Keywords
arthrodesis - lumbosacral region/surgery - spine/surgery - spinal fusion
Introduction
Spine surgery is one of the areas with the most remarkable development among surgical
specialties concerning the technologies employed in the equipment for obtaining images,
navigators, implants, and materials, as well as the surgical techniques and access
routes. Less traumatic retractors, tubes, and endoscopes have evolved, thus providing
increasingly less invasive accesses and promising results.[1] Spinal fusion surgery was described for the first time in 1911 by Hibbs, who described
the technique of decortication and morselization of the autologous graft in a case
of chronic osteomyelitis caused by Pott's disease.[2]
In 1933, Burns and Capener found the possibility of approaching the spondylolisthesis
of L5-S1 through the anterior route after several cadaveric studies.[3] They performed the surgery on a 14-year-old boy, performing anterior route access
to the region of the retroperitoneum with a left paramedian incision and transperitoneal
access where they accessed the spine, placing an autologous graft. After two months
of plastered immobilization, the boy recovered.[4]
The first descriptions of percutaneous intradiscal procedures were described in the
1960s by Lyman Smith, such as chemonucleolysis with papain, shortly after Hijikata
described the possibility of removing the nucleus pulposus percutaneously with the
aid of small tubes and a pituitary tweezers using the same parameters that he used
to perform his discographies.[5]
In 1986 Kambin described the safe anatomical corridor to access the intervertebral
disc, between the nerve root and the superior facet, receiving the name "Kambin's
triangle" his pioneering work allowed the development of the first endoscopic surgeries.[5]
The different accesses to the lumbar and lumbosacral spine allowed us a significant
evolution in surgical techniques and methods, as well as the development of technologies
for the resolution of the main pathologies, which continue to be objects of discussions
and studie[6] ([Fig. 1]).
Fig. 1 Possible approaches to lumbar intervertebral fusion.
Posterior Approach
The posterior access routes to the vertebral column allow a direct approach to the
vertebral canal without manipulating larger vascular or neural structures. They are,
therefore, the first to be discovered by ancient surgeons, despite little anatomical
knowledge and frank discouragement of the surgical approach.
The posterior access to the spine appears in some descriptions of antiquity, mainly
intending to remove fragments of fractures from the vertebral canal. However, the
lack of knowledge of antisepsis and hemostasis only allowed the flourishing of spinal
surgery from the 19th century onwards.[7]
We consider the median subperiosteal and paravertebral options when considering the
posterior approaches. For this, it is essential to know the posterior muscular anatomy
of the lumbosacral spine, which is formed by the following muscles: Multifidus (M),
Longissimus (L), and Iliocostalis (Il).
The multifidus is the largest and most medial posterior muscle, poly segmental and
multiplies innervated. It has intimate contact with the lamina and the spinous and
transverse processes and is considered the most critical posterior stabilizer of the
lumbosacral, commonly presenting itself atrophic in lumbar degenerative pathologies.[8]
The three muscles run longitudinally along the spine, inserting into the sacrum, the
sacroiliac joint, and the iliac wing, but the multifidus has a unique short, robust
shape. Its architecture allows the creation of large forces in short distances, producing
more forces with the spine in anterior flexion, protecting it in its most vulnerable
position.[8]
Posterior median approach: in this access route, an incision is made in the skin over the spinous processes,
continued by the subperiosteal bone dissection with the detachment of the multifidus
muscle from the spinous processes, laminae and reaching the region of the transverse
processes using Cobb instruments and electrocautery, being able to offer complete
exposure of the posterior bone elements of the spine, allowing extensive decompression
surgeries through a laminectomy, resection of bone or intracanal tumours, in addition
to allowing posterolateral and inter somatic fusion through the PLIF (posterior inter
somatic fusion) and TLIF (transforaminal inter somatic fusion) techniques, in addition
to surgical correction of scoliosis.[9]
The disadvantage of this method is the surgical aggression to the paraspinal musculature,
which leads to postoperative muscular atrophy, mainly of the multifidus muscle, reducing
up to 27% of its area below the arthrodesis site, which may lead to less satisfactory
surgical results, when compared to with techniques that preserve more posterior musculature.[10]
[11]
The mechanisms by which muscle injuries occur are dissection, which tears the tendon
insertions, and the excessive use of electrocautery, causing thermal injury and tissue
necrosis. However, the most associated factor is the use of self-static retractors
for prolonged periods. The degree of injury is linked to the time of retraction, and
the intermittent loosening of the retractors reduces the area of muscular injury.[12]
[13]
Paraspinal Approach: This approach uses the dissection of the intermuscular plane between the multifidus
muscle and the longissimus muscle, described by Wiltse in 1968 as a modification of
the approach described by Watkins, used an approach between the sacrospinatus muscle
and the quadratus lumborum.[14]
[15]
This access has a lower rate of bleeding and less muscle destruction, in addition
to allowing direct access to the transverse processes, pedicle, and intervertebral
discs, being advantageous in approaching mainly hernias in the region of the vertebral
recess, foraminal and extraforaminal.[16]
The access can be performed as the original description with two paramedian incisions
or a single central incision and two in the subfascial plane, as modified by Wiltse
himself in 1988.[17] However, the original technique with two incisions seems more advantageous with
a lower rate of complications such as suture dehiscence and seroma.[16] This access allows several surgical approaches, with TLIF transforaminal inter somatic
fusion being one of the most popular, as it is a less invasive approach par excellence.
