Download Surgical Anatomy and Approaches to the Anterior Thoracolumbar

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Surgical Anatomy and Approaches to the Anterior
Thoracolumbar Spine Region
Anatomia cirúrgica e abordagens para a coluna tóraco-lombar
Andrei F. Joaquim1
Leonardo Giacomini2
Enrico Ghizoni1
Fábio Araújo Fernandes3
Marcelo L. Mudo4
Helder Tedeschi5
RESUMO
ABSTRACT
A anatomia cirúrgica da região tóraco-lombar da coluna
vertebral (T11-L2) é revisada. As características principais
dos grupos musculares, vascularização e estruturas neurais
são descritas em detalhes. Apresentamos também uma
discussão técnica dos acessos anterior a essa região, como
o transtorácico retroperitoneal e o retropleural lateral.
Concluímos que o conhecimento anatômico é fundamental
para se obter resultados mais seguros e eficazes em cirurgias
desta região.
We review the surgical anatomy of the thoraco-lumbar
spine region located between the eleventh thoracic and the
second lumbar vertebrae (T11-L2). Anatomical features
of muscular, vascular and neural structures important to
surgical approaches are described in details. We also discuss
surgical nuances of the transthoracic retroperitoneal and the
lateral retropleural approaches. We conclude that anatomical
knowledge is important to improve the efficacy and safety of
surgical procedures in the thoraco-lumbar spine region.
Palavras Chave: junção tóraco-lombar, transtorácico
retroperitoneal, retropleural lateral, anatomia
Keywords:
thoraco-lumbar
junction,
transthoracic
retroperitoneal, retropleural lateral, anatomy
Neurosurgeon. Neurosurgery Division, State University of Campinas (UNICAMP), Campinas-SP, Brazil.
Neurosurgery Resident. Neurosurgery Division, State University of Campinas (UNICAMP), Campinas-SP, Brazil.
3
Orthopaedic surgeon, Spine Surgeon – Irmandade da Santa Casa de Misericórdia de São Paulo, São Paulo-SP
4
Neurosurgeon. Head, Neurosurgery Division, Hospital Estadual de Sorocaba. Sorocaba-SP
5
Neurosurgeon. Head of the Neurosurgery Division, State University of Campinas (UNICAMP), Campinas-SP, Brazil.
Institution: Universidade Estadual de Campinas (UNICAMP), Campinas-SP.
1
2
Recebido em 10 de julho de 2012, aceito em 25 de setembro de 2012
Joaquim AF, Giacomini L, Ghizoni E, Fernandes FA, Mudo ML, Tedeschi H. - Surgical Anatomy and Approaches to the Anterior Thoracolumbar Spine Region
J Bras Neurocirurg 23 (4): 295-300, 2012
296
Revisão
I ntroduction
Anatomy
The thoraco-lumbar spine comprises the region located
between the eleventh thoracic and the second lumbar
vertebrae (T11-L2)3. The thoraco-lumbar region is one of the
most common sites for spinal fractures, once it constitutes a
transitional zone between the rigid thoracic spine and the
relative mobile lumbar spine17,19. This region is also affected by
other diseases, such as infections, neoplastic and degenerative
lesions.
The anatomy of the thoracolumbar spine requires the
understanding of the relationship between the ribs, the muscles,
the regional vessels and the neural structures of this region.
Many surgical routes have been described to approach this
region. Anterior approaches may provide a wide anterior
decompression with grafting and instrumentation and also
restore the anterior column support14,16, whereas posteriorly
based approaches are used for stabilization with pedicle
screws, with or without decompression. Posterior approaches
include standard laminectomy, transpedicular decompressions,
posterolateral costotransversectomy and the lateral
extracavitary approach.
The main anterior-based approaches to the thoracolumbar
junction are performed antero-laterally, which can be performed
via a thoracotomy or, more recently, by thoracoscopy. These
transthoracic approaches can be performed together with
retroperitoneal approaches. A recently described technique
for this region is the lateral retropleural approach that avoids
entering into the chest cavity15. In a general view, the approach
is chosen based on the surgeon’s experience and preference,
patient’s clinical condition and body habitus and also according
to the characteristics of the disease. However, regardless
the chosen surgical route, anatomical knowledge is still the
cornerstone to achieve a good surgical result.
In this paper, we review the main anatomical features of the
anterior thoracolumbar spine region, from a spinal surgeon’s
perspective, discussing anatomical nuances of the anteriorbased approaches to this area.
Ribs
Usually the ribs have two articular facets – one articulates with
the vertebral body of the same level and the other with the
vertebra above - covering the disc on its posterolateral aspect11.
As an example, the seventh rib articulates with the body and
transverse process of T7, but also with the body of T6, covering
the disk space of T6-7. Exceptions are the first, eleventh and
twelfth ribs that articulate only with the same level vertebra18.
