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20 Lateral Lumbar Interbody Fusion (LLIF) for the Treatment of Adult Spinal Deformity (ASD)
177
Fig. 20.16 Tape marking the C-arm gantry with each
planned operative lumbar level labeled. This provides
gical level throughout the operation, even with different
radiology technologists
reproducible guide for visualization of each planned sur-
ab
Psoas major
Quadratus
lumborum
Transverse
abdominis
Internal oblique
External oblique
Subcostal
Iliohypogastric
Ilioinguinal
Lateral femoral
cutaneous
L1
L2
L3
L4
L5
Fig. 20.17 ( a ) The abdominal wall and its innervation. The subcostal, iliohypogastric, and ilioinguinal nerves are
labeled. ( b ) Patient with right abdominal paresis after a right-sided LLIF approach that resolved a 6-month post-op
the umbilicus. This muscle layer can be bluntly
dissected to expose the internal oblique (IO)
muscle, whose muscle fi bers run perpendicular to
the EO muscle. The IO can be bluntly dissected
over each individual lumbar disk level to reveal
the transverse abdominal muscle or it can be
cut. Care must be taken to bluntly dissect the IO
muscle fi rst to avoid injuring the subcostal, ilio-
hypogastric, and ilioinguinal nerves, which originate from the T12 and L1 nerve roots and course
anteriorly and inferiorly and pierce and innervate
the abdominal wall musculature. Injury to any of
these nerves can result in abdominal wall paresis causing an abdominal bulge or droop, which
can be permanent or temporary depending on the
degree of nerve injury (Fig.
20.17 ). Cahill and
178
J.M. Zavatsky et al.
colleagues reported a 4.2 % incidence of postoperative abdominal wall bulge, which they related
to permanent injury to the motor nervous supply
to the lateral abdominal wall [ 47 ]. Once the IO
muscle is dissected, the transverse abdominal
(TA) muscle is visualized and dissected. As its
name contends, the TA fi bers run transversely or
horizontally. Immediately deep to the TA muscle
is the transversalis fascia. This aponeurotic membrane can be distinct and lies between the inner
surface of the TA muscle and the parietal peritoneum. Once this is dissected, the retroperitoneal
fat can be visualized.
Access can also be obtained through a twoincision technique. After the fi rst incision located
directly over the planned surgical disk space is
performed, dissection is carried to the transversalis fascia as described above. A second small
incision can then be placed a fi nger-length posterior to the fi rst incision and can be used as a direct
access point to the retroperitoneal space. Once
the second incision is made, blunt muscle dissection is performed to the transversalis fascia posteriorly, which can be penetrated with a pointed
clamp into the retroperitoneal space (Fig.
20.18 ).
Through the second more posterior incision,
blunt fi nger dissection can sweep the peritoneum,
fat, and any adhesions off the transversalis fascia
and psoas muscle. The transverse process is a
bony landmark that can be palpable for localization confi rming the position in the retroperitoneal
space. Once blunt dissection is performed, the
same fi nger can be directed to the fi rst incision
and used as a visual marker for dissection of the
transversalis fascia ensuring entry into the retroperitoneal space. The initial dilator can then be
placed through the fi rst incision using the fi nger
in the second incision to guide the dilator to the
retroperitoneal space and psoas muscle.
