MEMORANDUM
`
`To: JJohn Pafford
`David Brumfield
`Larry Boyd LfJ
`January 11, 1994
`
`From:
`
`Date:
`
`cc: Brad Estes
`Ted Bird
`
`Subject:
`
`NOTES ON THREADED DOWEL CONCEPTS OF DR. MICHELSON
`
`Following for your review and information are some of my notes and comments on the
`Michelson technology_ These are based on my review of information prior to our meeting
`and contain some of the answers to my various questions, which were answered by Dr.
`Michelson on Tuesday. The notes refer to some terminology used by Dr. Michelson and
`found in the patent application. Let me know if you have any questions or comments.
`
`I.
`
`Various Features and Benefits
`
`1.
`
`2.
`
`3.
`
`Instrumentation is guarded to protect against tissue contact and contact with the
`neurovascular structures.
`Instrumentation also features drill stops to prevent over
`drilling. No external retractors (e.g., lamina spreaders) are used.
`
`Implant is atraumatically screwed in, as opposed to other implant systems which
`may require potentially damaging pounding in order to fully seat the implant.
`
`Instrumentation can be used ALlF, PUF, as well as laparoscopic implantation for
`anterior use (Iaparscopic approach could be anterior or anterolateral, depending
`on instrumentation used).
`
`4.. The instrumentation allows for simultaneous removal of the disclbone and implant
`preparation. Three options are possible here:
`(1) drilVreamer to remove and
`contain disc and bone (no distractor present, except in contralateral side), (2)
`cannulated reamer for drilling over long distractor, and (3) trephine for coring out
`disc and the circular portions of endplate via drilling over a long distractor.
`
`5. Specialized threadforms help resist unscrewing.
`
`6. Bone ingrowth surface texturing acts to anchor the implant system. Hydroxyapatite
`coating could further enhance bone bonding and attachment to the implant
`surface. Dr. Michelson later mentioned that we will need to look at the various
`means of applying the coating. Plasma spraying may result in excessive
`temperatures, so alternative means (e.g., ion beam assisted deposition?) will need
`to be explored.
`
`Confidential-Attorneys' Eyes Only
`
`MNUV0005672
`
`PX0957-0001
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`PX0957
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`WARSAW2006
`NuVasive, Inc. v. Warsaw Orthopedic, Inc.
`Case IPR2013-00206
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`Page 1
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`Notes on Threaded Dowel Concepts of Dr. Gary Michelson
`January 11, 1994
`Page 2
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`7. Greater surface area is achievable via predistraction method. This should result in
`reduced incidents of subsidence. Predistraction allows for a larger and more
`controlled working area.
`
`8. Bilateral placement should allow for load bearing further peripherally on the
`stronger cortical bone along the vertebral body rim.
`
`9.
`
`Iliac crest autograft bone is used. This cancellous autograft is highly osteogenic
`and should further encourage a strong fusion. Future use of active bone
`substitutes could be envisioned as those materials become available. This is
`placed within a bone press and injected into the implant prior to implantation. The
`compressive preloading is a key feature and advantage of the system.
`
`II.
`
`Historical Outline of Use of Bone Dowels for Spinal Fusion
`
`1. Cloward (1956) was the first to use a single central bone dowel for anterior
`cervical fusion.
`
`2. Wilterberger (1957) used bilateral bone dowels for posterior lumbar interbody
`fusion.
`
`3. Crock (1981) developed the use of bilateral bone dowels for anterior lumbar
`fusion.
`
`All methods use relatively weak autograft or non-osteogenic allograft.
`
`III.
`
`Basics clthe Surgical Method
`
`1. Protective tubular member is placed.
`
`2. Distraction is achieved via insertion of the bullet-nosed, long distractor.
`
`3. A outer sleeve (with engagement teeth) is placed in order to maintain distraction.
`
`4. A diameter-reducing inner sleeve is placed.
`
`5. A drilVreamer with drill stop is then used to remove disc and bone.
`
`6. The threaded implant is inserted into this hole, engaging the bone.
`
`Overall, this method protects against:
`
`1. Vessel or soft tissue damage (the outer tube provides protection from contact with
`surrounding tissues).
`
`2. Over penetration (the fixed drill stops prevent over penetration),
`
`3. Debris in wound (the system closed debris is contained within inner sleeve),
`
`Confidential-Attorneys' Eyes Only
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`MNUV0005673
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`PX0957-0002
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`Page 2
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`., ......
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`Notes on Threaded Dowel Concepts of Or. Gary Michelson
`January 11. 1994
`Page 3
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`4. Damage from power instruments (drill stops prevent over drilling),
`
`5. Misalignment (various long distractors and individual distractors hold place during
`procedure),
`
`6.