There are four ligaments attached to the ribs: 1) The radiate
ligament that spans out from the ventral portion of the proximal
rib head and attach to the adjacent vertebra and intervertebral
disc; 2) The costotransverse ligament attaching the neck of the
rib to the articulating transverse process; 3) The intertransverse
ligament which connects the transverse processes and 4) The
capsular ligaments which span from the ventral transverse
process to the dorsal portion of the articulating rib11.
Also important, the thoracic vertebral body has a unique anatomy,
with a concavity relative to the spinal canal in the axial plan. The
pedicles arise in the superior portion of the body, higher than in
the cervical or lumbar vertebrae. The disc space is narrower than
in the lumbar spine.
Diaphragm
The diaphragm is a dome-shaped muscle that separates the
thoracic from the abdominal cavity at the level of T12 to L1. Its
convex superior surface forms the floor of the thoracic cavity,
and its concave inferior surface forms the roof of the abdominal
cavity. Its peripheral part consists of muscular fibers that originate
from the circumference of the inferior thoracic aperture and
converge to be inserted into a strong aponeurosis, the central
tendon. Its muscular fibers can be grouped according to their
origin in: 1) sternal (origin from the xiphoid process), 2) costal
(attached to the six costal cartilages and the four lower ribs)
Joaquim AF, Giacomini L, Ghizoni E, Fernandes FA, Mudo ML, Tedeschi H. - Surgical Anatomy and Approaches to the Anterior Thoracolumbar Spine Region
J Bras Neurocirurg 23 (4): 295-300, 2012
297
Revisão
and 3) lumbar (in the anterolateral aspect of the upper lumbar
spine, the most significantly manipulated region during anterior
thoracolumbar junction surgeries). The lumbar portion has
two origins: one from the medial and lateral arcuate ligaments
(two fibrous arches over the psoas and quadrates muscles) and
another from the crura2,12.
The crura are musculotendinous bands of the diaphragm that
extend along the anterolateral lumbar spine on each side. The
left crus extends to L2, whereas the right crus extends to L3,
blending with the anterior longitudinal ligament of the vertebral
columns. The aortic hiatus is located between them, at the level
of T1210.
The posterior portion of the diaphragm is separated from the
peritoneum by a fat layer and by the superior aspect of the kidneys
and adjacent structures. In this posterior portion, the diaphragm
forms two ligamentous bands, on either side: the medial and
lateral arcuate ligament. The lateral arcuate ligament arises
from the tip of the twelfth rib and spans around the quadratus
lumborum and the medial arcuate ligament spans across the
psoas muscles. The common intervening point between them is
on the transverse process of L118.
There are three large openings in the diaphragm: the aortic
hiatus (contains the aorta, the azygos vein, the thoracic duct,
between the left and the right crura), the esophageal hiatus
(esophagus, anterior and posterior vagal trunks) and the vena
cava hiatus (inferior vena cava and branches of the right phrenic
nerve). Small apertures also are present, especially near the crus
(containing the splanchnic nerves and the hemiazygos veins)12.
The phrenic nerve supplies the diaphragm, entering medially
toward the periphery, formed by the C3-4-5 cervical nerves,
more intense in its central portion. The peripheral portions of the
diaphragm have sensorial afferents from the intercostals nerves
(T5-11) and the subcostal nerve (T12)12.
Injuries to the diaphragm can lead to atelectasis, reduced vital
capacity and hypoxemia.
Psoas Muscle
The psoas major is a long muscle that originates from the
transverse processes of the lumbar vertebrae (deep portion) and
from the lateral surface of the lower thoracic and lumbar vertebrae
(superficial portion). It is located in the anterolateral aspect of
the lumbar spine (between the lateral portion of the vertebral
bodies and the transverse process). It has two portions: 1) the
anterior and lower edges of the lumbar transverses processes, 2)
the lateral bodies and intervertebral discs of the last thoracic and
all the lumbar vertebrae. The lumbar plexus lies between the two
psoas layers, whose anterior rami of L1 to L4 are responsible for
its innervations. Sometimes, a psoas minor muscle accompanies
the psoas major. It joins with the iliacus muscles, forming the
iliopsoas, passing beneath the inguinal ligament and anterior
to the hip joint capsule, inserting onto the lesser trochanter of
the femur. The function of the psoas is flexing the thigh at the
hip joint and assist in maintaining an erect posture, avoiding
hyperextension at the hip. During surgery, the thigh must be
slightly flexed to relax the psoas and avoid excessive traction at
the lumbar plexus12.
Quadratus Lumborum
The quadratus lumborum arises from the aponeurotic fascia
from the iliolumbar ligament and the adjacent portion of the
iliac crest, inserting into the lower border of the last rib and in
the small tendons into the apices of the transverse processes of
the upper four lumbar vertebrae. This muscle is responsible for
lateral flexion and extension of the vertebral column.
