GLOBUS MEDICAL, INC.
`EXHIBIT 1019
`IPR2015-to be assigned
`(Globus v. Flexuspine)
`
`Page 1 of 11
`
`

`
`March 1. 1998
`Volume 23, Number 5
`
`
`
`I Basic Science
`
`Influence of Muscle Forces on Loads in Internal
`
`537
`
`In Vivo Bcl—2 Oncogene Neuronal Expression in
`the Rat Spinal Cord
`The Bcl—2 oncogene in vitro has the ability to blocle apoptotic
`cell death proportional to the level of Bcl-2 gene expression by
`regulating an antioxidant pathway at sites of free radical gen-
`eration. In this study, the authors document rat spinal cord in
`vivo expression of the Bcl—2 oncogene with a statistically de-
`creased zone of injury in a rat spinal cord injury model with
`prior Bcl-2 recombinant adenovirus inoculation versus a con-
`trol. Further investigation of the Bcl-2 oncogene for poten-
`tially enhancing neuronal survival after spinal cord injury ap-
`pears indicated.
`
`Jueren Lou, Lawrence G. Lenke, Fang Xu, and Michael O'Brien
`
`Inflammatory Cells in Full-Thickness Anulus
`Injury in Pigs: An Experimental Disc Herniation
`Animal Model
`
`524
`
`I nflammatory cells (macrophages and T lymphocytes) were
`analyzed in an experirnental full-thickness anulus injury
`model in adult pigs. Macrophages were predominant (58% of
`discs), and T lymphocytes were less common (33% of discs),
`findings which agree with those of previous studies on human
`herniated disc material and which support a role for inflam-
`mation in disc injury and herniation.
`Aklilu Habtemariam, Johanna Virri, Mats Grfinblad, Sten Holm,
`Allison Kaigle, and Erkki Karaharju
`
`I Biomechanics
`
`A Biomechanical Comparison of Open and
`Thoracoscopic Anterior Spinal Release in 21 Goat
`Model
`
`530
`
`Anterior release with discectomy was performed rising open
`and thoracoscopic techniques in a goat model. Three-dinzcn-
`sioiial biornechanical testing was performed, and the two tech-
`niques demonstrated comparable increases in neutral zone
`spinal motion.
`Peter 0. Newton, J. Marc Cardelia, Christine L. Farnsworth,
`Kelly J. Baker, and Dwight G. Bronson
`
`517
`
`Spinal Fixation Devices
`
`instrumented internal spinal fixation devices were used to
`study the influence ofinuscle forces on implant loads. Muscle
`forces strongly influence implant load and prevent an axial
`tensile load on the spine when the patient is hanging by his
`hands or feet. The implant loads may be altered strongly when
`the patient is under anesthesia.
`
`Antonius Rohlmann, Georg Bergmann, Friedmar Graichen, and
`Heinz-Michael Mayer
`
`543
`
`551
`
`Stability Potential of Spinal lnstrumcntations in
`Tumor Vertebral Body Replacement Surgery
`Using it /-riultirlirectional flexibility protocol and fresh human
`lumbar spine specimens, posterior and combined instrumenta-
`tions showed greater stability potential than the’ tint:--rior de-
`vice in a C()t’[)£‘£'I()T7I_V niodcl simulating tumorous surgery.
`Michael J. Vahldiek and Manohar M. Panjabi
`
`I Deformity
`
`A Comparison of Manual Versus Computer-
`Assisted Radiographic Measurement:
`Intraobserver Measurement Variability for Cobb
`Angles
`Computer-assisted measurement of the Cobb angle can reduce
`intrinsic sources of error and intraohscrver measurement I'tZI'i-
`ability. Digital radiographs can be transferred easily between
`research centers. Digital radiography has the potential to in-
`crease the precision of radiographic data collection and facili-
`tate multicenter studies.
