Abstract
`
`The Spine Journal 3 (2003) 301–309
`
`Contemporary Concepts In Spine Care
`
`Intervertebral cages for degenerative spinal diseases
`
`Scott L. Blumenthal, MD, Donna D. Ohnmeiss, PhD
`Texas Back Institute Research Foundation, 6300 W. Parker Road, Plano, TX 75093, USA
`
`Received 1 June 2000; accepted 2 December 2002
`
`Interbody fusion techniques have been used for many years for the treatment of a variety of lumbar
`spine diagnoses. Part of the interest in increasing methods of interbody fusion has stemmed from
`concern that posterior fusion alone may allow micro-motion, which may generate pain in a ruptured
`or degenerated disc. Stabilization of the anterior segment led to the development of interbody fusion
`cages. These devices were designed to stabilize the spine while bony ingrowth from the vertebrae to
`the bone graft occurred. There are a variety of techniques for cage insertion, including open and lap-
`aroscopic techniques anteriorly, and open posterior approach. A lateral approach for cage placement
`has also been reported. The purpose of this paper is to present a review of the literature on lumbar in-
`tervertebral fusion performed using interbody cages. The reported results for these procedures vary,
`but in general the majority of patients have had favorable results. The complications are similar to
`those encountered with traditional interbody fusion procedures using bone grafts. There is a learning
`curve associated with the procedures, particularly with the laparoscopic techniques. Appropriate
`training for the spine surgeon as well as the access surgeon is important. There is a great deal of dis-
`parity in reports on using the cages as stand-alone devices as well as on laparoscopic approaches.
`Overall, the use of interbody cages for fusion appears to be a viable treatment, yielding good results.
`Fusion cages appear to have a role in spine care; however, as with any procedure, patient selection
`and proper training of the surgeon are critical. © 2003 Elsevier Inc. All rights reserved.
`
`Keywords:
`
`Interbody fusion; Lumbar spine; Fusion cages; Degenerative spine; Review
`
`Introduction
`
`One of the major objectives of spinal fusion is to relieve
`pain arising from spinal structures by removing potentially
`pain-generating disc tissue and stabilizing one or more mo-
`tion segments. Various methods of posterior lumbar fusion
`(PLF) have long been used for this purpose. Interbody fu-
`sion procedures became more widely used for their stabiliz-
`
`The board of the North American Spine Society (NASS) has reviewed
`this Contemporary Concepts review article. As such, it represents the cur-
`rent position on the state of knowledge of the above subject in spine care.
`Alexander Vaccaro, MD, edits this series. Before entering the review pro-
`cess for
`, the authors were assisted by members of the
`The Spine Journal
`NASS Committee on Contemporary Concepts, Alexander Vaccaro, MD,
`Chair.
`FDA device/drug status: not applicable.
`Author SLB acknowledges a former consultant relationship with US
`Surgical. No financial support has been received related to the preparation
`of this manuscript.
`* Corresponding author. Dr. Scott Blumenthal, Texas Back Institute,
`6300 West Parker Road, Plano, TX 75093, USA. Tel.: (972) 608-5114;
`fax: (972) 608-5020.
`: sblumenthal@texasback.com (S.L. Blumenthal).
`E-mail address
`
`1529-9430/03/$ – see front matter © 2003 Elsevier Inc. All rights reserved.
`doi:10.1016/S1529-9430(03)00004-4
`
`ing effect on the spine segment and as the role of the lumbar
`disc as a pain generator became better appreciated. The pri-
`mary concept behind lumbar interbody fusion is that by re-
`moving all or most of the disc and stabilizing the operated
`segment with bone graft, the primary pain generator is re-
`moved. Stabilizing the segment should then eliminate me-
`chanical stimulation that may provoke symptoms and may
`avoid future problems associated with collapse of an unsup-
`ported space. In a biomechanical study, interbody fusion
`was found to be stiffer than posterior lumbar fusion [1]. In
`addition; the surface area between the host bone and the
`graft is much greater with interbody fusion than with inter-
`transverse process fusion.
`Many interbody fusion methods have been described in
`the literature, which have included various surgical ap-
`proaches to the disc as well as using different types of graft
`material. In recent years, several types of fusion cages have
`been developed. All are designed to be packed with graft,
`and all have holes in the inferior and superior surfaces to al-
`GLOBUS MEDICAL, INC.
