United States Patent
`
`[19]
`
`[11] Patent Number:
`
`5,306,309
`
`Apr. 26, 1994
`[45] Date of Patent:
`Wagner et al.
`
`|lllllllllllllHIIllllIllllllllllllllIlllllllllllllllllllllllllllllllllllll
`USOOS306309A
`
`[54] SPINAL DISK IMPLANT AND
`IMPLANTATION KIT
`
`[75]
`
`Inventors: William R. Wagner; Richard L.
`Lariviere, both of Escondido; Scott
`D. Slabbekoorn, Vista, all of Calif.
`
`[73] Assignee: Calcitek, Inc., Carlsbad, Calif.
`
`[21] Appl. No.: 878,196
`
`[22] Filed:
`
`May 4, 1992
`
`[51]
`Int. c1.5 ................................................ A61F 2/44
`
`[52] US. Cl. ..................... 623/17; 606/61
`[58] Field of Search ...................... 623/17, 16; 606/53,
`606/60, 61
`
`[56]
`
`References Cited
`U.S. PATENT DOCUMENTS
`
`5/1954 Knowles ............................... 623/17
`2677,3629
`3,848,601 11/1974 Ma et al.
`.
`.. 128/305
`4,309,777
`1/1982 Patil
`...............
`623/17
`4,349,921
`9/1982 Kuntz .................
`.. 623/17
`623/17
`4,714,469 12/1987 Kenna .....
`.. 623/17
`4.743.256
`5/1988 Brantigan
`623/17
`4,743,256
`5/1988 Brantigan ...............
`4,759.766
`7/1988 Buettner-Janz et a1.
`623/17
`4,759,769
`7/1988 Hedman et a1.
`.......
`623/17
`4,772,287
`9/1988 Ray et al.
`.............................. 623/17
`(List continued on next page.)
`
`
`
`..
`..
`
`FOREIGN PATENT DOCUMENTS
`
`89/02791
`9000037
`90/002319
`
`.
`1/1990 .PCTInt‘l Appl.
`1/1990 PCT 1m‘1 Appl..
`5/1991 PCT Int‘l Appl..
`
`. OTHER PUBLICATIONS
`
`John Frymoyer et a1., “The Adult Spine", Raven Press.
`pp. 1167—1170 (1991).
`T. Koyama et a1., “Porous Hydroxyapatite Ceramics
`for Use in Neurosurgical Practice”, Surg. Neurol, vol.
`25, pp. 71—73 (1986).
`Stephen D. Cook et a1., “Evaluation of Hydroxylapatite
`Graft Materials in Canine Cervical Spine Fusions",
`Spine, vol. 11, No. 4, pp. 305—309 (1986).
`Howard Senter et al., “Anterior Cervical Discectomy
`
`with Hydroxylapatite Fusion", Neurosurgery. vol. 25,
`No. 1, pp. 39-43 (1989).
`G. Lozes et a1., “Discectomies of the Lower Cervical
`Spine Using Interbody Biopolymer (B.O.P.) Implants",
`Acm Neurochirurgica, vol. 96, pp. 88-93 (1989).
`M. Jarcho, “Calcium Phosphate Ceramics as Hard Tis-
`sue Prosthetics”, Clinical Orthopaedics, vol. 157, pp.
`259—278 (1981).
`M. Jarcho, “Biomaterial Aspects of Calcium Phos-
`phates", Dental Cline: of North America, vol. 30, No. 1,
`pp. 25-47 (1986).
`M. Block et al., “Loaded Hydroxylapatite Coated and
`Grit—Blasted Titanium Dental Implants in Dogs”, Int'l.
`(List continued on next page.)
`
`Primary Examiner—Randall L. Green
`Assistant ExaminermDinh X. Nguyen
`Attorney. Agent, or Firm—Gregory Garmong; Donald
`R. Greene; Saul Leitner
`
`[57]
`
`ABSTRACT
`
`A spinal disk implant comprises a solid body having
`four faces arranged to define a right-rectangular solid
`body and two faces that define the ends of the solid
`body. The faces that define the right-rectangular body
`include two opposed side faces and two opposed trans-
`verse faces. The transverse faces have a central region
`with three-dimensional features thereon and an anterior
`platform region lying along an anterior margin of the
`transverse faces. The faces defining the ends of the solid
`body include a convexly curved anterior face and a
`posterior face. The solid body is made of a biocompati-
`ble synthetic material. A kit that may be used by a sur-
`geon includes an implant and an implant delivery tool
`dimensioned to releasably hold the implant. The deliv-
`ery tool preferably has a pair of flexible opposed arms
`extending from a base, separated so that the implant can
`fit between the arms, and may have a breakable release
`band extending around the implant to hold it in place
`until a weak link in the release band is intentionally
`broken during implantation.