`
`Kevin G. Shea, Peter M. Stevens, Mark Nelson, John T. Smith,
`Kevin S. Masters, and Suzanne Yandow
`
`I Diagnostic Testing
`
`Biomechanical Aspects of the Subarachnoid
`Space and Cervical Cord in Healthy Individuals
`Examined With Kinematic Magnetic Resonance
`Imaging
`
`556
`
`Point of View
`
`David S. Bradford
`
`536
`
`In vivo magnetic resonance imaging studies of the cervical
`spine were performed during flexion and extension in healthy
`individuals to determine the physiologic changes of the cervi-
`cal cord and the subarachnoid space. At flexion, a narrowing
`
`Reprints, except special orders of 100 or more, are available only from authors. This publication is protected by copyright. Permission to photocopy must
`be secured in writing from: Permissions Dept., Lippincott—Raven Publishers, 227 East Washington Square, Philadelphia, PA 19106-3780; FAX: 215-238-4419,
`OR Copyright Clearance Center (CCCl, 222 Rosewood Dr., Danvers, MA 01923; FAX: 508-750-4470, OR UMI, Box 49, 300 North Zeeb Road, Ann Arbor, MI
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`Lippincott—Raven Publishers, 227 East Washington Square, Philadelphia, PA 19106-3780; (516) 741-1772.
`
`Page 2 of 11
`Page 2 of 11
`
`

`
`Contents
`Continued
`
`ofthc ventral suharachnoirl space ofup to 43% and a widen-
`ing of the dorsal suharachnoid space of up to 89% (r‘on1par¢'d
`with the nvu.z‘ral position /0°/) worn observed. At extension, an
`increase in the diarnctvr of the ventral suharachnoid space of
`up to 9% was ohscriied, whereas the dorsal suharachnoid
`space was r('clItc‘('(l to 77%. l)cpaiiclii1g on the cervical seg-
`ment. a reduction in the sagittal diarncrcr of the cervical cord
`to ‘l4% at /lcxion and an iricrmsv at extension ofup 1o 15%
`were found.
`Claus Muhle, Jakub Wiskirchen, Dieter Weinert, Axel Falliner,
`Frank Wesner, Gisbert Brinkmann, and Martin Heller
`
`Evaluation of Clinician and Machine
`Performance in the Assessment of Low Back Pain
`
`568
`
`The [?l'r/l))’IIIiH1L'(’ ofcliniriims in assessing hwiign low hzule
`pain is critically rc'i'it’Ii'ml and com/uir<'d with that Of-HM auto-
`I)lL1l(’(l physiml (’.‘\‘clI7ll1lclll()l1 trlml is lmsvd on the ability to
`function and not on rt’/)()rI‘c‘rl pain. Rriluvtz/i¢'c' to the rliagrzosis
`o/‘low hack pain is diSL'll$S(’tl.
`
`Serge A. Gracovetsky, Nicholas M. Newman, Mark P. Richards,
`Steeve Asselin, Victor F. Lanzo, and Anne Marriott
`
`netic movement analysis system. Position sense is accurate to
`within a mean of 5.27 :9: 3.47 degrees and showed no signifi-
`cant variation on separate testing days.
`Annette Swinkels and Patricia Dolan
`
`I Functional Restoration
`
`Socioeconomic Outcomes of Combined Spine
`Surgery and Functional Restoration in Workers’
`Compensation Spinal Disorders With Matched
`Controls
`
`598
`
`S/)i/10 surgery in or workers’ compensation population has dc-
`monstrahly poorer outcomes than in a general health cohort.
`This setting ofi‘2rrcd the unique opportunity for quantitative
`ourmnu- i.15$(’SSINL’rlt using oh/"active socioeconomic data. Co-
`horts of paticrzts who underwent spinal discertomy and fusion
`were matclml with unoperatcd controls; all were undergoing
`the $41!!!!’ rvlmhilitation approach. Unparalleled outcomes
`lL'(‘1’L' found for all groups compared with historic refL'rcnccs,
`with the fusion group doing marginally hotter than discectomy
`and control groups in spite of longer periods of disability and
`more [)r‘i'tr('atH1vnl‘ surgery.
`
`576
`
`Torn Mayer, Margaret J. McMahon, Robert J. Gatchel,
`Brett Sparks, Anna Wright, and Pauline Pegues
`
`The Influence of Muscle Fiber Size and Type
`Distribution on Electromyographic Measures of
`Back Muscle Fatigability
`Musclv hio/1systzinplz's u.Icr<' olmiiru-ll from thoracic and lum-
`har n'_x;ior1s o/'vrr'clor s/iiruzv in .31 uorinal hmilthy iiu/iriicluizls.
