through which the canal is continuous with pelvic and dorsal sacral from the sacral apex; its pelvic surface is tilted upwards and forwards,
foramina. Its caudal opening is the sacral hiatus. The canal contains the its dorsum downwards and backwards. Orientation varies with mobility
cauda equina and the filum terminale, and the spinal meninges. Oppo- and between individuals.
site the middle of the sacrum, the subarachnoid and subdural spaces The base or upper surface of the first coccygeal vertebral body has
close; the lower sacral spinal roots and filum terminale pierce the arach- an oval, articular facet for the sacral apex. Posterolateral to this, two
noid and dura mater at that level. The filum terminale with its menin- coccygeal cornua project upwards to articulate with sacral cornua; they
geal coverings emerges below the sacral hiatus and passes downwards are homologues of the pedicles and superior articular processes of other
across the dorsal surface of the fifth sacral vertebra and sacrococcygeal vertebrae. A rudimentary transverse process projects superolaterally
joint to reach the coccyx. The fifth sacral spinal nerves also emerge from each side of the first coccygeal body and may articulate or fuse
through the hiatus medial to the sacral cornua, and groove the lateral with the inferolateral sacral angle, completing the fifth sacral foramina.
aspects of the fifth sacral vertebra. The second to fourth coccygeal vertebrae diminish in size and are
usually mere fused nodules. They represent rudimentary vertebral
MuscleattachmentsThe pelvic surface gives attachment to piri- bodies, though the second may show traces of transverse processes and
formis in its second to fourth segments, to iliacus superolaterally, and pedicles.
to coccygeus inferolaterally. The dorsal surface gives attachment to the The gap between the fifth sacral body and the articulating cornua
aponeurosis of erector spinae along a U-shaped area of spinous and represents, on each side, an intervertebral foramen that transmits the
transverse tubercles, covering multifidus, which occupies the enclosed fifth sacral spinal nerve. The dorsal ramus descends behind the rudi-


area (see Fig. 43.50). On the lateral border below the auricular surface, mentary transverse process, and the ventral ramus passes anterolaterally
gluteus maximus is attached dorsal and coccygeus is attached ventral to between the transverse process and sacrum.
the sacrotuberous and sacrospinous ligaments.
MuscleandligamentattachmentsThe lateral parts of the pelvic
OssificationThe sacrum resembles typical vertebrae in the ossifica- surface, including the rudimentary transverse processes, give attachment
tion of its segments (Fig. 43.52). Primary centres for the centrum and to the levatores ani and coccygei. The anterior sacrococcygeal ligament
each half vertebral arch appear between the tenth and twentieth weeks. is attached to the front of the first and sometimes second coccygeal
Primary centres for the costal elements of the upper three or more seg- vertebral bodies (see Fig. 80.9A). The cornua give attachment to the
ments appear superolateral to the pelvic sacral foramina, between the intercornual ligaments. The lateral sacrococcygeal ligament connects
sixth and eighth prenatal months. Each costal element unites with its the transverse process to the inferolateral sacral angle. Gluteus maximus


BACk
730
5
NOITCES
A B
Sacral canal
Superior articular
process
Spinous tubercle
1
2
Promontory
3
Intervertebral
foramina in
lateral wall of
Remains of intervertebral discs sacral canal
4
Sacral cornu
5
Part of first coccygeal segment Coccygeal cornu
recently united to sacrum
C
Fig .43 .51 A, The sacrum, lateral aspect . Key: 1, promontory; 2, auricular (articular)
surface; 3, attachments of interosseous sacroiliac ligaments; 4, spinous process;
5, sacral cornu (left) . B, A median sagittal section through the sacrum . C, A lateral
radiograph of the lumbosacral junction in a 14-year-old male . Key: 1, L5–S1 disc;
2, sacral promontory; 3, S1–2 disc; 4, greater sciatic notches; 5, S3 .
1
2
3
5
4
is attached to the dorsal surface, and both levator ani and sphincter ani OssificationEach coccygeal segment is ossified from one primary
externus are attached to the tip of the bone. The median area gives centre. A centre in the first segment appears about birth and its cornua
attachment to the deep and superficial posterior sacrococcygeal liga- may soon ossify from separate centres. Remaining segments ossify at
ments, the superficial descending from the margins of the sacral hiatus wide intervals up to the twentieth year or later. Segments slowly unite:
and sometimes closing the sacral canal. The filum terminale, which is union between the first and second is frequently delayed until 30 years.
situated between the two ligaments, blends with them on the dorsum The coccyx often fuses with the sacrum in later decades, especially in
of the first coccygeal vertebra. females.