Lumbar Plexus
The lumbar plexus is formed by the ventral branches of the
spinal lumbar nerves from L1 to L4, sometimes for branches
of the subcostal nerve from T12. It is located inside the psoas
muscle. The main nerves are the iliohypogastric, ilioinguinal,
lateral cutaneous nerve of the thigh and femoral nerves, emerging
laterally to the lateral edge of the muscle, and the genitofemoral
and obturator nerves, emerging medially to the medial edge of
the psoas major muscle. The nerves emerging from the lumbar
plexus are responsible for the innervation of the anterior region
of the thigh, differently from the nerves from the sacral plexus
that are responsible for the posterior portion of the inferior limbs,
especially the leg and foot5.
The lumbar nerve roots are situated in the posterior third portion
of the psoas muscle, most of them running under the surface of
the lumbar pedicle and across the transverse process ligament. In
the transpsoas approaches, to access the disc space and vertebral
body, nerve injury can be avoided by incising the ventral 2/3 of
the muscles4.
Joaquim AF, Giacomini L, Ghizoni E, Fernandes FA, Mudo ML, Tedeschi H. - Surgical Anatomy and Approaches to the Anterior Thoracolumbar Spine Region
J Bras Neurocirurg 23 (4): 295-300, 2012
298
Revisão
Vascular Structures
The segmental vessels originate from the aorta and need to be
occluded before retraction of the artery to exposure the spine
vertebrae. The most important point is to consider that some
arterial branches can irrigate the spinal cord. The artery of
Adamkiewicz is the most important radiculomedullary artery.
It generally originates from the left side of the aorta at any point
from the mid thoracic to the upper lumbar region, and its injury
is associated with paraplegia after aortic or spine surgery1.
ANTERIOR-BASED APPROACHES TO THE THORACOLUMBAR JUNCTION
We describe two anterior-based approaches to the thoracolumbar
junction: the traditional transthoracic/ retroperitoneal approach
and the lateral retropleural approach, emphasizing anatomical
nuances.
1. Transthoracic Retroperitoneal approach
Used for thoracolumbar junction access (T11-L1), the side
of approach depends on the pathology characteristics: some
authors , including us, suggest that the left side is the best side
to surgery, because the mobilization of the aorta is easier and
safer than the vena cava, as well as the spleen is easier to be
retracted than the liver13.
Most of the time, release of the diaphragm is necessary to
work properly in the thoracolumbar junction, especially above
L1. Patient positioning is primordial to achieve the surgical
goals – the spine must be perfectly perpendicular to the room
floor, improving surgeon’s orientation to insert the screws and
decompress the spinal canal. The patient must be centralized in
the table, once the surgeon can work in his back or in his front,
changing his angle of view. We put a small pad roll just below
the approached level to elevate the spine and make the approach
easier. The incision is generally is placed over the tenth rib,
or sometimes the eleventh, with subperiosteal dissection for
further resection, but the incision is centered on the approached
level based on fluoroscopy image - not in the rib ( Fig. 1 and
2). The incision is extended to the oblique external and anterior
serrate muscles , and then the transversal abdominal muscle,
avoiding entering the transversalis fascia. The adipose tissue is
then visualized, indicating the entrance of the retroperitoneal
space, whose dissection is easily started supero-posteriorly. The
peritoneal sac can be retracted forward, protected with moist
sponges. The quadratus lumborum is identified, as well as the
psoas. The retropsoas space should not be violated. The medial
portion of the quadratus is palpated, identifying the transverse
process of L1. When necessary, to access the body of T11 and
T12, opening the pleura allows entry into the thoracic cavity, with
visualization of the diaphragm and its costal attachment. The
lung is retracted and the diaphragm is divided in its peripheral
portion, to avoid extensive denervation. The attachment of the
lateral arcuate ligament in the twelfth rib and in the transverse
process of L1 is divided. The ipsilateral crus is also divided to
improve the exposure, in its supratendinous portion.
The kidney and the ureter are located anterior to the psoas and
are usually retracted medially in retroperitoneal approaches.
Ureter lies anterior to the psoas muscle and then courses
anterior to the iliac vessels12.
The psoas muscle can obscure the access to the spine in its
posterolateral aspect. The muscle is generally retracted
towards the incision and lateral to the spine or even incised
(but this maneuver may lead to a high risk for lumbosacral
plexus injury)9. The anterior surface of the psoas insertions are
exposed, dissecting the muscle from its anterolateral surfaces
of the vertebrae. The segmental vessels are ligated, and the
periosteum is exposed8.