The retroperitoneal fat can be swept anteriorly
to visualize the fascia enveloping the psoas muscle. The genitofemoral (GF) nerve lies directly on
top of the psoas fascia. The GF nerve originates
from the upper L1 to L2 segments of the lumbar
plexus and passes caudally and emerges from the
anterior surface of the psoas muscle. It can be
encountered in the center on the LLIF operative
fi eld commonly at L3–L4. The nerve continues
downward and divides into two branches, the genital branch and the femoral branch. The genital
branch passes through the deep inguinal ring and
enters the inguinal canal. The genital branch con-
st
1
Internal
oblique
incision
External
oblique
Transversalis
fascia
Quadratus
lumborum
1st incision
Direct lateral incision
to access the disk
space
2nd incision
Posterior incision
to access the
retroperitoneal
space
Retroperitoneal space
2nd incision
Transverse process
Erector spinae
Latisimus dorsi
Fig. 20.18 Two-incision technique. The fi rst incision allows access to the LLIF level. The second incision allows
access to the retroperitoneal space and guidance from the fi rst incision to the psoas muscle
20 Lateral Lumbar Interbody Fusion (LLIF) for the Treatment of Adult Spinal Deformity (ASD)
179
tinues down and supplies the scrotal skin in men
and accompanies the round ligament of the uterus
terminating in the skin of the mons pubis and labia
majora in women. The femoral branch passes
underneath the inguinal ligament, traveling adjacent to the external iliac artery, supplying the skin
of the upper anterior thigh and groin. Whether
each operative level is approached with individual
small dissections through the muscle layers and
fascia or a mini-open incision is performed for better visualization, the psoas fascia should be
released to expose the muscle fi bers beneath it.
Using a “no-look” approach, moving the initial
dilator 2–3 mm cranially and caudally, in-line
with the muscle fi bers, can release the fascia as
the dilator is advanced into the psoas muscle and
docked (Fig.
20.19 ). This can decrease the risk of
dragging the fascia and GF nerve into the psoas
causing stretch with dilator advancement or compression with retractor opening, both of which
can cause injury and anterior thigh symptoms.
Wanding the initial dilator more than 2–3 mm cranially and caudally could result in nerve injury.
Fig. 20.19 The genitofemoral (GF) nerve crossing the
psoas muscle at L34. The psoas fascia has been released,
exposing the psoas muscle fi bers and freeing the GF nerve
prior to dilator insertion
20.3.4 Transpsoas Approach and Retractor Docking
Sequential dilation of the psoas muscle can then
be performed for each planned operative level
using biplanar fl uoroscopy and directional electromyography (EMG) or mechanomyography
(MMG) neuromonitoring. The initial dilator is
placed through the psoas and docked at the anterior 1/3 of the disk space where it is secured with
a guide wire and confi rmed with lateral x-ray.
Sequential dilation of the psoas muscle is
performed followed by placement of the retractor,
which is fi xed to the operating table. Each dilator
should be monitored with directional EMG or
MMG. Neuromonitoring alerts using triggered
EMG or MMG can allow repositioning of the
dilators and retractor to avoid nerve injury. Most
nerve injuries are associated with instrumentation at the L4–L5 level [
Surgeons can start at increasing thresholds of
15–20 milliamps (mA), which may provide a
safer transpsoas working corridor. If a response is
obtained, the mA can be lowered until a response
is not elicited. Feedback can be provided visually
from the patient with muscle jerk of the extremity
and from the neuromonitoring technologist, with
thresholds below 5 mA usually indicating direct
nerve contact [ 53 ]. Threshold responses between
5 and 10 mA indicate close proximity, and
responses greater than 10 mA usually are indicative of a safe working distance away from the
motor nerves [
54 , 55 ].
Prior to placing the retractor, the fi nger of a
sterile latex glove can be cut off and placed over
the retractor, which can allow retractor opening while preventing retroperitoneal fat and
psoas muscle from entering the operative fi eld.
Additionally, angling the retractor fi xation arm
vertically, instead of horizontally, can apply additional downward pressure and stability and may
eliminate the need for a bone fi xation pin or shim
in the disk (Fig. 20.20 ). This can prevent retrac-
tor migration and creep of the psoas muscle under
the retractor blades. Vertebral body blade fi xation
pins can result in unrecognized bony bleeding or
segmental artery injury, and disk shims fi x the posterior retractor blade, which is in close proximity
48 – 52 ].
180
ab
J.M. Zavatsky et al.