Ligaments of the vertebral column
731
34
RETPAHC
A B Centre for A Anterior
vertebral arch
Lateral
epiphysis
Anulus fibrosus
Costal element Centre for body Nucleus pulposus
C
* *
1 Posterior
ø
* *
ø
ø ø
D E
Epiphyses 2
Fig .43 .52 Ossification of the sacrum and coccyx . A, At birth . B, The
base of the sacrum of a child about 4 years old . C, At the twenty-fifth
year: epiphysial plates for each lateral surface are marked by asterisks .
D–E, The epiphyses of the costal and transverse process of the sacrum
Posterior longitudinal
at the eighteenth year .
ligament
3
A Pelvic aspect Coccygeal cornua B Dorsal aspect B Intervertebral foramen Superior
articular process
Anterior longitudinal
ligament Supraspinous
ligament
Hyaline cartilage
Ligamentum
Anulus flavum
Rudimentary Intervertebral fibrosus Interspinous
transverse disc ligament
process Nucleus Thoracolumbar
pulposus fascia
Attachment Attachment area of
area of gluteus maximus
coccygeus Lamina
Foramen for
Attachment area of basivertebral vein
levator ani and
sphincter ani
Posterior
Fig .43 .53 The coccyx . A, Anterior (pelvic) aspect . B, Posterior (dorsal)
longitudinal ligament Pedicle
aspect .
Fig .43 .54 A, The main structural features of an intervertebral disc . For
clarity, the number of fibrocartilaginous laminae has been greatly reduced .
Note the alternating obliquity of collagen fascicles in adjacent laminae .
LIGAMENTS OF THE VERTEBRAL COLUMN Key: 1, lumbar disc; 2, detailed structure of anulus fibrosus; ø =
approximately 65°; 3, cervical disc . B, A median sagittal section through
the upper lumbar vertebral column showing discs and ligaments . (A, After
ANTERIOR LONGITUDINAL LIGAMENT
Bogduk N 1997 Clinical Anatomy of the Lumbar Spine and Sacrum, 3rd


ed . Edinburgh: Churchill Livingstone . B, With permission from Waschke J,
The anterior longitudinal ligament (Fig. 43.54B) is a strong band Paulsen F (eds), Sobotta Atlas of Human Anatomy, 15th ed, Elsevier,
extending along the anterior surfaces of the vertebral bodies. It is Urban & Fischer . Copyright 2013 .)
broader caudally, and thicker and narrower in thoracic than in cervical
and lumbar regions, and is also relatively thicker and narrower opposite
vertebral bodies than at the levels of intervertebral symphyses. It extends adjacent vertebral bodies, and are loosely attached at intermediate levels
from the basilar part of the occipital bone to the anterior tubercle of of the bodies, where the ligament fills their anterior concavities, flatten-
C1 and the front of the body of C2, and then continues caudally to the ing the vertebral profile. At these various levels, ligamentous fibres
front of the upper sacrum. Its longitudinal fibres are strongly adherent blend with the subjacent periosteum, perichondrium and periphery of
to the intervertebral discs, hyaline cartilage end-plates and margins of the anulus fibrosus. The anterior longitudinal ligament has several


BACk
732
5
NOITCES
Space between
ligamenta flava
Posterior Blends with capsule
longitudinal of facet joint
ligament
Transverse
Lateral costal facet
costotransverse
ligament
Ligamentum
flavum
Joint capsule
Costotransverse
Intervertebral ligament Lamina
disc
Rib Pedicle
Pedicle
Fig .43 .56 The ligamenta flava and costotransverse ligaments, ventral
Body of fifth
aspect . (With permission from Waschke J, Paulsen F (eds), Sobotta Atlas
lumbar vertebra
of Human Anatomy, 15th ed, Elsevier, Urban & Fischer . Copyright 2013 .)
Sacrum laminae in spinal flexion, preventing abrupt limitation, and also assist
restoration to an erect posture after flexion, perhaps protecting discs
from injury.
The morphology and histology of the ligamentum flavum have been
studied in the thoracolumbar region (Viejo-Fuertes et al 1998). On a
macroscopic level, it has two layers, superficial and deep, whose fibres
Fig .43 .55 The posterior longitudinal ligament in the lumbar region . (With
permission from Waschke J, Paulsen F (eds), Sobotta Atlas of Human run in opposite directions. The superficial layer is innervated by medial
Anatomy, 15th ed, Elsevier, Urban & Fischer . Copyright 2013 .) branches from the dorsal roots of the spinal nerves. The deep layer is
innervated by sinuvertebral nerves.
layers. The most superficial fibres are the longest and extend over three INTERSPINOUS LIGAMENTS
or four vertebrae, the intermediate extend between two or three, and
the deepest from one body to the next. Laterally, short fibres connect Interspinous ligaments (see Fig. 43.54B) connect the facing edges of
adjacent vertebrae. consecutive spinous processes, and extend ventrally as far as the liga-
mentum flavum and dorsally to the supraspinous ligament, when this
ligament is present (see below). They differ structurally at thoracic,
POSTERIOR LONGITUDINAL LIGAMENT lumbar and cervical levels. The thoracic interspinous ligaments are
narrow and elongated, whereas those at lumbar levels are thick and


