Download Muscles of the Back

Basic Anatomy 693
Fractures of the Odontoid Process of the Axis
Fractures of the odontoid process are relatively common and
result from falls or blows on the head (Fig. 12.8). Excessive mobility of the odontoid fragment or rupture of the transverse ligament
can result in compression injury to the spinal cord.
Fracture of the Pedicles of the Axis (Hangman’s
Fracture)
Severe extension injury of the neck, such as might occur in an
automobile accident or a fall, is the usual cause of hangman’s
fracture. Sudden overextension of the neck, as produced by the
knot of a hangman’s rope beneath the chin, is the reason for the
common name. Because the vertebral canal is enlarged by the
forward displacement of the vertebral body of the axis, the spinal
cord is rarely compressed (Fig. 12.8).
Congenital Spondylolisthesis
In congenital spondylolisthesis, the body of a lower lumbar
vertebra, usually the fifth, moves forward on the body of the
vertebra below and carries with it the whole of the upper
Muscles of the Back
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Degenerative Spondylolithesis
This condition is common in the elderly and involves degeneration of the intervertebral discs in the lumbar region and osteoarthritis of the intervertebral joints. Anterior slippage of the fifth
lumbar vertebra often occurs, and the lumbar nerve roots may
be pressed upon causing low back pain and pain down the leg in
the distribution of the involved nerve.
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The muscles of the back may be divided into three groups:
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portion of the vertebral column. The essential defect is in
the pedicles of the migrating vertebra. It is now generally
believed that, in this condition, the pedicles are abnormally
formed and accessory centers of ossification are present
and fail to unite. The spine, laminae, and inferior articular
processes remain in position, whereas the remainder of the
vertebra, having lost the restraining influence of the inferior
articular processes, slips forward. Because the laminae are
left behind, the vertebral canal is not narrowed, but the nerve
roots may be pressed on, causing low backache and sciatica.
In severe cases, the trunk becomes shortened, and the lower
ribs contact the iliac crest.
The superficial muscles connected with the shoulder
girdle. They are described in Chapter 9.
The intermediate muscles involved with movements of
the thoracic cage. They are described with the thorax in
Chapter 2.
The deep muscles or postvertebral muscles belonging
to the vertebral column.
Deep Muscles of the Back
(Postvertebral Muscles)
In the standing position, the line of gravity (Fig. 12.9)
passes through the odontoid process of the axis, posterior
site of nipping
of spinal nerve
site of destruction
of spinal cord
B
A
anterior arch of atlas
transverse ligament of atlas
C
waist fracture of odontoid process
odontoid process
of atlas
base fracture of odontoid process
fracture of pedicle
D
posterior arch of atlas
E
FIGURE 12.8 Dislocations and fractures of the vertebral column. A. Unilateral dislocation of the fifth or the sixth cervical vertebra. Note the anterior displacement of the inferior articular process over the superior articular process of the vertebra below.
B. Bilateral dislocation of the fifth or the sixth cervical vertebra. Note that 50% of the vertebral body width has moved forward on the vertebra below. C. Flexion compression–type fracture of the vertebral body in the lumbar region. D. Jefferson’stype fracture of the atlas. E. Fractures of the odontoid process and the pedicles (hangman’s fracture) of the axis.
694 CHAPTER 12 The Back
semispinalis capitis
longissimus capitis
longissimus cervicis
iliocostalis cervicis
spinalis thoracis
iliocostalis thoracis
semispinalis thoracis
multifidus
longissimus thoracis
iliocostalis lumborum
B
A
FIGURE 12.9 A. Arrangement of the deep muscles of the back. B. Lateral view of the skeleton showing the line of gravity.
Because the greater part of the body weight lies anterior to the vertebral column, the deep muscles of the back are important in maintaining the normal postural curves of the vertebral column in the standing position.
to the centers of the hip joints, and anterior to the knee
and ankle joints. It follows that when the body is in this
position, the greater part of its weight falls in front of the
vertebral column. It is, therefore, not surprising to find
that the postvertebral muscles of the back are well developed in humans. The postural tone of these muscles is the
major factor responsible for the maintenance of the normal
curves of the vertebral column.
The deep muscles of the back form a broad, thick column
of muscle tissue, which occupies the hollow on each side of
the spinous processes of the vertebral column (Fig. 12.9).
They extend from the sacrum to the skull. It must be realized that this complicated muscle mass is composed of
many separate muscles of varying length. Each individual
muscle may be regarded as a string, which, when pulled on,
causes one or several vertebrae to be extended or rotated
on the vertebra below. Because the origins and insertions
of the different groups of muscles overlap, entire regions of
the vertebral column can be made to move smoothly.
The spines and transverse processes of the vertebrae
serve as levers that facilitate the muscle actions. The muscles of longest length lie superficially and run vertically
from the sacrum to the rib angles, the transverse processes,
and the upper vertebral spines (Fig. 12.9). The muscles
of intermediate length run obliquely from the transverse
processes to the spines. The shortest and deepest muscle
fibers run between the spines and between the transverse
processes of adjacent vertebrae.