`
`Loss of distraction (Long & short distractors and outer sleeve maintain distraction).
`
`7. Off-center or non-parallel drilling (co-axial use of instrumentation centered about
`initial placement and confirmation of placement of bullet-nosed distractors assures
`accurate placement, outer sleeve engaged in vertebral bodies prevents
`spreading as drills engage),
`
`B. Penetration of soft tissues or blood vessels (Blunt tips on initial long distractor
`prevents such damage, drill stops prevent over drilling).
`
`IV.
`
`Issues/QuestionslAnswers
`
`1. Pre-distraction allows the full diameter implant to be inserted. This is in contrast to
`other methods. Without the pre-distraction method (key to Michelson) a significant
`portion of the forward end of the implant is needed for the purpose of separating
`opposing vertebrae. This can be clearly seen in the Spine Tech BAK implant
`where a significant lead-in. ramped portion is required, which significantly reduces
`the threaded portion available for load-bearing and engagement.
`
`2, A sharp thread can be used for the Michelson technique due to pre-distraction and
`protection of surrounding tissues by use of the external outer sleeve distractor for
`maintenance of distraction.
`
`3.
`
`I was unclear about the need for an initial discectomy prior to insertion of the intra(cid:173)
`I was also unclear about the amount of disc that should be
`discal distractors.
`removed. According to Dr. Michelson, some select discectomy may be needed.
`This could be achieved via use of a simple curette for removing some small
`portion of disc prior to inserting the initial, bUllet-nosed long distraetors.
`
`4. The sequential placement of bilateral long distractors are inserted in order to
`assess the ideal disc height. Once the proper distractor size is placed it is very
`clear that the disc has reached ~5 ideal tension. As has been mentioned by other
`surgeons. there is a very clear stopping point at which the annulus is in maximum
`tension and the disc has been restored to its normal disc height. The surgeon will
`determine when a balanced distraction is achieved via either a tactile sensation of
`a tight fit of the distractor or via actual radiographic confirmation of the re(cid:173)
`establishment of disc height.
`
`The surgeon may need to remove one of the short distraetors on one side in order
`to increase disc height during balancing. The anti-expulsion teeth may resist. but
`instrumentation exists for removing these short distractors in order to place a
`larger distractor. An alternative procedure allows for the use of the long distractor
`only with the trephine used to drill over this long distraetor. This is especially
`
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`MNUV0005674
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`Notes on Threaded Dowel Concepts of Dr. Gary Michelson
`January 11, 1994
`Page 4
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`important where lordosis may be achieved via the wedge-shaped long distractors
`that may be used to re-establish the trapezoidal shape of the disc anatomy during
`PLIF. The advantages of the short distractors center around the fact that they may
`be placed and maintain disc height and distraction while the surgeon works on the
`other side. They also allow surgeons to balance the disc space, which may be
`very important for example in the case of reducing a spondylolisthesis.
`
`5.
`
`In many cases a tap is not necessary. One would normally not tap following bone
`and disc removal in Michelson's preferred method. This Is due to the fact that if
`one were to tap prior to inserting the implant it would be possible to accidentally
`crossthread the tapped disc vertebral endplates. That is, the very sharp threads
`on the Michelson implant could initially bite into the vertebral body bone and
`establish their own thread path as they are inserted. Obviously, if such a disc
`space had been previously tapped and were crossthreaded the implant bone
`interface would be less than ideal. The implant is, therefore, essentially self(cid:173)
`tapping and cuts very well into the cancellous vertebral body bone. The tap that is
`provided with the set does allow for ideal tapping in that it compresses the bone
`rather than actually cutting a trough through the bone and removing valuable bone
`cells. We will need to test the various alternatives as we proceed with this
`program to determine the need for tapping and advantages/disadvantages.
`
`6.
`
`The ideal implant configuration features the following:
`
`1. The preferred material is titanium (commercially pure or titanium alloy),
`
`2. The implant would be porous coated or textured in order to improve implant
`anchorage,
`
`3.
`
`The implant would be coated with hyroxyapatite coating in order to enhance
`bone attachment, bone migration around and thru the implant innerspace,
`
`4. The implant is only approximately 1mm in wall thickness. This is strong
`enough for short-term load bearing while a fusion occurs and provides for a
`maximum amount of bone within the center of the implant, as well as
`optimized bone bridging and thru-growth into the implant.
`
`5. The thread form may be interrupted and self-locking if such additional means
`of resisting expulsion are needed,
`
`6. The implant thread form is self-tapping, and
`
`7.
`
`the implant should be pre-loaded with autograft bone which is compressed
`into the implant until it extrudes out of the pores of the implant.
`
`lB/dg
`
`Confidential-Attorneys' Eyes Only
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`MNUV0005675
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`PX0957-0004
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`Page 4