`
`33 Claims, 3 Drawing Sheets
`
`
`
`NUVASIVE 1009
`
`1
`
`

`

`Page 2
`_____—___—_______________——____..____—_—-—
`
`5,306,309
`
`U.S. PATENT DOCUMENTS
`
`OTHER PUBLICATIONS
`
`5/1989 Brantigan .............................. 623/17
`4,834,757
`4,863,476 9/1989 Shepperd .
`.. 623/17
`
`4’863’477
`9/1989 Monso“
`“ 63/”
`.. 623/17
`4,874,389 10/1989 Downey
`-
`
`.. 623/17
`4,878,915 11/1989 Brantlgan .....
`_____
`.. 623/17
`4,904,260 2/1990 Ray C, a1.
`.. 623/17
`4,904,261
`2/1990 Dove et a1.
`..
`4,911,718
`3/1990 Lee et a1.
`.....
`.. 623/ 17
`4,917,704 4/1990 Frey et al.
`., 623/ 17
`4,932,969 6/1990 Frey et 31-
`623/17
`
`""" 623/17
`4332375 6/1990 Mam 6‘ a"
`4,936,848 6/1990 Bagby ..............
`623/17
`
`~
`.. 623/17
`4,946,378
`8/1990 erayama et a1.
`
`9/1990 Frey etal. .......
`4,955,908
`623/17
`4,997,432
`5/1991 Keller ...........
`623/17
`5/1991 Fuhrman et a1.
`.. 623/17
`5,002,576
`
`5/1991 Michelson ............................. 606/61
`5,015,247
`
`
`
`Implants, vol. 4(3), pp. 219—225
`
`1 Oral Maxi/[ofac,
`(1989).
`Stephen D. Cook et al., “Hydroxylapatite—Coated Tita-
`.
`.
`.
`.
`,,
`.
`.
`mum for Orthopedlc Implant Appllcanons , Clmlcal
`2
`,
`Orthopedzcs and Related Research, No. 232, pp. 225— 43
`(1988).
`T. Yamamuro et al., “Replacement of the Lumbar Ver-
`tebrae of Sheep with Ceramic Prostheses”, The Journal
`ofBone and Joint Surgery, vol. 72—B, pp. 889—893 (1990).
`P. Ylinen et al., “Lumbar spine interbody fusion with
`.
`~
`-
`19
`remforced hydroxyapatlte Implants , Arch. Orthop.
`50—256 1991
`T’W’W- SW3" V0" 130’???
`(
`)'
`.
`Marbm Bloom et.al., Anterlor Intervenebral Fu51on of
`the Cerv1ca1 Spme", J. Bone and Jam! Surgery, vol.
`63(5), p. 842 (1981).
`
`2
`
`

`

`US. Patent
`
`Apr. 26, 1994
`
`Sheet 1 of3
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`5,306,309
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`3
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`

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`US. Patent
`
`Apr. 26, 1994
`
`Sheet 2 of 3
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`5,306,309
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`4
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`

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`US. Patent
`
`Apr. 26, 1994
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`Sheet 3 of 3
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`5,306,309
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`
`
`/0/
`
`\
`\
`M
`wk :39
`" ”a
`//z
`W
`02
`//z
`m, ”a
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`/02
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`5
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`

`

`1
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`5,306,309
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`SPINAL DISK IMPLANT AND IMPLANTATION
`KIT
`
`BACKGROUND OF THE INVENTION
`
`5
`
`2
`maintain the space originally occupied by the interver-
`tebral disk. Although there may result some minor loss
`of flexibility in the spine, because of the large number of
`vertebrae, the loss of mobility is usually acceptable.