Fig. 20.20 ( a ) A fi nger can be cut off of a sterile latex
glove and placed over the retractor blades. This can prevent retroperitoneal fat and muscle from entering the
operative fi eld while still allowing the retractor to open.
( b ) Angling the retractor fi xation arm vertically can apply
additional downward pressure preventing retractor migration and may eliminate the need for bone fi xation pins or
disk shims
Vertebral segmental artery
Fig. 20.21 Excessive retractor opening can result in stretch and compression of the lumbar plexus and/or injury to the
segmental vessels
to the lumbar plexus risking injury. AP and lateral
images are then used to confi rm position of the
working corridor.
Once the retractor is placed and a safe working corridor is established and confi rmed with
x-ray, the discectomy can be performed.
Minimize retractor opening to prevent stretch of
the lumbar plexus or injury to the vertebral segmental vessels located at the midportion of the
vertebral body (Fig.
20.21 ).
The retractor is opened just enough for adequate visualization and cage placement, the limits of which are usually just cranial and caudal to
the endplates. Additionally, be conscious that
excessive posterior blade retraction can compress
the nerve between the retractor blade and the
transverse process. Work quickly to decrease the
risk of compressive or ischemic injury to the
nerve due to prolonged psoas retraction. In a prospective multicenter trial, Uribe and colleagues
evaluated whether triggered EMG monitoring
could predict postoperative symptomatic neuropraxia (SN) throughout the retraction process
during LLIF procedures. Postoperatively, 13
of 323 (4.03 %) patients had a new motor
weakness that was consistent with SN of the lumbar plexus on the approach side. Retraction time
was signifi cantly longer in those patients with SN
versus those without (32.3 vs. 22.6 min, p = 0.031)
[ 56 ]. Chaudhary et al. observed diminished motor
evoked potentials (MEPs), not at the time of initial retractor placement, but after prolonged
retractor opening in patients with postoperative
motor nerve injuries. Prolonged mechanical
20 Lateral Lumbar Interbody Fusion (LLIF) for the Treatment of Adult Spinal Deformity (ASD)
181
compression and stretch were felt to be the mechanisms of injury [ 57 ]. This proposition is sup-
ported by studies that have reported a higher
likelihood of nerve injury with increasing surgical times [ 31 ].
Even with meticulous conscientious dilator
and retractor placement in relation to the lumbar
plexus, nerve and psoas muscle irritation is a
potential side effect even in single-level LLIF
procedures. Suggestions to reduce the risk of
nerve injury include preoperative administration
of gabapentin or Lyrica, along with 10 mg IV
dexamethasone may prophylactically combat the
infl ammatory cascade in nervous and muscular
tissue limiting the extent of injury [
58 , 59 ]. In
cases where extended psoas retraction is required,
such as in multilevel deformity cases, releasing
the retractor and allowing for the muscle and soft
tissue to relax may decrease the likelihood of
such injury. Lastly, shallow docking above the
psoas muscle allows dissection of the psoas with
a Penfi eld dissector allowing direct visualization
of lumbar plexus prior to dilator placement [ 60 ].
As with most minimally invasive techniques,
there is a learning curve to overcome. We have
found, as have others, that the risk of nerve injury
declines steadily with greater experience [ 61 ]. Le
et al. reported a signifi cant reduction in the incidence of postoperative numbness of nearly 60 %
(26.1–10.7 %), with their refi ned technique over a
3-year period [ 62 ]. Experience and evolution of a
surgeon’s technique can minimize the risk of iatrogenic nerve injury resulting in dramatic
changes in patient outcome.
providing clear identifi cation of the annulus. The
annulus can then be incised vertically with a scalpel both dorsal and ventral to the guide wire
delineating the AP working space for cage insertion (Fig.
20.22 ).