The posterior longitudinal ligament (Fig. 43.55) lies on the posterior quadrilateral, and occur as closely applied pairs, the left and right liga-
surfaces of the vertebral bodies in the vertebral canal, attached between ments being separated by a narrow or potential cleft. In the lumbar
the body of C2 and the sacrum, and continuous with the membrana ligaments, collagen fibres run obliquely inferiorly and ventrally, and
tectoria above. Its smooth, glistening fibres, attached to intervertebral only the deepest fibres are truly ligamentous. The more dorsal fibres are
discs, hyaline cartilage end-plates and adjacent margins of vertebral derived from tendons of longissimus thoracis that dip into the inter-
bodies, are separated between attachments by basivertebral veins and spinous space to gain attachment to the superior edge of the spinous
the venous channels that drain them into anterior internal vertebral process rather than to its tip. Distinctive interspinous ligaments are not
plexuses. At cervical and upper thoracic levels the ligament is broad and evident at cervical levels, where they are represented by the median
of uniform width, but in lower thoracic and lumbar regions it is den- septum of the ligamentum nuchae as it passes between the cervical
ticulated, narrow over vertebral bodies and broad over discs. Its super- spinous processes.
ficial fibres bridge three or four vertebrae, while deeper fibres extend
between adjacent vertebrae as perivertebral ligaments, which are close
to and, in adults, fused with the anulus fibrosus of the intervertebral SUPRASPINOUS LIGAMENT
disc. The layers of the posterior longitudinal ligament and the relation-
ship of the ligament to associated membranes in the epidural space are The supraspinous ligament (see Fig. 43.54B) is a strong, fibrous cord
fully discussed by Loughenbury et al (2006). that connects the tips of spinous processes from C7 to L3 or L4. It is
regularly deficient. The most superficial fibres extend over three or four
vertebrae, the deeper span two or three, and the deepest connect adja-
LIGAMENTA FLAVA cent spines and are continuous with the interspinous ligament. Most


of the ligament is formed by the tendons of muscles with posterior
The ligamenta flava (see Fig. 43.54B; Fig. 43.56) connect laminae of midline attachments, i.e. semispinalis, longissimus, trapezius and latis-
adjacent vertebrae in the vertebral canal. Their attachments extend from simus dorsi. Only the most superficial fibres lack any connection with
facet joint capsules to the point where laminae fuse to form spines. muscle. Below L4, the ligament is replaced by the decussating fibres of
Here their posterior margins meet and are partially united; the intervals latissimus dorsi.
between them admit veins that connect the internal and posterior exter-
nal vertebral venous plexuses. Their predominant tissue is yellow elastic
tissue, whose almost perpendicular fibres descend from the lower ante- INTERTRANSVERSE LIGAMENTS
rior surface of one lamina to the posterior surface and upper margin of
the lamina below. The anterior surface of the ligaments is covered by a Intertransverse ligaments run between adjacent transverse processes. At
fine, continuous, smooth lining membrane (Newell 1999). The liga- cervical levels, they consist of a few, irregular fibres that are largely
ments are thin, broad and long in the cervical region, thicker in the replaced by intertransverse muscles; in the thoracic region, they are
thoracic and thickest at lumbar levels. They arrest separation of the cords intimately blended with adjacent muscles; and in the lumbar


