiscal
`height,
`in the process of placing the fusion material
`or appliance. When the procedure is performed using
`
`the commonly employed posterior approach, a variety of
`
`spreaders may be placed between various posterior bony
`
`10
`
`elements normally attached to the vertebrae, such as,
`dorsal spinous processes or laminas. Using such
`spreaders, a forward tiit or wedging of the discal
`
`Space occurs,;-with the posterior aspect of the space
`
`becoming more open than the anterior. When a bone
`
`i5
`
`graft of any shape is driven into a cavity that is
`
`wedged more open posteriorly between two opposing
`
`movable vertebrae,
`
`there is a strong propensity for
`
`the graft to be retropulsed during the postoperative
`
`recovery period as a result of to and fro movement
`
`20
`
`between the opposing vertebrae. Thus,
`
`to aid in the
`
`“prevention of graft expulsion, it would be desirable
`
`to have the cavity either maintain parallelism or be
`
`slightly narrower at its most posterior portion.
`
`Ventral to this cavity,
`
`the stout ligamentous disc
`
`25
`
`annulus remains and prevents ventral migration of the
`
`graft into the retroperitoneal space. Further,
`
`there
`
`is value in restoring the original spinal lordotic
`
`curve, as the fusion grows; this requires that the
`
`cavity and the interbody fusion element be placed to
`
`30
`
`promote a normal spinal anatomical position, that is,
`
`without wedging of the space in either direction.
`
`
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`WO 91/06261
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`PCT/US90/05318
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`In U.S. Pat. No. 4,743,256 (Brantigan) pairs
`
`of plugs are implanted as struts spanning and
`
`maintaining the disc space between adjacent vertebrae.
`
`While bone plugs were previously used in the same way,
`
`Brantigan employs “rigid plugs of structural material
`
`having porous surfaces to facilitate ingrowth of hone
`
`tissue" (col. 2,
`
`lines 66-68),
`
`inserting these into
`
`"grooves bridging the cancellous bone of one vertebral
`
`body to the cancellous bone of the subjacent vertebral
`
`10
`
`body ..." (col. 2,
`
`lines 1-6).
`
`"The plugs are
`
`preferably made of an inert metal substrate such as
`
`stainless steel ... having a porous coating of metal
`
`particles ..— (col. 3,
`
`lines 8-14).
`
`The plug of Fig.
`
`12 "has bone piercing tangs or points 31"
`
`(col. 5,
`
`15
`
`line 61).
`
`SUMMARY OF THE INVENTION
`
`The present invention provides a method for
`
`implanting a fusion cage in order to fuse adjacent
`
`20
`
`bony structures, which method is safer, surer, easier
`
`and faster as compared to the implantation of bone
`
`dowels or Brantigan’s rigid plug or Bagby’s fusion
`
`basket or Longfellow’s "reinforce." Briefly,
`
`the
`
`novel implantation method involves the following
`
`25
`
`steps:
`
`(a)
`
`forming between said bony structures a
`
`lateral bore with a female thread that penetrates
`
`into their cancellous regions,
`
`(b)
`
`forming a hollow cylindrical fusion cage
`
`30
`
`to have a: external, substantially continuous
`
`helical th. sad (preferably a V-thread) that is
`
`
`
`WO 91/0626]
`
`PCT/US90/05318
`
`perforated in the valley between adjacent turns
`and can mate with said female thread,
`
`(ec)
`
`serewing the cage into said thread bore,
`
`and
`
`(ad)
`substance.
`
`packing the cage with bone-inducing
`
`10
`
`15
`
`The female thread formed in step (a)
`
`preferably is tapped by hand, using a slow motion to
`ensure against burning the bone. This freshens the
`bone margins of the bore so that if any bone had been
`burned by drilling to form the bore, it is now cut
`away slowly by hand.
`The tapping process is quite
`safe,
`in that the surgeon can feel the progress of the
`
`technique.
`
`The V-thread or other male-thread fusion cage
`
`preferably is screwed by hand into the threaded bore,
`again permitting the surgeon to feel if the resistance
`is too great and that rethreading of the bore might be
`
`required.
