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Anatomy

Thoracic, Lumbosacral and Pelvic RegionsAuthors: Dr. Juan EmmerichEditor In Chief: Dr Néstor Fiore Senior Editor: Luiz Gustavo Dal Oglio da Rocha

2Thoracic, Lumbosacral and Pelvic Regions. Author: Dr. Juan Emmerich.

OBJECTIVES

■■ To describe the anatomical areas corresponding to thoracic, lumbosacral and pelvic regions.

■■ To distinguish the important points of the relationship between the spine and the neural axis.

■■ To recognize relevant data that should be taken into account with respect to surgical approaches.

■■ To understand the region’s anatomy through practical data for spinal surgeons, important for everyday practical procedures.

CONTINUOUS LEARNING LIBRARY

Anatomy

Thoracic, Lumbosacral and Pelvic Regions


CONTENTS1. Overview ...................................................................................................................04

2. Bone structure..................................................................................................05

Thoracic vertebrae .............................................................................................................05

Lumbar vertebrae ............................................................................................................. 07

Sacrum .................................................................................................................................10

Coccyx ...................................................................................................................................12

Ribs .........................................................................................................................................13

Pelvis ..................................................................................................................................... 15

3. Joints ................................................................................................................................ 16

Intervertebral joints ........................................................................................................... 16

Sacroiliac joints .................................................................................................................... 19

4. Ligaments ................................................................................................................20

5. Basic anatomy .................................................................................................. 23

Posterior thoracolumbosacral region .......................................................................... 23

Anterior thoracolumbosacral region ............................................................................ 27

6. Spinal cord and nerves ...................................................................... 33

Cord characteristics at the thoracolumbar level ...................................................... 33

Spinal nerve characteristics at the thoracolumbar level ...................................... 33

References ......................................................................................................................36


1. INTRODUCTION1 Overview

The thoracic, lumbar and sacral regions of the spine continue caudally from the cervical spine before leading on to the lower limbs through the pelvis.

■■ The thoracolumbar spine and pelvic girdle collectively form the bone

structure for the thorax, abdomen and pelvis.

■■ The thorax is contained within the structure formed by the thoracic spine at

the back and closed at the front by the ribs and sternum.

■■ The abdomen is posteriorly confined by a bone structure, the lumbar spine,

and by abdominal muscles at the front.

■■ The thoracic and abdominal cavities are separated by the diaphragm muscle.

■■ The pelvic cavity is formed by the sacral bone at the back and closed at the

front by the union of the iliac with the pubic symphysis.


2 2. BONE STRUCTUREApproach

Several authors refer to them as the dorsal vertebrae. However, since all the vertebrae of the human body are located in the dorsal region, to avoid misinterpretations it is preferable to denominate them as the thoracic vertebrae.The thoracic vertebrae dif fer from the other vertebrae because of their articulation with the ribs. As such they present articular facets on the sides of the vertebral bodies and on the transverse processes.

Presented below are diagrams of a typical thoracic vertebra, they identify the articular facets on the body and on the transverse processes which articulate with the ribs. It is also possible to observe the marked angle of the spinous process.

superior articular process

vertebral body

arch spinous process

transverseprocess

arch

pedicle ofvertebralarchvertebral

orifice

spinous processtransverseprocess

transversecostalfacet

superiorarticularprocess

superiorcostalfacet

Top view of a typical thoracic vertebra (Sobotta, 1985) Anterior view of a typical thoracic vertebra (Sobotta, 1985)


2 superior costal facet superiorarticular process

transverseprocess andtransverse costalfacet

inferior costal facet

spinous process

inferior articularprocess

inferior vertebralnotch

right ribvertebral arch

ligamentum flavum

spinous processvertebral orifice


transverse process

lateral costotransverse ligament

neck and tubercle of rib

costotransverse ligament

radiate ligamentof head of rib

vertebral body

articulationof head of rib

costotransverseligament

costotransversejoint

Lateral view of a typical thoracic vertebra (Sobotta, 1985)

Top view of the costovertebral articulations (Sobotta, 1985)

Points of contact are through the demifacets of the body, the facets on the transverse processes to thesides of the vertebrae and the facets on the head and lateral costal tubercle of the rib.

■■ The size of the vertebral body is in between that of the cervical and lumbar

bodies, increasing in a caudal direction. Its posterior surface is concave (in

an axial plane) and forms part of the spinal canal. In some upper thoracic

vertebrae it is possible to observe a flattening of the left side of the body

caused by contact with the descending aorta.

