Full text of DOI:10.1097/00127927-200106000-00006

Techniques in Neurosurgery
Vol. 7, No. 2, pp. 127–139
© 2001 Lippincott Williams & Wilkins, Inc., Philadelphia
Posterior Lumbar Interbody Fusion
Mark D. Oliver, M.D., David W. Cahill, M.D., and Michael V. Hajjar, M.D.
Department of Neurological Surgery, University of South Florida College of Medicine, Tampa, Florida
Abstract: Posterior lumbar interbody fusion has been practiced for more than 50 years.
There is little question that interbody techniques offer a significantly higher fusion rate
than traditional posterolateral techniques, but the morbidity associated with autograft
harvest, the risks of root injury or dural tear during graft placement, and the high
pseudarthrosis rate noted when allograft is substituted for autograft have conspired to
minimize the widespread use of the procedure.
Recently, various types of interbody cages have been developed in an effort to
minimize autograft harvest requirements, reestablish disc and foraminal height, and
decrease the risks of graft extrusion or collapse. Instrumentation developed for the
placement of such cages has improved the surgeon’s ability to perform complete
discectomy, to properly prepare endplates, to reestablish lordosis, and to minimize the
risk to the exiting nerve roots and dural canal.
An experienced surgeon may expect fusion rates of 80% to 90% in one or two level
lumbar fusions performed for degenerative disease using current techniques. Future
improvements using more biocompatible or bioresorbable devices and various bone
morphogenetic proteins will extend the life of these techniques well into the next
century. Key Words: PLIF—Spinal fusion—Interbody devices.
Fusion as a therapy for degenerative disc disease and
spondylosis in the lumbar spine has been widely prac-
ticed for more than 50 years. During that interval, most
such procedures have used posterior or posterolateral
techniques that have the advantages of simplicity of ex-
ecution and minimal associated risks to the patients so-
treated. Despite their widespread use, however, the suc-
cess rates of such procedures have been far from perfect.
The pseudarthrosis rate for uninstrumented posterolateral
lumbar fusion may approach 50%. The addition of seg-
mental (pedicle screw) instrumentation to these tech-
niques greatly improves overall success rates, but fusions
may still fail in approximately 20% of cases. Even with
successful fusion, such procedures often fail to reestab-
lish disc and foraminal height or listhesis reduction.
Conversely, interbody fusion techniques may usually
expect 10% or less pseudarthrosis rate and greatly facili-
tate the restoration of disc and foraminal height, a more
normal lordosis, and a functional anterior weight-bearing
column. Posterior lumbar interbody fusion (PLIF) has
been in practice for virtually as long as posterior or pos-
terolateral technique in the case of degenerative disease,
but has found only limited usage because of difficulties
inherent in the traditional techniques used.
Traditional PLIF uses structural autograft, structural
allograft, or nonstructural autograft (so-called chip
PLIF). Structural autografts harvested from the iliac crest
are often difficult or impossible to obtain, may be of
inadequate strength secondary to osteoporosis, and may
be associated with significant donor site morbidity. Non-
structural (chip) autograft is much easier to obtain but
often allows recollapse of the disc space and foramina,
thus obviating some of the advantages of the procedure.
Both structural and nonstructural allograft eliminate all
harvesting requirements but are associated with a high
(˜40%) pseudarthrosis rate and the potential for disease
transmission (Fig. 1).
Additional problems with traditional PLIF include a
significantly higher risk for dural tear and nerve root
Address correspondence and reprint requests to Dr. David W. Cahill,
4 Columbia Drive, Suite 730, Tampa, FL 33606.
127

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M. OLIVER ET AL.
FIG. 1. Traditional PLIF using structural autograft
several years after surgery. (A) Excellent fusion
and maintenance of alignment noting some subsi-
dence and broken intraspinous wires. (B) Four cor-
ticocancellous autografts left the patient with a
flank hernia and chronic pain.
injury due to the traction necessary to gain adequate
access to the disc space for graft placement. All these
difficulties have led to a relatively limited use of the
procedure among the community of spine surgeons as a
whole.
During the past 10 years, however, various interbody
devices have been developed to minimize risks and fa-
cilitate successful outcomes in posterior, as well as an-
terior, interbody techniques. With recent Food and Drug
Administration approval of the first generation of such
devices, PLIF is finally becoming accepted among a rap-
idly growing number of practicing surgeons.
PLIF, the use of distractive interbody cages often man-
dates a wider exposure. With our services, generous Gill
laminectomies, sometimes coupled with judicious drill-
ing of the rostromedial portion of the caudal pedicles, are
usually performed to allow safer resection of whatever
interbody device is to be used. This is especially neces-
sary when using cylindrical devices in cases that require
more than 15 mm of interbody distraction (Figs. 2,3).
Steffee acknowledged the limitations of interbody fu-
sions and suggested augmentation of PLIF with segmen-
tal posterior instrumentation more than a decade ago.