Joints
733
34
RETPAHC
region, they are thin and membranous. For the detailed anatomy of the are absent at birth, do not contain synovium, and are probably clefts
lumbar intertransverse ligaments, see Bogduk (2005). in the intervertebral discs (Fig. 43.59).
LIGAMENTOUS INSTABILITY INTERVERTEBRAL JOINTS
Damage to the ligaments controlling stability of the column may occur Jointsbetweenthevertebralbodies
in the absence of evident bony pathology. This is particularly prevalent
in inflammatory disease of the upper cervical spine, where rheumatoid
Joints between vertebral bodies are symphyses. Typical vertebral bodies
arthritis may weaken or destroy the ligaments on which atlanto-axial
are united by anterior and posterior longitudinal ligaments and by
stability depends (Fig. 43.57). The transverse ligament is stronger than
fibrocartilaginous intervertebral discs between sheets of hyaline carti-
the dens, which therefore usually fractures before the ligament ruptures.
lage (vertebral end-plates).
The alar ligaments are weaker, and combined head flexion and rotation
may avulse one or both alar ligaments; rupture of one side results in
Articulatingsurfaces:intervertebraldiscsThe intervertebral
an increase of about one-third in the range of rotation to the opposite
discs are the chief bonds between the adjacent surfaces of vertebral
side. Pathological softening of the transverse and adjacent ligaments or
bodies from C2 to the sacrum. Except at the sites of the uncovertebral
of the lateral atlanto-axial joints results in atlanto-axial subluxation,
(neurocentral) joints of Luschka, disc outlines correspond with the
which may cause spinal cord injury. Ligamentous damage may also
adjacent bodies. Their thickness varies in different regions and within
occur in spinal injuries (Fig. 43.58), particularly at cervical levels.
individual discs. Each disc consists of an outer lamellated anulus fibro-
Developmental laxity of ligaments may also lead to problems with
sus and an inner nucleus pulposus (see Fig. 43.54A(1)).
instability, especially if there is an episode of trauma; this combination


In cervical and lumbar regions the discs are thicker anteriorly, con-
is probably responsible for atlanto-axial rotational instability. Laxity of
tributing to the anterior convexity of the vertebral column. In the tho-
cervical spinal ligaments may be a normal variant in children and lead
racic region they are nearly uniform, and the anterior concavity is
to diagnostic difficulties. In radiographs of the upper cervical spine in
largely due to the vertebral bodies. Discs are thinnest in the upper
children aged less than 8, a deceptive appearance of subluxation (‘pseu-
thoracic region and thickest in the lumbar region. They adhere to thin
dosubluxation’) may result from a combination of ligamentous laxity
layers of cartilage on the superior and inferior vertebral surfaces, the
and facet orientation. This usually occurs between C2 and C3 but may
vertebral end-plates. The latter do not reach the periphery of the verte-
occasionally be seen at C3/4. Clinical and other radiological features
bral bodies but are encircled by ring apophyses. The end-plates contain
should facilitate the correct diagnosis.
both hyaline cartilage and fibrocartilage. The fibrocartilaginous compo-
nent lies nearer to the disc and is sometimes considered not to be part
of the end-plate itself. The fibrocartilaginous components of the end-
JOINTS
plates above and below the nucleus pulposus, together with the inner-
most lamellae of the anulus fibrosus, form a flattened sphere of collagen
All vertebrae from C2 to S1 articulate by secondary cartilaginous joints that surrounds and encloses the nucleus (Fig. 43.60). The overall pro-
(symphyses) between their bodies, synovial joints between their articu- portion of fibrocartilage in the end-plate increases with age. While all
lar processes, and fibrous joints between their laminae, transverse and discs are attached to the anterior and posterior longitudinal ligaments,
spinous processes. In the cervical region, from C3 to C7, joints have discs in the thoracic region are additionally tied laterally, by intra-
been described between the uncinate or neurocentral processes of the articular ligaments, to the heads of ribs articulating with adjacent ver-


inferior vertebral body and the bevelled lateral border of the superior tebrae. Intervertebral discs form about one-quarter of the length of the
body at each level. These small uncovertebral or neurocentral ‘joints’ postaxial vertebral column; cervical and lumbar regions make a greater
contribution than the thoracic and are thus more pliant.
Fig .43 .59 A coronal
Anulus fibrosus The anulus fibrosus has a narrow outer collagenous
CT reconstruction: note
uncovertebral ‘joint’ zone and a wider inner fibrocartilaginous zone. Its lamellae, which are
(arrow) . convex peripherally when seen in vertical section, are incomplete
collars. The internal vertical concavity of the lamellae conforms to the
surface profile of the nucleus pulposus. In all quadrants of the anulus,
about half the lamellae are incomplete; the proportion increases in the
posterolateral region. The exact nature of the interlamellar substance
remains in some doubt. Posteriorly, lamellae join in a complex manner.
Fibres in the rest of each lamella are parallel and run obliquely between
vertebrae at about 65° to the vertical (see Fig. 43.54A(2)). Fibres in
successive lamellae cross each other obliquely in opposite directions,
thus limiting rotation. The obliquity of fibres in deeper zones varies in
different lamellae. Posterior fibres may sometimes be predominantly
vertical, which possibly predisposes them to herniation.
Vertebral end-plate
Anulus
fibrosus Nucleus pulposus
Ring apophysis
Fig .43 .60 The structure of the vertebral end-plate: the collagen fibres of
the inner two-thirds of the anulus fibrosus sweep around into the vertebral
end-plate and form its fibrocartilaginous component . The peripheral fibres
of the anulus are anchored into the bone of the ring apophysis . (With
permission from Bogduk N 1997 Clinical Anatomy of the Lumbar Spine
and Sacrum, 3rd ed . Edinburgh: Churchill Livingstone .)


