United States Patent [191
`United States Patent
`[19]
`Michelson
`Michelson
`
`[54] APPARATUS AND METHOD OF INSERTING
`[54] APPARATUS AND METHOD OF INSERTING
`SPINAL IMPLANTS
`SPINAL INIPLANTS
`
`[76]
`Inventor: Gary K. Michelson, 438 Sherman
`[76] Inventor: Gary K. Michelson, 438 Shennan
`Canal, Venice, Calif. 90291
`Canal, Venice, Calif. 90291
`
`[21] APPL N0-5 749731
`[21] APPL No-i 74,781
`[22]
`Filed:
`Jun. 10, 1993
`[22] Filed:
`Jun. 10,1993
`
`llllllllllllllllllllllllllllllllglllumlllllllllllllllllllllllllllllll
`
`||||||llllllllIllIllll||||||||||||I||lllll|||||||||||||||||||||||I|ll||||||
`USO05484437A
`[11] Patent Number:
`[11] Patent Number:
`[45] Date of Patent:
`[45] Date of Patent:
`
`5,484,437
`5,484,437
`Jan. 16, 1996
`Jan. 16, 1996
`
`3,892,232
`7/1975 Neufeld ................................... .. 606/80
`3,892,232 7/1975 Neufeld ................................... .. 606/80
`4,341,205
`7/1982 Perrett ... ..
`... .. 606/80
`
`7/1982 Perrett . . . . .
`4,341,206
`. . . .. 606/80
`5/1984 Fischer .................................... .. 606/80
`4,450,834
`5/1984 Fischer .................................... .. 606/80
`4,450,834
`
`Primary Examiner—Michael A. Brown
`Primary Examiner——Michael A. Brown
`Attorney, Agent, or Firm—Lewis Anten; Amedeo Ferraro
`Attorney, Agent, or Firm—Lewis Anten; Amedeo Feiraro
`'
`
`Related US. Application Data
`Related U.S. Application Data
`
`[57]
`[57]
`
`ABSTRACT
`ABSTRACT
`
`[60] Continuation—in-part ofSer. No. 205,935, Jun. 13, 1988, Pat.
`[60]
`Continuation—in—part of Ser. No. 205,935, Jun. 13, 1988, Pat.
`No. 5,015,247, which is a division of Ser. No. 698,674, May
`No. 5,015,247, which is a division of Ser. No. 698,674, May
`10’ 1991’ abandoned‘
`10’ 1991’ abandoned‘
`1111- C1-6 -------------------- A513 17/56; A5113 17/00
`[51]
`[51] Int- Cl-6 ------------------ -- A61B 17/56; A6113 17/00
`US. Cl.
`..............
`......
`[58] Field of Search ............................ 606/60-80, 86-88,
`[58] Field Of Search .......................... .. 606/60-80, 86-88,
`606/96~98’ 104
`606/96~98, 104
`
`Cl- . . . . . . . . . . . . . .
`
`. . . . ..
`
`Apparatus and a method of inseming Spinal implants is
`A_PPa’a“‘S_ and _a ‘“e‘_h°d °f insming SP_i“31 im}’1a“‘S is
`disclosed in which an intervertebral space 1S first distracted,
`disclosed in which an intervertebral space is ?rst distracted,
`a hollow sleeve having teeth at one end is then driven into
`a hollow sleeve having teeth at one end is then driven into
`the vertebrae adjacent that disc space. A drill is then passed
`the vertebrae adjacent that disc space. A drill is then passed
`through the hollow sleeve removing disc and bone in
`preparation for receiving the Spinal implant which is than
`preparation for receiving the Spinal implant which is then
`inserted through the sleeve.
`. lnserted through the sleeve.
`
`through the hollow sleeve removing disc and bone in
`
`35 Claims, 24 Drawing Sheets
`35 Claims, 24 Drawing Sheets
`
`
`
`
`[56]
`[56]
`
`'
`
`References Cited
`References Cited
`U.S. PATENT DOCUMENTS
`U.S. PATENT DOCUMENTS
`3,848,601
`11/1974 Ma ............................................ 606/80
`3,848,601 11/1974 Ma .......................................... .. 606/80
`
`140
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`|PR2013—O0508
`
`