`
`In contrast, a bone dowel typically is
`
`20
`
`driven into a bore using a hammer, and in order to
`
`guard against an overly tight fit, the surgeon listens
`
`to the sound of the striking hammer and also monitors
`
`the degree of resistance.
`
`Parent U.S. patent application S.N.
`
`25
`
`07/259,031 indicates that the V-thread fusion cage
`
`preferably is made of implantable-grade stainless
`
`steel and that titanium is also useful. Currently,
`
`titanium is preferred, it having been shown to be more
`
`compatible to bone.
`
`30
`
`Parent U.S. patent application S.N.
`
`07/259,031 also teaches that the V-thread fusion cage
`
`preferably is fitted with end caps.
`
`The end caps
`
`
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`WO 91/06261
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`PCT/US90/05318
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`preferably are X-ray transparent to permit post-
`operative checks on the status of the developing bone.
`X-ray transparent end caps can be stamped from a
`
`flexible sheet of thermoplastic resin such as "Delrin"
`
`acetal resin or polypropylene and may have a small
`
`opening for an instrument by which they can be put
`
`into place.
`
`A threaded bore into which a hollow
`
`cylindrical fusion cage can be surgically implanted to
`
`10
`
`fuse adjacent bony structures can be prepared by the
`
`steps of:
`
`(a) drilling a pilot hole laterally between
`
`said bone structures,
`(b)
`inserting a pilot rod into the pilot
`
`15
`
`hole,
`
`rod,
`
`(ec)
`
`fitting a hollow drill over the pilot
`
`20
`
`25
`
`30
`
`(ad) with the hollow drill, enlarging the
`
`pilot hole to form a bore that penetrates into the
`
`cortical bone of each of said bony structures, and
`
`(e)
`
`tapping a female thread into the wall of
`
`said bore with the crown of the thread penetrating
`
`into the cancellous portion of each of said bony
`
`structures.
`
`When using a male-thread fusion cage between
`
`adjacent vertebrae to promote bone ingrowth,
`
`the
`
`fusion cage should be implanted in pairs on opposite
`
`sides of the disc space. After placement of the first
`
`cage,
`
`there is an impressive,
`
`instant stabilization of
`
`the previously unstable vertebral segment.
`
`The second
`
`cage is then screwed into its tapped hole,
`
`thus
`
`rendering the space completely immobile.
`
`Each cage is
`
`
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`WO 91/06261
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`.
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`PCT/US90/05318
`
`held in place by its male-thread, biting into female
`threads that were formed in step (e). Gravity, muscle
`pull and elastic recoil of the spread (or stretched)
`outer disc annulus together exert force against each
`of the fusion cages.
`Thus the fusion cages are held
`in place by compression forces between the adjacent
`vertebrae.
`
`Because the cancellous bone of the vertebral
`
`bodies has internal strength similar to wet balsa wood
`and a hard shell similar to about a 1.5 mm veneer of
`
`white oak, it is difficult to drill parallel bores
`without the drill bits wandering into a common center,
`unless a drill guide or jig is provided. This problem
`is met by the following method of forming and
`threading a bore between adjacent vertebrae, which
`method involves the following steps:
`(a)
`cutting away ligaments to expose the
`
`site,
`
`(b)
`(c)
`
`spreading the vertebrae apart,
`nibbling away as much of each lamina as
`
`is necessary to access the site,
`
`{d) drilling a pilot hole laterally between
`said vertebrae, each of sufficiently small
`
`diameter to be self-seeking of the center of the
`
`disc space,
`(e)
`inserting a pilot rod into the pilot
`
`hole,
`
`.