Most of the current literature supports this approach in
cases of iatrogenic spinal instability, fusion failure, and
degenerative spondylolisthesis (1–4). Resection of the
Although Cloward and others used only hemilaminec-
tomy and medial facetectomy to decompress before
FIG. 2. One of Dr. Cloward’s patients. (A and B)
First operation using structural autograft for PLIF
was successful at L5/S1. Second operation using
structural allograft at L3/4 has led to obvious pseud-
arthrosis with grade I slip in flexion and obvious
instability.
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INTERBODY FUSION
129
FIG. 3. Same patient as in Figure 2. Carbon-fiber reinforced polymer cages packed with
cancellous autograft allow for excellent reconstruction of lordotic alignment, disc and fo-
raminal height (A and B). Radiolucent cages allow visualization of living bone in the
interbody space even at 3 months after reoperation. At 10 months after reconstruction, bony
ingrowth is easily visualized and clearly maturing (C and D).
laminae, spinous processes, facets, posterior longitudinal
cedure following debridement for Potts disease. This fu-
sion technique quickly gained acceptance as a potential
treatment of other spine disorders and soon became the
method of choice for lumbar spinal arthrodesis. Unfor-
tunately, unacceptably high pseudarthrosis rates forced
the development of newer techniques. In 1948, Cleve-
land et al. (6) described a salvage technique for pseud-
arthrotic lumbar fusions wherein autologous corticocan-
cellous strips of iliac bone were laid down unilaterally
over freshly exposed lateral facets, pedicles, and trans-
verse processes of affected segments. Although these
posterolateral hemifusions attempted to take advantage
of larger, less mobile and more vascular graft beds, they
lacked biomechanical soundness and experienced similar
ligament, and disc induces three-column instability to the
bony spine. Posterior lumbar interbody fusion without
posterior reconstruction is dependent on tension-
distraction of a documented diseased remnant of disc
annulus for stability. Although this may be adequate in
some cases, such techniques fly in the face of biome-
chanical reason. The authors use segmental fixation and
posterolateral fusion in all PLIF cases.
HISTORY
Hibbs and Albee (5) first introduced interlaminar fu-
sion of the lumbar spine in 1911 as a stabilization pro-
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M. OLIVER ET AL.
rates of pseudarthrosis when compared with previous
fusion methods.
discs should be fused” created a cloud of controversy,
which is still present today. Nevertheless, current litera-
ture may support the use of PLIF in the treatment of the
following disorders (1–4,19):
Mercer (7) is credited with first describing the concept
of lumbar interbody fusion as a treatment of spondylo-
listhesis. In his 1936 article, Mercer stated, “...the ideal
operation for fusing the spine would be an interbody
fusion, but the surgical difficulties encountered in per-
forming such a feat would make the operation techni-
cally impossible....” During the next decade, surgeons
overcame the technical impossibilities and began per-
forming PLIF. In 1944, a report by Briggs and Milligan
(8) described packing the intervertebral space with bone
chips in an attempt to obtain fusion. Owens and Williams
(9), in 1945, and Jaslow (10), in 1946, published their
techniques using local bone from resected posterior ele-
ments as interbody graft material.
1. Degenerative disc disease
A) radiculopathy
B) mechanical back pain
C) cauda equina syndrome
2. Degenerative spondylolisthesis (grade I-II)
3. Isthmic spondylolisthesis (grade I-II)
4. Iatrogenic spinal instability
A) post-laminectomy instability
B) post-facetectomy instability
C) post-discectomy instability
5. Pseudarthrosis (following posterior or posterolateral
fusion)
Despite contributions from the preceding authors, no
surgeon was more instrumental in the development of
PLIF than Cloward (11). He became the biggest propo-
nent of the technique applying its principles to the treat-
ment of ruptured lumbar discs. Cloward’s contention was
that PLIF would remove the possibility of disc rehernia-
tion while stabilizing a vertebral joint, which was the
likely source of chronic back pain and disability for
many postoperative discectomy patients. His theory was
opposed by many, including Dandy, who felt that spinal
fusions for lumbar disc disease were unnecessary. Nev-
ertheless, Cloward continued his work and, in 1953, pub-
lished his landmark paper which described his technique
of radical discectomy coupled with structural interbody
autografts producing an 85% long-term cure rate with
PLIF in a series of 321 patients with ruptured lumbar
discs.
Variations in the original PLIF technique have contin-
ued to develop through the years. The first major alter-
ation came in 1988 when Steffee and Sitkowski (12)
introduced the use of pedicle screw plate fixation as an
adjunct to PLIF. More recently, the contributions of
Bagby and Kuslich (13–15), Ray (16), Brantigan (17,18),
and others to the concept of interbody cages have revo-
lutionized PLIF and appear to have addressed some of
the previous problems with interbody grafts, such as sub-
sidence, pseudarthrosis, and donor site morbidity. The
strength and versatility of these new interbody devices
have made the use of adjuvant pedicle screw fixation
more controversial in certain circumstances.
