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112
C. Gragnaniello and K. Seex
levels. L5/S1 requires special instrumentation
and techniques that are only briefl y covered later
in the chapter.
15.2 Indications
• As per lateral transpsoas approaches
• Interbody fusion for degenerative disc disease,
segmental instability, and spondylolisthesis
from L1 to S1
• Tumors affecting the vertebral body
• Vertebrectomies
15.3 Contraindications
• Prior retroperitoneal pathology/surgery on the
side of proposed approach
15.4 Equipment
• Operating table must be radiolucent. Unlike
transpsoas where a break in the table is
required, as ATP passes obliquely anterior
to the iliac crest, this is only occasionally
helpful.
• C-arm from start to fi nish. Time effi cient use
of the C-arm makes the operation much
smoother. One should reimage and adjust the
spine to true AP and lateral position before
each separate level.
• One key element to effi cient and safe retroperitoneal surgery is rapid identifi cation of anatomical structures. Extra light and magnifi cation
make this miniopen procedure much easier and
is strongly recommended.
• Loupes for magnifi cation is routine, but we
have used the intraoperative microscope to
decompress a contralateral foraminal disc protrusion. In this case, the patient is placed with
the side of the foraminal disc protrusion on the
far side (i.e., for a right-sided foraminal disc
protrusion, the patient is placed in right lateral
decubitus).
• Intraoperative neuromonitoring is not required
so the muscles can be kept relaxed for easier
retraction.
15.5 Surgical Technique
15.5.1 Patient Positioning
Positioning and taping do not differ from those
used in a transpsoas approach. The patient is
placed in lateral decubitus. The hip is gently
fl exed to relax the psoas muscle and the femoral
nerve both of which will be retracted. All areas
that are at risk of pressure injury are protected,
including a pillow that is placed in between the
knees. Taping of the lower pelvis and uppermost
hip and femur stabilizes the pelvis and spine.
Breaking the table while not routine can be helpful to tighten the skin, elevate the ribs, or open a
scoliosis if approaching from the concavity
(Fig. 15.1 ). AP fl uoroscopy is essential to ensure
Fig. 15.1 Artist’s depiction of the positioning of the patient
in lateral decubitus, taping, and padding of contact surfaces
NB: the chest is only taped after AP fl ouroscopy
15 Anterior to Psoas (ATP) Fusion of the Lumbar Spine
113
that the level being approached is not rotated
usually before taping the chest. Following this
lateral fl uoroscopy is used to adjust the target
disc space perpendicular to the fl oor by adjusting
the table head up or head down. The projection of
the discs on the fl ank and abdomen is marked
including the anterior projection of the disc
space. Posteriorly this line helps the radiographer
to align the C-arm parallel with the disc space
(Fig. 15.2 ). Anteriorly this projection can be con-
sidered the “runway” for all the instruments
entering the disc space to avoid endplate injury
(Dr Paul Taylor personal communication).
Q: Left or right side up?
Ans: The approach is generally performed in
right lateral decubitus (left side up) as this
avoids the need for any vascular retraction, but
a scoliotic spine concave on the right may
benefi t from a right-side-up approach for multilevel surgery. It is useful to be able to
approach the spine from either side, e.g., for
revisions or adjacent levels. An advantage of
learning this miniopen technique is that it is
the same for a left- or right-sided approach,
which is an advantage over the Medtronic’s
OLIF25™ as this uses wires and tubes that
would be unsuitable on the right. This miniopen technique requires identifying structures
in the path to ensure safe passage; on the left,
this is simple but on the right, the inferior vena
cava (IVC) requires identifi cation and a
healthy respect although it is not diffi cult to
mobilize..
15.5.2 Incision
At L4/5, the surgical corridor approaches the disc
space through the natural space between psoas
and the left common iliac vessels. If the disc
space is oblique, the skin incision should be onethird below and two-thirds above the anterior
projection of the disc onto the abdominal skin.