■■ The pedicles emerge from the upper and lateral parts of the body (higher

than those of cervical vertebrae), which is why the inferior costal notch is

more marked than the superior.

■■ The superior articular facets project from the top of the union between the

laminae and pedicles. Their surface is ovoid; they are slightly convex and

almost vertical with respect to the axis of the pedicles. They direct backwards,

plus slightly upward and outward. The inferior facets are located close to the

lower edge and anterior face of the laminae and fit together with the superior

facets.

■■ The transverse processes are strong, they project laterally outwards and

slightly backwards and upwards. They have a concave articular facet which

receives the tubercle of the rib, the head of which articulates with the superior

demifacet of the same vertebra.


2 ■■ The spinous processes are large and triangular. Their angle with respect to

the axis of the spine changes according to their level:

■■ The first four form an angle of approximately 40° with respect to the

spinal axis.

■■ The next four are larger and even more inclined, forming an angle of 60°.

■■ The last four are at an angle of 40°, similar to the group in the first level.

■■ The first and final four vertebrae have different characteristics:

■■ T1 has a complete facet to receive the first rib and an inferior demifacet

for the second rib.

■■ T10 only has a superior demifacet.

■■ T11 and T12 only have a complete inferior facet to receive the

corresponding rib.

Lumbar VertebraeThe bodies in the lumbar region are the largest of all the pre-sacral vertebrae, with a transverse diameter larger than the anteroposterior one. The spinal canal takes the shape of a triangle with its base formed by the vertebral body.

The reason they have the largest pre-sacral vertebral bodies is to coincide with the large loads they have to support.

Presented below are diagrams showing different views of the lumbar vertebrae. They demonstrate how long and thin the transverse processes are, they are even known as costiform processes because of their resemblance to an atrophic rib.

spinous process

vertebral arch


costiform process

pedicle of vertebral arch

accessory process

mammillary process

vertebral arch

vertebralorifice

Top view of a lumbar vertebra (Sobotta, 1985)


2 superior articular process

costiform process

inferior articular process

inferior articular surface

vertebral body

superior articular processmammillary process

spinousprocess

transverseprocess

accessoryprocess


Anterior view of a lumbar vertebra (Sobotta, 1985)

Posterior view of the joints between L3 and L4 (Sobotta, 1985)


2 ■■ The pedicles, short and thick, emerge from the sides of the posterior face of

the body. As occurs with the thoracic spine, the inferior margin has a notch

that is significantly more marked than the superior notch.

■■ The transverse processes are planar, with large dimensions in the

craniocaudal axis and small in the anteroposterior. They project out of the

union of the pedicle with the lamina.

■■ The superior articular processes project out of the union of the pedicle with

the lamina. Their facets are concave and directed backwards and medially,

such that they are almost in front of each other. The inferior processes project

directly out of the laminae, their articular surfaces face downwards and

outwards, coinciding with the superior facets of the vertebra below.

The section of posterior arch found between the superior and inferior articular

facets is known as the vertebral isthmus or pars interarticularis.

■■ The spinous processes project from the point where the laminae unite.

They are short, strong and have a characteristic quadrilateral shape.

■■ If the L5 vertebra is assimilated by the sacrum, it is known as sacralization

of L5. It occurs because of an exaggerated development of the transverse

processes which tend to determine the size and shape of the sacral alae.

This can produce different degrees of fusion with the sacrum:

■■ simple contact;

■■ new joint formation;

■■ complete synostosis.

superior articular process mammillary process

transverse process


spinousprocess

inferiorvertebralnotch

superiorvertebralnotch

intervertebralforamen

Lateral view of the whole lumbar spine (Netter, 1999)


2 SacrumThe sacrum is triangular, with its base at the top and its apex facing downwards, and has a forward concave curvature (convex from behind).

One of the sacrum’s main functions is to transfer load from the spine to the pelvis.

sacralportion of the

terminal line

base of sacrum superior articular process

lateralportion

pelvicsacralforamina

pelvic surface

apex of sacrum

transverselines

median sacral crest

sacral canalsuperior articular process

costiform processof the first

sacral vertebrae

lateral portion

base of sacrum

sacral portion ofthe terminal line

superior vertebralnotch

intermediate sacral crest

Anterior view of the sacrum (Sobotta, 1985)

Top view of the sacrum (Sobotta, 1985)


2 The sacrum is formed by the fusion of the five embryonic sacral vertebrae. Despite the fusion in adults, it is still easy to identify the segments by the transverse crests along the anterior surface, representing the fusion of the vertebral discs.