`During a spinal fusion following a discectomy, an
`implant is inserted into the intervertebral space. This
`intervertebral implant is often a bone graft removed
`from another portion of the patient’s body, termed an
`autograft. The use of bone taken from the patient’s body
`has the important advantage of avoiding rejection of the
`implant, but has some shortcomings. There is always a
`risk in opening a second surgical site for obtaining the
`bone graft, which can lead to infection or pain for the
`patient, and the site of the bone graft is weakened by the
`removal of bony material. The bone implant may not be
`perfectly shaped and placed,
`leading to slippage or
`absorption of the implant, or failure of the implant to
`fuse with the vertebrae.
`’
`Other options for a graft source for the implant are
`bone removed from cadavers, termed an allograft, or
`from another species, termed a xenograft. In these cases,
`while there is the benefit of not having a second surgical
`site as a possible source of infection or pain, there is the
`increased difficulty with graft rejection and the risk of
`transmitting communicable diseases.
`An alternative approach to using a bone graft is to use
`a manufactured implant made of a synthetic material
`that is biologically compatible with the body and the
`vertebrae. Several compositions and geometries of such
`implants have been utilized, ranging from simple blocks
`of material to carefully shaped implants, with varying
`success. No fully satisfactory implant has been reported.
`In some instances,
`the implanting surgery is readily
`accomplished, but the results are unsatisfactory due to
`side effects or dislocation of the implant. In other in-
`stances, the implant requires a complex surgical proce-
`dure that is difficult to perform and still may not lead to
`correction of the problem for the reasons indicated.
`There is therefore a need for an improved Spinal disk
`implant, which is both readily utilized In a surgical
`procedure and has a high probability of success without
`undesirable side effects. The present invention fulfills
`this need, and further provides related advantages.
`SUMMARY OF THE INVENTION
`
`50
`
`55
`
`60
`
`The present invention provides a readily manufac-
`tured and implanted spinal disk implant. The disk im—
`plant is configured to engage the cortical bone region of
`the vertebrae after implantation, so that the majority of
`the loading transmitted through the implant is carried
`by the cortical bone. Since the cortical bone is harder
`than the cancellous bone region of the vertebrae, it
`is
`less likely that the spinal column will post-operatively
`compress around the implant. The implant also provides
`structure to improve the engagement between the im-
`plant and the adjacent vertebrae, minimizing the likeli—
`hood that there will be post-operative slippage of the
`implant from its proper intervertebral position. The
`implant is made of an artificial material that can be fully
`sterilized prior to implantation.
`The invention also includes a disk implantation kit
`containing an implant and a delivery tool useful in per-
`forming the intervertebral placement of the implant
`during a surgical procedure. The disk implant may be
`provided in a presterilized, prepackaged form held by
`the delivery tool, which can be used without reposition-
`ing the implant in the tool. The implantation tool carries
`
`'10
`
`15
`
`2O
`
`25
`
`30
`
`35
`
`4O
`
`45
`
`This invention relates to implants surgically placed
`into the human body and the tool used to perform the
`implantation, and, more particularly,
`to an implant
`placed between two vertebrae to fuse them together
`and its implant delivery tool.
`The human spine is composed of a column of 33
`bones, termed vertebrae, and their joining structures.
`The 24 vertebrae nearest the head, collectively termed
`the presaccral vertebrae, are separate bones capable of
`individual movement. The bodies of the presaccral ver-
`tebrae are generally connected by anterior and poste-
`rior longitudinal ligaments and by discs of fibrocarti-
`lage,
`termed intervertebral disks, positioned between
`opposing faces of adjacent vertebral bodies. These mo-
`bile vertebrae may be classified by their position and
`function into either cervical, thoracic, or lumbar verte-
`brae. The remaining 9 vertebrae are fused to form the
`saccrum (5 vertebrae) and the coccyx (4 vertebrae) and
`are incapable of individual movement.
`This column of vertebrae and intervertebral disks
`forms a central axis for supporting the load of the head
`and torso. The vertebral body and the dorsal vertebral
`arch of each of the 24 mobile presaccral vertebrae en-
`close an opening,
`termed the vertebral
`for amen,
`through which the spinal cord, a column of nerve tissue
`which communicates nerve impulses between the brain
`and the rest of the body, and the spinal nerve roots pass
`and are protected from damage.