Annulotomy size is based on the selection of
the width of the LLIF cage. Cage widths range
from 18 to 27 mm, but more common widths
include 18, 21, and 22 mm. Marchi et al. reviewed
the incidence and effect of subsidence in patients
with stand-alone short-segment 1- or 2-level
lateral lumbar interbody fusions with two different width cages, 22 and 18 mm [
63 ]. Patients
who had wider 22 mm cages had greater lordosis
correction, along with lower rates and grades of
subsidence. At 12 months, 70 % in the standard
group (18 mm) and 89 % in the wide group
(22 mm) had Grade 0 or I subsidence, and 30 %
in the standard group and 11 % in wide group had
Grade II or III subsidence (Fig. 20.23 ).
Subsidence was detected early at 6 weeks postoperatively and correlated with transient clinical
worsening in VAS scores. Progression of subsidence was not observed after the 6-week time
point. Additionally, subsidence occurred predominantly (68 %) at the inferior endplate.
Although fusion rate was not affected by cage
dimension ( p > 0.999) or by the incidence of sub-
sidence ( p = 0.383), most patients requiring sec-
ondary revision spinal procedures experienced
Grade II and III subsidence (six of ten patients).
20.3.5 Preparing the Disk Space
With the retractor in place and opened, the dilators are removed leaving the guide wire in place.
The guide wire can provide a reference point for
the annulotomy. Using an EMG or MMG probe,
the annulus and remaining strands of psoas muscle around the guide wire and edges of the retractor blades are stimulated to ensure there are no
nerves crossing the operative fi eld. A bipolar cautery and Penfi led dissector can be used to facilitate removing the remaining strands of muscle
Guide-wire
Ventral cut
Dorsal cut
Fig. 20.22 Leaving the guide wire in place until the ventral and dorsal annulotomies are performed provides a
constant reference point for localization
182
J.M. Zavatsky et al.
Grade 0 Grade I Grade II Grade III
Fig. 20.23 Subsidence is classifi ed based on the percent loss of postoperative disc height. Grade 0, 0–24 % loss of
postoperative disk height; Grade I, 25–49 %; Grade II, 50–74 %; and Grade III, 75–100 %
violation seen with sharp-edged instruments such
as the Cobb or shavers. The disk material can be
removed with pituitary rongeurs, and the cartilage
can be removed with up-going, down-going, and
stirrup curettes. To ensure good bleeding, endplates preparation can be completed with a rasp.
Once the endplates are prepared, the contralateral
annulus should be released. The contralateral
annulus should not be released until the diskectomy is fully completed. This can decrease the
risk of expelling disk material, which can compress the contralateral nerve resulting in radiculopathy. A Cobb elevator is used to release the
contralateral annulus both at the superior and
inferior margins of the endplates. After the Cobb
pierces the annulus, rotate the Cobb approxi-
Fig. 20.24 A blunt intradiscal spreader (8 mm shown)
can facilitate the discectomy without the risk of endplate
violation seen with shavers (12 mm shown)
mately 30°, ensuring complete release cranially
and caudally to maximize release and deformity
correction (Fig.
20.25 ). This is a critical step in
the disk preparation process as it can maximize
This illustrates the importance of not violating
the endplates and limiting subsidence.
After the annulotomies, the guide wire can be
removed, and pituitary rongeurs are used to
remove the annulus and perform the discectomy.
A Cobb elevator or disk shavers can be used to dissect the cartilage of the endplates and assist in the
discectomy, but there is an increased risk of violating the endplates particularly in patients with poor
bone quality. Alternatively, sequential blunt intradiscal spreaders (6, 8, 10, 12, and 14 mm high) can
be used to free up the disk material until there is
resistance against the endplates (Fig.
20.24 ).
This technique can be very effective at freeing
up the disk material without the risk of endplate
mobility at each disk level allowing for maximal
correction of disk height, lordosis, rotation, and
coronal deformity.
With the disk completely prepared and
released, the intradiscal spreaders can again be
utilized to size the height and length of the cage
for each level (Fig.
