Reprinted from SPINE, Vol. 23, No. 13, July I, 1998
`Copyright © 2000, Lippincott Williams & Wilkins
`Printed in the U.S.A.
`
`Minimally Invasive Anterior
`Retroperitoneal Approach to the
`Lumbar Spine
`Emphasis on the Lateral BAK
`
`Paul C. McAfee, MD, John J. Regan, MD, W. Peter Geis, MD,
`and Ira L. Fedder, MD
`
`MC0000005
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`1
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`NUVASIVE 2065
`Medtronic v. NuVasive
`IPR2014-00075
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`IPR2019-00362, Ex. 1054, p. 1 of 10
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`

`SPINE Volume 23, Number 13, pp 1476d484
`©1998, Lippincott-Raven Publishers
`
`• Minimally Invasive Anterior .
`Retroperitoneal Approach to the
`Lumbar Spine
`Emphasis on the Lateral BAK
`
`Paul C. McAfee, MO,* John J. Regan, MO,t W. Peter Geis, MO,:J:
`and Ira L. Fedder, MO*
`
`Study Del:lign. Eighteen patlfmts with lumbar Insta(cid:173)
`bility from fractures, postlamlnfictomy syndromfi, Of in(cid:173)
`fection were treated prospectlvfily with minimally Inva(cid:173)
`sive retroperitoneal lumbar fusions.
`Objeetivel:l, To determine If Interbody Bagby and
`KUslich fusion cages and femoral aUograft bone dowels
`can be inserted In a transverse direction via a lateral
`endollcopic retroperitoneal approach to achleva spinal
`stability,
`Summary of Back,round Data. Endoscopic spinal
`approachall hava bean u!;led to achi(lva lower lumbar
`fusl·on when instrumentation Is placed through a laparo(cid:173)
`scopic, transperitoneal route. However, complications of
`using this approach include postoperative Intra-abdomi(cid:173)
`nal adhasions, retrograde ejaculation, IJreat vesael In(cid:173)
`jury, and implant migration. This stucly h, the first elinl(cid:173)
`cal series investigating the use of the latllral
`retroperitoneal minimally Invasive approach for lumbar
`fusion!! from 1..1 to J.P,
`Methods. fllghtaen pgtiemts underw{lnt antarior intIJr(cid:173)
`bocly decompression and/or stabiligation vIa andotUIOplQ
`retroperitonaal approach ell. In most Oallel:l, thrae 12·mm
`portals were used. Two parallel tranl:lv@rse interbody
`cages restorad the neufoforamlnal height and the de(cid:173)
`sired amount of lumbar lordosis was aohlaved by in(cid:173)
`serting a larger anterior cage, dilltraotion plug, or bona
`QQWQI.
`Ro&ult&. Tho Qvorall morbidity Qf thll prQcadura w~s
`lower than thiilt iillillociated with traditional "opem" rafro(cid:173)
`perlt(m~~1 or laparotomy teqhniquall, with a maan
`lan9th of hQllplt~1 stay of 2.9 Qays (range, outpathmt
`prQQedure to § Qays), The mean estimated Intraopera·
`tive blood 101:111 w~& 205 cc (rangs, 25=1000 QQ), There
`were nQ casEls of Implant migration, significant lIubsi(cid:173)
`dfiloQa, Of peeudo~rthrosis at mean foiiow-yp examina(cid:173)
`tion of 24.3 months (r~n.ge, 12-40 month!» after
`surgery.
`
`From the *Scoliosis and Spine Center, St. Josephs Hospital, Baltimore,
`Maryland, the tTexas Back Institute and the Institute for Spine and
`Biomedical Research, Plano, Texas, and the :j:Minimally Invasive Ser(cid:173)
`vices Training Institute, St. Josephs Hospital, Baltimore, Maryland.
`Acknowledgment date: August 28, 1997.
`First revision date: October 23, 1997.
`Acceptance date: December 2, 1997.
`Device status category: 9.