34
RETPAHC
Back
11.42 mm
A
1.97 mm
A
B
Fig .43 .57 Atlanto-axial instability in the setting of rheumatoid arthritis .
Note the marked widening of the atlanto–dens interval seen on extension
radiographs (arrow) (A), when compared with flexion (B) .
B
Fig .43 .58 A, A sagittal CT reconstruction showing an osseous and
ligamentous injury at T10–11 sustained by a 54-year-old male after a
major compression injury . B, The MR image shows gross disruption of
the supraspinous and interspinous ligaments (arrow) .
733.e1


BACk
734
5
NOITCES
This standard description of the anulus may not apply at all spinal supplies both the disc at the level of its spinal nerve of origin and the
levels; a cadaveric study indicates that the anulus is usually incomplete disc one level above. The anterior part of the anulus is supplied by the
posteriorly in adult cervical discs (Mercer and Bogduk 1999) (see Fig. sympathetic (preganglionic, grey ramus communicans) rather than by
43.54A(3)). the mixed nerve. In damaged and degenerate discs, the nerves may
penetrate more centrally into the disc substance. The sinuvertebral
Nucleus pulposus The nucleus pulposus is better developed in cervical nerves are condensations within extensive nerve plexuses that lie on the
and lumbar regions and lies between the centre of the disc and posterior longitudinal ligament. Similar plexuses have been demon-
its posterior surface. At birth it is large, soft and gelatinous, and is com- strated anteriorly, covering the anterior longitudinal ligament, and later-
posed of mucoid material. It contains a few multinucleated notochordal ally in the fetus.
cells and is invaded by cells and collagen fibres from the inner zone of
the adjacent anulus fibrosus. Notochordal cells disappear in the first Relationsand‘atrisk’structuresPosterior, lateral and anterior
decade, and the mucoid material is gradually replaced by fibrocartilage, relations of the intervertebral disc are important in the planning of
derived mainly from the anulus fibrosus and the plates of hyaline car- interventional investigative and therapeutic procedures ranging from
tilage adjoining the vertebral bodies. The nucleus pulposus becomes discography to open disc surgery. The posterolateral surface of the disc
less differentiated from the remainder of the disc as age progresses, and forms the anterior boundary of the intervertebral foramen on each side,
gradually becomes less hydrated and increasingly fibrous. The type II and so is closely related to the spinal nerve and its accompanying
collagen of the nucleus becomes more like the type I of the anulus as vessels. More centrally, the disc is related posteriorly to the dura mater
its fibril diameter increases. The quantity of aggregated proteoglycans covering the spinal cord and the cauda equina. Anterior relations of the


in the nucleus decreases, while the keratan sulphate/chondroitin sul- discs vary considerably with vertebral level, but important ‘at risk’ struc-
phate ratio increases. As increased cross-linking occurs between colla- tures include the pharynx and oesophagus, the descending aorta and
gen and the proteoglycans, the discs lose their water-binding capacity the inferior vena cava. Laterally, relations change with level, but the
and become stiffer and more liable to injury. Contrary to what was parietal pleura in the thorax, and the sympathetic trunk and psoas
previously thought, it has now been shown that lumbar discs do not muscles in the lumbar region, are important examples.
decrease in overall height as a part of normal ageing. The anulus gradu-
ally loses height as its radial bulge increases, but the nucleus retains ProlapsedintervertebraldiscA prolapsed intervertebral disc
height and may increase in convexity as it increasingly indents the end- most commonly affects the 20–55-year age group and is most often
plate. Loss of trunk height with age results from a decrease in vertebral seen at the L4/5 and lumbosacral levels. It may also affect the cervical
body height (Bogduk 2005). When the disc is not loaded, pressure in discs, particularly at C5/6 and C6/7. The thoracic discs are rarely
the nucleus pulposus is low at all ages. affected. Acute tearing or chronic degeneration of the posterior lamellae
For a review of the structure and function of the human interverte- of the anulus fibrosus allows deformation and herniation of the disc
bral disc, see Adams and Dolan (2005). contents. The disc most often prolapses just lateral to the posterior
longitudinal ligament and can compress one or two spinal nerves uni-
LigamentsThe ligaments associated with the joints between the laterally (Fig. 43.62). Much less commonly, the prolapse is central, in
vertebral bodies are described on pages 731–733. the midline posteriorly. The compression of neural structures may then
be bilateral, affecting the cord itself or the whole cauda equina. If the