`low bone to grow from the vertebral bodies through the
`EXHIBIT 1012
`cage and unite with the bone inside the cage. Currently, the
`IPR2015-to be assigned
`(Globus v. Flexuspine)
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`Abstract
`
`The Spine Journal 3 (2003) 301–309
`
`Contemporary Concepts In Spine Care
`
`Intervertebral cages for degenerative spinal diseases
`
`Scott L. Blumenthal, MD, Donna D. Ohnmeiss, PhD
`Texas Back Institute Research Foundation, 6300 W. Parker Road, Plano, TX 75093, USA
`
`Received 1 June 2000; accepted 2 December 2002
`
`Interbody fusion techniques have been used for many years for the treatment of a variety of lumbar
`spine diagnoses. Part of the interest in increasing methods of interbody fusion has stemmed from
`concern that posterior fusion alone may allow micro-motion, which may generate pain in a ruptured
`or degenerated disc. Stabilization of the anterior segment led to the development of interbody fusion
`cages. These devices were designed to stabilize the spine while bony ingrowth from the vertebrae to
`the bone graft occurred. There are a variety of techniques for cage insertion, including open and lap-
`aroscopic techniques anteriorly, and open posterior approach. A lateral approach for cage placement
`has also been reported. The purpose of this paper is to present a review of the literature on lumbar in-
`tervertebral fusion performed using interbody cages. The reported results for these procedures vary,
`but in general the majority of patients have had favorable results. The complications are similar to
`those encountered with traditional interbody fusion procedures using bone grafts. There is a learning
`curve associated with the procedures, particularly with the laparoscopic techniques. Appropriate
`training for the spine surgeon as well as the access surgeon is important. There is a great deal of dis-
`parity in reports on using the cages as stand-alone devices as well as on laparoscopic approaches.
`Overall, the use of interbody cages for fusion appears to be a viable treatment, yielding good results.
`Fusion cages appear to have a role in spine care; however, as with any procedure, patient selection
`and proper training of the surgeon are critical. © 2003 Elsevier Inc. All rights reserved.
`
`Keywords:
`
`Interbody fusion; Lumbar spine; Fusion cages; Degenerative spine; Review
`
`Introduction
`
`One of the major objectives of spinal fusion is to relieve
`pain arising from spinal structures by removing potentially
`pain-generating disc tissue and stabilizing one or more mo-
`tion segments. Various methods of posterior lumbar fusion
`(PLF) have long been used for this purpose. Interbody fu-
`sion procedures became more widely used for their stabiliz-
`
`The board of the North American Spine Society (NASS) has reviewed
`this Contemporary Concepts review article. As such, it represents the cur-
`rent position on the state of knowledge of the above subject in spine care.
`Alexander Vaccaro, MD, edits this series. Before entering the review pro-
`cess for
`, the authors were assisted by members of the
`The Spine Journal
`NASS Committee on Contemporary Concepts, Alexander Vaccaro, MD,
`Chair.
`FDA device/drug status: not applicable.
`Author SLB acknowledges a former consultant relationship with US
`Surgical. No financial support has been received related to the preparation
`of this manuscript.
`* Corresponding author. Dr. Scott Blumenthal, Texas Back Institute,
`6300 West Parker Road, Plano, TX 75093, USA. Tel.: (972) 608-5114;
`fax: (972) 608-5020.
`: sblumenthal@texasback.com (S.L. Blumenthal).
`E-mail address
`
`1529-9430/03/$ – see front matter © 2003 Elsevier Inc. All rights reserved.
`doi:10.1016/S1529-9430(03)00004-4
`
`ing effect on the spine segment and as the role of the lumbar
`disc as a pain generator became better appreciated. The pri-
`mary concept behind lumbar interbody fusion is that by re-
`moving all or most of the disc and stabilizing the operated
`segment with bone graft, the primary pain generator is re-
`moved. Stabilizing the segment should then eliminate me-
`chanical stimulation that may provoke symptoms and may
`avoid future problems associated with collapse of an unsup-
`ported space. In a biomechanical study, interbody fusion
`was found to be stiffer than posterior lumbar fusion [1]. In
`addition; the surface area between the host bone and the
`graft is much greater with interbody fusion than with inter-
`transverse process fusion.