`
`U.S. Patent
`US. Patent
`
`Jan. 16, 1996
`Jan. 16, 1996
`
`Sheet 1 of 24
`Sheet 1 of 24
`
`5,484,437
`5,484,437
`
`F/G./
`
`

`
`U.S. Patent
`US. Patent
`
`Jan. 16, 1996
`Jan. 16, 1996
`
`Sheet 2 of 24
`Sheet 2 of 24
`
`5,484,437
`5,484,437
`
`

`
`U.S. Patent
`US. Patent
`
`Jan. 16, 1996
`Jan. 16, 1996
`
`Sheet 3 of 24
`Sheet 3 0f 24
`
`5,484,437
`5,484,437
`
`FIG. 5
`F/G. 5
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`
`F/G. 38
`
`

`
`U.S. Patent
`US. Patent
`
`Jan. 16, 1996
`Jan. 16, 1996
`
`Sheet 4 of 24
`Sheet 4 0f 24
`
`5,484,437
`5,484,437
`
`F/G. 30
`
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`
`

`
`U.S. Patent
`US. Patent
`
`Jan. 16, 1996
`Jan. 16, 1996
`
`Sheet 5 of 24
`Sheet 5 of 24
`
`5,484,437
`5,484,437
`
`FIG. 4
`FIG. 4
`
`

`
`U.S. Patent
`U.S. Patent
`
`Jan. 16, 1996
`Jan. 16, 1996
`
`Sheet 6 of 24
`Sheet 6 0f 24
`
`5,484,437
`5,484,437
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`U.S. Patent
`U.S. Patent
`
`Jan. 16, 1996
`Jan. 16, 1996
`
`Sheet 7 of 24
`Sheet 7 0f 24
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`5,484,437
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`U.S. Patent
`US. Patent
`
`Jan. 16, 1996
`Jan. 16, 1996
`
`Sheet 3 of 24
`Sheet 8 of 24
`
`5,484,437
`5,484,437
`
`F/G. 7A
`F/G. 7,4
`
`342
`
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`F/G. 8
`
`

`
`U.S. Patent
`US. Patent
`
`Jan. 16, 1996
`Jan. 16, 1996
`
`Sheet 9 of 24
`Sheet 9 0f 24
`
`5,484,437
`5,484,437
`
`P76. 75
`
`P76. 75
`
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`
`

`
`U.S. Patent
`US. Patent
`
`Jan. 16, 1996
`Jan. 16, 1996
`
`Sheet 10 of 24
`Sheet 10 of 24
`
`5,484,437
`5,484,437
`
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`U.S. Patent
`US. Patent
`
`Jan. 16, 1996
`Jan. 16, 1996
`
`Sheet 11 of 24
`Sheet 11 of 24
`
`5,484,437
`5,484,437
`
`

`
`U.S. Patent
`US. Patent
`
`Jan. 16, 1996
`Jan. 16, 1996
`
`Sheet 12 of 24
`Sheet 12 0f 24
`
`5,484,437
`5,484,437
`
`

`
`U.S. Patént
`U.S. Pate-nt
`
`Jan. 16, 1996
`Jan. 16, 1996
`
`Sheet 13 of 24
`Sheet 13 0f 24
`
`5,484,437
`5,484,437
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`

`
`U.S. Patent
`US. Patent
`
`Jan. 16,1996
`Jan. 16, 1996
`
`I
`
`Sheet 14 of 24
`Sheet 14 of 24
`
`5,484,437
`5,484,437
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`U.S. Patent
`US. Patent
`
`Jan. 16, 1996
`Jan. 16, 1996
`
`Sheet 15 of 24
`Sheet 15 of 24
`
`5,484,437
`5,484,437
`
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`
`

`
`U.S. Patent
`U.S. Patent
`
`Jan. 16, 1996
`Jan. 16, 1996
`
`Sheet 16 of 24
`Sheet 16 of 24
`
`5,484,437
`5,484,437
`
`