`for whom vlvrrrimiyogm/ihic I)l(‘iISlH‘(’.s‘ o/'z’rc*rIor s/ziniur fari-
`gnliilily had also how; ohmimid. A grmlc-1' arm of the muscle
`occupied by slow oxidalimi typo l /ihvrs was iissocintml with it
`louw rate ofdvclin<' in the electronzyogriz/7/nc /rower s/m'«
`lrum Nl(’ditHl frcqmrmxy.
`Anne F. Mannion, Genevieve A. Dumas, Joan M. Stevenson, and
`Robert G. Cooper
`
`Imaging Assessment of Sacroiliac Screw
`Placement Relative to the N euroforamen
`
`585
`
`Results showed that ¢'om/Mn’d1tIllfl7 coniicnfionul (axial) mm-
`putcd tomography, computed /omogruphy using mulziplanar
`reconstruction Orl('IIl(’d roughly /mrallel to axis oftlur neuro-
`foramen and perpendicular to the long axis of the screw is
`more accuratv in determining sacroiliac screw position relative
`to the neurofommcn. It also was ohservcd that titanium
`screws had less scatter than stainless~steel screws.
`
`Benjamin A. Goldberg, Ronald W. Lindsey, Christian Foglar,
`Thomas D. Hedrick, Theodore Miclau, and John L. Hadad
`
`Point of View
`
`Dennis C. Turk
`
`606
`
`I Health Services Research
`
`Medication Use for Low Back Pain in Primary
`Care
`
`607
`
`Mudiaitions used by 219 patients with back pain were exam-
`inrd. Nonstcroidal anti-inflammatory drugs, which often were
`used with muscle relaxants, were the most common medica-
`tions. Patients who were prescribed medications, particularly
`muscle rclaxants, reported less severe symptoms after 1 week
`than those receiving no medications. Randomized trials are
`needed to determine which medications are most eflective.
`
`Daniel C. Cherkin, Kimberly J. Wheeler, William Barlow, and
`Richard A. Deyo
`
`I Surgery
`
`I Ergonomics
`
`Regional Assessment of Joint Position Sense in
`the Spine
`The reproducibility ofactive position sense measurements in
`the spine was assessed using a three-dimensional electromag-
`
`590
`
`Spondylodiscitis After Lumbar Discectomy:
`Incidence and a Proposal for Prophylaxis
`
`615
`
`In 508 patients undergoing lumhosacral microdiscectomy
`without antibiotic prophylaxis and close clinical, laboratory
`and racliologic follow—up examinations, a 3.7% incidence of
`postoperative spondylodiscitis was found. A gentamicin-con-
`
`Page 3 of 11
`Page 3 of 11
`
`

`
`Contents
`Continued
`
`trziniiig eollagenozis sponge ])]L1r‘(:d in the cleared disc space in
`an additional Z134 jmtienis reduced this incidence to 0%.
`
`Veit Rohde, Bernhard Meyer, Carlo Schaller, and
`Werner E. Hassler
`
`“End Result Idea " was the turning point from the prinzitiue,
`19th century, iirtisan-style mediml practice ton/czrd the current
`scientific basis of medicine and enzphnsis on ozttconzes.
`
`Serge C. Kaska and James N. Weinstein
`
`Point of View
`
`0. L. Usti
`
`I Tumor
`
`620
`
`I Spine Update
`
`Aneurysmal Bone Cyst of the Spine: Management
`and Outcome
`
`621
`
`The tretztment and uuteome of52 ptztierits with imeurysnml
`hone eysfs ofrhe spine were rez./iewed. Improved irmiging and
`upemtiue reelmiques almost vermin/y decreased the 7‘l’CII7ft’H('L’
`rate for these lesions. Current treimnenz‘ rev:nmnendations
`involz/e preoperative se/eetizre arterial emlmlizution, inzmIe-
`siomil e:\:i‘1'sion cziremige, hone grtiftirzg. and fusion of the af-
`fected area ifirzsmlnlity is present.