`sliding over the pilot rod a hollow
`(f)
`lamina drill to cut the spinous process and to
`
`10
`
`15
`
`20
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`25
`
`30
`
`score the lamina,
`
`(g) drilling to remove the lamina within the
`
`score,
`
`
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`WO91/06261
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`PCT/US90/05318
`
`fitting into the resulting arcuate
`(h)
`opening in the lamina a C-retractor which has a
`split cylindrical sleeve of the same diameter as
`the lamina drill, a handle extending from one end
`
`toward the upper end of the spine, and spikes at
`
`its outer end,
`
`(i)
`
`forcing at least one of the spikes into
`
`each of said adjacent vertebrae to anchor the C-
`
`retractor,
`
`(j)
`
`rveinserting the pilot rod to rest on the
`
`bottom of the pilot hole,
`(k)
`sliding a hollow vertebral drill over
`the pilot rod and inside the sleeve of the C-
`
`retractor,
`
`(1)
`
`forming with the hollow drill a bore
`
`that penetrates into the cortical bone of each of
`
`said vertebrae,
`
`(m)
`
`removing the hollow drill, the pilot
`
`rod, and the cut bone, and
`
`using the C-retractor as a guide,
`(n)
`tapping a female thread,
`the crown of which
`extends into the cancellous bone of each of the
`
`vertebrae.
`
`10
`
`15
`
`20
`
`As indicated in the drawing, said pilot rod and
`
`25
`
`the shafts of said hollow lamina drill and tap having
`
`markings to show the depths to which they penetrate
`
`into the bore.
`
`When male-thread fusion cages are to be
`
`the sides that
`positioned between adjacent vertebrae,
`are to face laterally preferably are closed to prevent
`
`30
`
`dise tissue from growing into the cages, because this
`
`could interfere with bone growth between the
`
`
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`WO 91/06261
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`PCT/US90/05318
`
`the
`By leaving the lateral sides closed,
`vertebrae.
`fusion cages have greater structural strength,
`thus
`permitting the perforations adjacent the vertebrae to
`be larger. When leaving the lateral quadrants closed,
`we have achieved 70% perforation of the area of the
`
`top and bottom quadrants (as projected onto the inner
`
`face of a cylinder) while maintaining good compressive
`
`strength.
`
`End caps can help to prevent dise tissue from
`
`growing into the cages, and for this reason, any
`openings in the end caps should be small.
`A large majority of patients requiring
`
`intervertebral fusions have narrowing of the disc
`
`space, typically 10 mm or less in the lower back.
`
`Because minimal penetration into the end piates of the
`
`vertebrae is required (about 3mm for each),
`
`three
`
`major diameters of the fusion cage thread should
`
`suffice for most patients, namely, 14, 16 and 18 mm.
`Because the anterior-posterior dimension of a typical
`lower lumbar vertebra is about 30 mm,
`the length of
`
`the fusion cage preferably does not exceed 25 mm but
`
`is at least 20 mm in length to give sufficient contact
`
`as well as a good platform when implanted in pairs.
`
`A novel interbody spreader in the form of a
`
`scissors jack has been developed to maintain a
`
`desirable parallel attitude between the adjacent
`
`vertebrae while the bore is drilled and then tapped by
`
`a novel instrument.
`
`Other instruments that have been developed
`
`10
`
`15
`
`20
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`25
`
`30
`
`for use in the implantation of the novel fusion cage
`
`include tapping instruments for forming helical
`
`ed
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`WO 91/06261
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`PCT/US90/03318
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`threads in a bore in recipient bone.
`
`A first novel
`
`tapping instrument comprises
`
`a hollow cylindrical shaft having a handle at
`
`one end and an external thread which is formed at
`
`the other end with at least one scallop that
`
`exposes a cutting edge, and
`
`a pilot rod that slideably fits into said
`
`bore, projects beyond said other end of the hollow
`
`shaft, and is formed with a central recess that
`
`communicates with the scallop in the hollow shaft
`
`and provides a reservoir for detritus removed by
`said cutting edge,
`thus permitting the detritus to
`be carried away by removing the pilot rod from the
`hollow shaft.
`
`The portion of the pilot rod that: projects beyond said
`other end of the hollow shaft preferably is threaded
`to carry detritus upwardly to the reservoir.