`
`U.S. Patent
`U.S. Patent
`
`Jan. 16, 1996
`Jan. 16, 1996
`
`Sheet 17 of 24
`Sheet 17 of 24
`
`5,484,437
`5,484,437
`
`

`
`U.S. Patent
`US. Patent
`
`Jan. 16, 1996
`Jan. 16, 1996
`
`Sheet 18 of 24
`Sheet 18 0f 24
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`5,484,437
`5,484,437
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`Jan.16, 1996
`
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`Jan. 16, 1996
`
`Sheet 22 of 24
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`U.S. Patent
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`Jan. 16, 1996
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`Sheet 23 of 24
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`
`U.S. Patent
`
`Jan. 16, 1996
`
`Sheet 24 of 24
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`
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`1
`APPARATUS AND METHOD OF INSERTING
`SPINAL IMPLANTS
`
`RELATED APPLICATIONS
`
`This application is a continuation in part of U.S. appli-
`cation Ser. No. 07/205,935, filed on Jun. 13, 1988, now Pat.
`No 5,015,247, which is a divisional application of Ser.
`No.07/698,674, filed May 10, 1981 now abandoned, both of
`which are incorporated into this application by reference.
`
`BACKGROUND OF THE INVENTION
`
`1. Field of the Invention
`
`The present invention relates to artificial fusion implants
`to be placed into the intervertebral space left remaining after
`the removal of a damaged spinaldisc and specifically to the
`apparatus for and method of, inserting the implants.
`2. Description of the Prior Art
`For the purpose of achieving long term stability to a
`segment of injured spine, a fusion (the joining together of
`two or more bones via a continuous bridge of incorporated
`bone) may be performed. Well-known to those skilled in
`such art is the interbody fusion wherein the disc is partially
`excised and bone placed within that space previously occu-
`pied by that disc material (between adjacent vertebrae) for
`the purpose of restoring a more normal spatial relationship,
`and to provide for stability; short
`term by mechanical
`support, and long term by the permanent cross bonding of
`bone from vertebra to vertebra. For fusion to occur within
`the disc space, it is necessary to prepare the vertebrae to be
`fused by breaking through, or cutting into, the hardened
`outside plates of bone (the endplates) to allow the interposed
`bone graft to come into direct contact with the more vascular
`cancellous (spongy) bone, and to thereby trick the body into
`attempting to heal this induced, but controlled, “fracturing”
`by both bone production and the healing of the grafts to both
`opposed vertebral surfaces such that they become one con-
`tinuous segment of bone.
`The purpose of the present invention is to provide an
`implant, and the apparatus and method of inserting the
`implant within the intervertebral space left after the removal
`of the disc material and permanently eliminate all motion at
`that location. To do so, the device of the present invention
`is space occupying within the disc interspace, rigid, self-
`stabilizing to resist dislodgement, stabilizing to the adjacent
`spinal vertebrae to eliminate local motion, and able to
`intrinsically participate in a vertebra to vertebra bony fusion
`so as to assure the permanency of the result.
`At present, following the removal of a damaged disc,
`either bone or nothing is placed into the remaining space.
`Placing nothing into this space allows the space to collapse
`which may result in damage to the nerves; or the space may
`fill with scar tissue and eventually lead to a reherniation. The
`use of bone to fill the space is less than optimal in that bone
`obtained from the patient requires additional surgery and is
`of limited availability in its most useful form, and if obtained
`elsewhere, lacks living bone cells, carries a significant risk
`of infection, and is also limited in supply as it is usually
`obtained from accident victims. Furthermore, regardless of
`the source of the bone, it is only marginal structurally and