■■ The joining of the sacral vertebrae means that there are no intervertebral

foramina (the site where spinal nerves usually exit the spine). Therefore, the

sacrum has anterior sacral foramina for ventral branches and posterior sacral

foramina for dorsal branches. The anterior foramina are larger than those in

front and coincide with the size of the anterior branches of the sacral nerves

passing through them. The anterior branches have a greater caliber than the

posterior ones because they form part of the lumbosacral plexus, which is the

origin of the sciatic nerve (the widest nerve in the human body).

■■ On the anterior surface, to the sides of the transverse crests, are the elliptical

anterior sacral foramina which continue laterally outwards into the anterior

sacral canals where the anterior branches of the sacral spinal nerves are

housed.

■■ The posterior face of the sacrum has five vertical crests. One is central, the

median sacral crest, and corresponds to the spinous processes of the fused

vertebrae. To each side of this crest, separated by a shallow sulcus, are the

crests representing the fused articular processes which are known as the

intermediate sacral crests or sacral articular crests. To the top of these crests

is found the articular facet of the sacrum which joins to the inferior articular

facet of L5. Inferiorly, these crests separate to form the inferior hiatus which

constitutes the access to the sacral vertebral canal. Further out from these

crests, on the lateral portion of the dorsal surface, are found the lateral crests

to which the posterior sacroiliac ligaments are attached.

■■ The strong, large sacral alae, created by the fusion of the transverse processes

of the first three sacral vertebrae, project from each lateral surface and

articulate with the pelvis. They have a crescent shape or, as described

classically, an auricular shape. They articulate with their homologous facets on

the posterior portion of the iliac bone, forming the sacroiliac joint.

■■ The superior surface of the sacral ala reveals a triangular shape. They are

located to the sides of the body of S1 and form part of the greater pelvis.

AOSPINE CONTINUOUS

TRAINING PROGRAM

Cycle 1

sacral tuberosity

auricular surfaceof sacrum

first coccygealvertebra

coccyx

coccygeal cornu

sacral cornu

mediansacralcrest

Right lateral view of the sacrum (Sobotta, 1985)


2 Coccyx Is the most caudal part of the spine. It is formed by a variable number of rudimentary vertebrae (3 to 5) that are usually fused together. Triangular in shape, while the size of vertebrae decrease from cranial to caudal. The first has similar characteristics to S5, while the rest are much smaller and they are normally fused together.

It does not have any supporting function, although the gluteus maximus inserts into its posterior face and the pelvic diaphragm muscles into the anterior surface.

coccygeal cornu

transverse process

first coccygeal vertebra

second coccygeal vertebra

third and fourth coccygeal vertebrae

Anterior view of the coccyx (Sobotta, 1985)


2 RibsThe ribs, typically in 12 pairs, are long, planar and arch-shaped bones. There are three types of rib:

True ribs

Floating ribs

False ribs

They are individually joined to the sternum by costal cartilage.

Found on the first seven thoracic vertebrae.

Their ends are free, without any contact with

the sternum.

They do not have a direct connection to the sternum,

rather they articulate with the sternum via shared cartilage.

They are the eighth, ninth and tenth ribs.

infrasternal angle

false ribs

true ribs

superior thoracic aperture

floating ribs

Anterior view of the thoracic skeleton (Williams, 1998)

The different ribs can be discerned. The thoracic skeleton is composed of the sternum, 12 pairs of ribs and 12 thoracic vertebrae.


2 Ribs are comprised of the following parts:

Body

Posterior end

Anterior end

The following areas can be identified: ■■ the lateral face which relates to the subcutaneous tissue and skin;

■■ the medial face has a groove along its lower border called the costal sulcus which houses the costal neurovascular bundle;

■■ blunt superior margin;

■■ thin, acute inferior margin.

The following areas can be identified: ■■ the head of the rib, the portion which articulates with the vertebrae;

■■ two articular demifacets that articulate with their counterparts on the lateral face of the vertebral bodies;

■■ the costal tubercle which articulates with the costal facet of the transverse process;

■■ the neck, which is a thinner segment located between the head and the costal tubercle.