`
`Panayiotis J. Papagelopoulos, Bradford L. Currier,
`William J. Shaughnessy, Franklin H. Sim, Michael J. Ebersold,
`Jeffrey R. Bond, and K. Krishnan Unni
`
`I Historical Perspective
`
`Ernest Amory Codman, 1869-1940: A Pioneer of
`Evidence-Based. Medicine: The End Result Idea
`
`629
`
`Lumbar Interbody Cages
`
`634
`
`This Ii/rdirle /u'esen2‘s :1 simple striictiiml c'lizssi/’ir.'zzrz'm1 ofIitm-
`Imr inzerlmdy cage deuiees mm’ ei/iiluizies their sriimhilify In
`midress a set ofi:/early defined szirgiml goals. The materials
`crmmmnly used in these r1'eiIiees also are assessed.
`
`Bradley K. Weiner and Robert D. Fraser
`
`Letters
`
`Meetings of Interest for Spine Physicians and
`Surgeons
`
`The origins of r'zIidence—hczsed nzediei/re and orifewm's research
`stem from the ideas and work of Ernest Amory Ciuimim. His
`
`Information for Authors
`
`641
`
`644
`
`647
`
`Page 4 of 11
`Page 4 of 11
`
`

`
`SPINE Volume 23, Number 5, pp 634—64()
`©1998, l.ippincott—Raven Pulvlislicrs
`
`Spine Update
`
`Lumbar Interbody Cages
`
`Bradley K. Weiner, MD,* and Robert D. Fraser, MD, FRACST
`
`interbody cage devices, used to assist interbody fu-
`sion, are rapidly gaining popularity in the surgical man-
`agement of chronic low back pain. This update pro-
`vides a structural classification of commonly used
`devices and assesses them against a set of clearly de-
`fined surgical goals, including ability to correct the ex-
`isting mechanical deformation, ability to provide me-
`chanical stability, ability to provide a suitable
`environment for arthrodesis, and ability to limit "built-
`in" morbidity. In addition, the materials used in the de-
`vices are examined regarding their biomechanical, bio-
`logic, and radiographic characteristics. [Key words:
`arthrodesis, cages, fusion, lumbar spine] Spine 1998;23:
`634-640
`
`Despite considerable controversy surrounding the effi-
`cacy of lumbar fusion in the management of low back
`pain secondary to disc degeneration, there has recently
`been a rapid and progressive increase in the use of inter-
`body cages as an adjunct to arthrodesis. Hopes of im-
`proving surgical outcomes while decreasing surgical
`morbidity undoubtedly have been the primary driving
`force, but secondary factors such as aggressive promo-
`tion on the part of manufacturers and the surgeons in-
`volved in the development of such products undoubtedly
`play a significant role. The recent history of spine surgery
`has too often seen legitimate hopes of improved patient
`care reduced to gadgetry and salesmanship. Accordingly,
`at this early stage of enthusiasm, there is the need for a
`logical approach to the assessment of lumbar interbody
`cages so that rational indications for their use may be
`developed. This update describes a structural classifica-
`tion of cage types and then measures each of these
`against a well—defined set of surgical goals. In addition,
`the materials used in the devices are assessed and their
`
`biomechanical, radiographic, and compatibility charac-
`teristics examined.
`
`I Goals
`
`it has long been
`improvement in functional status.
`thought that this would best be achieved by correction of
`the existing mechanical deformation to its anatomic
`baseline and by the provision of stability to the segment
`to prevent future abnormal
`(z’.e., excessive or pain-
`provoking) motions. Lumbar interbody fusion has in
`theory been the preferred surgical technique to achieve
`these goals. Unfortunately, this procedure has demon-
`strated extremely variable results, with fusion rates rang-
`ing from 19% to 95% and satisfactory clinical results
`ranging from 14% to 93%.” In addition, Dennis et al14
`noted that 100% of patients lost disc height during the
`postoperative phase.
`As a result, interbody cage devices have been devel-
`oped with the aim of overcoming these problems. They
`strive to:
`
`1) correct the existing mechanical deformation,
`2) provide stability to the segment until arthrodesis is
`obtained,
`
`3) provide the best possible environment for success-
`ful arthrodesis, and
`4) achieve this with limited morbidity associated with
`their use.
`
`Correction of Existing Mechanical Deformation
`From basic principles, an interbody cage device should
`restore disc height, place the anular fibers in a “normal”
`tension, create lordosis through the segment, obtain sag-
`ittal balance through the segment, reduce subluxed facet
`joints, enlarge the neuroforaminal space, and restore to
`normal the proportion of weight bearing through the
`anterior column. However, it must be conceded that at
`present there is not convincing evidence from controlled
`studies that correcting the aforementioned mechanical
`deformation is actually associated with symptom relief in
`patients who have these devices implanted.