`The presaccral vertebrae are normally held in a pre:
`cise relation to each other by the intervertebral disks,
`the longitudinal ligaments, and the musculature of the
`body. These vertebrae can move relative to adjacent
`vertebrae in various manners, permitting the head to be
`turned relative to the body and providing a wide range
`of flexibility to the spine. The movement between indi-
`vidual pairs of vertebrae is limited to prevent
`local
`pressure on the spinal cord or excessive bending of the
`spinal cord. Such pressure or bending could possibly
`result in disorders associated with blockage of the nerve
`impulses traveling along the spinal cord, in turn produc—
`ing pain, paresthesia, or loss of motor control which
`must be resolved by removing the causative condition.
`The nerve conduction disorders may also be associ-
`ated with the intervertebral disks or the bones them-
`selves. One such condition is a herniation of the inter-
`vertebral disk, in which a small amount of tissue pro-
`trudes from the sides of the disk into the foramen to
`compress the spinal cord. A second common condition
`involves the development of small bone spurs, termed
`osteophytes, along the posterior surface of the vertebral
`body, again impinging on the spinal cord.
`Upon identification of the abnormality causing the
`conduction disorders, surgery may be required to cor-
`rect the problem if more conservative treatment fails.
`For those problems associated with the formation of
`osteophytes or herniations of the intervertebral disk,
`one such surgical procedure is intervertebral discec-
`tomy. In this procedure, the involved vertebral bodies
`are exposed and the intervertebral disk is removed, thus
`removing the offending tissue, or providing access for
`the removal of the bone osteophytes. A second proce-
`dure, termed a spinal fusion, may then be required to fix
`the vertebral bodies together to prevent movement and
`
`6
`
`

`

`3
`
`5,306,309
`
`5
`
`25
`
`the implant so as to avoid damage to the implant prior
`to and during surgical implantation. The tool also per-
`mits the surgeon to securely hold the implant during
`implantation and to easily place it at the proper loca-
`tion.
`In accordance with the invention. a spinal disk im-
`plant comprises a solid body havlng four faces arranged
`to define a right-rectangular body, including two op-
`posed side faces and two opposed transverse faces. At
`least one of the transverse faces is provided with a cen- 10
`tral region with three-dimensional features thereon and
`an anterior platform region lying along an anterior mar-
`gin of the transverse face. A convexly curved anterior
`face defines one end of the right—rectangular body, and
`a posterior face defines the other end of the right-rec- 15
`tangular body. The solid body is made of a material
`selected from the group consisting of a ceramic, a metal,
`a polymer, and a composite material.
`Stated more formally, the spinal disk implant is a solid
`body made of a biocompatible synthetic material and 20
`has a convexly (outwardly) curved anterior face with a
`curvature of about
`that of the anterior surface of a
`human vertebra. The anterior face has an anterior face
`lateral margin and a curved anterior face transverse
`margin.
`_
`The disk implant also has a posterior face spaced
`apart from the anterior face with a posterior face lateral
`margin and a posterior face transverse margin. The
`posterior face may be flat or convexly curved.
`A pair of generally parallel, spaced apart, opposed 30
`side faces extend between the lateral margins of the
`anterior face and the posterior face.
`A pair of spaced apart, opposed transverse faces ex-
`tend between the transverse margins of the anterior face
`and the posterior face. The transverse faces may be flat 35
`or convexly curved. The transverse faces may be paral—
`lel or angled toward each other. Each transverse face
`has an anterior platform. At least one of the transverse
`faces, and preferably both transverse faces, has an en—
`gagement region located posterior of the anterior plat- 40
`form with three-dimensional
`features thereon. The
`width of the anterior platform is about that of the thick-
`ness of anterior cortical bone of a human vertebra.