`Many interbody fusion methods have been described in
`the literature, which have included various surgical ap-
`proaches to the disc as well as using different types of graft
`material. In recent years, several types of fusion cages have
`been developed. All are designed to be packed with graft,
`and all have holes in the inferior and superior surfaces to al-
`low bone to grow from the vertebral bodies through the
`cage and unite with the bone inside the cage. Currently, the
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`S. L. Blumenthal and D. D. Ohnmeiss / The Spine Journal 3 (2003) 301–309
`
`most commonly used cages are threaded metal cylinders.
`Also available are rectangular design cages and plates with
`struts to adjust the height and angle between the upper and
`lower plates. Cages are available in a variety of sizes to ac-
`commodate variation in individual patient anatomy. The
`purpose of this paper is to provide a review of the literature
`related to using fusion cages in lumbar interbody fusion
`procedures.
`
`Historical background of interbody fusion
`
`Burns [2] of Great Britain reported the first lumbar inter-
`body fusion in 1933. From an anterior approach (anterior lum-
`bar interbody fusion, ie, ALIF), he used an autogenous tibial
`peg to treat an adolescent with spondylolisthesis. Posterior lum-
`bar interbody fusion (PLIF) was first performed in the early
`1940s [3–5]. These early posterior procedures involved pack-
`ing bone fragments into the disc space after discectomy.
`Through the years, various techniques and grafts have been
`used for interbody fusion. Also, interbody fusion has been com-
`bined with a posterior fusion. The most recent advances for in-
`terbody fusion are fusion cages and endoscopic techniques by
`which to insert the cages. Bagby [6] first described the use of a
`basket to hold bone graft used for cervical spinal fusion in
`horses. This concept evolved into threaded fusion cages for use
`in humans. Other types of cages have also been developed for
`spinal fusion, such as ringlike cages, rectangular cages, plates
`connected with struts, tapered cylinders and threaded hollow
`bone dowels. More detailed reports about the development of
`cages and the various types have been published by Weiner and
`Fraser [7], McAfee [8] and Steffen et al. [9].
`
`Anatomy/pathophysiology
`
`The two primary purposes of interbody fusion are to re-
`lieve pain and stabilize the symptomatic spine segment. In
`cases of disc-related pain, the symptom-related tissue is re-
`moved. However, the removal of this tissue may cause the
`disc space to collapse with a concomitant narrowing of the
`foramen and related changes of the facet joints, causing
`nerve root compression. By filling the disc space with bone
`graft, the disc space height is reestablished. This may also
`increase the height of the foramen. The bone graft grows
`into the bone of the adjacent vertebra, fusing them into a
`single unit. This stabilizing effect is particularly important
`in cases of pseudarthrosis, spondylolisthesis, spinal instabil-
`ity and postlaminectomy syndrome.
`PLF is likely not as effective in the treatment of disc-
`related pain as interbody fusion procedures. During PLF
`procedures, some herniated tissue may be removed, but the
`majority of the disc is left; thus, the pain generator may re-
`main present after the surgery. Also, PLF does not provide
`the same degree of stability to the fused segment as do inter-
`body procedures. Evidence supports interbody fusion over
`posterior fusion alone in the treatment of lumbar disc-related
`pain. Weatherley [10] reported using discography to iden-
`
`tify symptomatic discs at the level of a solid posterior fu-
`sion. More recently, successful outcome was reported for
`such patients with persistent symptoms despite a solid pos-
`terior fusion when symptomatic disc(s) within the previ-
`ously fused segment were treated with ALIF [11]. Results
`of a biomechanical study found that following simulated
`posterior fusion with pedicle screw fixation, the intradiscal
`pressure during spinal flexion was as great as that measured
`in the intact, nonoperated segment [12]. These studies pro-
`vide biomechanical and clinical support for the need to use
`an interbody fusion technique to adequately address pain
`arising from the disc. ALIF and PLIF have been found to be
`effective in the treatment of disc-related pain [13–18], par-
`ticularly that associated with a chemically sensitized disc
`identified by discography [19]. Fusion not involving an in-
`terbody technique has yielded poor results for disc-related
`pain [19–21]. Although one study reported poor results of
`ALIF for discogenic pain [22], only 22 patients were stud-
`ied and the fusion success rate was unusually low.