`lacks a means to either stabilize itself against dislodgement,
`or to stabilize the adjacent vertebrae.
`a. Prior Art Implants
`There have been an extensive number of attempts to
`develop an acceptable disc prosthesis (an artificial disc).
`Such devices by design would be used to replace a damaged
`
`5
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`2
`
`disc and seek to restore the height of the interspace and to
`restore the normal motion of that spinal joint. No such
`device has been found that is medically acceptable. This
`group of prosthetic or artificial disc replacements, seeking to
`preserve spinal motion and so are dilferent from the present
`invention, would include:
`U.S. Pat. No. 3,867,728 to STUBSTAD—-describing a
`flexible disc implant.
`U.S. Pat. No. 4,349,921 to KUNTZ—describing a flexible
`disc replacement with file-like surface projections to dis-
`courage device dislocation.
`U.S. Pat. No. 4,309,777 to PATIL—describing a motion
`preserving implant with spiked outer surfaces to resist
`dislocation and containing a series of springs to urge the
`vertebrae away from each other.
`U.S. Pat. No. 3,875,595 to FRONING——describing a
`motion preserving bladder-like disc replacement with two
`opposed stud-like projections to resist dislocation.
`U.S. Pat. No. 2,372,622 to FASSIO (France)——describing
`a motion preserving implant comprising complimentary
`opposed convex and concave surfaces.
`In summary, these devices resemble the present invention
`only in that they are placed within the intervertebral space
`following the removal of a damaged disc. In that they seek
`to preserve spinal motion, they are diametrically different
`from the present invention which seeks to permanently
`eliminate all motion at that spinal segment.
`_
`A second related area of prior art includes those devices
`utilized to replace essentially wholly removed vertebrae.
`Such removal is generally necessitated by extensive verte-
`bral fractures, or tumors, and is not associated with the
`treatment of disc disease. While the present invention is to
`be placed within the disc space, these other vertebral devices
`cannot be placed within the disc space as at least one
`vertebra has already been removed such that there no longer
`remains a “disc space”. Furthermore,
`these devices are
`limited in that they seek to perform as temporary structural
`members mechanically replacing the removed vertebrae (not
`a removed disc), and do not intrinsically participate in
`supplying osteogenic material to achieve cross vertebrae
`bony fusion. Therefore, unlike the present invention which
`provides for a source of osteogenesis, use of this group of
`devices must be accompanied by a further surgery consisting
`of a bone fusion procedure utilizing conventional technique.
`This group consisting of vertebral struts rather than disc
`replacements would include the following:
`U.S. Pat No. 4,553,273 to WU—describing a tumbuckle-
`like vertebral strut.
`
`U.S. Pat No. 4,401,112 to REZAIAN—describing a turn-
`buckle- like vertebral strut with the addition of a long
`stabilizing staple that spans the missing vertebral body.
`U.S. Pat No. 4,554,914 to KAPP—describing a large
`distractible spike that elongates with a screw mechanism to
`span the gap left by the removal of an entire vertebra and to
`serve as an anchor for acrylic cement which is then used to
`replace the missing bone (vertebrae).
`U.S. Pat No. 4,636,217 to OGlLVIE—describing a ver-
`tebral strut mechanism that can be implanted after at least
`one vertebrae has been removed and consists of a mecha-
`nism for causing the engagement of screws into the verte-
`brae above and the vertebrae below the one removed.
`In summary, this second group of devices diifers from the
`present invention in that they are vertebral replacements
`struts, do not intrinsically participate in the bony fusion, can
`only be inserted in the limited circumstances where an entire
`vertebra has been removed from the anterior approach, and
`are not designed for, or intended to be used for the treatment
`of disc disease.
`
`