`
`1476
`
`Conclusions. This preliminary study of 18 patiants
`illustrates that endoscopic technlque& can be applied
`effeQtively through a retroperitoneal approach with the
`patient in the lateral position. Unlike the patient& who
`had undergone transperitoneal procedurEls Qescribed in
`previous reports, in these preliminary 18 patients, there
`were no cases of retrograde Eljaculatlon, injury to the
`great vessels, or implant migration. [Key words; ando(cid:173)
`SQopic retroperitoneal, minimally invasive retroperito(cid:173)
`neal lumbar fusions, transverse axis BAKJ Spine 1998;
`23:1476-1484
`
`The use of minimally invasive and endoscopic ap(cid:173)
`proaches has been described for multiple abdominal pro(cid:173)
`cedures, including cholecystectomy,29,3l,32 appendecto(cid:173)
`my,28 colon resection,12 and Nisson fundoplication. 33
`Recently, increased attention has been paid to the use of
`these approaches with lumbar discectomy25,26 and lum(cid:173)
`bar anterior interbody arthrodesis. l,4,8 Most endoscopic
`approaches described thus far have been transperitoneal
`and have depended on CO2 insufflation to provide work(cid:173)
`ing space and to retract the small bowel out of the sur(cid:173)
`gical field. Gaur6 and McDougall et a124 were the first to
`describe retroperitoneoscopy, an endoscopic retroperi(cid:173)
`toneal approach for urologic procedures. The current
`report describes the natural transition toward retroperi(cid:173)
`toneal minimally invasive endoscopic spinal surgery,
`which does not require CO2 insufflation, Trendelenburg
`position, entrance into the peritoneum, or anterior dis(cid:173)
`section near the great vessels to provide safe exposure for
`spinal surgery.
`• Materials and Methods
`
`Twelve minimally invasive retroperitoneal lumbar procedures
`were performed at St. Josephs Hospital in Baltimore, Mary(cid:173)
`land, and six were performed at Presbyterian Hospital of
`Plano, Texas, between March 1994 and September 1996.
`There were 6 female and 12 male patients, with a mean age of
`53.4 years (range, 31-76 years).
`The indications for surgery included 13 cases of degenera(cid:173)
`tive conditions, three cases of infections, one unstable burst
`fracture, and one case of a retroperitoneal neurofibroma in-
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`MC0000006
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`Endoscopic Retroperitoneal Interbody Fusions· McAfee et al 1477
`
`Figure 1. This 75-year-old man
`had back pain and right anterior
`thigh pain 2 years after he had
`undergone laminectomies from
`L3 to SI with a posterolateral fu(cid:173)
`sion from L4 to SI. The lateral (A)
`and anteroposterior (B) radio(cid:173)
`graphs show "vacuum disk" sign
`at L3-L4 with lateral translation
`of the L3 vertebral body on L4.
`His characteristic pain was re(cid:173)
`produced by an L3-L4 discogram
`performed by an independent ra(cid:173)
`diologist. Lateral (e) and antero(cid:173)
`posterior (D) radiographs were
`obtained after the procedure us(cid:173)
`ing the endoscopic retroperito(cid:173)
`neal approach was performed
`and a transversely oriented BAK
`fusion cage was inserted (15 mm
`in diameter and 24 mm length).
`The patient's back and right leg
`pain resolved after surgery.
`
`volving the lumbosacral plexus. Ten of the 13 patients in the
`degenerative category had undergone previous destabilizing
`laminectomy procedures elsewhere before referral to the au(cid:173)
`thors' institutions. Flexion-extension lateral radiographs dem(cid:173)
`onstrated more than 3.5 mm of translation, and anteroposte(cid:173)
`rior radiographs showed 10 degrees or more of scoliotic disc
`space collapse with "vacuum disc sign." Positive discograms
`documented a provocative pain response at the unstable level
`(Figure 1). The one patient in the degenerative category who
`had not undergone previous destabilizing surgery had a mas(cid:173)
`sive L2-L3 central disc herniation with left quadriceps weak(cid:173)
`ness.
`
`The retroperitoneal approach proved to be very versatile in
`the range of vertebral levels addressed throughout the 18 cases.