`The potential benefits of using cages in interbody fu-
`sion procedures are that they may increase the chances of
`achieving a successful fusion and they provide some imme-
`diate stability to the operated segment while the bone graft
`incorporates.
`
`Anterior versus posterior approach to interbody fusion
`
`Several cages are designed to be implanted into the disc
`space using either the anterior or posterior approach. Based
`on the review of the literature, there is no general preference
`for the approach to be used. The decision on the type of ap-
`proach should be made based on several factors, such as the
`pathology present, spinal anatomy, patient’s history of prior
`surgery (either approach may be more difficult if there is
`significant scarring from prior surgeries), vascular anatomy
`(and conditions that may make an anterior procedure more
`difficult, such as calcification of vessels) and the surgeon’s
`individual training and experience.
`ALIF has the potential advantage of avoiding possible
`injury to the nerve roots caused by overretraction that may
`occur with PLIF. Also, ALIF provides a broader access to
`the disc space with greater room to work. Portions of the
`posterior elements do not need to be removed as with the
`posterior approach.
`The primary advantage of PLIF compared with ALIF is
`that potential complications related to major vascular struc-
`tures and sympathetic injury are more easily avoided. Also,
`if a pathology such as stenosis is present, it can easily be ad-
`dressed during the PLIF procedure.
`
`Clinical research
`
`Indications and operative considerations
`
`The general indications for fusion cages are basically the
`same as for traditional interbody fusion: symptomatic disc
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`disruption and/or symptomatic disc degeneration, postlami-
`nectomy syndrome with/without recurrent disc herniation,
`pseudarthrosis, low-grade spondylolisthesis, instability and,
`in some cases, degenerative scoliosis. As with other spine
`surgeries, in the absence of progressive neurologic prob-
`lems, patients should have failed an aggressive attempt of
`nonoperative care before considering lumbar fusion with
`cages. As with any spine surgery, it is important to be aware
`of the strong influence of psychological factors on treatment
`outcome [23–25]. In patients in whom one suspects a psy-
`chogenic component to the pain complaints, presurgical
`psychosocial screening is advised [26,27].
`One should analyze the size and geometry of the disc
`space to be fused when considering the type and size of
`cage to use. Patients who are difficult to manage with
`threaded cylindrical cages are those with a tall disc space,
`particularly if the width of the disc space is relatively nar-
`row. In the Ray study [28], one of the exclusion criteria was
`a disc space height of greater than 12 mm.
`
`Fusion rates
`
`As with any type of fusion surgery, it is difficult to deter-
`mine with certainty if a segment has successfully achieved
`bony union other than by open reexploration. In different
`studies, the criteria for determining successful fusion using
`cages have varied, and thus the results cannot therefore be di-
`rectly compared. Most studies define fusion in terms of the
`absolute or relative lack of motion at the operated segment as
`measured on flexion/extension radiographs. One study al-
`lowed as much as 5 degrees of motion in the definition of a
`fused segment [29]. Some studies include additional criteria,
`such as no halo or lucency around the implant. Initially, it
`was thought that computed tomography (CT) would provide
`a reliable assessment of fusion in cages. However, Heithoff et
`al. [30] reported that radiographic assessment, including by
`CT, is not reliable in identifying symptomatic pseudarthrosis
`when comparing the images to findings at reoperation. Six
`of seven CT scans falsely met the criteria for radiographic fu-
`sion in patients who had failed to fuse. Although the study
`included only a small number of patients, the findings likely
`have significant clinical implications when evaluating pa-
`tients with persistent pain after fusion. As discussed by
`McAfee [8], one good indication of fusion with open-ended
`cages is bridging of bone anterior to the disc space. With the
`broad range of definitions used for fusion in the various stud-
`ies, combined with the difficulty of determining fusion from
`radiographs, one cannot make valid comparisons of fusion
`rates across multiple studies.
`Several large, prospective, multicenter studies have eval-
`uated fusion rate with threaded cylindrical titanium cages.