`In a preferred form, the implant is made available to
`surgeons in a kit prepackaged with a delivery tool com— 4S
`prising means for holding the implant and then control-
`lably releasing the implant. The delivery tool preferably
`includes a base and a pair of flexible opposed arms ex-
`tending from the base. The arms are spaced and dimen-
`sioned to releasably hold the implant there between. A 50
`release band, preferably (but not necessarily) extending
`between the distal ends of the arms, holds the implant to
`the delivery tool. The release band has a breakable
`weak link, which is readily parted with a slight tug after
`the implant has been properly positioned by the sur- 55
`geon. This configuration of delivery tool avoids the
`need for threaded bores or other types of grasping fea-
`tures on the implant, as these types of features may
`significantly weaken the implant. A delivery tool han-
`dle is also provided so that the tool can be easily manip— 6O
`ulated by the surgeon.
`In the preferred kit form, the delivery tool is made of
`a sterilizable plastic. The kit is provided with the im-
`plant grasped between the arms of the delivery tool, in
`a presterilized package. The implants are provided in a 65
`range of sizes for different size perSOns and different
`locations of the disk to be replaced. The surgeon makes
`a preoperative estimation of the range of sizes most
`
`4
`likely to be required. and delivery tool/implant sets
`spanning this range are prepared for surgery. During
`the implant procedure, the surgeon can select the one
`implant that is most appropriate, and substitute another
`if for some reason, typically incorrect dimensions, the
`first choice is not operable. The surgeon need not mod»
`ify the shape of the implant, but uses it directly from the
`package. The implant is placed into the correct position
`using the delivery tool, the implant is controllably re-
`leased, and the delivery tool is removed and discarded.
`This approach minimizes the time of the operation,
`thereby decreasing the chances of complications for the
`patient.
`The present invention provides an important advance
`in the art of spinal disk implants. The implant itself is
`configured to provide the most reliable and secure load
`path through the reconstructed region, and also to se-
`curely hold its position post—operatively.’ The delivery
`tool encourages the proper placement of the implant
`during surgery, and also aids in achieving orderly func-
`tioning of the operating theater with reduced risk of
`patient complications. Other features and advantages of
`the invention will be apparent from the following more
`detailed description of the preferred embodiments,
`taken in conjunction with the accompanying drawings,
`which illustrate, by way of example, the principles of
`the invention.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 is a side elevational view of the spine;
`FIG. 2 is an enlarged plan view of a cervical vertebra;
`FIG. 3 is a perspective view of a first embodiment of
`a spinal disk implant;
`FIG. 4 is a plan View of the spinal disk implant of
`FIG. 3;
`FIG. 5 is a side elevational View of one form of the
`spinal disk implant of FIG. 3;
`FIG. 6 is a side elevational view of a second form of
`the spinal disk implant of FIG. 3;
`FIG. 7 is a side elevational view ofa third form of the
`spinal disk implant of FIG. 3;
`FIG. 8 is a plan view of a cervical vertebra similar to
`the view of FIG. 2, with the properly positioned spinal
`disk implant of FIG. 3 indicated in phantom lines;
`FIG. 9 is a perspective view of a second embodiment
`of a spinal disk implant;
`FIG. 10 is a plan view of an implant delivery tool
`with the disk implant of FIG. 3;
`FIG. 11 is a plan view of an implant delivery tool
`with the disk implant of FIG. 9;
`FIG. 12 is an elevational view of one form of the
`implant tool of FIG. 10;
`FIG. 13 is an elevational view of another form of the
`implant tool of FIG. 10; and
`FIG. 14 is a plan view of an implant delivery tool of
`FIG. 13 and implant of FIG. 10, with attached handle.
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENTS
`
`FIG. 1 depicts a human spine 20. The spine 20 is
`formed from thirty-three individual vertebrae. 22, with
`the twenty-four uppermost vertebrae in most cases sep-
`arated by intervertebral disks 24. The spine 20 is de-
`scribed as having an anterior side 26 and a posterior side
`28.
`
`FIG. 2 depicts one of the vertebrae, here one of the
`cervical vertebrae 30. (A cervical vertebra has been
`chosen for illustration, but the other vertebra are similar
`
`7
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`

`

`5,306,309
`
`i)-
`
`10
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`15
`
`20
`
`5
`in relevant aspects and differ primarily in details of
`geometry.) The vertebra 30 includes a vertebral body
`region 32, and various processes 34. A cervical disk 36,
`indicated in phantom lines, overlies the vertebral body
`region 32 in the natural condition. A central opening
`through the vertebra 30 is the foramen 38,
`through
`which the spinal cord and the spinal nerve roots pass.