Compared with the traditional media approach, it has several advantages, such as less
postoperative muscle atrophy, lower incidence of adjacent degeneration level, lower
infection rate, and less intraoperative bleeding.[18]
[19]
Lateral Access
The lateral approach to the spine was first described by Ozgur et al.[20] as a less invasive alternative to vertebral inter somatic fusion, and its use has
become popular in the treatment of a variety of pathologies of the spine, more recently
being adapted for the L5-S1 use in an anterolateral approach, anterior to the iliopsoas
muscle, also called the iliopsoas access oblique.[21]
[22]
According to the original description of the technique, the positioning is in lateral
decubitus on an inverted radiolucent table, with the greater trochanter positioned
on the fold of the table, placed in an orthogonal position with the radioscopy. The
table is flexed to facilitate the dissection by moving away the ribs of the iliac
crest. The skin incision should be made towards the disc for one level or towards
the vertebral body for two levels; for three levels or more, more than one incision
is required, the dissection of the external oblique, internal oblique, and transversus
abdominis muscle, it must be done bluntly, without the use of electrocautery. In order
to avoid injury to peritoneal structures, the index finger must clear the retroperitoneal
space before inserting the guide wire, dilators, and retractor that cross the iliopsoas
directly with the aid of a magnifying glass or microscope. This approach is used for
lateral intersomatic fusion called LLIF (Lateral Lumbar Intersomatic Fusion) or XLIF
(Extreme Lateral Intersomatic Fusion), they are synonyms , but XLIF were patented
by a company as the implant name too, so is more correct to use LLIF for the Lateral
approach of intersomatic fusion.
Multimodal neurophysiological monitoring is mandatory to avoid lumbar plexus and genitofemoral
nerve injuries.[23] Knowledge of the regional neuroanatomy, the time of retraction of the iliopsoas
muscle, and appropriate training in the technique allow its performance without needing
an access surgeon.[24]
Anterior Access
Anterior approaches to the lumbar spine (ALIF) first emerged in the 1930s for the
treatment of spondylolisthesis by Capener[3] and Pott's disease by Ito et al.[25]
Since then, various surgical techniques, including open or laparoscopic transperitoneal
approaches and retroperitoneal exposures, have been developed. Since the end of the
1990s, the preferred and most used surgical technique has been the minimally invasive,
popularized by Brau[26] The ALIF approach provides direct midline exposure of the lumbar disc, thereby allowing
for a wide discectomy and placement of a sizeable interbody graft that maximizes coverage
of the vertebral plateau. L5-S1 is the preferred level of treatment as it avoids the
complexity of the aorta/caval/iliac bifurcation. However, higher levels from L2 to
S1 have already been performed by experienced surgeons.[27]
The anterior access technique to the lumbosacral spine is helpful in degenerative
disc disease, isthmic or degenerative spondylolisthesis, spondylodiscitis, pseudarthrosis,
removal of mispositioned or migrated TLIF or PLIF cages, disease, or degeneration
of the adjacent level.[28]
The posterior approach has a higher risk of neurological damage and dural tear due
the presence of fibrosis, with the anterior access being preferred and with less morbidity.[27] Restoration of sagittal balance allows using hyper lordotic implants (up to 30 degrees)
and the desired rebalancing of vertebral body injuries from fractures or tumours.