`Kuslich et al. [29] reported that among 247 ALIF patients
`evaluated 24 months postoperatively, the fusion rate was
`98% among single-level procedures and 80% among two-
`level procedures using Bagby and Kuslich (BAK; Sulzer
`Spine Tech, Minneapolis, MN) cages. Among 165 patients
`who underwent PLIF, the fusion rate was 94% among one-
`
`level cases and 71% in two-level cases. In a multicenter
`study, Ray [28] reported a fusion rate of 96% for the Ray
`threaded fusion cage (Ray TFC, Surgical Dynamics, Nor-
`walk, CT) at 24-month follow-up in a group of 226 patients
`undergoing PLIF. In a series of 221 patients undergoing
`PLIF using a carbon fiber cage supplemented with pedicle
`screw fixation, Brantigan et al. [31] reported a fusion rate of
`100% in a subgroup of 91 patients. Agazzi et al. [32] re-
`ported the results of PLIF in 71 patients with carbon fiber
`cages used with pedicle screw fixation and found a 90% fu-
`sion rate. In another study investigating PLIF with carbon
`fiber cages combined with posterior fixation, Tullberg et al.
`[33] reported an 86% fusion rate in a group of 51 patients. In
`our review, no large-scale studies were found investigating
`the use of mesh cages for interbody fusion performed specif-
`ically for degenerative conditions. However, Eck et al. [34]
`reported on a series of 66 patients undergoing fusion with ti-
`tanium mesh cages (DePuy-Motech, Warsaw, IN). The study
`group included a mix of diagnoses, including degenerative
`conditions as well deformity, fracture and osteomylitis. The
`study included a mix of surgical techniques as well, includ-
`ing cages only or cages supplemented with anterior and/or
`posterior segmental fixation. They reported that 78% of the
`anterior levels were classified as fused. There were no cases
`of device failure or migration. Cage subsidence of more than
`2 mm was noted in 14% of cases.
`
`Clinical outcome
`
`Clinical outcome is difficult to evaluate. It is even more
`difficult to compare results across studies because of the
`variety of outcome measures employed, many of which
`have not been validated. In the Kuslich study [29], pain
`was rated on a 0 to 6 scale and function was rated on a
`scale from 7 to 32 points evaluating sitting, standing,
`walking, other activities of daily living and recreational
`activities. Results were not provided separately for PLIF
`and ALIF, but the pain scores decreased significantly from
`a preoperative mean of 5 to a mean of 2.9 at 2 years. How-
`ever, from the data presented, it appears that the 2-year
`follow-up values were available for a subgroup of approx-
`imately 32% of the group from which the preoperative
`data were derived because of patients who were not 24
`months postoperative at the time the results were reported;
`therefore, comparison of the two values should be inter-
`preted with care. The functional scores improved from a
`preoperative mean of 20.9 to 15.2 at 2-year follow-up (no
`statistical analysis was provided by the authors for these
`data). In Ray’s study [28,35], outcome was assessed using
`a slightly modified Prolo scale, which separately evaluated
`work and function on a 1 to 5 point scale. At the time of
`2-year follow-up, data were collected for 226 of the 236
`patients. Sixty-five percent of patients reported good or
`excellent results, 65% reported good or excellent function
`and 14% reported poor function. No data were provided
`comparing preoperative to postoperative evaluations. In
`the series reported by Brantigan et al. [31], 77% of a sub-
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`group of 91 patients (of 221 patients) had good or excel-
`lent results and 86% were classified as having a clinical
`successful outcome at 24 months after PLIF with a carbon
`fiber cage and pedicle screw fixation. In a series of pa-
`tients undergoing PLIF with different carbon fiber cages
`and pedicle screw fixation, Agazzi et al. [32] reported that
`66% of patients were satisfied and would undergo the
`same procedure for the same result at median follow-up of
`28 months. Using the Prolo scale, only 39% had good or
`excellent results.
`Kleeman and Hiscoe [36] compared laparoscopic ALIF
`using threaded cortical bone dowels to posterior fusion us-
`ing pedicle screws. The laparoscopic ALIF group had
`shorter hospital stay, less blood loss and less operative time
`than the PLF group. However, this study was not random-
`ized and may therefore have included differences in the pa-
`tients treated with the two procedures. In a prospective ran-
`domized study, Schofferman et al. [37] compared threaded
`titanium cylindrical cages packed with autograft to threaded
`bone dowel cages with demineralized bone matrix. At
`12-month follow-up, both groups improved significantly
`based on Oswestry and pain scores. There were no signifi-
`cant differences in outcome between the two groups.