`Four patients underwent procedures at LI-L2, seven patients
`at L3-L4, and two patients at L4-L5. There were four endo(cid:173)
`scopic decompressions and fusions at L2-L3. One patient with
`vertebral osteomyelitis underwent a decompressive procedure
`from L2 to L4.
`
`Surgical Technique. The approach is a combination of video(cid:173)
`assisted thoracoscopic and laparoscopic methods. The patient
`is put under general endotracheal anesthesia, then turned in the
`
`MCOOOOOO?
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`1478 Spine· Volume 23· Number 13 • 1998
`
`Figure 2. A view of a transparent optical trochar (Optiview, Ethi(cid:173)
`con Endosurgery, Cincinnati, OH) that was used in dissecting the
`retroperitoneal space. Notice the "winged keel cutting edges,"
`which only will penetrate a fascial layer, such as the peritoneum,
`if the trochar is forcibly twisted backwards and forwards.
`
`lateral decubitus position on a radiolucent, graphite, Jackson
`Maximum lateral access table (0.5.1. Corporation, Union City,
`CAl made specifically for the endoscopic approach, with side
`rails designed to accommodate robotic arms? and to facilitate
`c-arm fluoroscopy. A l-cm incision is made at the anterior
`portion of the 12th rib for approaching from LI or L2. Below
`L2, a lateral c-arm fluoroscopic image is obtained, with a metal
`marker overlying the patient's skin in the midaxillary line. This
`method optimizes the placement of the working portal directly
`over the unstable disc or vertebral segment. The three tech(cid:173)
`niques used to dissect the retroperitoneal space are: finger dis(cid:173)
`section, balloon insufflation, or the use of an optical, transpar(cid:173)
`ent, dissecting trochar? called an Optiview (Ethicon
`Endosurgery, Cincinnati, OH; Figure 2).
`The 10-mm laparoscope is inserted into the Optiview dis(cid:173)
`secting trochar and refocused once the trochar enters the sub(cid:173)
`cutaneous tissue. The trochar has two "winged keel" cutting
`surfaces that will not penetrate a fascial layer such as the peri(cid:173)
`toneum unless the trochar is twisted. Therefore, the three ab(cid:173)
`dominal muscular layers overlying the peritoneum are pene(cid:173)
`trated in sequence under direct visualization until the
`preperitoneal fat is encountered. The trochar is used to create a
`potential space that is superficial to the peritoneum until the
`laterally oriented fibers of the psoas major muscle are viewed.
`Usually, the genitofemoral nerve is visualized on the surface of
`the psoas muscle. At this juncture, a dissection balloon, such as
`that manufactured by Origin (Menlo Park, CAl, can be filled
`with I liter of normal saline or air to dissect the retroperitoneal
`layer, more correctly referred to as the retrotransversalis fascia.
`Alternatively, carbon dioxide insufflation can be forced into the
`retroperitoneal cavity up to a pressure of 20 mm of mercury to
`create a working space to triangulate endoscopically. 3D Once
`the retroperitoneal space is enlarged, at least three portals are
`used-working portal, for pituitary rongeur; curettes; a high(cid:173)
`powered burr; or Kerrison rongeurs. A second portal is neces(cid:173)
`sary for the 10-mm laparoscope. A third portal is used for
`retraction of the psoas major muscle off of the spine in a pos(cid:173)
`terior direction. The relatively avascular intervertebral discs are
`exposed first. Then, the respective midportions of the adjacent
`vertebral bodies are exposed, and the lumbar segmental vessels
`
`are ligated and divided. Occasionally, a fourth 10-mm portal is
`used for suctioning in highly vascular cases requiring corpecto(cid:173)
`mies for tumors or infections. Occasionally, for longer strut
`grafts or instrumentation, the lO-mm working portal is ex(cid:173)
`tended in size as much as 5 cm, and an endoscopically assisted,
`mini-laparotomy type of retroperitoneal exposure facilitates
`the corpectomy or spinal instrumentation. If the size of the
`working portal is extended, of course, the CO2 insufflation is
`lost, and the working space in the retroperitoneum has to be
`maintained by using retractors. This technique is advantageous
`because the spinal decompression can be accomplished without
`airtight seals, and because standard thoracoscopic instruments
`can be used on the lumbar spine. In other words, throughout
`the remainder of the procedure, spine instruments of heterog(cid:173)
`enous shaft diameters can be used, and airtight seals around
`trocars are not required.