Some advantages of this technique include the direct view of the midline of the disc
space and the extensive lateral exposure of the vertebral bodies, which allows an
efficient release of the disc space, adequate access to the entire ventral surface
of the disc exposed, allowing complete discectomy, restoration of disc space, automatically
reducing deformity through ligamentotaxis, leading to indirect decompression. It allows
the sparing of the spine and muscles anterolateral posterior muscles to the psoas,
which can reduce postoperative pain and disability.[6]
[27]
[28]
Disadvantages of the ALIF technique include approach-related complications such as
vascular injuries, retrograde ejaculation, and visceral injuries.[29]
[30] The ALIF technique is suitable for the L4/L5 and L5/S1 levels due to the vascular
anatomy that provides a large working corridor between the iliac vessels. Higher levels,
such as L2/3 and L3/L4, can be explored by teams with experienced and trained access
surgeons due to the need for extensive vascular mobilization of the aorta and iliac
arteries and retroperitoneal viscera, such as the pancreas and kidneys.[6]
The contraindication for any anterior approach includes previous major abdominal surgeries,
severe peripheral vascular disease, patients with a history of radiotherapy, stents,
and endoprostheses of abdominal vessels. In addition, specific contraindications include
the need for direct posterior decompression, acute infection, severe osteoporosis
due to the risk of subsidence (fracture and sinking of the plateau), extruded disc
herniation, migrated, especially if calcified, requiring posterior approach.[6]
[31] Obesity is a relative contraindication showing similar intraoperative morbidity,
postoperative complications, and arthrodesis similar to patients with BMI within the
normal range.[32]
Oblique Access
The first description of an OLIF approach was published in 1997 by Mayer.[33] However, the official name and acronym were not coined until 2012 when Silvestre
et al.[34] used a minimally invasive retroperitoneal approach similar to the Mayer approach
for anterior lumbar intervertebral fusion. This technique is reported by Silvestre
et al.[34] as OLIF and accesses the anterolateral surface of the disc space before the psoas
muscle, which is mobilized posteriorly. After preparing the disc space, the inter
somatic device is inserted at an oblique angle and rotated in a lateral position.
The evolution of technique and instrumentation provided adequate access to the lumbar
spine, with low rates of perioperative complications, short surgical times and low
morbidity and mortality, little postoperative pain, and early return to daily activities.
Indications include degenerative disc diseases, discogenic lumbar pain, degenerative
lumbar scoliosis, low-grade spondylolisthesis, lumbar instability, revision, mild
to moderate canal stenosis, sagittal deformity, fractures, tumours, adjacent level
disease.[28]
The oblique device can raise the intervertebral space's height and expand the intervertebral
foramen's size, indirectly achieving decompression.[35] Regarding anatomical accessibility, the OLIF technique can reach L1 to S1 using
an oblique corridor between the aorta, inferior vena cava, and psoas muscles to access
the disc space.
There is adequate operating space with the left oblique corridor from levels L2 to
L5, with the additional ability to be extended during surgery with lateral positioning
and retraction of the psoas muscle. The ribcage can limit access at the level of L1-L2
and the iliac crest and iliac vessels at the level of L4-L5.[27]
[31]
The advantages are less invasive operative technique, reduced operative time, and
less chance of injury to the lumbar plexus, allowing direct access to the disc. Without
injury to the lamina, it leads to less damage and bleeding, lower rate of nerve injury,
faster postoperative recovery, less pain, short hospital stay, and increased rates
of inter somatic fusion caused by a large amount of disc removal, promoting a large
area of contact with the plateaus, and suitable correction of the deformities.[6]
[36]
[37]
There is also the possibility of approaching greater levels through the same access
without enlarging the operative window. Disadvantages include anatomical alterations
that limit the procedure and the potential risks involved, such as sympathetic dysfunction
and vascular injury.[21]
[31]
We can observe that in the aorta/cava/high iliac bifurcations (those that occur above
the upper 1/3 of L-4), the iliac vessels are already well open and with an almost
lateral trajectory at the level of the L4-5 disc, the which would lead to vascular
damage in the supposed OLIF access corridor.
Considering the report above, in positioning the lower blade of the retractor/retractor,
we must avoid its fixation in the vertebra of L-5 with the fixation screw.[6]
[21]
[31]
There are several limitations to the oblique access approach.
There is the risk of canal stenosis caused by the inter-somatic device in the posteromedial
trajectory, leading to the disc or ligament material displacement towards the central
canal or the contralateral foramen. A second limitation relates to patients with high-grade
spondylolisthesis because there is not enough "overlapping" of the two vertebral plateaus
to accommodate the inter somatic device in an oblique trajectory.
The procedure may also be affected in congenital vertebral canal stenosis and for
injuries that occupy the intervertebral space, in a spontaneous fusion of intervertebral
space or posterior facets, and by the shape of the psoas muscle. Therefore, on the
concave side of scoliosis patients, the space between the vessels and the psoas muscle
decreases, which is not conducive to the OLIF pathway.
Psoas sign interiorized, that is, on axial images at the level of L4-L5, the psoas
muscle in the area of entry into the lateral annulus of the vertebral disc. The space
between the psoas muscle and the quadratus lumborum muscle increases in some patients,
which could lead to misunderstanding the distance gap between the artery and the psoas
muscle. The different positions influence the shape of the psoas muscle. In the right
lateral decubitus position, the left psoas major muscle is affected by gravity and
is close to the vertebral body.[6]
[31]
[38]
Endoscopic Approach
For a spinal approach to be considered a fully endoscopic surgery, it needs to meet
the following criteria: the use of an endoscope that has a working channel and endoscopic
system, an utterly percutaneous approach with a small incision like a skin puncture
("stab incision"), a single-portal technique performed under constant saline irrigation.[39]
[40]
There are other methods of endoscopic approach to the spine, such as bi-portal endoscopy,
microendoscopy, epiduroscopy, and video-assisted tubular surgery. However, endoscopic
or completely endoscopic percutaneous spine surgery ([Fig. 2]) is the most commonly used in our setting.[39]
[40]
Fig. 2 Transforaminal endoscopic approach. (A) location of the nerve root ganglion, (B)
direct access to the disc abscess, (C) positioning of the team, (D) endoscopic view
of the neural root.