`
`3
`
`4
`
`5,484,437
`
`A third area of prior art related to the present invention
`includes all devices designed to be applied to one of the
`surfaces of the spine. Such devices include all types of
`plates, struts, and rods which are attached by hooks, wires
`and screws. These devices differ significantly from the
`present invention in that they are not inserted within the disc
`space and furthermore do not intrinsically participate in
`supplying osteogenic material for the fusion.
`Therefore, where permanent spinal
`immobilization is
`desired, an additional surgery, consisting of a spinal fusion
`performed by conventional means or the use of supplemen-
`tal methylmethacrylate cement is required. Such devices
`applied to the spine, but not within the disc space, would
`include the following:
`U.S. Pat No. 4,604,995 to STEPHENS——describing a “U”
`shaped metal rod attached to the posterior elements of the
`spine with wires to stabilize the spine over a large number
`of segments.
`U.S. Pat No. 2,677,369 to KNOWLES—describing a
`metal column device to be placed posteriorly along the
`lumbar spine to be held in position by its shape alone and to
`block pressure across the posterior portions of the spinal
`column by locking the spine in full flexion thereby shifting
`the maximum weight back onto the patient’s own disc.
`Other devices are simply variations on the use of rods
`(e.g. Harrington, Luque, Cotrel-Dubosset, Zielke), wires or
`cables (Dwyer), plates and screws (Steffee), or struts (Dunn,
`Knowles).
`In summary, none of these devices are designed to be nor
`can be used within the disc space. Moreover, these devices
`do not replace a damaged disc, and do not intrinsically
`participate in the generation of a bony fusion.
`Another area of related prior art to be considered is that
`of devices designed to be placed within the vertebral inter-
`space following the removal of a damaged disc, and seeking
`to eliminate further motion at that location.
`Such a device is contained in U.S. Pat No. 4,501,269
`issued to BAGBY which describes an implantable device
`and limited instrumentation. The method employed is as
`follows: a hole is bored transversely across the joint and a
`hollow metal basket of larger diameter than the hole is then
`pounded into the hole and then the hollow metal basket is
`filled with the bone debris generated by the drilling.
`While the present invention (device, instrumentation, and
`method) may appear to bear some superficial resemblance to
`the BAGBY invention, it is minimal, while the diiferences
`are many fold and highly significant. These differences
`include the following:
`1. Safety-—The present invention provides for a system of
`completely guarded instrumentation so that all contiguous
`vital structures (e.g. large blood vessels, neural structures)
`are absolutely protected. The instrumentation of the present
`invention also makes overpenetration by the drill impos-
`sible. Such overpenetration in the cervical
`spine,
`for
`example, would result in the total paralysis or death of the
`patient. In the thoracic spine, the result would be complete
`paraplegia. In the lumbar spine, the result would be paraple-
`gia or a life-threatening perforation of the aorta, vena cava,
`or iliac vessels.
`
`The present invention is atraumatically screwed into place
`while the BAGBY device, in contradistinction, is pounded
`into position. BAGBY describes that its implant is signifi-
`cantly larger in size than the hole drilled and must be
`pounded in. This is extremely dangerous and the pounding
`occurs directly over the spinal cord which is precariously
`vulnerable to percussive injury. Furthermore, while it is
`possible, for example in the lumbar spine, to insert the
`
`present invention away from the spinal cord and nerves, the
`BAGBY device must always be pounded directly towards
`the spinal cord.
`Furthermore, since the BAGBY device is pounded into a
`smooth hole under great resistance, and lacking any specific
`design features to secure it, the device is highly susceptible
`to forceful ejection which would result in great danger to the
`patient and clinical failure. The present invention, in con-
`tradistinction, is securely screwed into place, and possesses
`highly specialized locking threads to make accidental dis-
`lodgement
`impossible. Because of the proximity of the
`spinal cord, spinal nerves, and blood vessels, any implant
`dislodgement as might occur with the BAGBY device might
`have catastrophic consequences.
`2. Broad applicability-——The BAGBY device can only be
`inserted from the front of the vertebral column, however, in
`contrast, the present invention can be utilized in the cervical,
`thoracic, and lumbar spine, and can be inserted from behind