`In most studies, there is a diagnostic mix of patients, and
`many patients have multiple diagnoses; therefore, comment
`on the outcome for any specific diagnosis cannot be reliably
`made. One study [38] dealt specifically with the use of
`cages in 15 patients with grade I spondylolisthesis. These
`authors reported good results using cages without pedicle
`screw supplementation.
`
`Cost comparisons
`
`Two studies have been published comparing the costs of
`PLIF performed with threaded fusion cages to combined an-
`terior-posterior fusion [39,40]. Both authors found that
`PLIF with cages was less expensive. However, the studies
`were not randomized, and surgery was dependent on the
`availability of using cages at the time the surgery was per-
`formed. In the Ray study [40], some patients considered not
`to be candidates for cages underwent combined fusion pro-
`cedures, thus introducing a potential selection bias. Klee-
`man and Hiscoe [36] compared the cost of laparoscopic
`ALIF using threaded cortical bone dowels to posterior fu-
`sion using pedicle screws. They found no difference in the
`costs for the two groups. Although the laparoscopic surgery
`was initially more expensive, the PLF group’s costs were
`increased because of the number of patients undergoing
`subsequent surgery to remove the hardware.
`
`Open versus laparoscopic ALIF
`
`Some fusion cages can be inserted anteriorly through ei-
`ther an open or laparoscopic approach. It has been hypothe-
`sized that the laparoscopic technique has the advantages of
`decreased operative morbidity and more rapid rehabilita-
`tion. However, these have not been established in a random-
`
`ized study. The primary disadvantage of the laparoscopic
`technique is the training required. Also, it is often associ-
`ated with increased operative time. As suggested by several
`authors, a learning curve is associated with laparoscopic
`spine surgery [41,42; Regan JJ, Ohnmeiss DD, unpublished
`data, 1998]. Typically, laparoscopic procedures are associ-
`ated with less blood loss but a greater operative time. In a
`multicenter study with 240 patients, Regan et al. [43] re-
`ported that the operative complication rates for open and
`laparoscopic ALIF procedures were comparable.
`Laparoscopic fusion at the L5–L1 level is becoming more
`accepted. The use of laparoscopic fusion at L4–L5 has been
`questioned, primarily because of difficulty accessing the disc
`as well as the resultant complications associated with expo-
`sure of this level [44–46]. Zdeblick and Cheng [46] reported
`that laparoscopic fusion involving the L4–L5 level was more
`likely to be associated with inadequate exposure to the disc
`space and had a greater complication rate than was seen in a
`group of patients undergoing mini-open ALIF. Katkhouda et
`al. [44] concluded that single-level laparoscopic fusion at
`L5–L1 was beneficial, but multilevel procedures were not ad-
`vocated because of their high complication rate. Their series
`involved only 24 patients accumulated over a 3- to 4-year pe-
`riod, and the surgeons performing the procedures had
`therefore not likely overcome the learning curve associated
`with laparoscopic spine surgery. Based on a series of radio-
`logic abdominal vascular examinations performed for vascu-
`lar conditions, Vraney et al. [45] suggested that laparoscopic
`fusion at L4–L5 would be feasible in only about 33% of pa-
`tients, with the limiting factor being vascular anatomy. How-
`ever, in a clinical series, Regan et al. [47] described that by
`varying the approach based on the location of the bifurcation
`of the great vessels with respect to the L4–L5 disc, laparo-
`scopic techniques can be safely used. They presented a series
`of 58 consecutive patients undergoing laparoscopic fusion at
`L4–L5 and commented that no patients were refused the lap-
`aroscopic approach because of vascular anatomy. In a com-
`parative study of mini-open to laparoscopic fusion at L4–L5
`involving threaded cylindrical cages, Regan et al. [48] found
`that the laparoscopic technique was associated with less
`blood loss but required a greater operative time than the mini-
`open procedure. The complications in the two groups were
`comparable.
`Using a swine model, Riley et al. [49] reported that open
`fusion was superior to laparoscopic fusion based on greater
`tensile testing values and observations of more bone around
`the implant. They attributed this to the fact that more disc
`tissue was removed during discectomy in the open group
`than in the laparoscopic group. McAfee et al. [50] have re-
`cently investigated the impact of partial versus complete
`discectomy on the results of ALIF with cages. They found
`that the pseudarthrosis rate was significantly less in the
`group of patients who had a complete discectomy than
`among patients with a partial discectomy. These results sug-
`gest that it is desirable to perform a complete discectomy
`when using fusion cages.