`
`When using this first novel tapping
`instrument to form female threads for an interbody
`fusion,
`the hollow shaft should have an odd number of
`
`scallops and cutting edges, preferably three, because
`an odd number provides more equal removal of recipient
`bone on both sides of the bore than would an even
`
`number.
`
`Said first novel tapping instrument and a
`
`together
`novel wrench are illustrated in the drawing,
`with other instruments that can be used to implant
`male-thread fusion cages surgically.
`
`In the drawing, all figures of which are
`
`WIN
`
`schematic,
`
`10
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`15
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`20
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`25
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`30
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`WO 91/06261
`
`PCT/US90/05318
`
`1 is an exploded isometric view of a first
`Fig.
`V-thread fusion cage of the parent U.S. Patent
`Application S.N. 07/259,031 and two perforated end
`
`caps;
`2 is an isometric view illustrating the
`Fig.
`formation of a body that can be cut to form a series
`
`of second V-thread fusion cages of said U.S. Patent
`
`Application S.N. 07/259,031;
`Fig.
`3 is an isometric view of a first tapping
`instrument (partly cut away to reveal details of
`
`construction) for forming female threads in bores into
`
`which male-thread fusion cage is to be inserted;
`
`Fig. 4 is an isometric view of a wrench for
`screwing a male-thread fusion cage into a threaded
`bore;
`Fig.
`
`5 is an exploded isometric view of a third
`
`male-thread fusion cage of said U.S. Patent
`
`Application S.N. 07/259,031;
`
`10
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`15
`
`Fig.
`
`6 is a plan view of a pilot drill that can be
`
`20
`
`used in preparation for forming a threaded bore
`
`laterally between two vertebrae into which a male-
`
`thread fusion cage can be surgically implanted;
`Fig.
`7 is a plan view of a pilot rod that also can
`be used in preparation for forming said threaded bore;
`
`Fig.
`
`8 is a plan view of a hollow lamina drill
`
`that can be used in conjunction with the pilot rod of
`
`Fig. 7;
`
`Fig.
`
`9 is an isometric view showing the use of a
`
`C-retractor in preparation for the surgical
`
`implantation of a pair of male-thread fusion cages
`
`between two vertebrae;
`
`25
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`30
`
`o
`
`
`
`WO 91/06261
`
`PCT/US90/05318
`
`Fig.
`10 is a plan view of a hollow vertebral
`drill that also can be used with the pilot rod of Fig.
`7; and
`
`11 is a plan view of a second tapping
`Fig.
`instrument that can be used in conjunction with the C-
`retractor of Fig.
`9 to tap a female thread in the bore
`formed by the hollow vertebral drill of Fig. 10.
`
`DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
`
`1 was formed from
`The fusion cage 10 of Fig.
`a solid steel cylinder by drilling eight small,
`equally space holes i1 in the axial direction, each
`hold being centered on a circle concentric with the
`axis of the cylinder.
`Then a large hole was drilled
`centered on the axis and having a radius substantially
`identical to that of the aforementioned circle.
`A
`
`V-thread 12 was then machined in the external surface
`of the cylinder,
`thus opening through that surface a
`perforation 13 extending through the rounded valley 14
`of the V-thread at each crossing of the valley and one
`of the small holes 11.
`A screw thread 15 was then
`machined in the internal surface of the fusion cage to
`threadably receive an end cap 16 that has apertures i8
`similar to those of a salt shaker.
`Snap-on end caps
`would also be useful.
`
`In making a fusion cage by the technique
`described in the preceding paragraph,
`the small holes
`11 could be enlarged to intersect each other,
`thus
`making it unnecessary to drill a central hole.
`Enlarged small holes would result in larger
`perforations 13.
