Minimally Invasive Lumbar Fusion
`
`Kevin T. Foley, MD,* Langston T. Holly, MD,† and James D. Schwender, MD‡
`
`SPINE Volume 28, Number 15S, pp S26–S35
`©2003, Lippincott Williams & Wilkins, Inc.
`
`Study Design. Review article.
`Objectives. To provide an overview of current tech-
`niques for minimally invasive lumbar fusion.
`Summary of Background Data. Minimally invasive
`techniques have revolutionized the management of
`pathologic conditions in various surgical disciplines. Al-
`though these same principles have been used in the treat-
`ment of lumbar disc disease for many years, minimally
`invasive lumbar fusion procedures have only recently
`been developed. The goals of these procedures are to
`reduce the approach-related morbidity associated with
`traditional lumbar fusion, yet allow the surgery to be
`performed in an effective and safe manner.
`Methods. The authors’ clinical experience with mini-
`mally invasive lumbar fusion was reviewed, and the per-
`tinent literature was surveyed.
`Results. Minimally invasive approaches have been de-
`veloped for common lumbar procedures such as anterior
`and posterior interbody fusion, posterolateral onlay fu-
`sion, and internal fixation. As with all new surgical tech-
`niques, minimally invasive lumbar fusion has a learning
`curve. As well, there are benefits and disadvantages as-
`sociated with each technique. However, because these
`techniques are new and evolving, evidence to support
`their potential benefits is largely anecdotal. Additionally,
`there are few long-term studies to document clinical
`outcomes.
`Conclusions. Preliminary clinical results suggest that
`minimally invasive lumbar fusion will have a beneficial
`impact on the care of patients with spinal disorders. Out-
`come studies with long-term follow-up will be necessary
`to validate its success and allow minimally invasive lum-
`bar fusion to become more widely accepted. [Key words:
`fusion, lumbar, minimally invasive, percutaneous] Spine
`2003;28:S26 –S35
`
`Lumbar fusion has become a widely accepted method for
`the management of a variety of disorders that require
`spinal stabilization, such as traumatic, degenerative, in-
`fectious, and neoplastic conditions. However, one of the
`drawbacks of conventional lumbar fusion is the exten-
`sive soft tissue dissection that is necessary in order to
`expose the anatomic landmarks for screw insertion,
`
`From *Semmes-Murphey Clinic and the Department of Neurosurgery,
`University of Tennessee, Memphis, Tennessee, †Division of Neurosur-
`gery, UCLA Medical Center, Los Angeles, California, and ‡Twin Cities
`Spine Center and the Department of Orthopedic Surgery, University of
`Minnesota, Minneapolis, Minnesota.
`The device(s)/drug(s) is/are FDA-approved or approved by correspond-
`ing national agency for this indication. No funds were received in
`support of this work. One or more of the author(s) has/have received or
`will receive benefits (e.g., royalties, stocks, stock options, decision mak-
`ing position) for personal or professional use from a commercial party
`related directly or indirectly to the subject of this manuscript
`Address reprint requests to Kevin T. Foley, MD, Image-Guided Surgery
`Research Center, Methodist Hospitals of Memphis, Semmes-Murphey
`Clinic, Department of Neurosurgery, University of Tennessee, 1211
`Union Avenue, Suite 200, Memphis, TN 38104. E-mail:
`kfoley@usit.net.
`
`S26
`
`achieve a proper lateral-to-medial screw trajectory, and
`develop an acceptable fusion bed. The tissue injury that
`occurs during the surgical approach can result in in-
`creased postoperative pain, lengthened recovery time,
`and impaired spinal function. Therefore, the develop-
`ment of procedures that minimize tissue trauma without
`compromising effectiveness represents an important ad-
`vancement in the field of spine surgery.