For L4/5, this is usually 20 mm in front of the
anterior superior iliac spine toward the umbilicus
(Fig. 15.2 ). A single- or double-level operation
can comfortably be done within a 60 mm skin
incision utilizing the so-called sliding window in
the relaxed abdominal wall [ 14 ]. For horizontal
lying discs, center the incision on the disc. Three
or four levels may require a longer skin incision
although in scoliosis cases, access on the concave
side can often be done with a surprisingly small
incision. For more than two levels, we use the
same skin incision but usually split the deeper
two muscles twice having extended the external
oblique split.
Fig. 15.2 Schematic demonstrating the marking of the
projections of the discs, posterior and anterior margins of
the vertebral bodies and discs. Also an example of skin
incision is demonstrated
15.5.3 Exposure of the Disc
All muscles are incised following the line of their
fi bers and bluntly dissected.
Iliohypogastric or ilioinguinal nerves may be
encountered and mobilized typically beneath the
internal oblique muscle. The transversalis fascia
is opened as laterally as possible to avoid the peritoneum, be particularly careful in the thin. If one
removes the self-retainer retractors at this point,
one can usually just feel psoas through the fat
114
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C. Gragnaniello and K. Seex
Fig. 15.3 Artist’s depict after initial dissection into the
retroperitoneum showing psoas with genitofemoral nerve
on its antero medial surface ( a ) and axial view of the
with the tip of a fi nger. This provides an immediate indication of correct direction. The retroperitoneal fat is “paddled” backward using a pair of
swabs on sticks. Initial dissection is posterolateral
and then vertical to push the retroperitoneal fat
(with peritoneum and ureter) anteromedially, until
psoas muscle comes into view (Fig.
15.3a, b ).
The muscles of the lateral abdominal and pelvic walls should not be stripped clean because of
the risk of injuries to the cutaneous nerves traveling in the retroperitoneal space on the abdominal
wall [ 4 ]. Similarly the psoas fascia should be kept
intact as this protects and retains the genitofemoral nerve (GFN) on its anterior surface. The GFN
is usually seen and retracted with psoas.
At this stage, psoas (and GFN) is gently
retracted posteriorly with a handheld retractor
and psoas followed carefully around its anterior
surface to reach the spine. Be aware that the
psoas may overhang the spine in the lateral position, so follow it closely back to the spine.
retroperitoneal fat in situ demonstrating the mobilization
necessary to expose psoas major ( b )
In order to expose the spine, gentle dissection
is required on the medial aspect of psoas through
retroperitoneal fat and fascia, retracting
peritoneum with ureter on its surface and passing
laterally to the great vessels.
A single L-shaped blade Curvy™ retractor
(Relax Retractors, Sydney, Australia) is applied
medially with its back retracting the retroperitoneal fat while protecting the vessels and its
orthogonal blade pushing psoas posteriorly. A
separate straight handheld retractor is used to
retract psoas (Fig. 15.4a, b ).
A long smooth-ended dissector and a Yankauer
suction tip are useful to dissect the loose fatty
connective tissue between psoas and the fat over
the vessels, to reveal the spine, the disc space, the
sympathetic chain, and the segmental vessels.
Occasionally the fascia needs to be torn. At this
stage, other anatomy on display may include
lymphatics, lymph nodes, small bridging vessels,
and occasionally tiny nerve branches of unclear
15 Anterior to Psoas (ATP) Fusion of the Lumbar Spine
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115
Fig. 15.4 Surgeon’s view of the single L-shaped Curvy™
retractor applied medially with its back retracting the retroperitoneal fat while protecting the vessels and its
origin. Below the L4/5 disc, the iliolumbar vein
may be seen. On the spine, one can see the
vertical fi bers of the anterior longitudinal ligament (ALL). It saves time to identify the disc
space early by feel (it’s the ridge) or x-ray. One
then concentrates solely on this area as diverging
from this path may lead to unpleasant encounters
with segmental vessels (in the valleys). The
Curvy™ retractor is positioned medially over the
disc space with the “leg” over the disc and the
“foot” lying in a medial-lateral direction protecting the iliolumbar vein inferiorly. The Curvy™
fi xation screw can be inserted into the target disc
for temporary fi xation, freeing up a hand
(Fig.