`
`10
`
`15
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`20
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`25
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`30
`
`
`
`WO 91/06261
`
`PCT/US96/05318
`
`Referring to Fig. 2, a series of fusion cages
`can be made from a plurality of rods 22 of rectangular
`
`ey
`
`cross-section that can be continuously extruded and
`
`fed into each of eight keyways 23 in the surface of a
`mandrel 24. Simultaneously, a rod 26 of triangular
`
`cross-section is extruded, wrapped helically around
`
`the rectangular rods 22, and soldered or welded to
`each of the rectangular rods 22 at every crossing to
`
`provide an external V-thread. Upon emerging from the
`keyways,
`the resulting body is cut into individual
`fusion cages each of which has perforation 28 between
`adjacent turns of the V-thread-forming rod 26 wherever
`it bridges a gap between adjacent rectangular rods 22.
`A fusion cage identical to that of Fig.
`2 can
`be made from a hollow cylinder by machining an
`
`external V-thread and broaching a plurality of
`
`rectangular internal keyways.
`
`Each of the fusion cages in Figs.
`
`1 and 2
`
`could be made from a model by the lost wax process.
`
`3 has a
`The tapping instrument 30 of Fig.
`hollow cylindrical shaft 31 with a T-handle 32 at one
`end and an external thread 33 at the other end.
`
`Slidably received within the hollow shaft is a pilot
`
`rod 34, one end 35 of which protrudes beyond the
`
`10
`
`15
`
`20
`
`25
`
`hollow shaft 31 and slidably fits into a bore that has
`
`been drilled into the recipient bone. At the other
`
`end of the pilot rod is a knurled cap 35A. Projecting
`
`from the threaded end of the hollow shaft 31 are
`
`30
`
`cutting teeth 36 that enlarge the bore to the minor
`diameter of the external thread 33 of the hollow shaft
`
`31.
`
`The threaded end of the hollow shaft also is
`
`formed with three symmetrical scallops 37 (one shown)
`
`
`
`WO 91/06261
`
`PCT/US90/05318
`
`to expose a cutting edge 38 at the leading edge of the
`external thread 33, which cutting edge forms female
`bone threads.
`
`Detritus created by tapping instrument 30 is
`deposited through the scallons 37 into a reservoir
`
`provided by a central recess 39 in the pilot rod 34.
`The end 35 of the pilot rod which extends from the
`
`recess 39 into the bore has external threads which,
`when the threaded pilot rod 34 is turned, carry
`detritus upwardly to be deposited through the scallops
`into the reservoir.
`
`Upon rotating the hollow shaft 31 to form
`female bone threads in the bore,
`the surgeon can feel
`inereased back pressure when the reservoir becomes
`full and should grasp the knurled cap 35A to remove
`and clean out the pilot rod.
`If the gummy nature of
`the detritus were to prevent the pilot rod from being
`easily pulled out of the hollow shaft,
`the knurled cap
`35A could be removed to permit the hollow shaft 31 to
`be unscrewed from the threaded bore,
`leaving the pilot
`rod in place.
`The pilot rod then serves as a guide if
`the bore has not yet been completely tapped and it is
`necessary to reinsert the hollow shaft to compete the
`tapping.
`
`4 has a cylindrical
`The wrench 40 of Fig.
`shaft 41 with a T-handle 42 at one end and an
`
`octagonal protuberance 44 at the other end.
`
`The
`
`corners of the protuberance 44 fit into recesses in
`the fusion cage to permit the fusion cage to be
`rotated by rotating the wrench.
`A spring-loaded bail
`46 frictionally holds the p: stuberance in piace when
`it is inserted into the fusion cage.
`
`10
`
`15
`
`20
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`25
`
`30
`
`
`
`WO 91/06261
`
`PCT/US90/05318
`
`Fig.
`
`5 shows a third male-thread fusion cage
`
`50 that has formed from a solid steel cylinder by
`
`drilling an axial bore 51 and then broaching out a
`pair of cylindrical channels 52 that extend to a
`
`diameter only a little smalier than the external
`
`surface of said cylinder.
`
`A V-thread 53 has then been
`
`machined in that external surface,
`
`thus creating
`
`perforations 54 in the valley between adjacent turns
`
`of the thread, each perforation extending completely
`across one of the channels 52. Each end of each land
`
`between the channels has been machined to have a
`
`recess 56 to enable an end cap 57 to fit flush with
`
`the end of the fusion cage. At each recess 56, each
`
`land has been formed with a small bore 58 into which
`
`one of a pair of projections 59 from the end cap 57
`
`fits snugly to hold the end cap in place.