`This article focuses on the application of minimally
`invasive techniques to commonly performed lumbar fu-
`sion procedures, emphasizing both the apparent benefits
`and limitations of this emerging technology. Minimally
`invasive approaches have been applied to a wide range of
`procedures to include anterior lumbar interbody fusion
`(ALIF), posterior lumbar interbody fusion (PLIF), trans-
`foraminal lumbar interbody fusion (TLIF), posterolat-
`eral onlay (intertransverse) fusion, and pedicle screw/rod
`placement.
`Despite the early encouraging clinical results, it must
`be remembered that minimally invasive lumbar fusion
`techniques are in their infancy and the results are prelim-
`inary at best. Prospectively conducted outcome studies
`with long-term follow-up will be the ultimate determi-
`nants of the safety and effectiveness of minimally inva-
`sive lumbar fusion.
`
`Minimally Invasive Spine Surgery
`
`Rationale. Minimally invasive techniques have become
`the gold standard for the management of pathologic con-
`ditions in various surgical disciplines. A classic example
`is in general surgery, where laparoscopic cholecystec-
`tomy has supplanted traditional open cholecystectomy
`as the primary operative treatment for symptomatic gall-
`bladder disease. The laparoscopic approach has been as-
`sociated with less surgical-related morbidity, better long-
`term postoperative outcomes, and decreased costs,
`largely due to shorter postoperative hospital stays.1,2
`Open instrumented lumbar fusion procedures are as-
`sociated with lengthy hospital stays and significant
`costs.3 Additionally, the morbidity associated with these
`procedures has become an increasing concern for many
`surgeons. In part, this morbidity is related to the signifi-
`cant iatrogenic muscle and soft tissue injury that occurs
`during routine lumbar fusion exposures. Multiple au-
`thors have documented the harmful effects of the exten-
`sive muscle dissection and retraction that normally occur
`during lumbar procedures.4 –10 Kawaguchi et al5,6 ana-
`lyzed the effects of retractor blade pressure on the
`GLOBUS MEDICAL, INC.
`paraspinous muscles during lumbar surgery. They deter-
`EXHIBIT 1015
`mined that elevated serum levels of creatine phosphoki-
`nase MM isoenzyme, an indicator of muscle injury, is
`IPR2015-to be assigned
`directly related to the retraction pressure and duration.
`(Globus v. Flexuspine)
`
`1 of 11
`
`

`
`Minimally Invasive Lumbar Fusion
`
`Kevin T. Foley, MD,* Langston T. Holly, MD,† and James D. Schwender, MD‡
`
`SPINE Volume 28, Number 15S, pp S26–S35
`©2003, Lippincott Williams & Wilkins, Inc.
`
`Study Design. Review article.
`Objectives. To provide an overview of current tech-
`niques for minimally invasive lumbar fusion.
`Summary of Background Data. Minimally invasive
`techniques have revolutionized the management of
`pathologic conditions in various surgical disciplines. Al-
`though these same principles have been used in the treat-
`ment of lumbar disc disease for many years, minimally
`invasive lumbar fusion procedures have only recently
`been developed. The goals of these procedures are to
`reduce the approach-related morbidity associated with
`traditional lumbar fusion, yet allow the surgery to be
`performed in an effective and safe manner.
`Methods. The authors’ clinical experience with mini-
`mally invasive lumbar fusion was reviewed, and the per-
`tinent literature was surveyed.
`Results. Minimally invasive approaches have been de-
`veloped for common lumbar procedures such as anterior
`and posterior interbody fusion, posterolateral onlay fu-
`sion, and internal fixation. As with all new surgical tech-
`niques, minimally invasive lumbar fusion has a learning
`curve. As well, there are benefits and disadvantages as-
`sociated with each technique. However, because these
`techniques are new and evolving, evidence to support
`their potential benefits is largely anecdotal. Additionally,
`there are few long-term studies to document clinical
`outcomes.