When considering the lumbar spine, the main endoscopic access routes can be divided
into the transforaminal and interlaminar approaches.[41]
[42]
Transforaminal Approach
It can be performed with the patient in a prone position with flexion of the hips
and knees under local anesthesia, sedation, or general anesthesia. In the latter case,
it may be accompanied by neurophysiological monitoring to allow the surgeon to monitor
the function of the emerging root and passer-by of the approached level.[41]
[42]
The principles of the endoscopic transforaminal route are to seek access as close
as possible to the disc pathology and to avoid irritation of the emerging root. To
achieve these principles, the foraminoplasty can be associated with the procedure,
which is the recalibration of the approached intervertebral foramen using ways to
remove or thin the bone edges.[42]
[43] This can be done with shaver burs, foraminoplasty burs, or percutaneous refers.
The angle of access and the access point in the foramen is essential for the technique's
success. They can be adjusted according to the patient's body size, disc level, and
pathology site to be approached. Generally, at lower lumbar levels (L4-L5 and L5-S1),
a distance from the midline of 10-12 cm is used, and at higher levels, a progressively
closer approach to the midline is used due to renal topography.
After a posterolateral incision, a guide wire is inserted, seeking to reach the space
of Kambin's triangle. This approach safety triangle is defined as the space between
the laterally emerging root, medially dura mater, and the base, the superior portion
of the pedicle of the inferior vertebra.
The access route is dilated with progressive blunt dilators until the working sleeve
is placed. After the work jacket is securely positioned, the endoscope is positioned.
The ideal way to guarantee the correct positioning is to adequately visualize the
structures that make up the intervertebral foramen to allow a safe surgery.[42]
[43]
There are some divergences in the literature regarding the disc approach. Initially,
the transforaminal endoscopic approach was performed from the central portion of the
disc and progressed towards the outer part of the disc, a technique known as inside-out.
With the evolution of surgical techniques and equipment technologies for disc pathologies
emerged the technique of approaching from the outside, known as outside-in.[42]
[43]
[44]
More recently, with the transforaminal approach to approach bone pathologies of the
foramen, without the need to approach the disc, the outside-out technique corresponds
to techniques of bone decompression of the foramen. This approach offers risk of residual
pain due root manipulation of the procedure, especially during surgeons learning curve,
even so neurologic complications are lower in percutaneous endoscopic techniques when
compared to open approach.[45]
Interlaminar Approach
Like transforaminal endoscopy, it can be performed under sedation or local or general
anesthesia. The approach's target point is the interlaminar window's lateral edge.[41]
[43] This window is usually more prominent at more caudal levels, progressively decreasing
in the cephalad direction. Thus, the L5-S1 is the level with the largest interlaminar
window. Initially, the interlaminar access route required good-sized windows to ensure
a safe approach.
The evolution of the surgical technique and bone decompression equipment made it possible
to approach even smaller interlaminar windows after adequate bone decompression.[43]
[46] In the interlaminar approach, the guide wire can be used initially or even the direct
approach with the blunt dilator due to the risk of inadvertent introduction of the
guide wire into the vertebral canal through the ligamentum flavum.
After the dilator, the working cannula is positioned with the bevel resting on the
most lateral portion of the window. Next, the endoscope is introduced to ensure visualization
of the ligamentum flavum.[41]
[46] This can be removed using appropriate tweezers and scissors, allowing visualization
of the epidural space.
After the flavectomy, the surgical field is prepared with more effective bone decompression
and/or soft tissue removal until it is possible to visualize and dissect the neural
structures.[41]
[46] Through this route, it is possible to treat disc or bone compressive pathology,
depending on the origin of the symptoms. At the end of the surgery, decompression
can be confirmed with a blunt probe used through the working channel and visualization
of free and pulsatile structures with the serum flow.[41]
[46]
Final Considerations
The various access routes and surgical approaches described here continue to be objects
of study, generating dozens of publications annually. There is no consensus on the
best approach for each pathology. However, a trend seeks a reduction in tissue damage,
especially muscle, effectiveness in the decompression of neural structures, and greater
safety with minimization of the risks of neurological damage and postoperative infections.
In addition, advances in imaging and magnification techniques allow smaller, more
effective, and safer accesses.