`
`The primary goal of lumbar surgery in the degenerative
`setting is relief of the patient’s pain with a subsequent
`
`From the "'Department of Orthopaedic Surgery, Spine Surgery Section,
`Summa Health Systems and Northeastern Ohio Universities, College of
`hledicine, Akron, Ohio, and the ‘l'Spinal Unit, University of Adelaide,
`Royal Adelaide Hospital, Adelaide, South Australia, Australia.
`Acknowledgment date: July 23, 1997.
`Acceptance date: October 20, 1997.
`Device status category: 10.
`
`Provision of Mechanical Stability
`In the worst case, motion through the operative segment
`leads to progressive mechanical device loosening and
`eventual failure of implant or bone. In the best case, it
`significantly decreases the chances of obtaining a solid
`bony arthrodesis. An interbody cage device should pro-
`vide immediate stiffness to the segment, be able to with-
`stand the vertical loads applied, and provide adequate
`
`634
`
`Page 5 of 11
`Page 5 of 11
`
`

`
`Lumbar Interbody Cages ' Weiner and Fraser
`
`635
`
`Bone Graft
`
`4:
`
`
`
`Figure 1. Sample horizontal cylinder. It is packed with bone graft
`and then screwed into position, commonly through an anterior
`laparoscopic approach.
`
`is placed through
`It
`Figure 2. Sample thick-walled vertical ring.
`an open anterior approach and a large anular window.
`
`resistance to translational and rotational forces in all
`directions.
`
`Provision of Optimal Environment for Arthrodesis
`The best environment for interbody fusion consists of 1)
`complete discectomy so that no intervening tissue lies
`between the bony fusion beds; 2) complete excision of
`the cartilaginous endplate down to healthy bleeding
`bone; 3) preservation of the bony endplate to maintain
`structural integrity and discourage subsidence; 4) use of
`the smallest volume of cage (as cage volume increases,
`graft volume decreases) that will provide for mechanical
`stability; 5) use of optimal grafting techniques—large
`amounts of graft (autogenous, cancellous) with the wid-
`est possible interface with the fusion beds (bony end-
`plates) and maximal graft filling the interspace; and 6)
`provision of compression through “distractive compres-
`sion” (i.e., restoration of anular tension) and return of
`load bearing to the anterior column.
`
`Limit Morbidity
`An ideal cage would provide for each of the preceding
`surgical goals while not adding any morbidities to its use,
`excepting those inherent in the operative approach.
`
`I Classification of Cages
`
`There are several cages available and, undoubtedly,
`many more will be designed. A logical classification
`based on the structural and material characteristics
`
`should permit an analysis of those available and the easy
`placement of those yet to be developed.
`
`Structure
`
`There are three general structures used:
`
`1. Horizontal cylinders. These are the manufactured
`equivalents of dowel techniques for interbody fusion.
`An example is shown in Figure 1.
`2. Vertical rings. These are the manufactured equiva-
`lents of femoral cortical rings. An example is shown in
`Figure 2.
`3. Open boxes. these are the manufactured equiva-
`lents of tricortical grafts (except in this case, quadri-
`cortical). An example is shown in Figure 3.
`
`Materials
`
`In general, two basic materials are used: metals and car-
`bon fiber.
`
`I Assessment of Cages
`
`The following assessment measures the ability of the
`aforementioned classes of cages successfully to achieve
`the previously defined goals of surgery.
`
`Horizontal Cylinders
`
`Brief History. In 1979, Wagner et al34 reported the re-
`sults of using such a device to achieve fusion in the cer-
`vical spine of horses with “wobbler syndrome.” His co-
`author and the designer of the “basket” was Bagby, who
`subsequently, in 1983, began working with Kuslich and
`a group of bioengineers to develop a similar implant for
`human use, which was reported in 1988.2 Since then,
`other horizontal cylinders have come on the market.
`These devices are usually placed in pairs resting side-by-
`side in the anteroposterior plane.