`Conclusions. Preliminary clinical results suggest that
`minimally invasive lumbar fusion will have a beneficial
`impact on the care of patients with spinal disorders. Out-
`come studies with long-term follow-up will be necessary
`to validate its success and allow minimally invasive lum-
`bar fusion to become more widely accepted. [Key words:
`fusion, lumbar, minimally invasive, percutaneous] Spine
`2003;28:S26 –S35
`
`Lumbar fusion has become a widely accepted method for
`the management of a variety of disorders that require
`spinal stabilization, such as traumatic, degenerative, in-
`fectious, and neoplastic conditions. However, one of the
`drawbacks of conventional lumbar fusion is the exten-
`sive soft tissue dissection that is necessary in order to
`expose the anatomic landmarks for screw insertion,
`
`From *Semmes-Murphey Clinic and the Department of Neurosurgery,
`University of Tennessee, Memphis, Tennessee, †Division of Neurosur-
`gery, UCLA Medical Center, Los Angeles, California, and ‡Twin Cities
`Spine Center and the Department of Orthopedic Surgery, University of
`Minnesota, Minneapolis, Minnesota.
`The device(s)/drug(s) is/are FDA-approved or approved by correspond-
`ing national agency for this indication. No funds were received in
`support of this work. One or more of the author(s) has/have received or
`will receive benefits (e.g., royalties, stocks, stock options, decision mak-
`ing position) for personal or professional use from a commercial party
`related directly or indirectly to the subject of this manuscript
`Address reprint requests to Kevin T. Foley, MD, Image-Guided Surgery
`Research Center, Methodist Hospitals of Memphis, Semmes-Murphey
`Clinic, Department of Neurosurgery, University of Tennessee, 1211
`Union Avenue, Suite 200, Memphis, TN 38104. E-mail:
`kfoley@usit.net.
`
`S26
`
`achieve a proper lateral-to-medial screw trajectory, and
`develop an acceptable fusion bed. The tissue injury that
`occurs during the surgical approach can result in in-
`creased postoperative pain, lengthened recovery time,
`and impaired spinal function. Therefore, the develop-
`ment of procedures that minimize tissue trauma without
`compromising effectiveness represents an important ad-
`vancement in the field of spine surgery.
`This article focuses on the application of minimally
`invasive techniques to commonly performed lumbar fu-
`sion procedures, emphasizing both the apparent benefits
`and limitations of this emerging technology. Minimally
`invasive approaches have been applied to a wide range of
`procedures to include anterior lumbar interbody fusion
`(ALIF), posterior lumbar interbody fusion (PLIF), trans-
`foraminal lumbar interbody fusion (TLIF), posterolat-
`eral onlay (intertransverse) fusion, and pedicle screw/rod
`placement.
`Despite the early encouraging clinical results, it must
`be remembered that minimally invasive lumbar fusion
`techniques are in their infancy and the results are prelim-
`inary at best. Prospectively conducted outcome studies
`with long-term follow-up will be the ultimate determi-
`nants of the safety and effectiveness of minimally inva-
`sive lumbar fusion.
`
`Minimally Invasive Spine Surgery
`
`Rationale. Minimally invasive techniques have become
`the gold standard for the management of pathologic con-
`ditions in various surgical disciplines. A classic example
`is in general surgery, where laparoscopic cholecystec-
`tomy has supplanted traditional open cholecystectomy
`as the primary operative treatment for symptomatic gall-
`bladder disease. The laparoscopic approach has been as-
`sociated with less surgical-related morbidity, better long-
`term postoperative outcomes, and decreased costs,
`largely due to shorter postoperative hospital stays.1,2
`Open instrumented lumbar fusion procedures are as-
`sociated with lengthy hospital stays and significant
`costs.3 Additionally, the morbidity associated with these
`procedures has become an increasing concern for many
`surgeons. In part, this morbidity is related to the signifi-
`cant iatrogenic muscle and soft tissue injury that occurs
`during routine lumbar fusion exposures. Multiple au-
`thors have documented the harmful effects of the exten-
`sive muscle dissection and retraction that normally occur
`during lumbar procedures.4 –10 Kawaguchi et al5,6 ana-
`lyzed the effects of retractor blade pressure on the
`paraspinous muscles during lumbar surgery. They deter-
`mined that elevated serum levels of creatine phosphoki-
`nase MM isoenzyme, an indicator of muscle injury, is
`directly related to the retraction pressure and duration.