15.5 ).
The most medial psoas attachments to the disc
margin are separated with a dissector or Cobb
elevator to allow more psoas retraction. The disc
is then incised with a knife to about 20–25 mm
behind the ALL. A limited discectomy is performed, and the reverse tooth of the selected G
orthogonal blade pushing psoas posteriorly and a separate
straight retractor to retract psoas. ( a ) The same seen on an
axial diagram ( b )
clamp blade is placed beneath the lateral uncut
annulus. This blade is attached to rest of the G
clamp which is then compressed to retract psoas.
The extent of the cut in the annulus limits the
posterior extent of psoas retraction, which provides an end point for retraction to avoid compression of the lumbar plexus.
The sympathetic chain can be mobilized usually medially by dividing its tiny branches, the
rami communicantes (Fig. 15.6 ).
At this stage, with psoas retracted and the end
plates identifi ed, the initial retraction with
Curvy™ blade on the disc is improved with repositioning of the blade lateral to the sympathetic
trunk with its screw inserted into the L5 body to
secure the blade. The medial blade usually lies
close to the posterior edge of the ALL (Fig. 15.7 ).
A lateral x-ray is then taken to verify the limit
of the posterior retraction, as retraction to about
mid body is suffi cient and adequate for disc preparation; this can be adjusted if required. Only a
116
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C. Gragnaniello and K. Seex
Fig. 15.5 The Curvy™ retractor is positioned medially
over the disc space with the “leg” over the disc and the
“foot” lying in a medial-lateral direction protecting the
iliolumbar vein inferiorly. A fi xation screw can be inserted
into the target disc for temporary fi xation, freeing up a
limited amount of psoas retraction is needed for
thorough disc preparation and contralateral
release. Both retractors, the Curvy and G clamp
are now stable without requiring table mounting.
The iliac vessels, if seen are protected under
the medial retractor blade.
The iliolumbar vein at L5 usually sits in the
middle of the body; rarely it may overlie the disc
space in which case it can be ligated between vessel clips. The vessel is always divided prior to
retracting the common iliac vein to expose the
L5/1 disc or a transitional L4/5 level. It is noteworthy that the lateral position and oblique
approach reveal a greater length of the iliolumbar
vein making ligation much easier than during
supine L4/5 ALIF surgery.
hand. Disc incision with a knife to about 20–25 mm
behind the ALL will allow the insertion of the G clamp
with the foot inside the annulus limiting its retraction of
psoas (surgeon’s view ( a ) and axial diagram ( b ) )
15.5.4 Discectomy and Endplate Preparation
This phase of the operation is the same as per
transpsoas except that surgeons need to be constantly aware that the tools are oblique and over
insertion through the annulus can enter the foramen or even the spinal canal. Osteophytes can be
removed by means of heavy rongeurs.
Initial discectomy with large pituitary ron-
geurs and disc curettes is performed.
“Dingo” instruments are shaped so that the
surgeon is still working orthogonally to the spine
as the handle and the terminal end of the instrument are in the same line. The offset (dog-leg)
serves to avoid the iliac crest.
15 Anterior to Psoas (ATP) Fusion of the Lumbar Spine
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117
Fig. 15.6 The reverse tooth of the G clamp blade is seen
beneath the lateral uncut annulus. The blade and the
clamp retracting psoas have been compressed to retract
A Cobb elevator is placed in the disc space
and under AP x-ray control, impacted through
the contralateral annulus and any bridging osteophytes (Fig. 15.8 ).
After completion of the discectomy and with
disc distraction, the oblique trajectory also allows
for potential direct visualization of the thecal sac
and contralateral foramen to allow decompression under direct vision. Pituitaries at these
depths are best used slowly.
Disc removal and Endplate preparation are
done with great care to ensure complete disc
removal (avoids pushing disc out on the contralateral side) and to preserve the end plates.