`(posteriorly) in the lumbar spine. This is of great importance
`in that the purpose of these devices is in the treatment of disc
`disease and probably greater than 99 percent of all lumbar
`operations for the treatment of disc disease are performed
`from behind where the present invention can easily be
`utilized, but the BAGBY device, as per BAGBY’S descrip-
`tion, cannot.
`3. Disc removal—’I‘he BAGBY invention requires the
`complete removal of the disc prior to the drilling step,
`whereas the present invention eliminates the laborious sepa-
`rate process of disc removal and efficiently removes the disc
`and prepares the vertebral end plates in a single step.
`4. Time required—The present invention saves time over
`the BAGBY invention since time is not wasted laboring to
`remove the disc prior to initiating the fusion. Also, with the
`present invention the procedure is performed through a
`system of guarded instrumentation,
`time is not wasted
`constantly placing and replacing various soft tissue retrac-
`tors throughout the procedure.
`5. Implant stability—-Dislodgement of the implant would
`be a major source of device failure (an unsuccessful clinical
`result), and might result in patient paralysis or even death.
`As discussed, the BAGBY device lacks any specific means
`of achieving stability and since it is pounded in against
`resistance to achieve vertebral distraction, and is susceptible
`to forceful dislodgement by the tendency of the two dis-
`tracted vertebrae, to return to their original positions-squeez-
`ing out
`the device. The present
`invention, however,
`is
`screwed into place. As there is no unscrewing force present
`between the vertebrae, compression alone cannot dislodge
`the implant. The implant is inherently stable by its design.
`Furthermore, the threads of the present invention are highly
`specialized in that they are periodically interrupted so that
`the tail ends of each of the tabs so formed are blunted and
`twisted so as to resist accidental unscrewing. The removal of '
`an implant with such “locking threads” requires the use of a
`special extractor included within the instrumentation. The
`stability of the present invention is still further enhanced,
`again in contradistinction to the BAGBY device, by the
`presence of a “bone ingrowth” surface texturing, which both
`increases the friction of the fit and allows for the direct
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`growth of the vertebral bone into the casing of the implant
`itself.
`
`6. Spinal stability——The present invention is not only
`self-stabilizing,
`it also provides stability to the adjacent
`vertebrae in at least three ways that the BAGBY device
`cannot. First, the BAGBY device is placed transversely
`across the joint in the center, leaving both vertebrae free to
`rock back and forth over this round barrel shaped axis, much
`like a board over a barrel, being used for a seesaw.
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`Secondly, as the BAGBY device lacks any specific design
`features to resist sliding, it may actually behave as a third
`body allowing the translation of the vertebrae relative to the
`device and to each other.
`
`Thirdly, any device can only provide stability if it remains
`properly, seated. The present invention is inherently stable,
`and therefore assures that
`it will stabilize the adjacent
`vertebrae, rather than, as with the BAGBY, the instability of
`the spine to be treated may cause a dislocation of the
`BAGBY implant, with further loss of spinal stability.
`7. The collapse of the interspace—While both the present
`invention and the BAGBY device can be fabricated to
`
`withstand the compression forces within the interspace, the
`interspace may nevertheless collapse under the superincum-
`bent body weight as the implant settles into the vertebral
`bone. This is related to the load per unit area. Again the
`present invention is superior to the BAGBY device in at
`least four ways.
`First, the present invention oifers considerably greater
`surface area to distribute the load. Secondly, while the
`BAGBY device is placed centrally, the present device is
`placed bilaterally where the bone tends to be more cortical
`and much stronger out towards the rim. Thirdly, the present
`invention supports the load achieving an “I” beam effect,
`whereas the BAGBY implant does not. Fourthly, it is not
`pressure alone that causes the collapse of the bone adjacent
`to the implant, but also bony erosion that is caused by the
`motion under pressure of the implant against the bone. As
`discussed in item 6 above, the present invention alone is
`highly resistant to such motion, again diminishing the like-
`lihood of erosion and interspace collapse.
`8. Bone ingrowth surface texturing—The present inven-