`
`2 of 11
`
`

`
`These findings support the work by Gejo et al,4 who
`examined postoperative MRIs and trunk muscle strength
`in 80 patients who previously had lumbar surgery. They
`concluded that the damage to the lumbar musculature
`was directly related to the time of retraction during sur-
`gery. Furthermore, the incidence of low back pain was
`significantly increased in patients who had long muscle
`retraction times. Styf and Willen10 determined that re-
`tractor blades may actually increase intramuscular pres-
`sure to levels of ischemia. Mayer et al7 evaluated trunk
`muscle strength in patients who had previous lumbar
`surgery and found that patients who had undergone fu-
`sion procedures were significantly weaker than those
`who had undergone discectomy. Rantanen et al8 con-
`cluded that patients with poor outcomes after lumbar
`surgery were more likely to have persistent pathologic
`changes in their paraspinal muscles.
`In addition to minimizing the long-term effects of ex-
`posure-related muscle injury, minimally invasive lumbar
`fusion procedures hold the promise of immediate and
`short-term advantages. Blood loss during open lumbar
`fusion surgery can be quite significant; not infrequently,
`patients are asked to donate autologous blood before
`surgery, or a cell saver is used during the procedure. In
`comparison, minimally invasive procedures are associ-
`ated with significantly lower blood loss.11 Also, the less
`traumatic surgical approach associated with minimally
`invasive spinal techniques results in less postoperative
`pain than do conventional open procedures. This dimin-
`ished postoperative pain can potentially yield other ben-
`efits, such as decreased postoperative narcotic use, earlier
`mobilization, shorter hospital stay, and a faster return to
`work.
`
`Limitations. Although there are many potential advan-
`tages to minimally invasive lumbar procedures, the tech-
`niques do have limitations and drawbacks. As with any
`novel surgical technique, a learning curve is associated
`with the development of proficient technical skills. The
`first requirement is a thorough knowledge of the under-
`lying three-dimensional spinal anatomy. In contrast to
`open procedures, where the surrounding anatomy is di-
`rectly visualized, minimally invasive exposures are gen-
`erally limited to the area of surgical interest and certain
`key anatomic landmarks within this limited field of view.
`Familiarity with the anatomy allows the surgeon to
`safely perform the procedure without exposing struc-
`tures that are not being surgically treated. Minimally
`invasive spinal techniques are also likely to be more tech-
`nically demanding than are the corresponding open pro-
`cedures. Surgeons must become facile working through a
`significantly smaller exposure using instruments that are
`longer and are frequently bayoneted. Although these
`procedures can be performed using loupe magnification,
`most surgeons presently use either the endoscope or an
`operating microscope because of the enhanced illumina-
`tion. The two-dimensional visualization offered by an
`endoscope and the ergonomics of using a microscope can
`
`Minimally Invasive Lumbar Fusion • Foley et al
`
`S27
`
`provide challenges to surgeons attempting to learn min-
`imally invasive lumbar fusion techniques. Consequently,
`early in the surgeon’s learning curve, the complication
`rates and duration of these procedures may be increased
`compared with those of conventional open procedures.
`Minimally invasive procedures commonly require the
`use of intraoperative imaging or image guidance. Not
`infrequently, the surgeon will rely on live or virtual flu-
`oroscopic images displayed on a monitor or three-
`dimensional images from an image guidance system for
`anatomic orientation. This can be challenging for sur-
`geons who have not had significant experience using
`two-dimensional images to determine their three-
`dimensional surgical position. There are also financial
`issues involved, as minimally invasive lumbar fusion re-
`quires the use of customized instruments and equipment
`that can be expensive. Finally, although their prelimi-
`nary results are promising and look quite good, the long-
`term efficacy of minimally invasive fusion techniques has
`not been proven. Many of these techniques are still
`evolving and need to be validated by longer-term studies.