15.5.4.1 ALL Release
In selected cases at this stage the ALL that has
been previously visualized can be fully
exposed with a narrow retractor blade passed
carefully and slowly across the front of the
psoas. The sympathetic chain has been mobilized by
dividing the rami communicantes (surgeon’s view ( a ) and
axial diagram ( b ) )
spine beneath the IVC, immediately anterior
to the ALL.
A long blade can be used to divide the ALL
with the blade directed toward the disc space and
always under constant vision. This is not a
technique for the inexperienced or faint of heart.
It is easier at 34 than 45.
15.5.5 Cage and Plate Insertion
Dingo design implant inserters allow for a standard
lateral cage or hyperlordotic implant to be inserted
across the disc space gaining bilateral cortical endplate coverage (Figs. 15.9 , 15.10 , and 15.11 ).
As with conventional transpsoas, lateral cages
in this position are a highly effective method for
correction of coronal deformity, lateral listhesis,
restoration of foraminal height, and some correction of spondylolisthesis (Fig. 15.12a–c ).
118
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C. Gragnaniello and K. Seex
Fig. 15.7 At this stage, psoas is retracted and the end
plates identifi ed. The initial retraction with Curvy
blade fi xed to the disc is improved with repositioning
of the blade lateral to the sympathetic trunk with its
In selected cases supplementation of the cage
with a four hole anterior plate placed through the
same large window avoids the need for any posterior fi xation (Fig. 15.13 ). Caveats are that
patients must have good bone density, adequate
lordosis with cage alone, foraminal height restoration is satisfactory and we suggest one or two
levels only. Endplates should still be intact. This
construct is very similar biomechanically to a
standard ALIF construct [
3 ]. The place for a
standalone cage without any fi xation requires
further evaluation [ 20 ].
For two level surgery, the second level can be
accessed through the same incision, repeating the
same procedure. For higher lumbar levels a second superior muscle split may be made in the
upper part of the incision, again, in the line of the
external oblique muscle fi bers. With scoliosis or
multilevel surgery doing the uppermost level fi rst
may be easier to avoid it moving further up under
the ribs.
screw inserted into the inferior vertebral body to secure
the blade. The medial blade usually lies close to the
posterior edge of the ALL (surgeon’s view ( a ) and axial
diagram ( b ) )
15.5.5.1 L5/S1
L5/S1 is also accessible using this approach but
is more complex not least because this level
always requires ligation of the iliolumbar vein
and some venous dissection and mobilization
prior to retraction of the left common iliac vein
medially for the placement of a reasonable cage
(Fig.
15.14 ).
The other option to approach the L5/1 disc
space with the patient in a lateral position is
through the great vessel bifurcation. The
OLIF51™ method from Medtronic is based on
a mini-open approach similar to a standard
ALIF through the vessel bifurcation using a different retractor system to the OLIF25™. The
best technique to approach the L5/1 disc space
is operator (and probably patient) dependent.
The senior author performs both techniques and
currently prefers to have both options available
as the individual anatomy and characteristics of
the patient appear to be critical, including BMI,
15 Anterior to Psoas (ATP) Fusion of the Lumbar Spine
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119
Fig. 15.8 A Cobb elevator is placed in the disc space and impacted through the contralateral annulus and any bridging
osteophytes under AP x-ray control (surgeon’s view ( a ) and axial diagram ( b ) )
the depth of the disc in the pelvis, the sacral
slope and the position of the left common iliac
vein. With either technique however the expo-
Closure is obtained by suture approximation
of muscle layers and repair of the external oblique
fascia.
sure is generally inferior to a supine ALIF, but
if complete disc clearance is not required and
the goal is anterior column support and fusion
15.6 Discussion
at L5/S1 as part of a multilevel construct (that
will include pedicle screws) then this approach
15.6.1 History
is very helpful in association with oblique surgery at other levels. Unfortunately no peerreviewed publications are yet available to
elevate the discussion beyond personal experi-
The modern oblique approaches OLIF25 ™
and ATP have their origins in Mayer’s 1996
description [ 11 ].
ence and bias. A signifi cant level of experience
is required for either L5/S1 approach, as surgeons have to be able to manage or at very least
15.6.2 Cages
control vascular “events” until help arrives.