6. Central disc herniations
7. Recurrent disc herniation
Degenerative lumbar disc disease can present with ra-
dicular symptoms or mechanical back pain or both. To
better understand these symptoms, the physician must
understand the natural history of disc degeneration and
its effects on the adjacent vertebrae, facets, and support-
ing ligaments. The nucleus pulposus is normally high in
proteoglycan content but with repeated changes in in-
tradiscal pressure, nuclear proteoglycans decrease and
the disc begins to desiccate. Fissures develop in the car-
tilaginous endplates and annulus followed by mucoid
degeneration, ingrowth of fibrous tissue, and finally, loss
of a distinct nucleus (20,21). Consequently, the inter-
space collapses leading to foraminal stenosis, increased
annular tension and bulging, reactive bone formation
(traction spurs), and eventual central canal stenosis.
These changes, either individually or combined, can pro-
duce radicular or cauda equina symptoms. A successful
PLIF in this setting may decompress stenotic segments,
relieve nerve root compression, and restore normal disc
height and foraminal diameter.
That lumbar discs can be a source of back pain is
evidenced by both neuroanatomic and biochemical stud-
ies (22–24). The outer one-third to one-half of the disc
annulus is innervated by free nerve endings that are
known to harbor substance P. In addition, enzymes re-
lated to prostaglandin metabolism have been isolated in
the disc suggesting the presence of an inflammatory cas-
cade which may release substance P. This can result in
the transmission of pain impulses from the free nerve
endings to the dorsal root ganglion or sympathetic chain
or both. These findings support the concept of discogenic
back pain and invite surgical consideration for those pa-
INDICATIONS
As a surgical concept gains wider acceptance, its ap-
plication is extended to many other conditions. However,
Cloward’s sweeping conclusion that “all ruptured lumbar
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INTERBODY FUSION
131
tients with lumbago and magnetic resonance imaging
evidence of one or two level degenerative disc disease.
The importance of a thorough psychosocial evaluation
in the patient with mechanical back pain cannot be over-
stated and the findings should weigh heavily in the sur-
gical decision-making process. Once committed to sur-
gery, the goal should be to reduce or eliminate the pain
related to the unstable joint by immobilization. Studies
by Rolander (25) demonstrated significant intervertebral
disc motion in a segment that had previously undergone
a successful posterolateral fusion. Moreover, cases of
persistent low back pain following a solid posterolateral
fusion were investigated by Weatherley et al. (26) who
noted substantial improvement in pain with the addition
of an interbody fusion.
Symptomatic degenerative and isthmic spondylolis-
thesis are other conditions in which PLIF can be an ef-
fective treatment. Cloward (27) has reported his experi-
ence with degenerative spondylolisthesis and concluded
that interbody fusion resulted in superior outcomes over
decompression alone. Herkowitz and Kurz (28) showed
in a prospective, randomized study that these disorders
are better treated with decompression and fusion in situ
rather than decompression alone. It is nonetheless clear
that failure to correct sagittal plane imbalance may lead
to chronic back pain in some cases. With degenerative
spondylolisthesis, attempts to correct the listhesis and
maintain the correction with pedicle screw constructs
alone often fail due to the lack of structural integrity
within the disc and surrounding ligaments with cantile-
vering over the deficient anterior column. In these cir-
cumstances, we prefer to use PLIF in addition to seg-
mental fixation to restore normal disc and foraminal
height as well as annular tension while reducing the slip
and maintaining the correction. In the case of isthmic
spondylolisthesis, our treatment is largely the same al-
though PLIF is usually not performed in those situations
where the slip is no more than grade I and the disc’s
height and structural integrity appear normal on mag-
netic resonance imaging (Fig. 4).
In cases of iatrogenic spinal instability including post-
laminectomy, post-facetectomy, and post-discectomy
slip, or symptomatic instability without obvious radio-
graphic abnormality, PLIF with segmental pedicle screw
fixation is able to restore a stable weight-bearing column
anteriorly and reestablish a tension band posteriorly.
Hutter (29) discovered a 78% satisfactory outcome and a
91% fusion rate in his review of 142 patients with symp-
tomatic postoperative spinal instability. The senior au-
thor’s results in his recent series of 43 patients with
postlaminectomy spondylolisthesis treated with cage
PLIF and pedicle screw fixation disclose a 77% satisfac-
tory outcome with a 93% apparent fusion rate (Fig. 5).