`
`Evolution of Minimally Invasive Lumbar Fusion. One of the
`principal reasons for the development of minimally in-
`vasive lumbar fusion has been to minimize the paraspi-
`nous muscle injury that occurs with traditional open pro-
`cedures. For similar reasons, strategies for minimally
`invasive lumbar fixation have evolved. Magerl12 first re-
`ported the use of percutaneous pedicle screws in con-
`junction with an external fixator in 1982. This technique
`was intended mainly for trauma applications, and its
`most salient disadvantage was the risk of infection. As
`well, it required the use of a cumbersome external appli-
`ance. In 1995, Mathews and Long13 described the use of
`percutaneous pedicle screws with longitudinal connec-
`tors that were placed under direct vision in the superficial
`subcutaneous space. As the longitudinal connector (a
`plate) was internalized, the risk of infection was small.
`Unfortunately, this instrumentation was associated with
`a significant nonunion rate, likely secondary to the long
`lever arms of the hardware. In addition, its superficial
`location was uncomfortable for patients. More recently,
`the Sextant system was introduced by Foley and col-
`leagues,14,15 enabling the minimally invasive placement
`of percutaneous pedicle screws and rods in a subfascial
`anatomic position similar to that of traditional open
`techniques (see Percutaneous Spinal Fixation).
`Another means of minimally invasive lumbar fixation
`is translaminar facet screw insertion. First described for
`use via an open approach by Magerl,16 this form of lum-
`bar fixation has been applied in a less invasive fashion by
`others.17
`In the 1990s, increasing experience with endoscopic
`techniques for general and urological surgery enabled
`the development of minimally invasive anterior and ret-
`roperitoneal approaches to lumbar fusion. Mathews et
`al18 and Zucherman et al19 reported on laparoscopic
`approaches for anterior lumbar interbody fusion in
`
`3 of 11
`
`

`
`S28 Spine • Volume 28 • Number 15S • 2003
`
`1995. Shortly thereafter, McAfee et al20 described their
`experience with a minimally invasive lateral retroperito-
`neal approach for the placement of lumbar interbody
`fusion cages. The microscope can also be used for a
`“mini-open” ALIF, first described by Mayer in 1997.21
`Variations on these techniques continue to be developed,
`including combinations of open and endoscopic ap-
`proaches (endoscopic-assisted).
`A novel means of performing a minimally invasive
`fusion and fixation at L5-S1 was described by MacMil-
`lan et al in 1996.22 This procedure required a transiliac,
`trans-sacral approach using fluoroscopic guidance. Al-
`though the technique was successful in the authors’
`hands, its use has remained limited.
`Techniques that facilitate posterior and posterolateral
`approaches to minimally invasive lumbar fusion have
`been described only recently. Leu and Hauser23 devel-
`oped a biportal percutaneous endoscopic approach to
`interbody fusion in 1986 and subsequently reported
`their work. The fusion was carried out with cancellous
`autograft placed through a 7.5-mm diameter cannula
`that was inserted into the disc space via a posterolateral,
`percutaneous approach. Unfortunately, the autograft
`resorbed and nonunion resulted. Leu then combined his
`original technique with an external spinal fixator.12 Al-
`though this approach proved successful, it required three
`surgeries on separate days (placement of the external
`fixator, percutaneous fusion, removal of the fixator) and
`was associated with a 16% nonunion rate and an infec-
`tion rate of 8%.23
`Using cadavers and experimental animals, Boden et
`al24 developed a minimally invasive technique for pos-
`terolateral fusion in 1996. Instead of autograft, the
`group used bone morphogenetic protein (rhBMP-2) to
`successfully induce fusion in the animals.
`A tubular retractor system was first developed for mi-
`crodiscectomy in 1994 by Foley and Smith,25 and its
`basic concept is the foundation on which several contem-
`porary approaches to minimally invasive posterior lum-
`bar fusion are based. The system consists of a series of
`concentric dilators and thin-walled tubular retractors of
`variable length. The spine is accessed via serial dilation of
`the natural cleavage plane between muscle fascicles, in-
`stead of a more traumatic muscle-stripping approach.