`Once the vertebral level is confirmed fluoroscopically, the
`transversalis fascia, perinephric fascia, and retroperitoneal
`contents are retracted anteriorly (Figure 3). Electrocautery is
`used to mark the intervertebral discs adjacent to the involved
`lesion. For example, for an L1 corpectomy, the L1-L2 and the
`T12-Ll intervertebral disc spaces are marked. A left-sided ap(cid:173)
`proach to the surgery is preferred to a right-sided approach,
`because it is easier to dissect the aorta off the spine than to
`dissect around the more friable inferior vena cava; this is par(cid:173)
`ticularly true in cases of pyogenic vertebral osteomyelitis or
`cases of neoplasm that occur after radiation therapy with ret(cid:173)
`roperitoneal fibrosis. The psoas muscle is retracted posteriorly,
`and the ureter is retracted anteriorly.
`If a corpectomy is being performed21 after the two adjacent
`discectomies, the surgeon must have access to three methods of
`hemostasis: 1) Endo-Avitene Microfibrillar Collagen (Alcon,
`Inc., Humacao, Puerto Rico), 2) Gelfoam (Upjohn Corp.,
`Kalamazoo, MI) soaked in Thrombin (GenTrac Corp., Middle(cid:173)
`town, WI), and 3) bipolar endoscopic electrocautery. At this
`point, the segmental vessels are dissected from the underlying
`bone and elevated with a right-angled clamp. It is important to
`use two vascular clips or an endoloop on the high-pressure side
`of the vessels; the vessels are divided with endoshears. As a
`general rule, with any spine procedure the segmental vessels are
`ligated and divided in the anterior half of the vertebral body to
`allow collateral circulation to the neuroforamen and spinal
`cord to occur to its maximum potential. If the lesion is a tumor
`or infection, then a culture and a frozen section are obtained at
`this time in the procedure. A 45-degree, 4-mm-wide endo(cid:173)
`scopic Kerrison rongeur is used to resect the pedicle. Starting
`cephalad, the instrument is pointed caudad to protect the exit(cid:173)
`ing spinal roots. Either Kaneda (Acromed Corp., Cleveland,
`OH) heavy-duty rongeurs or a high-powered, 5-mm burr, such
`as the Zimmer (Wausau, IN) Ultra-power or Anspach with
`long extensions, can be used to hollow out the vertebral body.
`Curettes and smaIl2-3-mm Kerrison rongeurs are used to com(cid:173)
`plete the corpectomy. It is important to decompress the spinal
`canal all the way across to the base of the opposite pedicle.
`Decompression is accomplished only when the opposite pedicle
`is palpated or visualized. An autogenous iliac strut graft is
`tamped into place, filling the anterior portion of the corpec(cid:173)
`tomy defect.
`Alternatively, if the patient only requires a discectomy or
`one-level fusion, an anterior interbody fusion can be accom(cid:173)
`plished endoscopically. The disc space height is restored by
`using a distraction plug placed from the side. Optimally, two
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`Endoscopic Retroperitoneal Interbody Fusions· McAfee et al 1479
`
`distraction plugs are tamped into the disc space: one anteriorly
`and one posteriorly. At this point, either a single-barrel or dou(cid:173)
`ble-barrel drill tube is placed over the distraction plugs. The
`position of the distraction plugs is monitored with anteropos(cid:173)
`terior and lateral fluoroscopy. The center of the distraction
`plugs will correspond with the center of the BAK inter body
`fusion cages or endoscopic bone dowels. 1 The double-barrel
`tube is tamped into place to engage its teeth into the superior
`and inferior vertebral bodies to maintain the normal height of
`the disc space during the reaming and tapping of holes into the
`intervertebral endplates. The BAK fusion cage or laparoscopic
`bone dowels, which are composed of femoral allograft, are
`packed with autogenous iliac graft. The morselized iliac au(cid:173)
`tograft can be harvested with minimally invasive techniques
`through a 12-mm incision by using a disposable T-shaped awl.