`The vertebral body region 32 includes two distinct
`types of natural bone. A layer of cortical bone is found
`at an outer edge 42 of the vertebral body region 32. The
`cortical bone is a hard, dense type of bone, having high
`strength. A central portion 44 of the vertebral body
`region 32 is made of cancellous bone, which is a more
`resilient, weaker, and less dense type of bone.
`A spinal disk implant 50, shown in FIGS. 3—7 in sev-
`eral variations, has a structure designed for implantation
`between the vertebral body regions of two adjacent
`vertebrae 22. This spinal disk implant 50 is readily in-
`serted between the vertebrae during a surgical proce-
`dure, produces a load-bearing joint in which the major-
`ity of the load on the spine 20 is borne through the
`cortical bone, and is highly resistant to dislocation away
`from its proper position between the vertebrae.
`Referring to FIGS. 3—5, the spinal disk implant 50 is
`a solid body having an anterior face 52 and an oppo-
`sitely disposed posterior face 54. The anterior face 52 of
`the implant 50 is convexly curved, to generally match
`the shape of the anterior portion ofthe outer edge 42 of
`the vertebra 22 (FIG. 2). As discussed herein, several
`features of the implant are configured to be approxi-
`mately the same shape or dimension as features of the
`vertebrae. It is recognized that different persons and
`different vertebrae have differing shapes and dimen-
`sions, and the implant features are selected to be close,
`but not necessarily exact, matches for those shapes and
`dimensions. As discussed subsequently, the implant may
`be made available to surgeons in a range of sizes to
`accommodate extremes and normal shapes and dimen—
`sions that are encountered in different persons.
`The anterior face 52 has an anterior face lateral mar-
`gin 56 and an anterior face transverse margin 58. The
`term “margin” 18 used herein generally in the same
`sense as in the “margin" of a page,
`its edge region.
`Similarly, the posterior face has a posterior face lateral
`margin 60 and a posterior face transverse margin 62.
`A pair of spaced apart, opposed, generally parallel
`side faces 64 and 66 extend between the respective ante-
`rior face lateral margins 56 and the posterior face lateral
`margins 60.
`A pair of spaced apart, transverse faces 68 and 70
`extend between the respective anterior face transverse
`margins 58 and the posterior face transverse margins 62.
`In the embodiment of FIG. 5, the transverse faces 68
`and 70 are parallel to each other, but that 18 not neces-
`sarily the case. Each transverse face (68, 70) has an
`anterior platform 72 thereon. When the implant 50 is
`surgically implanted, the anterior platform 72 with the
`anterior face 52 generally aligned with the anterior side
`26 of the vertebra 22, the anterior platform is in facing
`relationship with the cortical bone region of the verte—
`bra. The anterior platform 72 is therefore made to be
`about the same width as the cortical bone region of the
`vertebra.
`
`6
`3—5, these three-dimensional features are pyramids 76.
`After the implant 50 is implanted between two verte-
`brae 22, as shown in FIG. 8, the pyramidal engagement
`features contact and engage the cancellous bone of the
`vertebrae in the central portion 44 of the vertebrae.
`Since the cancellous bone is softer than the cortical
`bone, the engagement features sink into the cancellous
`bone as load is applied and over time after the patient is
`again carrying weight through the spine. This engage-
`ment prevents the implant 50 from shifting its position
`and moving away from the proper position established
`by the surgeon.
`The implant is made of a ceramic, a metal, a polymer,
`or a composite material. The implant 50 is desirably
`made from a material that, after surgical implantation,
`bonds to the natural bone of the adjacent vertebrae to
`form a rigid structure. The implant is preferably made
`from a ceramic, most preferably the ceramic calcium
`hydroxylapatite, having a chemical
`formula CalO-
`(PO4)6(OH)2. The use of such materials in implants is
`known, see for example US. Pat. No. 4,863,476, whose
`disclosure is incorporated by reference. The implant 50
`may also be made from a composite material such as the
`carbon-fiber reinforced plastics disclosed in US. Pat.