`
`correction of Mechanical Deformation. Disc height is re-
`stored well with these devices, given that an appropri-
`ately sized cage is used. As a result, anular fibers are
`placed under increased tension. One advantage of hori-
`zontal cylinders is that they can be placed through
`smaller anular windows than a vertical ring—the larger
`the window, the greater the laxity noted through the
`segment.“
`Lordosis and sagittal balance are best restored by be-
`
`Bone Graft —> :
`
`
`
`Figure 3. Sample open box cage. It is commonly placed through a
`posterior lumbar interbody ‘fusion approach,
`in which case sup-
`plemental fixation usually is required.
`
`Page 6 of 11
`Page 6 of 11
`
`

`
`636 Spine - Volume 23 0 Number 5 - 1998
`
`ing built into the device (i.e., a thickness greater anteri-
`orly than posteriorly). Initial designs of horizontal cylin-
`ders, being true cylinders, failed to account for this.
`Newer designs, in the form oftruncated cones, have been
`designed to restore lumbar lordosis, and their incorpo-
`ration into the devices has been shown to decrease seg-
`ment laxity.3Z
`Restoration of facet alignment and neuroforaminal
`volume and area rely on restoration of disc height, espe-
`cially posteriorly. Horizontal cylinders have been shown
`to increase neuroforaminal volume by approximately
`20% and to increase the area by approximately 30% at
`L4—L5 and L5—s1.”
`
`The implications of restoration of disc height, anular
`tension, lordosis, sagittal balance, and facet alignment
`on the distribution of loads across the segment, although
`assumed to result in an anterior shift, have yet to be
`studied.
`
`Provision of Stability. Horizontal cylinders appear to
`provide excellent stability to a segment. Butts et al,“
`using the Bagby and Kuslich (BAK) system in porcine
`and bovine spines, demonstrated increased stiffness of
`motion segments. Zdeblick et al'i’7 found that by using
`two BAK devices in calf spines, the stiffness doubled over
`uninstrumented segments. Grobler et al]6 found similar
`results in the primate spine. Tencer et al3Z observed the
`same using the Ray device in calf and human specimens.
`They also found that the number of implants or direction
`of placement had little effect on stiffness when subjected
`to flexion, extension, or lateral bending forces. Interest-
`ingly, they noted that torsional stiffness was minimally
`changed. Glazer et al,” testing a new device being devel-
`oped by Sofamor Danek in human specimens, noted sim-
`ilar increases in stiffness in all directions, including tor-
`sion.
`
`Resistance to compressive loading is excellent as well.
`Kuslich et al22 noted no failure over 5 million cycles, and
`Tencer et al32 demonstrated bony failure long before de-
`vice failure.
`
`Environment for Arthrodesis. Although it is clear that the
`mechanical goals of cages are achieved by horizontal cyl-
`inders, it is equally clear that their ability to provide a
`satisfactory milieu for fusion, given current designs and
`techniques, is suspect. It has long been stressed that com-
`plete disc excision is requisite, and this is not achieved
`routinely-— especially with the recently developed lapa-
`roscopic techniques. Similarly, the cartilaginous end-
`plate is not routinely excised throughout the disc space.
`Both represent avascular tissues that can impede solid
`arthrodesis. By virtue of shape, the volume available for
`bone graft in the cylinders is less than that obtained with
`either vertical ring or open box designs. The interface
`between graft contained within the cage and the graft
`bed is dictated by the size of the holes in the cage and the
`
`number of holes interfacing with vascularized bone.
`Biedermanf’ calculated that the BAK cage allowed max-
`imum interface of only 10% of the surface area of the
`endplate. This results in a dilemma; to maximize graft
`Contact with high-quality bony bed, greater amounts of
`bony endplate need to be excised and larger cages need to
`be used. This risks destabilization of the bony endplate
`with secondary potential subsidence. Sandhu et al,” in
`an in zflivo model using horizontal cylinders, showed an
`average of 20% postoperative loss of disc height attrib-
`utable to such bony subsidence.
`At the Spinal Unit of the Royal Adelaide Hospital, a
`sheep model with horizontal cylinder implants has been
`used to assess fusions with autogenous cancellous bone
`versus autogenous cultured bone, and it was found that
`solid fusion through the cages did not occur—bony
`“locking,” with some growth through the holes but with
`intervening cartilaginous tissues remaining centrally,
`was the rule.”