`After surgery, the patient is placed in a warm and form
`corset (interbody fusion) or a thoracolumbar sacral orthosis
`(after a corpectomy), until radiographic fusion is accom(cid:173)
`plished. Intraoperatively, it is important to countersink the
`BAK fusion cages or laparoscopic bone dowel. The authors
`advocate packing additional bone graft superficial to the cage.
`At 3-6 months after surgery, arthrodesis can be confirmed if
`solid trabecular bone is observed to bridge one vertebrae to the
`adjacent level; this is the most reliable radiographic sign of a
`solid arthrodesis. Three-dimensional, computed-tomography
`reconstruction images of the bone within the cages and flexion(cid:173)
`extension lateral radiographs also can provide useful informa(cid:173)
`tion.
`
`• Results
`
`The mean length of the postoperative follow-up period
`was 24.3 months (range, 12-40 months). Fourteenpa(cid:173)
`tients underwent left-sided retroperitoneal approaches,
`and, in four patients, the pathology was addressed more
`easily on the right side. There were four patients who in
`whom a single incision was made of 5 centimeters or less.
`Fourteen patients had either three or four portals mea(cid:173)
`suring approximately 12 mm in length. These fourteen
`patients had CO 2 insufflation to assist the retrotransver(cid:173)
`salis dissection. The patients with one incision of 5 cen(cid:173)
`timeters or less had lesions compatible with infection or
`tumor, and the use of CO2 insufflation was avoided to
`prevent pressurizing the tumor cells or bacteria systemi(cid:173)
`cally into the patient's bloodstream.9 ,10,11,15
`Fusions were performed in 15 of 18 cases by using
`structural bone graft and/or inter body fusion cages. A
`38-year-old radiologist's wife with a neurofibroma aris(cid:173)
`ing from the lumbosacral plexus adjacent to the left com(cid:173)
`mon iliac vein did not demonstrate preoperative or in(cid:173)
`traoperative instability; therefore, a fusion procedure
`was not indicated.
`Ten patients underwent fusion surgery with custom
`BAK inter body fusion cages. The long axes of the cages
`were in the transverse direction (Figure 4). 4 In each case,
`the cages were packed with autogenous iliac bone graft
`harvested using a minimally invasive, T-shaped trochar,
`that was 10 mm in diameter. Four patients underwent
`placement of laparoscopic bone dowels fashioned from
`
`femoral allograft. The long axes of the implants were
`positioned in a transverse direction.
`There were no cases of implant migration or pseudo(cid:173)
`arthrosis. There were no cases of a radiolucent interface
`between the implant and the vertebral body. There were
`no cases of subsidence more than 1 mm, and there was
`trabecular bony bridging across the adjacent vertebrae
`laterally by 6 months after surgery.
`One additional patient did not undergo an endoscopic
`stabilization procedure. He was a 47-year-old man with
`an unstable burst fracture who had undergone left ante(cid:173)
`rior Kaneda instrumentation at the referring institution 3
`months earlier. He had had an incomplete neurologic
`deficit; a preoperative computed tomography scan had
`demonstrated continued right-sided cauda equina com(cid:173)
`pression. A right-sided endoscopic decompression was
`performed at the authors' institution, and additional sta(cid:173)
`bilization was not required.
`For all 18 cases, the mean duration of the surgical
`procedure, including the harvesting of iliac crest bone
`autograft, was 115.2 minutes (range, 60-260 minutes).
`The mean estimated blood loss, which, at the authors'
`institutions, is determined by the attending anesthesiol(cid:173)
`ogist, was 205 cc (range, 25-1000 cc). The mean length
`of hospital stay was 2.9 days (range, outpatient proce(cid:173)
`dure to 5 days).
`
`Complications
`There were three patients with postoperative complica(cid:173)
`tions. Case 2 was a 71-year-old man on renal dialysis
`who presented with sepsis. Endoscopic, retroperitoneal,
`L3-L4 discectomy; debridement; and fusion were per(cid:173)
`formed to culture and manage an L3-L4 pyogenic osteo(cid:173)
`myelitis. Six weeks after surgery, after treatment with
`intervenous antibiotics, the patient underwent posterior;
`segmental stabilization with Texas Scottish Rite Hospi(cid:173)
`tal implants from L1-L5 for more definitive stabilization
`and fusion. The single-level, anterior, interbody, endo(cid:173)
`scopic fusion was not believed to be adequate to prevent
`long-term lumbar kyphosis and instability.