20.26 ). Spanning the LLIF
cage over the strongest portion of the endplate,
the ring apophysis, can maximize deformity correction and disk height restoration, decrease subsidence, and improve stability and fusion rates
[ 44 , 64 ]. Oversizing the length of the cage 10 mm
longer than the radiographic width of pedicles
ensures that the cage spans the entire ring apophysis to facilitate maximum contact with the
20 Lateral Lumbar Interbody Fusion (LLIF) for the Treatment of Adult Spinal Deformity (ASD)
183
Fig. 20.25 ( a ) Cobb elevator releasing the cranial annulus. ( b ) Cobb rotation 30° to maximize release. ( c ) Cobb eleva-
tor releasing the caudal annulus. ( d ) Cobb rotation 30° to maximize release
periphery of the endplate. Using the pedicles is a
more reproducible radiographic reference point
due to osteophytes seen in most scoliotic spines
making the true end of the vertebral bodies diffi cult to identify (Fig. 20.26 ).
Cage height should be determined based on
spreader and the ring apophysis and confi rmed
with fl uoroscopic guidance. Forced rotation of
the intradiscal spreader could result in endplate
violation. Additionally, placing a cage that is
sized too aggressively in height can result in
adjacent vertebral body fractures [ 65 – 67 ]
(Fig. 20.27 ).
intradiscal spreader and the endplates. There
should be a snug fi t between the intradiscal
A trial can be placed to ensure proper sizing of
the cage, but runs the risk of endplate violation.
184
ab
J.M. Zavatsky et al.
Fig. 20.26 ( a ) A blunt intradiscal spreader being utilized
to facilitate the discectomy and sizing of the LLIF cage.
( b ) The lateral border of the pedicles ( yellow arrows ) are
a more reproducible radiographic marker for cage sizing
due to the presence of osteophytes ( black arrows ), which
can distort the normal anatomy. Sizing the LLIF cage
10 mm longer than the width of the lateral border of the
pedicles can ensure spanning the ring apophysis
the inferior endplate below the LLIF instrumentation, ( yellow dashed lines ) identify the coronal split fractures. ( Red
dashed lines ) line identifi es a compression fracture below the LLIF cage.
20 Lateral Lumbar Interbody Fusion (LLIF) for the Treatment of Adult Spinal Deformity (ASD)
Fig. 20.28 Skids can be utilized to assist cage insertion in tight disk spaces decreasing the risk of endplate violation
185
The fi nal cage can be placed immediately after
sizing with the intradiscal spreader without trial
placement, reducing the risk of endplate or ring
apophysis damage. Once the optimal fi nal cage
size has been determined, it can be prepared on
the back table with the surgeon’s preference of
graft material. The disk space should be thoroughly irrigated and suctioned to remove any
debris. The implant is then placed into the disk
space under direct fl uoroscopic guidance in the
AP view to ensure the cage does not violate the
endplates. The surgeon’s hand and the cage insertion handle should be straight up in the air, perpendicular to the fl oor, to ensure the cage is not
directed posterior into the neuroforamen or anterior out the front of the vertebral body. Skids can
be utilized to assist cage insertion in very collapsed disc spaces, and they can also prevent
graft dislodgement from the cage when malleting
the cage into the disk space (Fig. 20.28 ). Once
the cage is in place, fl uoroscopic AP and lateral
images are obtained prior to removing the retractor in the event adjustments have to be made.
20.3.6 Maximizing Correction
Maximizing deformity correction is one of the
main goals of scoliosis surgery. Nevertheless,
exactly how to maximize the correction of the
lumbar rotation, coronal deformity, lordosis, and
sagittal vertical angle (SVA) utilizing the lateral
approach is a topic of debate. Variability in radiological outcomes may result from the lack of a
standardized technique for discectomy and annular release as discussed previously. Additionally,
optimal cage sizing and placement can affect the
amount of correction achieved. Lastly, there is a
lack of data analyzing the risks and benefi ts of
approaching the lumbar curve through its concavity vs. convexity.