Segmental vessels are ligated and retracted – they should be
ligated far from their origin once their retraction can lead to
difficult location in case of bleeding. Some segmental vessels,
besides the spine elements, can nourish the spinal cord in its
anterior portion – the anterior segmental medullary arteries
(see above - the artery of Adamkiewicz, at the thoracolumbar
junction level). The ligation of the segmental vessel that
originates the Adamkiewicz artery can lead to spinal cord
infarction and paraplegia12.
The rib head and the costovertebral ligaments are then
removed (at T11 or T12). The pedicle can be removed using
a high speed drill, with exposure of the anterior dural sac.
The vertebral body can be assessed and removed if necessary,
trying to preserve its anterior portion to avoid injury to soft
structures in non-neoplastic diseases. Interbody fusion with
graft or titanium mesh cages followed by plate and screws can
then be performed.
Of note, the isolated retroperitoneal approach without
diaphragm release and thoracotomy is used to approach L1-2 to
Joaquim AF, Giacomini L, Ghizoni E, Fernandes FA, Mudo ML, Tedeschi H. - Surgical Anatomy and Approaches to the Anterior Thoracolumbar Spine Region
J Bras Neurocirurg 23 (4): 295-300, 2012
299
Revisão
L4-5. Sometimes, we can also approach T12 without opening
the pleura. To access the L5-S1 level, is better to use a midline
transperitoneal or retroperitoneal approach. Access to L2-4
space generally does not require crura incision.
Figure 1: A 43 years-old woman with ASIA D and a L1 burst fracture (A) without
evident posterior ligament complex injury. (B) Lateral spine x-ray showing
decrease of body height. (C) Sagittal T2 weighted MRI. (D and E) Postoperative
AP and lateral radiograph showing T12-L2 screws and the mesh cage at L1.
2. Lateral Retropleural Approach
The lateral retropleural approach is an alternative anteriorlybased approach to the thoracolumbar junction. The advantages
over the open transthoracic retroperitoneal
approach
are the avoidance of opening the chest cavity and over the
thoracoscopic approach is the steep learning curve required for
this procedure. The retropleural approach can be performed
without extensive muscle dissection, with less postoperative
pain and blood loss. It allows the surgeon a satisfactory ventral
decompression without entering the pleura, with avoidance
of many important complications, such as intercostal
neuralgia, atelectasis, pneumothorax, pleural infection and
hemothorax6,7,15.
Figure 2:(A) Patient is positioned with the spine perpendicular to the floor. Skin
incision is marked previous to start the procedure with fluoroscopy. (B) Soft
tissue dissection and (C) rib exposure after subperiostal dissection. (D) After
opening the transversal abdominal muscle, visualization of the diaphragm.
Figure 3: Intraoperative view (A) diaphragm is superiorly retracted with a sponge,
showing the spine. (B) After left crura incision, disk space is confirmed (C) After
discectomies (one above and one below), corpectomy is performed and (D) after
instrumentation insertion.
The patient is positioned in lateral decubitus, with the side
of approach chosen according to the location of the main
compression. An oblique incision is performed in the rib
trajectory of the level to be approached, with subperiosteal
dissection, showing the underlying pleura and neurovascular
bundle. The rib is stored as a bone graft and once the parietal
pleura is exposed, a plane between the endothoracic fascia is
found with blunt dissection. Pleura is retracted anteriorly along
with the diaphragm, until exposing the lateral vertebral body
and its adjacent disks. The great vessels are also anteriorly
retracted. At this point, similarly to the transthoracic/
retroperitoneal approach, the rib head and the costovertebral
ligaments are then removed, with ligation of the segmental
vessels. The pedicle can be removed using a high speed drill,
with exposure of the anterior dural sac. The vertebral body
can be assessed and removed if necessary, trying to preserve
its anterior portion to avoid injury to soft structures15. Further
instrumentation with titanium plates and screws can be
performed.
Joaquim AF, Giacomini L, Ghizoni E, Fernandes FA, Mudo ML, Tedeschi H. - Surgical Anatomy and Approaches to the Anterior Thoracolumbar Spine Region
J Bras Neurocirurg 23 (4): 295-300, 2012
300
Revisão
Conclusion
The anterior-based approaches to the thoracolumbar junction
are useful alternatives to spine surgeons, when accessing
ventral pathologies of the thoracolumbar junction. Accurate
anatomical knowledge leads to better surgical results,
decreasing complications of unnecessary and potentially
catastrophic injuries.
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Corresponding author
Dr. Andrei F. Joaquim
e-mail: [email protected]
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Joaquim AF, Giacomini L, Ghizoni E, Fernandes FA, Mudo ML, Tedeschi H. - Surgical Anatomy and Approaches to the Anterior Thoracolumbar Spine Region
J Bras Neurocirurg 23 (4): 295-300, 2012