Pseudarthrosis rates following a standard posterolater-
al fusion may approach 50% whereas the addition of
segmental instrumentation to the fusion procedure de-
creases failure rates to 10% to 20% (30,31). In symp-
tomatic patients with a failed posterolateral fusion, the
authors maintain that a combination of pedicle screw
fixation with PLIF offers the best opportunity for a solid
FIG. 4. Post-menopausal female status after correction of grade I isthmic spondylolisthesis with ramped, rectangular, carbon fiber/polymer cages
(Brantigan IDE). Preservation of reduction of slip and lordosis is evident as fusion matures around radiolucent cages at 3 (A), 8 (B), and 24 (C) months
after surgery. At 24 months, complete arthrodesis is easily visualized through radiolucent devices.
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M. OLIVER ET AL.
FIG. 5. (A) Post-laminectomy spondylolisthesis, grade II. (B) Immediately after operation with adequate reduction and cage position. (C) One month
later with recurrent listhesis and extruded cage. This complication was secondary to endplate damage during cage insertion precluding adequate
distraction of the interspace as well as adequate compression of devices with posterior fixators. Coronal plane anatomy precluded the use of a large
diameter cage. This reflects a limitation of cylindrical devices used posteriorly.
fusion as it makes use of the virgin endplates of the
pseudarthrotic segment.
axial and torsional loading of the lumbar spine, particu-
larly if the anterior and middle columns are severely
diseased. There is no other surgical fusion technique in
which grafts bearing no load are expected to bridge re-
ceptor sites centimeters apart to produce weight bearing
structures whose center of load is centimeters offset from
its axis of rotation.
Lumbar interbody fusion is a more biomechanically
sound construct than posterolateral fusion because it
places bone grafts where 80% of mechanical loads are
imparted, allowing for optimal load sharing with maxi-
mal compression and subsequent incorporation of the
grafts. Cautilli (36) has outlined the biomechanical ad-
vantages of PLIF over other lumbar fusion techniques:
An increasing body of evidence is mounting to support
the use of PLIF in the treatment of both centrally located
as well as recurrent disc herniations. With central disc
herniations, a more extensive surgical decompression is
required than with laterally situated discs. Consequently,
posterior elements as well as the disc and annulus are
more disrupted in the process and may require anterior
and posterior column restabilization.
Symptomatic recurrent disc herniations requiring re-
operation are associated with much less favorable out-
comes (32). With multiple same-side, same-level hernia-
tions, PLIF becomes an attractive option because it ne-
gates the possibility of further recurrences. Lin et al. (33)
and Branch et al. (34) reported their 1-year results with
PLIF in the scenario of recurrent disc herniations with a
75% to 80% satisfactory outcome with a Ն90% success-
ful fusion rate.
1. Posterior lumbar interbody fusion has a wider area of
bone surface with grafts covering more than 90% of
the intervertebral space.
2. Grafts have an adequate blood supply through the
cancellous portion of the vertebral body once the sub-
chondral endplate is exposed or partially removed.
3. Grafts are placed proximate to the center of motion
(instantaneous axis of rotation) and compressive
forces.
4. Surgical exposure allows complete visualization of
the area of nerve root compression and offers com-
plete access for removal of the areas of compression
centrally, as well as laterally, at the intervertebral ca-
nal.
BIOMECHANICS
As discussed earlier in this text, posterolateral fusions
have the disadvantage of allowing significant interverte-
bral disc motion despite a solid fusion mass. Biomechan-
ical models have revealed that 20% of mechanical loads
applied to the lumbar spine are transmitted across the
facet joints and posterior elements (35). As such, the
limitations of posterolateral fusions are evident with
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INTERBODY FUSION
133
5. Structural grafts preserve interbody distance so there
will be no ensuing disc space collapse, lateral recess
stenosis, or foraminal stenosis as a sequela of disc
excision.
6. Posterior lumbar interbody fusion annuls the possibil-
ity of recurrent lumbar disc herniation at the fused
level.
The development and increased application of inter-
body cages has stimulated much discussion regarding
their potential for induced biomechanical failure second-
ary to stress shielding. This concept arises from Wolff’s
law, which states that bone is laid down where stresses
require its presence. It has been postulated that the in-
herent strength of titanium, the primary component of
metallic cages, may prohibit fusion by disallowing de-
formation of the interbody cages under physiologic loads
with subsequent shielding of the grafts from the stresses
required for osteogenesis. To address this concern, car-
bon fiber polymer cages were developed that have the
same modulus of elasticity as cortical bone and, under
more normal physiologic loads, may allow deformation
with subsequent stressing of the grafts.
FIG. 7. In virgin cases, retraction of the dural tube to or beyond the
midline is safe.
and effectively decompress the neural elements, to re-
store structural integrity to the anterior weight bearing
column, and to reestablish and maintain normal lordosis
as well as disc and foraminal height until a solid fusion
develops.
TECHNIQUE
Prior to the development of any surgical technique, the
goals of the procedure must be clearly defined. In the
case of PLIF, the purpose of surgery must be to safely
The PLIF technique, as first described by Cloward,
consists of four major steps:
1. Neural element exposure and decompression via bi-
lateral partial hemilaminectomies and medial facetec-
tomies (Figs. 6,7).