`tion has a surface treatment of known and conventional
`technology to induce the growth of bone from the vertebrae
`directly into the casing material of the implant itself. The
`BAGBY device has no similar feature. {L.A.—we may want
`to list examples of these bone growth factors}
`9. Fusion mass—The BAGBY invention calls for remov-
`
`ing the disc and then drilling a hole between the adjacent
`vertebrae. The bony debris so generated is then put into the
`device. The present invention takes a core of pure bone
`producing marrow from the iliac crest, and then by use of a
`special press, forcibly injects the implant device with an
`extremely dense compressed core of that osteogenic material
`until the material itself virtually extrudes from every cell of
`the implant.
`»
`10. The probability of achieving fusion——The fusion rate
`within the spine is known to be related directly to the amount
`of exposed vascular bone bed area, the quality and quantity
`of the fusion mass available, and the extent of the stabili-
`zation obtained with all other factors being half constant. It
`would then be anticipated, that the fusion rate would be
`superior with the present invention as compared to the
`BAGBY device, because of optimal implant stability (#5),
`optimal spinal stability (#6), bone ingrowth surface treat-
`ment
`(#8), superior fusion mass (#9), and the greater
`exposed vertebral bony surface area (#7).
`The last area of prior art possibly related to the present
`invention and therefore, to be considered related to “bony
`ingrowth”, are patents that either describe methods of pro-
`ducing materials and or materials or devices to achieve the
`same. Such patents would include:
`U.S. Pat. Nos. 4,636,526 (DORMAN), 4,634,720 (DOR-
`MAN), 4,542,539 (ROWE), 4,405,319 (COSENTINO),
`4,439,152 (SMALL), 4,168,326 (BROEMER), 4,535,485
`(ASHMAN),
`3,987,499
`(SCHARBACH),
`3,605,123
`(HAHN), 4,655,777 (DUNN), 4,645,503 (LIN), 4,547,390
`
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`(ASHMAN), 4,608,052 (VAN KAMPEN), 4,698,375
`(DORMAN), 4,661,536 (DORMAN), 3,952,334 (BOK-
`ROS), 3,905,047 (LONG), 4,693,721
`(DUCHEYNE),
`4,070,514 (ENTHERLY).
`invention
`However, while the implant of the present
`would utilize bone ingrowth technology, it would do so with
`conventional technology.
`b. Prior Art Instrumentations And Methods
`
`The following is a history of the prior an apparatus and
`methods of inserting spinal implants:
`In 1956, Ralph Cloward developed a method and instru-
`ments which he later described for preparing the anterior
`aspect (front) of the cervical spine, and then fusing it.
`Cloward surgically removed the disc to be fused across and
`then placed a rigid drill guide with a large foot plate and
`prongs down over an aligner rod and embedded said prongs
`into the adjacent vertebrae to maintain the alignment so as
`to facilitate the reaming out of the bone adjacent the disc
`spaces. As the large foot plate sat against the front of the
`spine, it also served as a fixed reference point to control the
`depth of drilling. The reaming left two opposed resected
`arcs, one each, from the opposed vertebral surfaces. The
`tubular drill guide, which was placed only preliminary to the
`drilling, was thereafter completely removed. A cylindrical
`bony dowel, significantly larger in diameter than the hole
`formed, was then pounded into the hole already drilled.
`Cloward’s method of instrumentation was designed for, and
`limited to, use on the anterior aspect and in the region of the
`cervical spine only. The hole was midline, which would
`preclude its use posteriorly where the spinal cord would be
`in the way.
`As the bone graft to be inserted in Cloward’s method was
`necessarily larger in diameter than the hole drilled, the graft
`could not be inserted through the drill guide. This mandated
`the removal of the drill guide and left the graft insertion
`phase completely unprotected. Thus Cloward’s method and
`instrumentation was inappropriate for posterior application.
`In addition, the failure to provide continuous protection to
`the delicate neural structures from the instruments, as well
`as the bony and cartilaginous debris generated during the
`procedure, made Cloward’s method inappropriate for pos-
`terior application. Also, the drill guide described by Cloward
`could not be placed posteriorly within the spinal canal, as the
`foot plate would crush the nerves. Modifying Cloward’s
`drill guide by removing the foot plate completely, would still
`leave the instrument unworkable as it would then lack
`
`stability, and would not be controllable for depth of seating.
`Nevertheless, Wilterberger, (Wilterberger, B. R., Abbott,
`K. H., “Dowel Intervertebral Fusion as Used in Lumbar Disc