It articulates with the costal cartilage.

body of the rib

superior marginheadneck ofrib

tubercle

body angleinferior margin

lateral face

anterior end

body of the rib superior margin head neck ofrib

tubercle

body angle

costal sulcusinferior margin

medial face

anterior end

body of the rib

superior marginheadneck ofrib

tubercle

body angleinferior margin

lateral face

anterior end

body of the rib superior margin head neck ofrib

tubercle

body angle

costal sulcusinferior margin

medial face

anterior end

Anterior view of a true rib (Sobotta, 1985)

Posterior view of a true rib (Sobotta, 1985)


2 PelvisThe coxal bones (formed from the fusion of the ilion, pubis and ischium in puberty), the sacrum and the coccyx all share articulations, collectively forming a ring of bone known as the skeletal pelvis or pelvic girdle.

fourth lumbar vertebrae

ventral sacroiliacligament

anterior longitudinal ligament

iliolumbar ligament

inguinalligament

coxofemoral

iliofemuralligament

obturatormembrane

interpubic disc

subpubic angle

arcuate pubicligament

superior pubicligament

greater trochanter

upper anterioriliac spine

sacrococcygealligament

anterior longitudinalligament

anterior sacroiliacligament

fourth lumbar vertebrae

iliolumbar ligament

Anterior view of the pelvis (Sobotta, 1985)

Top view of the pelvis (Sobotta, 1985)


3 3. JOINTS

The vertebrae are connected together by intervertebral joints. Each mobile segment (two vertebrae) is connected by three articulations:

■■ joints between vertebral bodies (medial and unique);

■■ joints between the articular processes (a lateral and symmetrical pair).

The sacrum is joined to the pelvis through the sacroiliac joints

Intervertebral Joints

We shall consider the articulations between the vertebral bodies and the intervertebral joints..

Articulations Between Vertebral Bodies

Articular Surfaces

These correspond to the superior and inferior surfaces of the vertebral bodies.The bone surfaces are covered by a lamina of cartilage which endures changes as the spine ages, as it is formed by hyaline cartilage in young people that turns into fibrocartilage in mature adults. These areas are known as the endplates.

Several authors include the endplates as a component of the intervertebral disc because of the important role they play in disc diseases, we also adopt this position.

The endplates provide nutrition to the disc through its porous surface, while also preventing the disc from bulging towards the vertebral bodies.

Intervertebral DiscsFrom a structural point of view, they comprise a quarter of the total length of the column and fulfill an important role in the maintenance of the spine’s physiological curves. They exhibit a biconvex shape which adapts to the concave surfaces of the vertebral endplates.

Thoracic intervertebral discs are of the least thickness (vertically), which corresponds to the smaller size of the thoracic vertebral bodies and segments with less mobility. Lumbar intervertebral discs are the thickest in the whole spine and those which have to bear the largest loads as they are located in the region with the largest and most caudal vertebrae.

They are subject to a daily process of dehydrating during activity and hydrating when at rest, which continually alters their height.


3 The discs comprise three components:

Annulus fibrosus

Nucleus pulposus

Endplates

It is a hard ring located around each disc, surrounding the nucleus pulposus and limiting its expansion.

It is composed of several concentric layers of [collagen] fibers. These fibers extend from one vertebral body to another following a diagonal direction that varies from one concentric layer to another, providing the disc with greater resistance to constant movements.

The following ligaments are inserted over the annulus fibrosus:

■■ towards the anterior, the anterior common vertebral ligament;

■■ towards the posterior, the posterior common vertebral ligament.

Is a soft, gelatinous substance, with a consistency similar to that of toothpaste, and which is formed by a proteoglycan gel.

It does not occupy a perfectly central position but is actually closer to the posterior margin of the disc.

Its color and consistency change over the years, starting as off-white and highly hydrated in childhood and becoming yellowish, opaque and dehydrated in older adults.

Discs are vascular from the age of 10 years onwards, after this point they receive nutrients via diffusion from neighboring structures, primarily the vertebral endplates.

Endplates can be considered as a transition between vertebral bodies and intervertebral discs, as the endplates are strongly attached to both structures.

They act to prevent migration of the nucleus to the cancellous bone and to distribute loads evenly.

The cartilage is in direct contact with the cancellous bone of the vertebral body, without any cortical bone, which is unlike the case for the majority of articular surfaces.

It is vital for the nourishment of the annulus fibrosus and the nucleus pulposus. It acts a semipermeable interface, allowing water and salts to pass through but preventing the loss of large proteoglycan molecules.

4 cm

7–10 mm

annulus fibrosus lamellar structure

nucleus pulposus

vertebral disc

annulus fibrosus

Diagram of the components forming an intervertebral disc (Williams, 1998)


3 nucleus

cartilage

bone

annulus

supraspinousligament

ligamentumflavum

interspinousligamentposterior

longitudinalligament

anteriorlongitudinal

ligament

intervertebraldisc

lumbar vertebralbody

Close relationship between the annulus fibrosus, nucleus pulposus and endplates

(Williams, 1998)

Lateral view of the lumbar spine (Netter, 1999)

The disc and different intervertebral ligaments are shown.