Unlike in the transpsoas approach however,
vascular control is not diffi cult as the vessels
are on view.
In the last decade the placement of large lateral
cages has been shown to provide increased
stability to the treated segment, and restore disc
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C. Gragnaniello and K. Seex
Fig. 15.9 Dingo inserters allow for placement of large lateral type cages with great bilateral end plate coverage, always
orthogonal to the spine (( a ) surgeon’s view, ( b ) axial diagram)
in many surgeons hands there have been diffi culties typically at L4/5, and in male patients with
large psoas muscle and a high iliac crest.
In order to address these diffi culties, particularly at L4/5, we modifi ed Mayer’s 1996 approach
late in 2011 [ 17 ]. Customized retractor system
and offset instruments to avoid the iliac crest
were developed with improved cage alignment.
Pierre Rousoully’s series reported by Silvestre in
2012 described 179 patients operated between
2006 and 2009 [
14 ]. They coined the term OLIF
to describe their Oblique Lumbar Interbody
Fig. 15.10 Anatomical dissection demonstrating the
position of the GFN right under psoas fascia. Abbreviations :
CIV common iliac vein, G ganglion, GFN genital branch
of genitofemoral nerve, IVD intervertebral disc, IF iliac
fascia, IVC inferior vena cava, LST right lumbar sympa-
thetic trunk, LV lumbar vertebra, Psoas psoas major. *:
segmental lumbar vein of IVC. **: segmental lumbar
artery of aorta. Cr cranial, Ca caudal, V ventral, D dorsal
Fusion and used a banana shaped TLIF style
cage, recommending <30 mm cages to reduce
possible damage to the contralateral traversing
nerve root. The Medtronic OLIF25™ technique
described later in 2012 described the insertion of
lateral cages without any fi xed psoas retraction
using Medtronic’s lateral retractor. Cages are
inserted with straight instruments into the disc
height with good coronal realignment [ 1 ]. The
standard technique to insert these cages has been
a transpsoas approach with neuromonitoring but
space with the additional step of rotating the cage
from an oblique to an “as orthogonal as possible”
position. Our experience with such straight
15 Anterior to Psoas (ATP) Fusion of the Lumbar Spine
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Retractor passed under IVC across ALL
121
Fig. 15.11 ( a ) Intraoperative photographs showing the
exposure of the ALL by this miniopen ATP technique.
ab c
Fig. 15.12 A 75-year-old woman affected by neurogenic
claudication and bilateral L4 radicular pain (R > L).
Preoperative CT, sagittal reconstruction showing advanced
instruments led to concerns about contralateral
( b ) The retractor has been placed under the IVC creating
the space to safely release the ALL with a long scalpel
disc degeneration with grade 1 spondylolisthesis at L4/5
( a ). Intraoperative lateral and AP x-rays showing restora-
tion of the disc height with resolution of the listhesis ( b , c )
15.6.3 Retractors
nerve injury as also noted by Sylvestre [ 14 ], and
led to the design of the Dingo (Australian wild
dog – dog legged) instruments, allowing for lateral cages to be consistently placed 90° to the
disc space.
All authors have used bone fi xed retractors in
some form. Mayer described a frame supporting
four blades secured to the spine with anchoring
screws through the cranial and caudal blades.
He also used a table-based system such as
15.6.2.1 Clinical Results
The authors’ personal series of 100+ cases are in
preparation. This lack of published data in general for the oblique approaches refl ects the early
stage of development and adoption and so the
arguments are largely theoretical. This however
could also have been said during the early years
of transpsoas.
Synframe (Synframe; Synthes Oberdorf,
Switzerland). Dr Tony Tannoury from Boston
has also developed this technique using
Synframe (personal communication). Silvestre
used four Steinman pins. The Medtronic technique is based on the MAST Quadrant™ lateral
retractor system that uses cranial and caudal
pinned blades. Our technique uses one bone