VascularsupplySmall offshoots of spinal branches of arteries sup- damaged anulus ruptures completely, some of the nuclear tissue may
plying the vertebral column form an anastomosis on the outer surface escape into the vertebral and ‘root’ canals. This sequestrated material
of the anulus fibrosus and supply its most peripheral fibres. Normal may migrate within the canals and cause nerve compression at spinal
discs are otherwise avascular and are dependent for their nutrition on levels distant from that of the disc rupture. The disc material itself may
diffusion from vertebral bone beneath adjacent end-plates and from the have an irritative effect on the spinal nerve.
peripheral anulus. Vascular and avascular parts differ in their reaction Regarding the anatomy of the vertebral canal and intervertebral
to injury. Venous drainage is via the external and internal vertebral foramen in relation to disc prolapse, it is important to understand that
venous plexuses to the intervertebral veins and thence to the larger one or both of two spinal nerves and their roots may be affected by a
named veins that drain the vertebral column. Lymphatic drainage of single prolapse, depending on the exact site of the prolapse in the hori-
the vertebral column is briefly considered above. Nothing specific is zontal plane. At the level of each disc and foramen, there are two spinal
known about the lymphatic drainage of the disc. nerves (and their roots) to consider: these are the exiting nerve and the
traversing nerve (Fig. 43.63) (MacNab and McCulloch 1990). The nerve
InnervationThe nerve supply of intervertebral discs has been studied usually affected at lumbar levels is the traversing nerve, which crosses
in detail in the lumbar region (Fig. 43.61). The outer third of the anulus the back of the disc on its way to become the exiting nerve at the level
is innervated by the sinuvertebral nerves; each sinuvertebral nerve below. Thus a lumbosacral (i.e. L5/S1) disc prolapse usually compresses
the S1 nerve. However, a prolapse may affect the exiting nerve at its own
level. This is especially likely if the prolapse is in the extraforaminal


zone of the ‘root’ canal, the so-called ‘far lateral’ prolapse. At cervical
Anterior longitudinal ligament
levels, because the roots and nerve leave the vertebral canal almost
horizontally, the prolapse usually affects the exiting nerve. This nerve
will still bear the number of the vertebra below the affected disc because
Grey ramus
cervical nerves exit the canal above the pedicle of their numerically
communicans
corresponding vertebra. Neurological presentation will include signs
and symptoms of spinal nerve damage at the affected level. Thus pain
Posterior longitudinal
and sensory loss will be dermatomal in distribution. Sensory changes
ligament
usually precede motor loss.
Sinuvertebral nerve
Internal disruption of a lumbar intervertebral disc is more common
than disc prolapse and is now an increasingly recognized cause of back
pain. Typically, the nucleus is decompressed and the inner lamellae of
the anulus appear to collapse into it.
For more detail on disc pathology and its consequences, see Adams
and Dolan (2005).
Facet(zygapophysial)joints
Joints between the vertebral articular processes (zygapophyses) are
synovial and have long been called zygapophysial joints by anatomists.
However, in current clinical practice they are commonly called ‘facet
Fig .43 .61 The nerve supply of a lumbar intervertebral disc . Branches of joints’. Detailed description of the anatomy of these joints is to be found
the grey rami communicantes and the sinuvertebral nerves are shown in Bogduk (2005), where the author explains why the term ‘facet joint’
entering the disc and the anterior and posterior longitudinal ligaments . is both incorrect and essentially ambiguous, on the grounds that facets
Branches from the sinuvertebral nerves also supply the ventral aspect of are not restricted to zygapophysial articular processes and occur, for
the dural sac and the dural nerve-root sleeve . example, in both costovertebral and costotransverse joints.


Joints
735
34
RETPAHC
Herniated disc material Compressed spinal nerve root Fig .43 .63 Exiting
and traversing nerve
roots . The upper
root (open arrow) is
the exiting root at
this level; the lower
(closed arrow) is the
traversing root here,
which becomes the
exiting root at the
level below . The
dotted roots are
traversing roots of
the lower segment .
A
The capsules are longer and looser in the cervical region. According to
Cauda equina in thecal sac Bogduk (2005), the anterior fibrous capsule is replaced entirely by the
ligamentum flavum in the lumbar spine.
Normal anulus fibrosus Cauda equina
Intracapsular structures Bogduk describes two types of intra-articular
structure in lumbar facet joints: namely, subcapsular fat and ‘meniscoid’
structures. The latter structures may be collagenous, fibroadipose or
purely adipose, and project into the crevices between non-congruent
articular surfaces. They resemble inclusions seen in the small joints of
the hand; their function is conjectural.
LigamentsLigaments that work in conjunction with, and modify the
function of, the facet joints throughout the vertebral column are
described on pages 731–733.
SynovialmembraneThe synovium is attached around the periph-
ery of the articular cartilages and lines the fibrous capsule. In the lumbar
region, it is reflected over the intracapsular structures described above.
VascularsupplyThe posterior spinal branches of the arteries that
supply the vertebral column form arterial anastomoses around the facet
joints. Venous drainage is via the external and internal posterior verte-
bral venous plexuses to the intervertebral veins and thence to the larger
named veins that drain the vertebral column. Lymphatic drainage
follows the principles described for the vertebral column.
Innervation The facet joints are profusely innervated by medial
branches of the dorsal primary rami of the spinal nerves, which give
articular branches to the joints above and below them.
Relationsand‘atrisk’structuresAnteriorly, the capsules of the
facet joints form the posterior boundaries of the intervertebral foramina.