`The use of a tubular retractor, rather than blades, allows
`the retractor itself to be thin-walled (0.9 mm), even when
`the wound is quite deep. Also, unlike blades, the tube
`circumferentially defines a surgical corridor through the
`paraspinous tissues. This helps prevent muscle from in-
`truding into the exposure. All of the midline supporting
`musculoligamentous structures are left intact with this
`technique. An appropriately sized working channel is
`created that permits spinal decompression and fusion.
`Surgery can be performed using the operating micro-
`scope, loupes, an endoscope, or a combination of tech-
`niques, depending on the preference of the surgeon. The
`tubular retractor approach can be utilized for minimally
`invasive lumbar fusion via posterolateral onlay, PLIF, or
`
`TLIF. Extreme lateral approaches to the lumbar spine
`are also possible (ELIF). Detailed descriptions of the var-
`ious techniques for minimally invasive lumbar fusion
`follow.
`
`Minimally Invasive Anterior Lumbar Interbody Fusion. Car-
`penter26 first described ALIF for the treatment of spon-
`dylolisthesis in 1932. Since that time the procedure has
`undergone a number of modifications and has become a
`widely accepted method for lumbar arthrodesis. The po-
`tential advantages of the procedure include avoidance of
`epidural scarring, preservation of posterior spinal ele-
`ments, and diminished risk of neural injury. A wide as-
`sortment of implants have been used for ALIF, including
`autologous iliac crest, cylindrical bone dowels, femoral
`ring allografts, carbon fiber cages,27 and cylindrical28
`and tapered metallic cages.
`ALIF can be performed as a stand-alone procedure,
`but concerns regarding low rates of fusion have
`prompted many surgeons to place supplemental poste-
`rior fixation. This is particularly useful in cases of spon-
`dylolisthesis, spinal instability, or in patients with rela-
`tively preserved disc height. The development of
`percutaneous pedicle screw and rod systems has made
`the placement of a supplemental posterior tension band
`simpler and more attractive. Percutaneous translaminar
`facet screws can be used for a similar purpose. ALIF was
`originally performed through an open retroperitoneal
`exposure with a large incision; more recently, mini-open
`retroperitoneal,21,29 laparoscopic transperitone-
`al,18,19,30 and endoscopic retroperitoneal20,31 ap-
`proaches have been introduced.
`
`Laparoscopic Transperitoneal ALIF. Laparoscopic trans-
`peritoneal ALIF is performed through three or four 1- to
`2-cm incisions, depending on the size of the patient and
`amount of bowel retraction required. There are usually
`one to two retraction ports, one camera port, and one
`working port. Laparoscopic approaches to the L5-S1
`level are most commonly performed, as the bifurcation
`of the great vessels is located rostral to this interspace.
`The posterior peritoneal wall is opened over the in-
`terspace, and the overlying retroperitoneal fat is bluntly
`dissected in order to avoid injury to the parasympathetic
`plexus. Once the disc space is well exposed, the fusion
`can be performed through the working port. Exposing
`the L4 –L5 level can be quite difficult, as this is the typical
`site for the bifurcation of the great vessels. Depending on
`the individual patient anatomy, the disc may be accessed
`between the aorta and vena cava, or the great vessels may
`be retracted together to either the left or the right. An-
`other factor that makes the laparoscopic approach to
`L4 –L5 significantly more difficult is the descending iliol-
`umbar vein that must be ligated and divided.