`The second complication occurred intraoperatively in
`Case 3, when a laparoscopic bone dowel partially frac(cid:173)
`tured at the point of attachment of the driver into the
`central drilling peg in the femoral cortical allograft. The
`fractured piece of allograft was extremely small (approx(cid:173)
`imately 0.5 cm X 0.5 cm X 0.5 cm), and the patient's
`spinal stability was not jeopardized. There were no long(cid:173)
`term sequelae, and the patient had a solid arthrodesis,
`which was facilitated by morselized iliac autograft
`placed in the central chamber of alllaparoscopic bone
`dowels.
`The third complication occurred in a 69-year-old man
`who underwent transverse BAK cage insertion for post(cid:173)
`laminectomy instability at L3-L4. The patient developed
`a hematoma in the psoas muscle at L3-L4 after surgery.
`This resulted in a temporary genitofemoral nerve palsy,
`which resolved spontaneously within 3 months.
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`1480 Spine· Volume 23 • Number 13 • 1998
`
`• Discussion
`
`Retroperitoneal lumbar fusion and stabilization offers
`several advantages over conventional anterior transperi(cid:173)
`toneal laparoscopic approaches of the lumbar spine. 8
`Retroperitoneal approaches obviate the risk of small
`bowel obstruction or postoperative intraperitoneal ad(cid:173)
`hesions.16,17 Additionally, there should be a reduced risk
`of retrograde ejaculation, because the autonomic plexus
`is not dissected, in contrast to preliminary reports of
`transperitoneallaparoscopic approaches. 13,22,30 The pa(cid:173)
`tient is in the lateral decubitus position, which facilitates
`exposure of the lumbar spine, as gravity helps retract the
`abdominal contents anteriorly. With the straight, lateral
`position, as opposed to the supine Trendelenburg posi(cid:173)
`tion required for transperitoneallaparoscopy, it is easier
`to get orthogonal to the disc space and spine with later(cid:173)
`ally directed placement of interbody threaded fusion
`cages. The surgeon can use two longer cages in the trans(cid:173)
`verse axis, with a larger-diameter cage anterior and a
`smaller-diameter cage posterior, thus "customizing" or
`"dialing in" the optimal degree of intervertebral lordosis
`(Figure 5). The same effect of altering the sagittal plane
`alignment was achieved in the majority of patients in this
`study by using distraction plugs of different diameters to
`adjust the degree of lordosis even before reaming the
`cage diameter. Two longer cages placed laterally via the
`retroperitoneal approach should be biomechanically
`more stable, because the surface area of the vertebral
`body cage contact area is greater than that achieved
`when using a transperitoneal approach. In addition, the
`anterior longitudinal ligament and posterior longitudi(cid:173)
`nalligament are not violated with the lateral retroperi(cid:173)
`toneal approach. With the transperitoneal approach, if
`the surgeon reams, taps, or drills too deeply, the spinal
`canal contents are at risk. With the lateral retroperito(cid:173)
`neal approach, however, the orthopedic drilling, ream(cid:173)
`ing, tapping, and cage insertion are directed toward the
`contralateral psoas muscle instead of the neurologic
`structures.8,22
`In the report of the laparoscopic BAK study13 submit(cid:173)
`ted to the Food and Drug Administration, the incidence
`of iatrogenic intraoperative disc herniation in patients
`undergoing surgery at one level was 2.8% (6 of 215
`patients) and that in patients undergoing transperito(cid:173)
`neal, two-levelBAKwas 12% (3 of25 patients). Overall,
`for BAK implants inserted via a straight anterior-to-
`
`posterior direction, the incidence of reoperation for iat(cid:173)
`rogenic penetration or for pushing intervertebral disc
`material into the spinal canal was 2.3%. Furthermore,
`lateral retroperitoneal procedures obviate the need to
`dissect and mobiiize the common iliac vein and artery, as
`is necessary with transperitoneal exposure of the L4-L5
`intervertebral disc. The authors have found that it is eas(cid:173)
`ier to make the long axis of two retroperitoneal cages or
`bone dowels parallel via a shotgun or double-barrel tro(cid:173)
`char than via a transperitoneal independent trochar.