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`Complications
`
`Various complications have been reported with cage use,
`which have been similar to the types of complications re-
`ported for traditional interbody fusion using bone grafts. To
`date, no reports of device failure with threaded cylindrical
`metal cages have been published. It is difficult to calculate
`an overall complication rate for fusion cages, because sev-
`eral published studies involve overlapping patient popula-
`tions, particularly subgroups of the Food and Drug Admin-
`istration (FDA) Investigations Device Exemption (IDE)
`studies. In the large study by Kuslich et al. [29], the most
`frequently occurring complications were dural tears with a
`10.1% incidence in the PLIF group. The next most frequent
`complication in that group was neurologic problems (3.9%).
`Among ALIF cases, the most common complications were
`ileus and superficial infections, each with an incidence of
`3.1%. No deaths, major paralysis or deep infections were re-
`ported in the total group of 947 patients. Major complica-
`tions occurred in 2.0% of the group. These included device
`migration necessitating reoperation, great vessel damage re-
`quiring repair, pulmonary embolism, pneumonia, a fracture
`of the S1 body requiring reoperation and reoperation result-
`ing from a cage being pushed into the abdominal cavity dur-
`ing PLIF. The overall incidence of neurological problems
`was 2.7%, including persistent paresthesia, foot drop and
`disc or implants impinging the nerve roots. Among men in
`the ALIF group, there was a 4.0% incidence of retrograde
`ejaculation. The overall rate of cage-related reoperation was
`4.4%. The reasons for the reoperations included implant mi-
`gration or poor placement requiring repositioning or re-
`moval, and adding fixation to provide additional stabiliza-
`tion in patients with persistent symptoms.
`In the large series of 236 patients undergoing PLIF with
`threaded fusion cages reported by Ray [28], no cages
`needed to be removed. However, in three cases, reoperation
`was undertaken to reposition cages that were placed too an-
`teriorly. There were 13 cases (5.5% incidence) of dural
`tears. There was a 10% incidence of foot weakness or
`numbness; this resolved in all but two cases. There were
`five superficial and two deep infections, all of which re-
`solved with antibiotic treatment.
`Regan et al. [43] reported on the use of threaded fusion
`cages implanted using a laparoscopic technique. They com-
`pared the results for 215 single-level laparoscopic cases
`with 305 open ALIF cases using the same type of cage. The
`only complication encountered more frequently in the lap-
`aroscopic group was disc herniation (2.8% vs. 0.0%). This
`was because of cages being placed so that they pushed disc
`tissue posteriorly from the disc space. Among open proce-
`dures, there was a 1.0% incidence of implant migration re-
`quiring reoperation, 0.7% incidence of great vessel damage
`and 0.3% rate of pulmonary embolism. These complications
`did not occur in the laparoscopic group. Ten percent of the
`cases initially approached laparoscopically were converted
`to an open procedure. The reasons for this were bleeding
`
`and/or iliac vein laceration, difficulty accessing the disc
`space because of the location of the bowel or major vessel
`or the presence of adhesions or scar tissue, difficulty with
`visualization or technical difficulties with cage placement.
`The most frequently occurring complication in the laparo-
`scopic group was retrograde ejaculation, occurring in 5.1%
`of male cases. This occurred in 2.3% of open cases. The
`most common complication in the open group was ileus, oc-
`curring in 3.3% of cases. This was noted in 4.7% of laparo-
`scopic cases. Reoperation was performed in 2.3% of the
`open cases and 4.7% of the laparoscopic cases. The primary
`reason for reoperation in the laparoscopic group was to ad-
`dress displaced disc tissue compressing a nerve root (3.2%).
`In a separate study, analyzing complications in a consecu-
`tive series, single-surgeon experience with laparoscopic
`ALIF, it was found that half of the complications occurred
`within the first 40 of 127 laparoscopic cases [Regan JJ,
`Ohnmeiss DD, unpublished data, 1998]. Also, at the time of
`the first cases in the series, the laparoscopic approach was
`still in the early developmental stages. The approach, as
`well as some of the instruments, has been modified since
`those early cases.
`Scaduto et al. [51] compared the complications encountered
`in anterior versus posterior interbody fusion. They reported that
`the relative risk of having a major complication was 7.1 times
`greater in the posteri