`
`Mini-open Retroperitoneal ALIF. This procedure begins
`with a 3- to 4-cm transverse incision centered slightly left
`of the midline and allows a proper trajectory to the in-
`terspace of interest as confirmed by fluoroscopy. The
`
`4 of 11
`
`

`
`dissection is carried down through the anterior rectus
`sheath and lateral to the rectus abdominus until the peri-
`toneum is encountered. The peritoneum is bluntly sepa-
`rated from the lateral abdominal wall, and the retroperi-
`toneum is entered. A self-retaining retractor system is
`then used to retract the peritoneal contents, and hand-
`held retractors are used for the great vessels. The appro-
`priate level is exposed, followed by discectomy and
`placement of the spinal implant and autologous bone
`graft or bone morphogenetic protein.
`
`Endoscopic Retroperitoneal Lumbar Fusion. The endoscopic
`retroperitoneal approach was first developed for urolog-
`ical surgery32 and later adapted by McAfee et al20 for
`lumbar spine fusion. The procedure can be performed
`using CO2 insufflation, balloon insufflation (gasless), or a
`combination of both techniques. The patient is usually
`placed in the lateral decubitus position, but the supine
`position has also been described by LeHuec.31 A 2- to
`3-cm transverse skin incision is created at the appropri-
`ate level that is centered on a line between the eleventh
`rib and anterior superior iliac spine. Blunt dissection is
`carried down through the muscle layers using an endo-
`scopic trocar until the fatty retroperitoneal space is
`reached. Once the space has been manually confirmed,
`the dissection balloon is placed and then slowly inflated
`until a retroperitoneal cavity has been created. At this
`point the balloon is removed and either a self-retaining
`retractor system or CO2 insufflation is used to maintain
`the retroperitoneal cavity. A minimum of three ports are
`placed for retraction, endoscope, and working instru-
`ments. Once the appropriate level has been confirmed
`fluoroscopically, the psoas muscle is elevated from the
`spine. The discectomy and fusion are then performed
`using standard techniques.
`
`Results of Minimally Invasive ALIF Techniques. Laparo-
`scopic transperitoneal ALIF was initially greeted with
`enthusiasm by spine surgeons. However, experience with
`this procedure has shown that it has some significant
`drawbacks compared with mini-open retroperitoneal
`ALIF. One of the major disadvantages of laparoscopic
`transperitoneal ALIF is the risk of retrograde ejaculation
`in men, presumably caused by injury to the superior hy-
`pogastric plexus during the approach. Zdeblick30 re-
`ported a 6% rate of retrograde ejaculation in a series of
`68 patients who underwent laparoscopic ALIF. In com-
`parison, Flynn and Price33 noted an incidence of 0.42%
`in a series of 4500 open ALIF procedures. Additionally,
`the bifurcation of the great vessels can significantly in-
`crease the difficulty of a laparoscopic L4 –L5 ALIF. In a
`series of 50 patients who underwent L4 –L5 ALIF (25
`mini-open and 25 laparoscopic), Zdeblick and David34
`reported a significantly higher complication rate (20%
`vs. 4%) in the laparoscopic group. They found that 16%
`of the laparoscopic cases were associated with inade-
`quate exposure, and only one cage could be placed in
`these patients; two cages were placed in all of the mini-
`open cases. Another potential concern with laparoscopic
`
`Minimally Invasive Lumbar Fusion • Foley et al
`
`S29
`
`transperitoneal ALIF is the rate of other complications
`(including conversion to an open procedure due to inad-
`equate exposure and vascular/visceral injury), which
`ranges from 10% to 20%.29,35
`In contrast, mini-open ALIF offers many of the same
`benefits as the laparoscopic approach, such as decreased
`blood loss, reduced postoperative pain, and shorter hos-
`pital stay, while minimizing some of the aforementioned
`disadvantages.35 Mini-open ALIF also has a much sim-
`pler learning curve for both spine and access surgeons.