`Mayer18 reported on 20 patients who underwent ret(cid:173)
`roperitoneal, microsurgical, anterior lumbar interbody
`fusion between January 1, 1995 and January 31, 1996.
`In this procedure, an extensive quadrilateral retraction
`frame was used, but anterior stabilization implants were
`not. All patients had undergone an additional posterior
`pedicle screw instrumentation procedure 1-2 weeks ear(cid:173)
`lier.
`Boden et al2 described a video-assisted, lateral, inter(cid:173)
`transverse-process arthrodesis in a rabbit and a non(cid:173)
`human primate model. This was a posterior approach,
`which did not involve spinal stabilization.
`Ordway et af7 compared the biomechanical charac(cid:173)
`teristics of a transversely oriented carbon-fiber cage with
`those of an anteriorly oriented cage in the bovine lumbar
`spine and found that, in most cases, the differences were
`not statistically significant. In addition, Ordway et al
`compared two anteriorly oriented cages with just one
`transversely oriented cage, which is a biased comparison.
`However, the carbon fiber cage has been studied exten(cid:173)
`sively at the current authors' laboratory as we1l3
`; it is
`basically an unreamed spacer that is not screwed into
`place. The BAK system is inherently more stable than the
`carbon fiber cage because it uses preinsertional distrac(cid:173)
`tion via distraction plugs, which results in better liga(cid:173)
`mentotaxis. The BAK involves a tap that cuts threads
`into the two adjacent vertebral end plates, and the BAK
`reduces the strain and micromotion on the bone graft
`contained within the cage more successfully than does
`the rectangular carbon-fiber design.14
`There are several potential disadvantages of the min(cid:173)
`imally invasive, retroperitoneal approach. Particularly at
`L4-L5, it may be necessary to remove part of the iliac
`crest or place the docking portal through the iliac wing to
`be orthogonal to the L4-L5 disc space. 22
`,30 In addition,
`a large mass of psoas muscle containing lumbosacral
`
`Figure 3. A, Schematic diagram showing the orientation for the retroperitoneal approach. The "X" marks the anterosuperior iliac spine,
`and the three portals are shown by black dots. B. Initial lateral radiograph of a 76-year-old, dialysis-dependent man with biopsy-confirmed
`osteomyelitis at L3-L4. Initially, he was treated at another institution with intravenous antibiotics and a thoracolumbosacral orthosis. When
`he arrived at the authors' institution, he was in septic shock. C, A sagittal magnetic resonance image revealing vertebral collapse with
`an associated retropulsed vertebral body fragment and thecal sac compression. D, A schematic diagram depicting the laparoscopic view
`through the transversalis fascia as the L3-L4 intervertebral disk is exposed. E. A laparoscopic view of the retroperitoneal space. The black
`arrows demonstrate the interval used to reach the vertebral body. The psoas major (P) is posterior, and the ureter (U) is anterior.
`Perinephric fat (K) is dissected bluntly to expose the interval. F, A schematic diagram showing debridement of the infected granulomatous
`tissue with the anterior thecal sac exposed between the L3 and L4 vertebral bodies posterior to the pituitary rongeur. G, A laparoscopic
`photograph showing a pituitary rongeur debriding the infected L3-L4 intervertebral disc.
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`Endoscopic Retroperitoneal Interbody Fusions· McAfee et al 1481
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`Endoshears
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`1482 Spine· Volume 23· Number 13 • 1998
`
`Figure 4. Anteroposterior and
`lateral radiographs of two pa(cid:173)
`tients obrained after endoscopic
`retroperitoneal BAK interbody fu(cid:173)
`sion was performed and instru(cid:173)
`mentation for postlaminectomy
`instability was placed. A and B
`show a one-cage technique. C
`and D show a two-cage tech(cid:173)
`nique.