`
`Limit Morbidity. Although most morbidities from cages
`result from the operative approach (anterior open, lapa—
`roscopic, or posterior lumbar interbody fusion [PLIH
`approaches) and can be disastrous, some may be “built
`into” the devices. For horizontal cylinders to maximize
`disc space distraction and graft—to—bed contact, large-
`diameter devices are required. Because horizontal cylin-
`ders are placed side by side, this results in a minimal
`width of the combined devices (twice the diameter). As a
`result, the posterolateral regions of the anulus area at
`risk. Disc material and the cylinders themselves can
`breach this posterolateral region, resulting in canal or
`foraminal compromise and associated neurologic se-
`quelae. The alternative of using a smaller—diameter cyl-
`inder has been found clinically to decrease stiffness and
`likelihood of successful arthrodesis.3" Design changes
`may allow avoidance of this problem.
`
`Vertical Rings
`
`Brief History. Beginning in 1972 and first publishing in
`'1 975, Ono et alzf’ began using metallic devices similar to
`vertical rings in the cervical spine after corpectomy for
`tumors. Since then, various devices have been used for
`reconstructions of the anterior column in tumor surgery.
`For degenerative disorders, the use of allograft femoral
`cortical rings packed with autograft cancellous bone had
`been popularized by Kozak and O’Brien.“ The blending
`of these concepts has led to manufactured vertical rings
`for use in degenerative conditions.
`
`Correction of Mechanical Deformation. Disc height resto-
`ration with vertical rings is sufficient provided an appro-
`priately sized device is used and minimal destruction of
`the endplate has resulted. Disc height is maintained well,
`with an average loss of only 1 mm over an average of 1
`year (Pagan A, Fraser RD. One year results using the
`Brantigan ALIF cage; unpublished data, 1996). Accord-
`
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`
`ingly, it is assumed that facet alignment and ncurofo—
`raminal area are increased in a fashion similar to that
`
`noted with horizontal cylinders.
`Using a wedged, thick-walled carbon-fiber device
`with the an anterior thickness 2 mm greater than poste-
`riorly, Fagan and Fraser (One year results using the Bran-
`tigan ALIF cage; unpublished data, 1996) demonstrated
`that lordosis and sagittal alignment are maintained or
`restored. Thick-walled devices appear to preserve lordo-
`sis, with an average loss of only 1° noted at 1 year.
`
`Provision of Stability. Stability is usually provided by
`small teeth or ridges that penetrate into the bony end-
`plates. Very little information on biomechanical testing
`of these devices has been published. Stiffness has not been
`studied directly, but is expected to be increased. No test-
`ing has been published regarding resistance to transla-
`tional and rotational forces applied to the stabilized mo-
`tion segment, although when thin—walled devices have
`been used, concerns about rotational control have been
`expressed. 19
`The ability to withstand vertical loads appears to de-
`pend on wall thickness. Thi11—walled devices, although
`affording a greater volume available for bone graft, tend
`to subside into the vertebral bony endplates, resulting in
`loss of lordosis and sagittal balance, and therefore they
`are often supplemented by additional internal fixation.
`Thicker-walled devices, in the authors’ experience, sub-
`sided in about 50% of cases (Fagan A, Fraser RD. One
`year results using the Brantigan ALIF cage; unpublished
`data, 1996). However, this occurrence has decreased sig-
`nificantly with less aggressive preparation of the bony
`endplates and the use of the largest possible ring to allow
`contact with the stronger periphery of the endplate.
`Thick-walled devices, of course, have the disadvantage
`of reducing the available volume for bone graft.
`
`Environment for Arthrodesis. A distinct advantage of ver-
`tical ring designs is their ability to provide an excellent
`milieu for arthrodesis. Their proper placement requires
`complete anterior discectomy, cartilage endplate exci-
`sion, and bony endplate preparation. As noted, any re-
`sidual disc or cartilage results in a significantly decreased
`chance of obtaining a solid arthrodesis.” A large volume
`is available within these cages for bone graft, whereas the
`interface graft and the prepared endplate are wide.