The LLIF technique is very powerful at correcting the coronal deformity, but has reported
limitations in global sagittal realignment, lordosis correction, and derotation [ 38 ]. To maximize
lordosis, coronal correction, and derotation, the
surgeon must perform an aggressive discectomy,
not violate the endplates, completely release the
contralateral annulus both cranially and caudally, and properly size and place the cage
(Fig. 20.29 ) Segmental lordosis correction using
the LLIF technique has been reported to range
from 2 to 5° [ 35 , 68 ]. Placing a lordotic LLIF
cage in the anterior 1/3 of the disk space can
maximize segmental lordosis correction. Kepler
and colleagues reported that the mean lordosis
increased 3.7° at instrumented segments,
increasing from 4.1° preoperatively to 7.8° postoperatively. Anterior cage placement resulted in
the largest lordosis gain (+7.4°/level), while
186
J.M. Zavatsky et al.
Fig. 20.29 ( a ) Preoperative lordosis of 20° vs. 34° of
intraoperative lordosis after four-level LLIF procedure,
prior to posterior instrumentation. ( b ) Preoperative coro-
posterior placement was pro- kyphotic (−1.2°/
level). The authors concluded that anterior cage
placement results in greater lordosis, while middle or posterior placement has minimal effect on
sagittal alignment.
20.3.7 Approach Through the Concavity vs. Convexity
In adult patients with degenerative thoracolumbar scoliosis, the decision to approach the curve
apex from either the concave or convex side is a
topic of debate. There are numerous studies demonstrating the considerable benefi ts of the LLIF
technique, resulting in signifi cant radiographic
correction and improved clinical outcomes, with
a minimal complication profi le [
However, these studies either did not report or
varied the side of approach with respect to the
curve apex, so data is lacking.
Sheer et al. performed a retrospective review
comparing approach-related (convex vs. concave) neurological complications and magnitude of correction in patients undergoing LLIF,
prior to any other supplemental procedures, in
the treatment of adult scoliosis [ 73 ]. Patients
were grouped based on the approach through the
curve apex concavity (CAVE) or the convexity
(VEX). There were 32 patients reviewed (CAVE,
17; VEX, 15) with a mean age of 65.5 years and
follow- up of 17.0 months. There were eight
postoperative neurological complications in
eight patients (25.0 %) and seven reoperations
29 , 69 – 72 ].
nal Cobb of 75° vs. 40° intraoperatively and signifi cant
derotation after a fi ve-level LLIF procedure, prior to posterior instrumentation
for six patients (18.8 %; CAVE, 4/17 [23.5 %];
VEX, 2/15 [13.3 %]). The CAVE group had 6
of 17 neurological complications (35.3 %; four
ipsilateral and two contralateral to approach
side) and VEX had 2 of 15 (13.3 %; one ipsilateral and one bilateral to approach side; p > 0.05).
All patients signifi cantly improved in the mean
regional and segmental Cobb angles ( p < 0.05),
except for T11–T12 ( p > 0.05). There were no
signifi cant differences between the groups for
any of the radiographic parameters measured
( p > 0.05). The authors concluded that approach-
ing the curve apex from either the concave or
convex side resulted in signifi cant improvements in correction, which were similar in magnitude. Although not statistically signifi cant,
the CAVE patient group had more postoperative
neurological complications, and they suggested
that surgeons should exhibit additional caution
when approaching from the concave side. Due
to spinal rotation, the psoas muscle and lumbar
plexus can translate anteriorly in the concavity of the lumbar curve placing them in a more
direct path with the normal docking site for the
retractor, theoretically placing them at higher
risk. Unfortunately, there were limitations of
the study, including the number of patients
analyzed. Additionally, the CAVE group had a
larger number of patients who had the L4–L5
level instrumented utilizing the LLIF technique
and underwent posterior osteotomies when compared to the VEX group. Both of these factors
can increase the risk of nerve injury, which can
skew the results.