2. Semi-radical discectomy with preparation of sub-
chondral endplates using osteotomes (Fig. 8).
3. Harvesting of tricortical iliac bone interbody grafts
(Fig. 9).
4. Insertion and packing of interbody grafts using puka
chisels.
Variations of the original PLIF method have been
mentioned briefly in this text; however, two of the more
significant alterations which we will discuss in greater
detail deal with interbody graft materials and pedicle
screw augmentation of PLIF segments.
Initially, Cloward proposed the use of 1.5 cm × 3.0 cm
strips of tricortical bone (structural autograft) harvested
from the patient’s iliac crest as suitable interbody grafts.
Unfortunately, this procedure proved to be time consum-
ing, bloody, and painful for the patient postoperatively.
Moreover, the ability to obtain multiple, precisely-sized
grafts remains technically challenging for most surgeons.
FIG. 6. Complete Gill laminectomy with resection to the middle to
upper pars allows excellent exposure of dural sac as well as exiting and
traversing nerve roots. Cage insertion may occasionally require judi-
cious drilling of the superomedial aspects of caudal facet or pedicle or
both.
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M. OLIVER ET AL.
graft bed. Although the applications of these cages are
similar, size selection is critical and remains dependent
on the anatomic dimensions and distractive properties of
the individual spine. With some threaded cylindrical in-
terbody cage systems, use of the appropriate size distrac-
tion device is limited by the exiting nerve root rostrally
and the supero-medial aspect of the pedicle caudally. In
these situations, the temptation has been to apply less
distraction and use a smaller cage. This fails to restore
normal annular and ligamentous tension to the support-
ing spine and predisposes the cage to back-out. Modifi-
cation of the bony anatomic constraints with a high speed
drill may enable the insertion of a more appropriate size
cage in some cases (Figs. 10–14).
The anatomy of the dural tube and exiting nerve root
restrict posteriorly placed devices in the coronal dimen-
sion more than in the sagittal dimension. Hence, devices
that are higher than they are wide are ideal to the resto-
ration of disc space height. Ramped, rectangular cages
and spacers function using the same principles as the
previously mentioned cylindrical interbody devices;
however, the anatomic advantages of over square shap-
ing and the instruments used in their application seem to
better accommodate the desired goals. Following cortical
endplate preparation, these cages either are hammered
into position while distraction is held or are inserted into
FIG. 8. The harvesting of structural, tricortical autografts of adequate
size and number may be limited by iliac crest dimensions, osteoporosis,
and donor site morbidity such as hernia, cluneal nerve or gluteal artery
injury, flank hernia, or sacroiliac joint disruption.
Consequently, efforts were directed toward the use of
allograft or local, laminectomized bone, or both to
achieve interbody arthrodesis.
Structural allografts and chip autografts permit shorter
procedure times and negate the morbidity associated
with the acquisition of structural autograft; however, al-
lografts have been linked to high pseudarthrosis rates,
and nonstructural, chip autografts have experienced a
high rate of graft collapse, particularly in the lower lum-
bar region where forces imparted through the spine are
high (3).
Cancellous autograft is osteogenic (37) and harbors
high concentrations of bone morphogenetic protein but
lacks strength. Most of the recent advances in PLIF have
centered on the development of metallic and carbon fiber
and polymer interbody cages. These cages are manufac-
tured in threaded cylindrical (13–16) and ramped or rect-
angular (17,18) shapes with a variety of available lengths
and diameters, which, when coupled with cancellous
bone, offer immediate structural integrity and mainte-
nance of normal anatomy while fusion occurs.
Each cage system provides its own method of inter-
space distraction (e.g., plug, spreader, Tang) and disc-
space preparation (e.g., shaver, reamer, broach) and, in
the case of threaded interbody devices, a means to tap the
FIG. 9. In performance of radical discectomy, care must be exercised
to 1) not overdistract, 2) not perforate the anterior longitudinal liga-
ment, and 3) not destroy the bony vertebral endplate. The use of cali-
brated instrumentation provides a useful safety measure.
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INTERBODY FUSION
135
FIG. 10. (A) Currently approved cylindrical de-
vices are limited by horizontal diameter (coronal
plane) anatomic restrictions and minimized
graft/recipient surface area. (B) Currently approved
threaded, cylindrical, titanium BAK device.
the interspace on their side and rotated up to achieve
distraction. In comparison to threaded cage systems,
these rectangular devices offer one other advantage in
that they do not require focal destruction of the endplates
for their insertion. As a result, subsidence is minimized
and overall stability may be improved (Fig. 15).
3. Vertebral body destruction from fracture, tumor, or
infection allows for less opposition between the cages
and the endplate of the affected vertebrae with sub-
sequent subsidence, extrusion, or angulation.
4. Severe epidural scarring may prohibit adequate expo-
sure of the neural elements and disc interspace from a
posterior approach.