`Surgery,“ The Joumal of Bone and Joint Surgery, Volume
`39A, pg. 234-292, 1957) described the unprotected drilling
`of a hole from the posterior into the lumbar spine between
`the nerve roots and across the disc space, and then inserting
`a stack of button-like dowels into that space. While Wilter-
`berger had taken the Cloward concept of circular drilling and
`dowel fusion and applied it to the lumbar spine from a
`posterior approach, he had not provided for an improved
`method, nor had he advanced the instrumentation so as to
`make that procedure sufliciently safe, and it rapidly fell into
`disrepute.
`Interbody
`Crock (Crock, H. V., “Anterior Lumbar
`Fusion——Indications for its Use and notes on Surgical Tech-
`nique, ”“Clinical Orthopedics, Volume 165, pg. 157-163,
`1981) described his technique and instrumentation for Ante-
`rior Interbody Fusion of the lumbar spine, wherein he drilled
`two large holes side by side across the disc space from
`anterior
`to posterior essentially unprotected and then
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`7
`pounded in two at least partially cylindrical grafts larger than
`the holes prepared.
`A review of the prior art is instructive as to a number of
`significant deficiencies in regard to the method and instru-
`mentation for the performance of Interbody Spinal Fusion
`utilizing drilling to prepare the endplates.
`As the great majority of spinal surgery is performed in the
`lumbar spine and from posteriorly, a review of the prior art
`reveals a number of deficiencies in regard to the spine in
`general, and to the posterior approach to the lumbar spine
`specifically. These deficiencies include the:
`1. Failure to protect the surrounding tissues throughout
`the procedure, specifically, prior to drilling and until
`after the insertion of the graft;
`2. Failure to contain the debris, bony and cartilaginous,
`generated during the procedure;
`3. Failure to optimize the contact of the cylindrical drill
`hole and bone graft, the mismatch in their diameters
`resulting in incongruence of fit;
`4. Failure to determine the optimal drill size prior to
`drilling;
`5. Failure to determine the optimal amount of distraction
`prior to drilling;
`6. Inability to optimize the amount of distraction so as to
`restore the normal spatial relationships between adja-
`cent vertebrae;
`'
`
`7. Inability to create sufficient working space within the
`spinal canal (between the nerve roots and the dural sac)
`to make the procedure safe;
`8. Absent a foot plate on the drill guide, as necessitated by
`the close tolerances posteriorly, the inability to reliably
`insure that
`the drilling is parallel
`to the vertebral
`endplates;
`9. The inability to insure equal bone removal from the
`opposed vertebral surfaces; and
`10. The inability to determine within the spinal canal, the
`proper side by side positioning for dual drill holes.
`
`BRIEF SUMMARY OF THE INVENTION
`
`The present invention comprises a series of artificial
`implants,
`the purpose of which is to participate in, and
`directly cause bone fusion across an intervertebral space
`following the excision of a damaged disc. Such implants are
`structurally load bearing devices,
`stronger
`than bone,
`capable of withstanding the substantial forces generated
`within the spinal
`interspace. The devices of the present
`invention have a plurality of macro sized cells and openings,
`which can be loaded with fusion promoting materials, such
`as autogenous bone, for the purpose of materially influenc-
`ing the adjacent vertebrae to perform a bony bond to the
`implants and to each other. The implant casing may be
`surface textured or otherwise treated by any of a number of
`known technologies to achieve a “bone ingrowth surface” to
`further enhance the stability of the implant and to expedite
`the fusion.
`
`The devices of the present invention are configured and
`designed so as to promote their own stability within the
`vertebral interspace and to resist being dislodged, and fur-
`thermore, to stabilize the adjacent spinal segments.
`The apparatus and method of the present invention for
`preparing the vertebrae for insertion of the implant allows
`for the rapid and safe removal of the disc, preparation of the
`vertebrae, performance of the fusion, and internal stabiliza-
`tion of the spinal segment.
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`The present invention is a method for Interbody Spinal
`Fusion utilizing novel instrumentation, whereby a protective
`tubular member is placed prior to the drilling part of the
`procedure and is left in place until the graft is fully seated.
`In the preferred embodiment two distractors are used to
`separate two adjacent vertebrae to a preferred distance. A
`hollow Outer Sleeve having teeth at one end is dr