Intervertebral JointsThe intervertebral joints are synovial. They possess a thin, loose articular capsule which grants stability to the articular surfaces.

The ar ticular sur faces are planar at the thoracic level, while at the lumbar level they present as complementary cylinders that form a trochoid joint.


3 Sacroiliac Joints

The sacroiliac joints have little movement, some authors even classify them as a symphysis, but in reality, due to their characteristics, they should be classified as diarthro-amphiarthrosis joints. The articular surfaces are provided by the slightly concave auricular faces of the sacrum, situated laterally, and by the auricular surfaces of the ilion, which have similar characteristics but are slightly convex so that they form a reciprocal connection with those on the sacrum.

Both articular surfaces are covered by a layer of fibrocartilage tissue. They each have a joint capsule and two ligaments.

Anterior sacroiliac ligament

It is a broad, thin ligament that extends across the anterior face of the joint acting as a reinforcement of the joint capsule. It narrows at its superior and inferior ends,

which are known as the superior and inferior bands.

Posterior sacroiliac ligament

It is more complex than the anterior ligament, with three planes:

Superficial plane

Deep plane

Middle plane

Composed of three parallel bundles known as short posterior sacroiliac ligaments, extending from the iliac tuberosity to the median sacral crest.

Composed of the large interosseous sacroiliac ligament that is inserted laterally into the iliac tuberosity and medially to the sides of the first two sacral foramina.

Composed of various bundles collectively known as the ileotransverse ligaments since they connect the tuberosity and the iliac crests with the lateral sacral crest (formed from the fusion of the transverse processes of the sacral vertebrae).

From cranial to caudal, they are given the following names:

• sacral bundle of ileotransverse ligament,

• ileotransverse ligament inserted into first to fourth sacral vertebrae.

Superiorly, they appear continuous with the superior and inferior iliolumbar ligaments which ascend from the iliac crest up to the transverse processes of the fourth and fifth lumbar vertebrae.


4 4. LIGAMENTSDescribed below is a series of ligaments that are common to the whole thoracolumbar region.

Ligaments in thoracolumbar region

Anterior longitudinal

Posterior longitudinal

Supraspinous

Interspinous

Ligamentum flavum

supraspinousligament

ligamentumflavum

interspinousligamentposterior

longitudinalligament

anteriorlongitudinal

ligament

intervertebraldisc

lumbar vertebralbody

Diagram of the intervertebral discs and ligaments (Netter, 1999)


4 Anterior Longitudinal Ligament

The anterior longitudinal ligament descends down the anterior surface of the spinal column, from the exocranial surface of the basilar portion of the occipital bone to the anterior surface of the second sacral vertebra.

It is a strong ligament of varying width, narrow at the upper cervical level. It gradually widens until it reaches its maximum width at the thoracic level and then narrows through the lumbar level down to just a small strip at the level of the sacrum.

The ligament is strongly attached to the anterior faces of the discs and also of the vertebral bodies, fundamentally in areas which are close to the disc.

Posterior Longitudinal Ligament

The posterior longitudinal ligament runs from the endocranial surface of the basilar process of the occipital bone down to the coccyx.

It runs along the posterior face of the vertebral bodies, located on the anterior margin of the spinal canal.

It takes on a scalloped shape because it is wider at the level of the discs than it is near the bodies.

As with the anterior longitudinal ligament, it is strongly attached to the disc and the vertebral body at points which are close to the disc.

posteriorlongitudinalligament

Posterior surface of the vertebral bodies with the posterior longitudinal ligament (Netter, 1999)


4 Supraspinous LigamentThe supraspinous ligament is a fibrous cord extending behind the interspinous ligaments along the length of the whole spine, anchoring to the apexes of the spinous processes.

Interspinous LigamentThe interspinous ligament differs from the previous ligaments because it has a segmented distribution without any continuity with the ligaments in the levels above or below.

It occupies the space between the spinous processes of a mobile segment, situated on the processes’ inferior and superior margins.

The anterior surface relates with the ligamentum flavum, while the posterior face connects with the supraspinous ligament.

Ligamentum Flavum The ligamentum flavum is a short, wide, strong and highly elastic ligament pair (right and left) that occupies the space between the laminae of each mobile segment. They extend in a horizontal direction from the lateral articular process to the median line where the two counterparts meet.

The size of the ligamenta flava depend on the level of the spine. Typically, their width, that is, their medial to lateral extension, decreases from the cervical to lumbar spine, while their height and thickness increase.