As mentioned in the previous section, titanium cages
have raised biomechanical concerns with regard to stress
shielding. Moreover, metallic cages make radiographic
examination of graft material exceedingly difficult,
largely obstructing the view of the graft and endplate
interface. As a result, we often prefer to use radiolucent,
carbon fiber reinforced polymer cages that more closely
parallel the modulus of elasticity of cortical bone while
simultaneously allowing easy radiographic visualization
of the maturing interbody grafts. These devices, which
have been pioneered by Brantigan and Steffee, still await
approval from the Food and Drug Administration.
With their growing popularity and widespread use, the
application of these interbody devices is being extended
to many spinal disorders. Although the PLIF technique is
proven, the surgeon must remember that the results of
cage application are only preliminary. Moreover, initial
experience with these devices has generated some con-
traindications to their safe and effective use (2–4):
RESULTS
The goal of PLIF, as for other spine stabilizing pro-
cedures, is successful arthrodesis of the affected segment
with a good clinical outcome. Sadly, to date, no study has
been able to demonstrate a significant relation between
fusion status and clinical outcome. Nonetheless, these
two endpoints are always emphasized in any retrospec-
tive or prospective examination of spinal fusion.
In an exhaustive review of the PLIF literature, overall
fusion rates ranged from 50% to 94% with the majority
reporting 85% to 90% success (4,11,19,29,33,34). A re-
view by Lin (4) of 1,000 PLIF cases revealed higher
fusion rates in a subset of cases in which pedicle screw
plate fixation was added. Cases of interbody fusion con-
ducted with both metallic and carbon fiber cages have
shown comparable results during the short term (15,16,
18).
1. Grade III, IV, and V spondylolisthesis are associated
with severely incompetent ligaments and nonparallel
vertebral endplates, which lead to the easy dislodge-
ment and subsequent failure of such devices.
2. Severe osteoporosis is associated with abnormally
soft vertebral endplates, which allow the interbody
cages to telescope or subside.
Although PLIF is associated with a high rate of fusion,
this by no means guarantees a favorable outcome. In fact,
all PLIF series reviewed by the authors revealed that the
percentage of satisfactory clinical outcomes lagged be-
hind fusion rates, even when compensation cases were
excluded. Simmons (19) made the same observation in
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M. OLIVER ET AL.
FIG. 11. (A) A newer modification to the BAK device originally designed for anterior use
(“proximity”) allows closer cage placement and improved graft and recipient contact area. (B
and C) Improved BAK proximity cage with decreased horizontal dimension and improved
graft surface area.
his comprehensive literature review noting satisfactory
clinical outcomes of between 54% and 94%.
occur in up to 5% of patients (3,4). Usually, these
injuries transpire during the insertion of structural
grafts or interbody cages and are related to root com-
pression or stretch during resection.
COMPLICATIONS
3. Graft or cage retropulsion usually occurs with more
inexperienced surgeons and is due to undersizing of
the interbody grafts or devices risking subsequent mi-
gration and possible neurologic injury. This is usually
due to underdistraction of the interspace or failure to
compress the grafts with posterior fixators or both.
4. Pseudarthrosis is more frequently observed with the
use of allograft although technical errors in endplate
preparation and carpentry may lead to autograft fail-
ure as well.
Posterior lumbar interbody fusion is a technically de-
manding exercise but, with care and experience, most of
the potential dangers can be avoided. Previous authors
have cited general complications that may occur but are
not unique to the PLIF procedure. We will mention only
those complications directly related to the procedure:
1. Dural lacerations are more likely to occur during re-
traction of the exiting root and dural tube while plac-
ing the cage or graft. This is especially true while
taking down epidural scar and preparing the neural
elements for retraction in the patient undergoing re-
operation.
5. Graft collapse is common with both allograft and non-
structural chip autograft. Interbody cages are being
used to curtail this problem.
2. Neurological injuries, particularly neuropraxias, can
6. Graft or cage subsidence (telescoping) is common in
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INTERBODY FUSION
137
FIG. 12. Threaded, cylindrical cage of radiolucent, carbon-fiber con-
struction designed by the senior author combining the ideas of Bagby,
and Kusslich, Ray, Brantigan, and Steffee (see Figs. 2,3).
elderly patients with osteoporosis and in cases in
which endplate preparation has been overly vigor-
ous.
FIG. 14. Lordotic rectangular titanium cages with rounded edges al-
lowing the cage to be used as its own distractor (Synthes, Paoli, PA).
dence and collapse, and will probably improve overall
fusion rates still further.
CONCLUSIONS
Nonetheless, certain risks inherent to the PLIF proce-
dure are unavoidable. It is likely that the risk for dural
tear and root injury will always be higher with PLIF than
with posterolateral techniques. The management of post-
operative infections may prove complicated in the face
of contaminated interbody devices. Cauda equina injury
secondary to cage extrusion will also remain a small but
finite risk.