`Despite its limitations, laparoscopic transperitoneal
`ALIF is a procedure that can be performed effectively and
`safely. It is unlikely, though, to supplant its open coun-
`terpart as has been seen with laparoscopic cholecystec-
`tomy. The situation is analogous to that of laparoscopic
`appendectomy, a procedure preferred by some general
`surgeons and not others,36 which has not been shown to
`offer short- or long-term results significantly different
`from those of open appendectomy.37,38
`
`Minimally Invasive Posterior Lumbar Interbody Fusion. The
`PLIF procedure was first performed by Cloward in
`194339 as a method to achieve simultaneous nerve root
`decompression and interbody fusion in a large series of
`patients with herniated lumbar intervertebral discs. Iliac
`crest bone graft was packed into the interbody space
`following discectomy. Cloward reported good clinical
`outcomes and fusion rates; however, many other sur-
`geons did not have the same success with PLIF.40 Their
`complication rates were relatively high and fusion rates
`low, and interest in the procedure waned.
`Enthusiasm for the procedure was rekindled decades
`later after several modifications to Cloward’s original
`PLIF technique were made. These refinements addressed
`concerns about the success rate of this technically de-
`manding procedure and were stimulated, in part, by ad-
`vances in spinal instrumentation. Steffee and Sitkowski41
`reported the use of pedicle screw and plate fixation to
`supplement the interbody fusion. This permitted sur-
`geons to perform a more generous bony decompression
`without risk of instability, thereby improving visualiza-
`tion and lessening the risk of neurologic injury.42,43 The
`development of titanium cages and precision-machined
`allografts improved structural support, decreased subsi-
`dence, and promoted bony fusion.44,45
`
`Technique. The latest refinement of this procedure has
`been the application of minimally invasive techniques
`using tubular retractors.11 The minimally invasive PLIF
`procedure begins by creating 25-mm skin incisions cen-
`tered on the disc space, located 25 mm lateral to the
`midline bilaterally. The paraspinous muscles are bluntly
`separated by the METRx dilators under fluoroscopic
`guidance, and the appropriate length tubular retractor is
`positioned at the lamina-facet junction overlying the disc
`space. The tubes are 0.9 mm in thickness and range from
`3 to 9 cm in length. We typically use 22-mm diameter
`tubes for lumbar fusion procedures, although 26-mm
`diameter tubes may also be used (Figure 1). A hemilami-
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`S30 Spine • Volume 28 • Number 15S • 2003
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`Figure 1. Bilateral 22-mm diameter tubular retractors are used to
`perform the minimally invasive PLIF procedure.
`
`Figure 2. Small, paramedian skin incisions resulting from a mini-
`mally invasive PLIF.
`
`notomy with medial facetectomy is performed, and the
`autologous bone is saved for the fusion. The ligamentum
`flavum is then resected, and the nerve root is gently re-
`tracted medially. A complete discectomy is followed by
`disc space distraction and endplate preparation using a
`customized set of instruments. The disc space is then
`packed with the autologous bone and machined cortical
`allografts (cages can also be used). Percutaneous place-
`ment of Sextant pedicle screws is performed through the
`same incisions once the tubular retractors have been
`removed.
`
`Results
`
`To date, 15 patients (7 male, 8 female; mean age, 61
`years) have undergone this procedure who have had at
`least 1-year of follow-up (range, 12 to 20 months). Ten
`patients had L4 –L5 involvement, and 5 had L5-S1 in-
`volvement. Six patients had degenerative disc disease
`and/or disc herniation, 8 patients had Grade I spon-
`dylolisthesis, and 1 had Grade II spondylolisthesis. One
`patient had neurogenic claudication only, 1 had mechan-
`ical back pain only, 4 had mechanical back pain and
`unilateral radiculopathy, and 1 had mechanical back
`pain and bilateral radiculopathy.
`Minimally invasive PLIF was performed successfully
`in all 15 patients, with no patient requiring conversion to
`open surgery. Bilateral pedicle screws were placed in 14
`patients, and unilateral pedicle screws were placed in 1
`patient. Figure 2 illustrates the incisions resulting from a
`minimally invasive PLIF with percutaneous pedicle
`screw and rod insertion. Figure 3 shows a lateral lumbar
`spine plain film following a minimally invasive PLIF and
`percutaneous instrumentation. There were no complica-
`tions. Average operative time wa