The superior margin is inserted on the anterior face of the lamina above and moves closer to the inferior margin of that upper lamina while moving down the vertebrae towards the sacrum. The inferior margin connects to the superior margin of the lamina situated in the level below.

ligamentumflavum

Anterior view of the posterior arches withthe ligamenta flava (Netter, 1999)


5 5. BASIC ANATOMY

Posterior Thoracolumbosacral Region

Although each section of the spine has its own characteristics, the topographical anatomies of the posterior areas of the thoracic and lumbar regions share several common features.

After dissecting the skin (which is thicker in the lumbar region) comes the subcutaneous plane which is thin at the thoracic level and greater at lumbar level where it can reach a considerable thickness in obese individuals.

Beneath the subcutaneous plane is found the superficial layer of the aponeurosis of the paravertebral muscles.

On the median line, it is usually easy to identify the spinous processes covered by the supraspinous ligament which is directly below the aponeurosis.

The muscles of the posterior region are located to the sides of the spines and behind the laminae, the articular processes and the transverse processes. These muscles principally function as extensors of the spinal column and, to a lesser degree, also as rotators.

Deep plane

The muscles that form the erector spinae group of the vertebral column (comprising the iliocostal, thoracic longissimus and spinalis thoracis muscles).

iliocostal muscle

thoracic longissimusmuscle

spinalis muscle

iliocostal muscle

Deep muscle plane of posterior thoracolumbar region (Rouviére and Delmas, 2005)

The muscles can be divided into three planes:

They are typically very difficult to differentiate. Their function is to maintain the spine erect.


5 Intermediate plane

These are short muscles spanning from the transverse processes to the spinous processes and laminae. They are collectively known as the transversospinal muscle group.

The group includes the following muscles:

■■ the semispinal muscles;

■■ interspinous;

■■ intertransverse;

■■ multifidus;

■■ rotators.

These muscles are involved in rotation and lateral inclination movements.

C’

D’

L’Intermediate muscle plane of posterior thoracolumbar region (Rouviére and Delmas, 2005)


5 Superficial plane

This plane is formed by the following muscles:latissimus dorsi;

■■ trapezius;

■■ serratus superior posterior;

■■ serratus inferior posterior;

■■ rhomboid major;

■■ rhomboid minor.

These muscles connect the spine to the cranium, the scapular girdle and the thorax.

spinalismuscle

thoraciclongissimus

muscle

serratus muscle,superior posterior

iliocostalmuscle

thoracolumbarfascia

serratus muscle,inferior posterior

Superficial muscle plane of posterior thoracolumbar region (Rouviére and Delmas,

2005)


5

Posterior view of the thoracolumbosacral spinal skeleton (Bauer, Kerschbaumer and Poisel, 1998)

Having dissected the back muscles, the vertebral skeleton is left


5 Anterior Thoracolumbosacral Region

Unlike the posterior plane of the spine, which is relatively superficial with respect to the main axis of the body and relates simply to the epaxial muscles, the anterior surface has a close relationship with the large vessels, the mediastinal organs and the retroperitoneum.

Presented below are some diagrams of thoracolumbar anatomical references.

body of sternum

pericardium

right atrium

ribs

esophagus

azygos vein

thoracic vertebra

intercostal vessels

spinal cord

hemiazygous vein

oblique fissure

descending aorta

left atrium

left ventricle

right ventricle

rectus abdominis muscle

gallbladder

peritoneal cavity

pancreas

lateral abdominalmuscles

thoracic diaphragm

parietalperitoneum

right lobeof liver

right kidney

intercostal muscles

latissimus dorsi muscle

serratus posteriorinferior muscle

quadratus lumborum muscle

psoas major muscleintrinsic

backmuscles

right renalvessels

left kidney

inferior vena cava

lumbar vertebra

sympathetic trunk

abdominal partof aorta

superiormesenteric

vessels

Axial view at level of the thoracic spine (Sobotta, 1985

Axial view at level of the lumbar spine (Bauer et al., 1998)


5 Thoracic Region

The lef t sur face of the spine is related to the aortic arch at the level of T3-T4. The thoracic aor ta descends sl ight ly running from the left towards the center of the anterior face of the column, after passing the diaphragm it is known as the abdominal aorta. It gives rise to the intercostal or segmental branches that cover the anterolateral face of each vertebrae and join with the vein and nerve of the same name to form the intercostal neurovascular bundle tracing the lower border of the rib, in the intercostal space.

esophagusazygos vein

trachea

left recurrentlaryngeal nerve

phrenic nerve

left subclavianartery

left recurrentlaryngeal nerve

intercostal nerves

thoracic duct

abdominalaorta

intercostal nerves

greater splanchnicnerve

ascending aorta

brachiocephalic trunk

right recurrentlaryngeal nerve

Anterior view of the thoracic spine (Sobotta, 1985)


5 The esophagus accompanies the spine along the length of the thorax. It starts on the right and as it descends moves to the center (just in front of the aorta), before displacing to the left as it passes through the diaphragm and finally opens into the stomach, now inside the abdominal cavity.