`
`In Fig. 6, a pilot drill 60 has a T-handle 62
`
`at one end of a shaft 63 and at the other end a collar
`
`10
`
`15
`
`64 holding a bit 66.
`
`A set screw 68 in the collar
`
`20
`
`permits the protruding length of the bit to be
`
`adjusted, and the larger diameter of the collar acts
`
`as a stop. Typically,
`the collar 64.
`
`the bit 66 extends 25 mm beyond
`
`In Fig. 7, a pilot rod 70 has a cylindrical
`
`shaft 71, at one end of which is a cylindrical boss 72
`
`that is 30 mm in length and slidably fits into a bore
`
`formed by the pilot drill 110 of Fig. 11.
`
`The boss 72
`
`has two scribe marks 73 that indicate the depth in cm
`
`of the bore. At its other end,
`
`the shaft 71 is formed
`
`with a flat 75 that has scribe marks 76 marked to
`indicate 0, 1,
`2 and 3 cm for purposes explained
`below.
`
`25
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`30
`
`On
`
`
`
`WO 91/06261
`
`PCT/US90/05318
`
`- 19 -
`
`Shown in Fig.
`
`8 is a hollow lamina drill 80
`
`which has a cutting edge 82 and a central bore 83 that
`
`Slidably fits over the shaft 71 of the pilot rod 70.
`
`An anodized aluminum handle 84 permits a surgeon to
`
`drive the lamina drill by hand.
`
`Shown in Fig.
`
`9 is a C-retractor 90 which has
`
`a cylindrical sleeve 91 that is formed with an opening
`92 across about one-fourth of its circumference over
`
`-its full length. Extending from one end of the sleeve
`
`10
`
`opposite to said opening 92 is a malleable handle 93
`
`by which the cylindrical sleeve 91 can be fitted
`
`through the arcuate laminotomy (formed by the lamina
`
`drill 80) down to the vertebrae 94 and 95. At the
`
`other end of the sleeve 91 are four spikes 96 in two
`
`15
`
`pairs, one pair on either side of a line that is 180°
`
`20
`
`25
`
`from the center of said opening 92. When the sleeve
`
`of the C-retractor 90 is concentric with a pilot bore
`that has been drilled laterally into the disc 97
`
`between the two vertebrae 94 and 95, one pair of the
`
`spikes can be set into the dorsal surfaces of each
`
`vertebra after careful orientation to be concentric
`
`with the pilot rod 70 while it is seated in the pilot
`bore. As also shown in Fig. 9, one purpose of the
`
`sleeve 91 of the C-retractor 90 is to keep tools from
`
`contacting the dura 98 and the spinal nerve 99.
`
`Shown in Fig.
`
`10 is a hollow vertebral drill
`
`100,
`
`the shaft 101 of which is formed with a central
`
`bore (not shown)
`
`that slidably fits over the shaft 71
`
`of the pilot rod 70 while the C-retractor 90 is in
`
`30
`
`place. At one end of the hollow drill are scalloped
`
`cutting edges 105, and at the other is a hard rubber
`
`handle 103 that permits a surgeon to drive the
`
`
`
`.
`
`;
`
`WO 91/06261
`
`PCT/US90/05318
`
`- 20 -
`
`vertebral drill by hand. Scribe marks 107 indicate 0,
`
`1,
`
`2 and 3 cm.
`
`The O mark is at the top of the
`
`cylindrical sleeve 91 of the C-retractor when the
`
`vertebral drill is first put into place, and it and
`
`the other marks sequentially disappear behind the
`cylindrical sleeve as the vertebral drilling
`progresses. At the same time the scribe marks 76 on
`the flat 75 of the shaft 71 of the pilot rod 70,
`
`appear behind the handle 103 of the vertebral drill.
`While the surgeon watches the disappearance of the
`scribe marks 107
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