`
`,
`
`' ,1 1 .
`
`"
`
`nerve roots may need to be mobilized laterally. However,
`the authors of this study still prefer mobilizing the psoas
`muscle to mobilizing the common iliac vein and artery,
`as is necessary with transperitoneal approaches. The po(cid:173)
`sition of the ureter constantly needs to be considered in
`uansperiioneal ana reuoperiioneal mlmmallY mvaSlve
`approaches. One additional advantage of the retroperi(cid:173)
`toneal approach is that spine surgeons probably will be
`more comfortable performing the approach without de(cid:173)
`pending on a general surgical "access surgeon."
`Obviously, it is difficult to prove statistically that the
`incidence of complications associated with the retroper(cid:173)
`itoneal approach is lower than that associated with the
`intraperitoneal endoscopic spinal procedures, because
`even transperitoneal spinal fusion is only a recently de(cid:173)
`scribed procedure and is still in its infancy. However,
`
`1 "
`
`11 '
`
`•
`
`many general surgical, gynecologic, and urologic proce(cid:173)
`dures in which the retroperitoneal approach is used have
`been reported showing fewer complications than their
`transperitoneal operative counterparts. Leverant et al17
`showed that intra-abdominal adhesions do occur with
`laparoscopy. They found intraperitoneal adhesions in 79
`of 124 patients whose only prior surgery was laparos(cid:173)
`copy; none of the 91 controls without prior laparosco(cid:173)
`pies in that study had adhesions. Lajer et al 16 reported a
`1 % incidence of hernias in trocar ports after abdominal
`laparoscopy. Hernias through trocar ports have not been
`described with retroperitoneal approaches.
`The authors of the current study have performed more
`than 150 endoscopic spinal procedures, and have had a
`patient with postoperative small bowel obstruction. This
`obstruction occurred in a patient 2 weeks after he had
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`Endoscopic Retroperitoneal Interbody Fusions· McAfee et al 1483
`
`plication rates of conventional versus minimally invasive
`techniques.
`In summary, in this report of 18 cases of minimally
`invasive, lateral retroperitoneal, lumbar procedures, the
`main advantages were:
`
`1) the length of stay was less than that associated with
`larger muscle-splitting "open approaches,"
`2) the need for mobilization of the great vessels was
`reduced compared with that of transperitoneallapa(cid:173)
`roscopic approaches,
`3) the procedure allowed for two larger cages to be
`inserted parallel to one another in a transverse direc(cid:173)
`tion, horizontal, rather than perpendicular, to the spi(cid:173)
`nalcanal.
`4) by varying the diameter of the retroperitoneally
`placed inter body fusion cages, inter body allograft
`bone dowels, or distraction plugs, customization of
`the amount of lumbar lordosis was possible without
`increasing the risk of implant dislodgement or
`pseudoarthrosis.
`
`Eighteen cases is not a large series, but the results are
`favorable compared with preliminary results of alterna(cid:173)
`tive techniques.
`
`References
`
`1. Bagby G. Arthrodesis by the distraction-compression
`methods using a stainless steel implant. Orthopaedics 1988;11:
`931-4.
`2. Boden SD, Moskovitz PA, Morone MA, Toeibitaby Y.
`Video-assisted lateral intertransverse process arthrodesis: Val(cid:173)
`idation of a non-minimally invasive lumbar spinal fusion tech(cid:173)
`nique in the rabbit and non-human primate (Rhesus) models.
`Spine 1996;21:2689-97.
`3. Brantigan ]W, McAfee PC, Cunningham BW, Wang H,
`Orbegoso CM. Interbody lumbar fusion using a carbon fiber
`cage implant versus allograft bone: An investigational study in
`the spanish goat. Spine 1994;19:1436-44.
`4. Brodke DS, Dick ]C, Kunz DN, McCabe R, Zdeblick TA.
`Posterior lumbar inter body fusion: A biomechanical compari(cid:173)
`son including a new threaded cage. Spine 1997;22:26-31.
`5. Cook T A, Dehn TC. Port-site metastases in patients under(