The azygos vein forms on the right, at the level of the eleventh intercostal space, from the confluence of two branches:

■■ laterally, formed by the union of the right ascending lumbar vein and right twelfth intercostal vein (or right subcostal vein);

■■ medially, inconstantly, from the inferior vena cava or the right renal vein.

From there it ascends vertically along the right side of the anterolateral face up to T3-T4 where it arches over to join with the superior vena cava. The hemiazygous vein is located on the left side, with a similar origin to the azygos but, as it ascends, at the level of T8 it crosses the median line to the right side where it joins with the azygos vein.

Lumbar Region

On the anterolateral face, on both sides of the body, are the thick, strong psoas muscles that are inserted into the following areas:

■■ costal margin;

■■ lateral face of the vertebral bodies;

■■ intervertebral discs;

■■ transverse processes.

They descend to their distal insertion in the lesser trochanter of the femur.

The abdominal aorta follows the lumbar spine from L1 to L4 where it divides into its terminal branches. It runs along the anterior face of the spine, slightly to the left, in close contact with the bodies and intervertebral discs. The lumbar or segmental arteries, homologous to the intercostal arteries of the thorax, branch off during its descent. There are three terminal branches of the aorta:

■■ small median sacral artery, descending medially towards the pelvis;

■■ two common iliac arteries, from their bifurcation they direct downwards and outwards, then after about 6 cm, at the level of the lumbosacral joint, they bifurcate into the internal and external iliac arteries and follow a path closely related to their equivalently named veins.

The inferior vena cava forms from the confluence of the common iliac veins at a level close to the top of L5, slightly beneath the aortic bifurcation, and from there it ascends up through the retroperitoneal space, along the anterior face of the spinal column and slightly to the right. When it reaches the height of L1, it passes through a specific opening in the diaphragm to enter the thoracic region, where it terminates in the lower surface of the right atrium, having passed through the pericardium.


5phreniccenter

esophagus

transverse muscleof abdomen

abdominal partof aorta

right pillar ofthe diaphragm

lumbar vertebrae

iliac crest

psoas majormuscle

urinary bladder

space forvessels

femoralartery

rectum

peritoneum

sacral promontory

iliac muscle

psoasmajor muscle

transverse muscleof abdomen

quadratuslumborum

muscle

psoas minormuscle

esophageal hiatus

costal partof diaphragm

tendon of thepsoas minormuscle

Anterior view of the lumbar spine and neighboring structures, deep plane (Sobotta, 1985)


5ureter

adrenal gland

arteria venal diafragmática inferior

adrenal gland

renal arteryand vein

intercostalmuscles

kidney

ureter

psoas major andminor muscles

iliac muscle

internaliliacartery

sigmoid colon

urinary bladder

renal arteryand vein

sigmoidarteries

internal iliacartery and vein

Anterior view of the lumbar spine and neighboring structures, deep plane (Sobotta, 1985)


5

sacral ganglia

fifth lumbar vertebra

internal iliacnode

obturator node

medial externaliliac nodes

lateral lacunar node

intermediate externaliliac nodes

lateral externaliliac nodes

intermediate externaliliac node

common iliac node

Sagittal section of the pelvic region (Latarjet and Ruiz Liard, 2005)

Sacrum

To the sides of the anterior or pelvic face of the sacrum are inserted the piriformis muscles. Just in front of them is the sympathetic chain, which, together with the sacral parasympathetic, forms the autonomic iliohypogastric or inferior hypogastric plexus. This plexus then continues to the following plexus

■■ vesical;

■■ prostatic (in the male);

■■ uterovaginal (in the female).

It has a close relationship with the sacral ganglia, which drain into the internal iliac lymph nodes in the pelvic region.

The anterior face of the bodies of the first and second sacral vertebrae are covered by the posterior parietal membrane of the peritoneum, while the third to fifth vertebrae and coccyx are in close relation to the rectum, terminal section of the digestive tract and a continuation of the sigmoid colon and continues into the anus.


6 5. SPINAL CORD AND NERVESCord Characteristics at the Thoracolumbar Level

The thoracic cord is the segment with the least amount of gray matter. This is because the intercostal nerves are smaller than the cervical and lumbosacral nerves which go on to form plexuses. The thoracic cord, therefore, is uniformly smaller than the cervical and lumbar sectors.