`No. 4,904,261, whose disclosure is incorporated by
`reference. The implant may also be made from a bi-
`ocompatible orthopedic polymer (“BOP"), such as a
`copolymer of methylmethacrylate and N-vinylpyrroli-
`done and calcium gluconate, reinforced with polyamide
`fibers. Such a material is known in the art, and is de-
`scribed. for example, in G. Lozes et al., “Discectomies
`of the Lower Cervical spine Using Interbody Biopoly-
`mer (BOP) Implants”, Acta Neurochir (Wien), vol. 96,
`pages 88—93 (1989). In some instances, the implant may
`be made from an uncoated biocompatible metal, such as
`titanium or a titanium alloy such as Ti-6AI-4V, or a
`nonreactive metal such as gold. The implant may also
`be made from such a metal coated with a layer of ce-
`ramic or a porous metal coating of sintered beads, mesh,
`or an amorphous porous layer.
`The implant 50 may be made at least in part micro
`porous, so that it functions as a delivery vehicle for
`antibiotics or bone stimulating factors such as bone
`morphogenic protein or osteogenin, which are intro—
`duced into the implant before implantation surgery. In
`the case of the preferred ceramic hydroxylapatite con-
`struction of the implant,
`the density and/or surface
`morphology of the ceramic can be varied in the sinter-
`ing process so that it retains the materials to be deliv—
`ered. The delivery of chemicals by this approach is
`known in the art, see, for example, H. A. Benghuzzi et
`al., “The Effects of Density of the Ceramic Delivery
`Devices on Sustained Release of Androgens in Cas-
`trated Rodents," 17th Annual Meeting of the Society
`for Biomaterials, May 1—5, 1991, page 159.
`In another approach, a coated implant is prepared by
`providing a piece of metal. such as titanium or titanium
`alloy, in the shape of the implant but slightly undersize
`in all dimensions. A coating of ceramic, metal, or poly-
`mer, of the types described previously, is applied over
`the piece of metal to enlarge the implant to the proper
`final dimensions.
`FIG. 6 is an elevational view of another embodiment
`of the implant 50, having several structural variations
`from that discussed previously. First, in the embodi-
`ment of FIG. 6 the transverse faces 68, 70 are not paral-
`lel to each other, but rather are tapered from the ante-
`rior end toward the more closely spaced posterior end.
`
`25
`
`30
`
`35
`
`4O
`
`45
`
`50
`
`60
`
`65
`
`An engagement region 74 is located on the transverse
`faces 68, 70 posteriorly of the anterior platform 72. The
`engagement region 74 has one or more three-dimen-
`sional features extending above the general level of the
`transverse faces 68, 70. In the embodiment of FIGS.
`
`8
`
`

`

`5,306,309
`
`7
`the engagement region 74 has engagement
`Second,
`features and are depressions 78 below the general level
`of the transverse face 68. Third, the engagement region
`74 is found on only one of the transverse faces, illus-
`trated as the transverse face 68. Consequently, unlike
`the symmetrical version of FIG. 5, the embodiment of
`FIG. 6 is asymmetric about a plane halfway between
`the transverse faces 68, 70.
`Fourth,
`the embodiment of FIG. 6 has a graded-
`porosity structure, indicated in the drawing as a dense
`central region 80 and a less dense, partly porous face
`region 82. The face region 82 extends about 0.1—0.3
`millimeters, preferably about 0.5—0.1 millimeters, from
`the surface of each transverse face 78, 80. In this em-
`bodiment, the entire implant 50 is made of calcium hy—
`droxylapatite (“I-IA”). The HA in the dense central
`region 80 has a density of about 95-100 percent of the
`theoretical density, with very little porosity. The HA in
`the face region 82 is intentionally somewhat porous,
`with a density of about 60—95 percent of the theoretical
`density. The pore sizes in the face region 82 are about
`50—500 micrometers in diameter, most preferably about
`100—250 micrometers in diameter.
`FIG. 7 presents another structural modification to the
`basic implant 50. In this embodiment, the transverse
`faces 68, 70 are convexly bowed outwardly. The bow-
`ing may be from the anterior end to the posterior end,
`or from side to side, or both.