`
`Limit Morbidity. The major disadvantage built into ver-
`tical rings is their size. They are to occupy the disc space
`and thereby require an open anterior surgical approach
`and a wide anular window for placement. Complications
`associated with open anterior approaches have been well
`documented.4 A larger anular window likely results in
`decreased stiffness to the segment” and may interfere
`with the “distractive-compression” mechanism (al-
`though this requires further study) — both potentially de-
`creasing the likelihood of obtaining a solid arthrodesis.
`
`Lumbar Interbody Cages - Wciner and Fraser 637
`
`Open Boxes
`
`Briel History. Cloward,]3 over 50 years ago, began us-
`ing PLIF in degenerative conditions. Modifications of the
`technique were subsequently designed that used tricorti—
`cal grafts to provide structural support at right angles to
`the endplates. As was the case for anterior cortical dow-
`els and rings, these tricortical grafts often failed to pro-
`vide suficient structural support. In 1991, Brantigan and
`Steffee7 designed a carbon—fiber PLIF cage that today is
`the most commonly used device with an open box con-
`figuration.
`
`Correction of Mechanical Deformation. Precise surgical
`technique allows the disc height to be restored and main-
`tained until arthrodesis, with an average loss of 0.6 mm
`during this time.8 The ability to correct lordosis and sag-
`ittal balance, to the authors’ knowledge, has not been
`measured and in any event is influenced by pedicle screw-
`—plate instrumentation, which is often used to address
`the instability created by the extensive posterior ap-
`proach. These cages initially were not wedged, although
`this shape, designed to restore lordosis, is now available.
`Obviously, however, through a PLIF approach the pos-
`terior anular window must have a height at least as large
`as the anterior thickness of the cage to allow device pas-
`sage. If the posterior device height is less (i.e., lordosis is
`built in), the superior endplate will settle to rest on the
`cage. Although this restores lordosis, it fails to put the
`remaining posterior anular fibers under tension and
`could limit the degree of facet realignment and neurofo-
`raminal widening.
`
`Provision of Stability. Much like vertical rings, little bio-
`mechanical information has been published on open box
`devices. Brantigan et al7 tested the device in compression
`and, as is the case for the other designs, found bony
`endplate failure before device failure. They also tested
`pullout strength and found the teeth design three times
`more resistant than standard PLIF bone grafting tech-
`niques, suggesting that retropulsion into the canal is un-
`likely. Stiffness was noted to be subjectively increased,
`but no formal testing of this or the ability to resist trans-
`lational and rotational forces was undertaken because,
`at the time, the device was considered merely a supple-
`ment to pedicle screw and plate fixation. To avoid com-
`plications inherent iii the PLIF approach and the need for
`supplemental posterior fixation, newer designs of open-
`box devices have and are being developed for anterior
`laparoscopic use. Clearly, further independent mechani-
`cal testing of these devices without supplemental poste-
`rior fixation is required.
`
`Environment lor Arthrodesis. The current techniques for
`implantation of these devices include near—complete disc-
`ectomy and cartilaginous endplate excision. A good vol-
`ume of space is available for bone graft within the cages,
`and the interface with the fusion bed is wide and the graft
`continuous. If the devices provide for adequate stability
`
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`638
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`Spine - Volume 23 0 Number 5 - 1998
`
`of the segment, these factors should afford an excellent
`milieu for arthrodesis. Clinical study has demonstrated
`good fusion rates when combined with posterior instru-
`mentation.8
`
`Limit Morbidity. Most morbidities with the use of these
`devices have been attributable to the use of a PLIF ap-
`proach and posterior pedicle screw—plate instrumenta-
`tion, and are rather numerous and serious.8 Direct de-
`vice-related morbidity, on the other hand, appears
`minimal.
`
`I Materials
`
`Three properties of the materials used in cages must be
`assessed: the biologic response to the material, the bio-
`mechanical strength of the material, and the radio-
`graphic characteristics.
`
`Metals
`
`Biologic Response. Before solid arthrodesis, micromo-
`tion through the segment was unavoidable and particu-
`late debris was likely. The local effects of such particles
`have been well studied in joint arthroplasty in viva as
`well as in I/itro. Cellular reaction to such debris is pri-
`marily led by macrophages and can result in the release
`of mediators such as interleukin—1, interleukin-6, prosta-
`glandin E2, and tumor necrosis factor, each of which can
`directly affect osteoblasts and osteoclasts to result in os-
`teolysis and subsequent device—bony interface loosen-
`ing.18 Such