Posteriorly and laterally, the joints are related to the deep muscles of
the back, some of whose fibres attach to the capsules. The joints also
lie in close relation to the medial branches of the dorsal rami of the
B
spinal nerves and to their accompanying arteries and veins. Damage to
the medial branches of the dorsal rami may denervate the deep back
Normal Herniated muscles. Access to the facet joints and their related nerves may be
nucleus pulposus nucleus pulposus required in the diagnosis and treatment of spinal pain.
Fig .43 .62 A left posterolateral disc extrusion . A, Axial view . B, Sagittal view .
LumbararticulartropismIn the lumbar region, asymmetrical
orientation of the facet joints occurs in about one-fifth of the popula-
ArticulatingsurfacesFacet joints are of the simple (cervical and tion. Such facet tropism does not appear to predispose to degenerative
thoracic) or complex (lumbar) synovial variety; the articulating surfaces disc disease.
are covered in hyaline cartilage and are carried on mutually adapted
articular processes. The size and shape of these processes vary with
spinal level and are described with the individual vertebrae. CRANIOVERTEBRAL JOINTS
FibrouscapsuleThe fibrous capsule is thin and loose and attached The articulation between the cranium and vertebral column is special-
peripherally to the articular facets of adjacent articular processes. ized to provide a wider range of movement than those that occur in the


BACk
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5
NOITCES
Anterior atlanto-occipital membrane Occipital bone, basilar part Posterior atlanto-occipital membrane Temporal bone, petrous part
Jugular foramen Foramen magnum, Internal acoustic meatus
posterior border
Occipital bone, basilar part
Membrana tectoria
Anterior atlanto-occipital
membrane
Apical ligament of dens
Superior longitudinal band
of cruciform ligament
Temporal Vertebral artery
bone, Atlas, anterior arch
Articular mastoid First cervical nerve Dens
capsule of Atlas, process Atlas, posterior arch Bursal space in fibrocartilage
atlanto-occipital transverse process
joint Transverse atlantal Remains of intervertebral disc
Anterior longitudinal ligament ligament
Articular capsule of at attachment to anterior
atlanto-axial joint tubercle of atlas Inferior longitudinal band Axis, body
of cruciform ligament
Anterior longitudinal Cleft between vertebral bodies Ligamentum flavum
ligament Posterior longitudinal
ligament
Anterior longitudinal
Fig .43 .64 The atlanto-occipital and atlanto-axial joints, anterior aspect . ligament
On each side a small cleft has been opened between the lateral part of
the upper surface of the body of the third cervical vertebra and the
bevelled, inferior surface of the body of the axis . Fig .43 .66 A median sagittal section through the occipital bone and first
to third cervical vertebrae .
External occipital protuberance
LigamentsThe ligaments are the anterior and posterior atlanto-
occipital membranes.
Anterior atlanto-occipital membrane The anterior atlanto-occipital
membrane (see Fig. 43.64; Fig. 43.66) is a broad, dense fibrous struc-
ture that connects the anterior margin of the foramen magnum to the
upper border of the anterior arch of the atlas. Laterally, it blends with
the joint capsule; medially, it is strengthened by a median cord, which
Occipital bone is the anterior longitudinal ligament stretching between the basilar
Posterior occipital bone and anterior atlantal tubercle.
Articular atlanto-occipital
capsule of left membrane
Posterior atlanto-occipital membrane The posterior atlanto-occipital
atlanto-