`Another form of spinal disk implant 50 is shown in
`FIG. 9. This embodiment has a convexly curved poste-
`rior face 54. as well as a convexly curved anterior face
`52., With the covex curvature on both ends, the implant
`of FIG. 9 may be made end-to-end symmetric, if de—
`sired. Ifthe implant is made end-to-end symmetric, then
`a posterior platform 84 is provided symmetric with the
`anterior platform 72. In the design of FIG. 3, a posterior
`platform 84 is normally present, but is not of any partic-
`ular width.
`-
`FIGS. 6 and 7 present a number of design variations
`for the implant 50. These variations have been illus-
`trated together for convenience. However, they may be
`used or not used in any combination that may be conve-
`nient and appropriate in a particular circumstance.
`The invention also extends to an implant delivery tool
`100 for use in the surgical operation to implant
`the
`implant 50. As illustrated in FIGS. 10—13 the tool 100
`has a base 101, and a pair of flexible opposed arms 102
`extending from the base 101. The arms 102 are spaced
`apart and dimensioned to releasably grasp and hold the
`implant 50 therebetween. FIG. 10 illustrates the config-
`uration of the tool 100 for use in holding the implant 50
`pictured In FIG. 3, having only the anterior face
`curved. FIG. 11 illustrates the configuration of tool 100
`for use in holding the implant 50 pictured in FIG. 9,
`having both the anterior and posterior faces curved.
`Other configurations could be provided as appropriate.
`A release band 104 is fastened to the delivery tool 100
`and extends around a portion of the implant 50 to releas-
`ably hold it
`in place on the delivery tool. In the pre—
`ferred form, the release band 104 extends from the tips
`106 of the arms 102 and around the end of the implant
`50 to hold it ln place between the arms 102. Equiva-
`lently,
`the release band could extend between other
`portions of the delivery tool.
`A breakable link is provided ln the structure that
`holds the implant to the delivery tool. The breakable
`link permits the implant
`to be controllably released
`from the delivery too]. In the preferred approach. a
`
`8
`breakable weak link 108 is provided in the release band
`104, so that the release band 104 can be broken with a
`slight tug on the tool 100 after the implant is properly
`positioned between the vertebrae during implantation,
`leaving the implant at a selected position when the tool
`is withdrawn. Equivalently, the breakable link could be
`provided in one of the arms or elsewhere.
`It is possible that in some cases the frictional engage-
`ment between the implant 50 and the arms 102 will not
`be sufficient to prevent the implant 50 from tilting or
`sliding in an end-to-end manner. To prevent such tilting
`or sliding, a stabilizing lip 110 can extend outwardly
`from an edge of the base 101. The stabilizing lip, shown
`in FIG. 12, engages the proximate end of the implant 50
`and prevents it from tilting or sliding in an end-to-end
`fashion. The stabilizing lip 110 may also be provided
`with an optional stop 111 on its exterior edge that aids
`the surgeon in positioning the implant during the im-
`plantation operation. As the delivery tool 100 is used by
`the surgeon to insert the implant 50 between two verte-
`brae, the stop 111 engages the anterior edge of one of
`the vertebra when the implant has reached the proper
`position. In a further embodiment shown in FIG. 13,
`two oppositely disposed stabilizing lips 110 (in this case
`having no stops 111) are provided to hold the implant
`50 even more securely. The stabilizing lips can be ta-
`pered to ease their insertion between the vertebral bod-
`ies during implant placement.
`An engagement tip 112 extends rearwardly from the
`base 101. This tip 112 engages with a handle,
`to be
`described subsequently. The tip may have any appropri-
`ate form that cooperates with the handle, as shown in
`the figures.
`The base 101, arms 102, release band 104, weak link
`108, engagement tip 112, and stabilizing lip or lips 110
`are preferably made of a sterilizable plastic such as item
`(®) available from General Electric Plastics, or Delrin
`(®) available from DuPont. The tool 100 can be made
`in one piece by injection molding, and is therefore rela-
`tively inexpensive and disposable. The release band 104
`is a thin ribbon of such plastic, and the weak link 108 is
`a constricted region of the ribbon that can be easily
`broken by a tug on the tool 100.
`The cooperative design of the implant 50 and the
`delivery tool 100 is an important feature of the inven-
`tion. In the past, it has been known in some cases to use
`a delivery tool that threadably engaged with a threaded
`bore in the implant. Studies associated with the present
`invention have demonstrated that a bore, whether
`threaded or not,