Currently approved interbody devices are of titanium
construction and make radiographic assessment of fusion
status difficult. Such devices may also stress shield-
implanted bone grafts and are practically unremovable in
the long term.
New interbody devices have led to a resurgence of
interest in an old fusion technique that still has the same
advantages, the same risks, and the same complications
as the originally described procedure. There is little ques-
tion that fusion rates are better with interbody fusion than
with purely posterior techniques. It is reasonably clear
that anterior column restoration facilitates listhesis re-
duction, restores lordosis, and produces a more anatomic
reconstruction of the degenerated lumbar spine.
It is likely that interbody cages will decrease the risks
associated with structural graft harvest, of graft subsi-
There is no agreement and little data on which to base
clinical decisions as to when to use these devices, which
devices may offer best clinical result, or on when or
whether to supplement the interbody devices with addi-
tional fixation.
We currently use PLIF with interbody cages in the
management of pseudarthrosis after posterolateral fu-
sion, in degenerative post-surgical and isthmic spondy-
lolisthesis, in all cases in which posterior decompression
must be coupled with discectomy, and in the occasional
case in which interbody fusion is desirable but an ante-
rior approach is contraindicated, such as with previous
retroperitoneal vascular injury. As of 2001, we use no
less than seven distinct interbody cage devices of various
shapes and constructed of metal, carbon-fiber and poly-
FIG. 13. Wedge or ramped rectangular cage of carbon-fiber polymer
construction of Brantigan (see Fig. 4).
Techniques in Neurosurgery, Vol. 7, No. 2, June 2001

138
M. OLIVER ET AL.
the advantages of biocompatibility (in most cases) and a
long track record for similar materials. Carbon-fiber re-
inforced polymer devices offer the significant advan-
tages of radiolucency and modulus of elasticity similar-
ity, and are our current first choice in most cases.
Cylindrical devices offer the advantages of threaded
insertion. Rectangular devices offer an improved graft
surface area. Wedge or ramp devices combine improved
graft surface area with anatomic shape and may facilitate
restoration of lordosis. Rectangular or ramped cages with
rounded edges may offer the ability of horizontal inser-
tion but vertical (distracted) final placement. Only clini-
cal research will define which device may be best suited
for a given clinical scenario.
Research in our laboratories is aimed at the develop-
ment of more biocompatible devices to be used in con-
junction with various genetically-engineered growth fac-
tors in an effort to ultimately eliminate both permanently
implanted devices and bone grafts. It is reasonable to
assume that these advances could become clinically ap-
plicable in the current generation. The loftier goal of
motion-segment reconstruction may take longer (Figs.
1–15).
REFERENCES
1. Branch CL, Jr.. The case for posterior lumbar interbody fusion.
Clin Neurosurg 1996;43:252–267.
2. Dickman CA. Internal fixation and fusion of the lumbar spine
using threaded interbody cages. Barrow Neuro Inst Q 1997;13:
4–25.
3. Keppler L, Steffee AD, Biscup RS. Posterior lumbar interbody
fusion with variable screw placement and isola instrumentation. In:
Bridwell KH, DeWald RL, eds. The Textbook of Spinal Surgery.
2nd ed. Philadelphia: Lippincott-Raven, 1997:1601–1621.
4. Lin PM. Posterior lumbar interbody fusion. In: Techniques in Spi-
nal Fusion and Stabilization. New York: Thieme Medical Publish-
ers, 1995.
5. Hibbs RA, Albee FH. An operation for progressive spinal defor-
mities. NY State J Med 1911;93:1013.
6. Cleveland M, Bosworth DM, Thompson F. Pseudarthrosis in the
lumbosacral spine. J Bone Joint Surg [Am] 1948;30:302–311.
7. Mercer W. Spondylolisthesis with a description of a new method
and notes of ten cases. Edinburgh Med J 1936;43:545–572.
8. Briggs H, Milligan PR. Chip fusion of the low back following
exploration of the spinal canal. J Bone Joint Surg [Am] 1944;26:
125–130.
9. Owens JV, Williams HG. Intervertebral spine fusion with removal
of intervertebral disk. Am J Surg 1945;70:24–6.
10. Jaslow IA. Intercorporal bone graft in spinal fusion after disc re-
moval. Surg Gyn Obstet 1946;82:215–8.
11. Cloward RB. The treatment of ruptured lumbar intervertebral discs
by vertebral body fusion: Indications, operative technique, after
care. J Neurosurg 1953;10:154–168.
12. Steffee AD, Sitkowski DJ. Posterior lumbar interbody fusion and
plates. Clin Orthop 1988;227:99–102.
13. Bagby GW. Arthrodesis by the distraction-compression method
using a stainless steel implant. Orthopedics. 1988;11:931–934.