The deep muscles of the back may be classified as follows:
Superficial Vertically Running Muscles
■
■■ Erector spinae
éiliocostalis
ê
ê longissimus
êspinalis
ë
Intermediate Oblique Running Muscles
■
■■ Transversospinalis
Deepest Muscles
Interspinales
■■ Intertransversarii
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é Semispinalis
ê
ê multifidus
ê Rotatores
ë
Basic Anatomy 695
Knowledge of the detailed attachments of the various
muscles of the back has no practical value to a clinical professional, and the attachments are therefore omitted in this text.
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Splenius
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The splenius is a detached part of the deep muscles of the
back. It consists of two parts. The splenius capitis arises
from the lower part of the ligamentum nuchae and the
upper four thoracic spines and is inserted into the superior
nuchal line of the occipital bone and the mastoid process of
the temporal bone.
The splenius cervicis has a similar origin but is inserted
into the transverse processes of the upper cervical vertebrae.
Nerve Supply
All the deep muscles of the back are innervated by the posterior rami of the spinal nerves.
Muscular Triangles of the Back
Auscultatory Triangle
The auscultatory triangle is the site on the back where
breath sounds may be most easily heard with a stethoscope.
The boundaries are the latissimus dorsi, the trapezius, and
the medial border of the scapula.
Lumbar Triangle
The lumbar triangle is the site where pus may emerge from
the abdominal wall. The boundaries are the latissimus
dorsi, the posterior border of the external oblique muscle
of the abdomen, and the iliac crest.
Deep Fascia of the Back
(Thoracolumbar Fascia)
The lumbar part of the deep fascia is situated in the interval
between the iliac crest and the 12th rib. It forms a strong
aponeurosis and laterally gives origin to the middle fibers of the transversus and the upper fibers of the internal
oblique muscles of the abdominal wall (see page 117).
Medially, the lumbar part of the deep fascia splits into
three lamellae. The posterior lamella covers the deep muscles of the back and is attached to the lumbar spines. The
middle lamella passes medially, to be attached to the tips
of the transverse processes of the lumbar vertebrae; it lies
anterior to the deep muscles of the back and posterior to
the quadratus lumborum. The anterior lamella passes
medially and is attached to the anterior surface of the transverse processes of the lumbar vertebrae; it lies anterior to
the quadratus lumborum muscle.
Blood Supply of the Back
Arteries
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In the cervical region, branches arise from the occipital
artery, a branch of the external carotid; from the vertebral artery, a branch of the subclavian; and from the
deep cervical artery, a branch of the costocervical trunk.
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In the thoracic region, branches arise from the posterior
intercostal arteries.
In the lumbar region, branches arise from the subcostal
and lumbar arteries.
In the sacral region, branches arise from the iliolumbar
and lateral sacral arteries, branches of the internal iliac
artery.
Veins
The veins draining the structures of the back form plexuses
extending along the vertebral column from the skull to the
coccyx.
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The external vertebral venous plexus lies external and
surrounds the vertebral column.
The internal vertebral venous plexus lies within the
vertebral canal but outside the dura mater of the spinal
cord (Fig. 12.10).
The external and internal vertebral plexuses form a capacious venous network whose walls are thin and whose
channels have incompetent valves or are valveless. They
communicate through the foramen magnum with the
venous sinuses within the skull. Free venous blood flow
may therefore take place between the skull, the neck, the
thorax, the abdomen, the pelvis, and the vertebral plexuses,
with the direction of flow depending on the pressure differences that exist at any given time between the regions. This
fact is of considerable clinical significance (see carcinoma
of the prostate, page 696).
The internal vertebral plexus receives tributaries from
the vertebrae by way of the basivertebral veins (Fig. 12.10)
and from the meninges and spinal cord. The internal plexus
is drained by the intervertebral veins, which pass outward
with the spinal nerves through the intervertebral foramina.
Here, they are joined by tributaries from the external vertebral plexus and in turn drain into the vertebral, intercostal,
lumbar, and lateral sacral veins.
Lymph Drainage of the Back
The deep lymph vessels follow the veins and drain into
the deep cervical, posterior mediastinal, lateral aortic, and
sacral nodes. The lymph vessels from the skin of the neck
drain into the cervical nodes, those from the trunk above
the iliac crests drain into the axillary nodes, and those from
below the level of the iliac crests drain into the superficial
inguinal nodes (see page 127).
Nerve Supply of the Back
The skin and muscles of the back are supplied in a segmental manner by the posterior rami of the 31 pairs of spinal
nerves. The posterior rami of the first, sixth, seventh, and
eighth cervical nerves and the fourth and fifth lumbar
nerves supply the deep muscles of the back and do not supply the skin. The posterior ramus of the second cervical
nerve (the greater occipital nerve) ascends over the back
of the head and supplies the skin of the scalp.
The posterior rami run downward and laterally and
supply a band of skin at a lower level than the intervertebral