The lumbar spinal cord has a low percentage of white matter, as it is the most caudal section, but, as with the cervical cord, its gray matter is well developed due to the presence of the nerve cells that form the lumbar and sacral coccygeal plexus. This increase can be seen in the spinal cord as its diameter increases with respect to the thoracic segment, which is known as lumbar widening or lumbar plexus widening.

The cord typically ends at the level of the inferior margin of the L1 body or the superior border of the L2 body, then continues with the filum terminale.

Spinal Nerve Characteristics at the Thoracolumbar Level

The thoracic and lumbar nerves take the name of the vertebra lying above them when they exit the spinal canal, for example, the third lumbar nerve emerges between L3 and L4.

The spinal nerve pairs, particularly the lower lumbar ones, follow a descending path within the spinal canal before passing through the intervertebral foramen.

This route means that the spinal nerve can be divided into four areas of clinical and surgical importance.

Retrodiscal sector

Parapedicle sector

Foraminal sector

Extraforaminal sector

Found immediately behind the intervertebral disc.

Located in the space between the dural sac and the pedicle.

Passing through the intervertebral foramen.

Outside the intervertebral foramen.


6retrodiscal

foraminal

parapedicle

extraforaminal

Diagram showing the different areas along the path of the spinal nerve root

In the typical cases of posterolateral herniated nucleus pulposus, the root traversing the intervertebral foramen below the affected disc will also be compromised. In the case of foraminal and extraforaminal hernias, the affected nerve (exiting root) will have the same number as the herniated disc. As a practical example, an L5-S1 hernia would affect the S1 nerve if it were a typical posterolateral hernia (traversing root) or the L5 nerve if it were an extraforaminal hernia (exiting root).

The borders of the intervertebral foramen are also clinically and surgically very important, these are:

■■ superiorly, the inferior margin of the pedicle of the overlying vertebra;

■■ inferiorly, the superior margin of the pedicle of the underlying vertebra;

■■ anteriorly, the posterior margin of the overlying vertebra, the posterior margin of the intervertebral disc covered by the horizontal expansion of the posterior longitudinal ligament, and, to a lesser degree, the posterior margin of the body of the underlying vertebra;

■■ posteriorly, the ligamentum flavum and the capsule of the articular processes.


6

The space between the superior ar ticular processes and the vertebral body is known as the lateral recess; a vitally important point, where the spinal nerve travels towards the intervertebral foramen, because it is often a site of compression.

inferior margin of theoverlying pedicle

SUPERIOR LIMIT

POSTERIOR LIMIT

INFERIOR LIMIT

ANTERIOR LIMIT

ligamentumflavum andarticularprocesses

superior marginof the underlyingpedicle

posterior faceof the vertebral

body and intervertebraldisc

superior articularprocess

osteophyte ofarticular process

root impinged inthe lateral recess

Limits of the intervertebral foramina at lumbar level

Oblique view from above of a lumbar vertebra showing the lateral recess (Bauer et al., 1998)

The route of the spinal nerve through the lateral recess can be observed.


REFERENCESBauer, R.; Kerschbaumer, F. and Poisel, S. (1998) Columna, Serie Cirugía Ortopédica.Madrid: MARBAN.

Latarjet, M. and Ruiz Liard, A. (2005) Anatomía humana (4th Ed.). Buenos Aires: Editorial Médica Panamericana.

Netter, F. H. (1999) Colección CIBA de ilustraciones médicas. Tomo I: Sistema nervioso. Tomo I (Parte 1): Anatomía y fisiología.Barcelona: Elsevier-Masson.

Rothman, R. H. and Simeone, F. A. (1985) La columna vertebral (2nd Ed.). Buenos Aires: Editorial Médica Panamericana.

Rouviére, H and Delmas, A. (2005) Anatomía humana: descriptiva, topográfica y funcional (11th Ed.). Barcelona: Masson.

Sobotta, J. (1985) Atlas de Anatomía Humana (18th Ed.). Madrid: Publisher Panamericana.

Testut, L. and Latarjet, A. (1971) Tratado de anatomía humana (9th Ed.). Barcelona. Editorial Salvat.

Williams, P. (1998) Anatomía de Gray (38th Ed.). Madrid: Harcourt Brace.

Project coordination Néstor Fiore, Luciana Braga Garcia

Instructional design and educational review María Alejandra Zangara, María Eugenia Bregliano

Project and graphic design André Secundino

Illustrations Gustavo Francesconi

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