14. Bagby GW, Kuslich SD. Arthrodesis of the lumbar spine utilizing
a rigid housing containing bone graft. The BAK interbody fusion
FIG. 15. (A) After discectomy and reduction (if necessary), retraction
of the dural tube and exiting nerve root while preparing the channel for
the graft or cage provides a risky opportunity for dural tear or nerve
root injury or both. (B) Contralateral interbody distraction (as shown)
or distraction between pedicle screws facilitates placement of the first
interbody device or graft.
mer, or allograft bone. Each device offers its own ad-
vantages and disadvantages.
Titanium threaded devices offer the advantages of cur-
rent Food and Drug Administration approval, simplicity,
and hardware availability. Human allograft devices offer
Techniques in Neurosurgery, Vol. 7, No. 2, June 2001

INTERBODY FUSION
139
method. In: Thalgott J, ed. Manual of Internal Fixation. New York:
Raven Press, 1994.
26. Weatherley CR, Prickett CF, O’Brien JP. Discogenic pain persist-
ing despite solid posterior fusion. J Bone Joint Surg 1986;68B:142.
15. Oxland TR, Kuslich SD, Kohrs DW, et al. The BAK interbody
fusion system: Biomechanical rationale and early clinical results.
In: Lumbosacral and Spinopelvic Fixation. Philadelphia: Lippin-
cott-Raven, 1996.
16. Ray CD. Threaded titanium cages for lumbar interbody fusions.
Spine 1997;22:667–680.
17. Brantigan JW, Steffee AD, Geiger JM. A carbon fiber implant to
aid interbody lumbar fusion: Mechanical testing. Spine 1991;16:
277–282.
18. Brantigan JW, Steffee AD. A carbon fiber implant to aid interbody
lumbar fusion: Two year clinical results in the first 26 patients.
Spine 1993;18:2106–2117.
27. Cloward RB. Spondylolisthesis: treatment by branch-laminectomy
and posterior interbody fusion. review of 100 cases. Clin Orthop
1981;154:74–82.
28. Herkowitz HN, Kurz LT. Degenerative lumbar spondylolisthesis
with spinal stenosis: a prospective study comparing decompression
with decompression and intertransverse process arthrodesis. J
Bone Joint Surg 199l;73A:802.
29. Hutter CG. Spinal stenosis and posterior lumbar interbody fusion.
Clin Orthop 1985;193:103–114.
30. Yuan HA, Garfin SR, Dickman CA, et al. A historical cohort study
of pedicle screw fixation in thoracic, lumbar and sacral fusions.
Spine 1994;19:S2279–S2296.
19. Simmons JW. Posterior lumbar interbody fusion. In: Frymoyer
JW, ed. The Adult Spine: Principles and Practice. New York:
Raven Press, 1991:1961–1987.
31. Zdeblick TA. A prospective, randomized study of lumbar fusion:
Preliminary results. Spine 1993;18:983–991.
20. Lyons G, Eisenstein SM, Sweet MBE. Biochemical changes in
intervertebral disc degeneration. Biochim Biophys Acta 1981;673:
443.
21. Oegema TR. Biochemistry of the intervertebral disc. Clin Sports
Med 1993;12:420.
22. Hacker RJ. Lumbar spine fusion using interbody fixation devices:
Indications and techniques. Contemp Neurosurg 1997;19.
23. Schwarzer AC, Aprill CN, Derby R, et al. The prevalence and
clinical features of internal disc disruption in patients with chronic
low back pain. Spine 1995;20:1878.
24. Wetzel FT, LaRocca SH, Lowery GL, et al. The treatment of
lumbar spinal pain syndromes diagnosed by discography. Spine
1994;19:792.
32. Hardy RW. Repeat operation for lumbar disc. In: Hardy RW, ed.
Lumbar Disc Disease. New York: Raven Press, 1982:193–202.
33. Lin PM, Cautilli RA, Joyce MF. Posterior lumbar interbody fusion.
Clin Orthop 1983;180:154–168.
34. Branch CL, Branch CL, Jr. Operative management of the failed
back syndrome. In: Youmans JL, ed. Neurological Surgery, Third
ed. Philadelphia, PA: WB Saunders; 1990:2731–2748.
35. Benzel EC. Biomechanics of Spine Stabilization, Principles and
Clinical Practice. New York: McGraw-Hill, 1985.
36. Cautilli RA. Theoretical superiority of posterior lumbar interbody
fusion. In: Lin PM, ed. Posterior Lumbar Interbody Fusion.
Springfield, IL: Charles C. Thomas, 1982:82–93.
25. Rolander S. Motion of the lumbar spine with special reference to
the stabilizing effect of posterior fusion. Acta Orthop Scand 1966;
90:1.
37. Urist MR. Bone transplants and implants. In: Urist MR, ed. Fun-
damental and Clinical Bone Physiology. Philadelphia: JB Lippin-
cott, 1980:331–368.
Techniques in Neurosurgery, Vol. 7, No. 2, June 2001