occipital joint membrane (see Figs 43.65–43.66) is broad but relatively thin, and
Arch which covers connects the posterior margin of the foramen magnum to the upper
Atlas, posterior arch vertebral artery, veins border of the posterior atlantal arch, blending laterally with the joint
and first cervical
spinal nerve capsules. It arches over the grooves for the vertebral arteries, venous
plexuses and first cervical nerve, and forms the ‘floor’ of the suboccipital
Ligamentum flavum Articular capsule of triangle. The ligamentous border of this arch is sometimes ossified. The
right atlanto-axial joint membrane is usually attached by a soft tissue ‘bridge’, which may
Axis, spine contain muscle or tendon fibres, to rectus capitis posterior minor, and
is firmly attached anteriorly to the spinal dura in the same area
(Zumpano et al 2006). The ligaments connecting the axis and the
Fig .43 .65 The atlanto-occipital and atlanto-axial joints, posterior aspect . occipital bone are functionally involved with the posterior atlanto-
occipital membrane.
SynovialmembraneThe synovial cavities of one or both joints may
rest of the axial skeleton. It consists of the occipital condyles, the atlas
communicate with that of the posterior component of the median
and the axis. It functions like a universal joint that permits horizontal
atlanto-axial joint.
and vertical scanning movements of the head, and is adapted for eye–
head coordination. VascularsupplyThe arterial supply of this region is derived from
an anastomosis between branches of the deep cervical, occipital and
Atlanto-occipitaljoints
vertebral arteries.
The atlas articulates with the occipital bone of the skull by a pair of InnervationThe joints are innervated by branches of the ventral
synovial joints. The bones are connected by articular capsules and by primary ramus of the first cervical spinal nerves.
the anterior and posterior atlanto-occipital membranes (Figs 43.64–
43.65). FactorsmaintainingstabilityFactors maintaining stability include
the fibrous capsules, the atlanto-occipital membranes, the shape of the


ArticulatingsurfacesEach joint consists of two reciprocally curved articular surfaces, the ligaments connecting the axis and the occipital
articular surfaces, one on the occipital condyle and the other on the bone, the ligamentum nuchae and the posterior neck muscles. The
lateral mass of the atlas. The atlantal facets are concave and tilted suboccipital muscles play an important proprioceptive and postural
medially. role.
FibrouscapsulesThe fibrous capsules surround the occipital con- MusclesproducingmovementsThe orientation and shape of
dyles and superior atlantal articular facets. They are thicker posteriorly the atlanto-occipital joints allow mainly for flexion–extension, which
and laterally, where the capsule is sometimes deficient, and may com- has a total range of about 15°. Axial rotation and lateral flexion have
municate with the joint cavity between the dens and the transverse not been measured in living subjects, but a few degrees of motion in
atlantal ligament. these directions can be produced by forceful movement in cadavers.


Joints
737
34
RETPAHC
The following muscles produce these movements: for flexion –
longus capitis and rectus capitis anterior; for extension – recti capitis
posteriores major and minor, obliquus capitis superior, semispinalis
capitis, splenius capitis and trapezius (cervical part); for lateral flexion Occipital
– rectus capitis lateralis, semispinalis capitis, splenius capitis, sternoclei- A bone, clivus
domastoid and trapezius (cervical part); and for rotation – obliquus Groove for
capitis superior, rectus capitis posterior minor, splenius capitis and sigmoid sinus Occipital
sternocleidomastoid. bone
Articular capsule
Relationsand‘atrisk’structuresPosteriorly, the joints are of atlanto-occipital joint
closely related to the vertebral arteries as they pass from the foramina
transversaria into the foramen magnum. The dorsal primary ramus of Atlas
the first cervical nerve and rectus capitis posterior major lie posterome-
dially and rectus capitis anterior lies anteriorly. Articular capsule of Membrana tectoria
lateral atlanto-axial joint
Atlanto-axialjoints Axis
The atlas articulates with the axis at three synovial joints. These are a Third cervical
pair between the lateral masses, and a median complex between the vertebra
B
dens of the axis and the anterior arch and transverse atlantal ligament.
Superior longitudinal band Occipital bone,
of cruciform ligament basilar part
ArticulatingsurfacesThe articular surfaces of the joints between
the lateral masses are often classified as planar. The bony articular sur- Hypoglossal Alar ligaments
canal
faces are more complex in shape and are usually reciprocally concave
Sigmoid sinus
in the coronal plane; the medial parts are somewhat convex in the sagit-
sulcus
tal plane (especially that of the axis). The cartilaginous articular surfaces
are usually less concave. The median joint is a pivot between the dens Atlanto-occipital
Articular capsule
and a ring formed by the anterior arch and transverse atlantal ligament. joint


A vertically ovoid facet on the anterior dens articulates with a facet on
the posterior aspect of the anterior atlantal arch.
Transverse atlantal Atlas, posterior
ligament arch
FibrouscapsulesThe fibrous capsules for the lateral joints are
Lateral atlanto-axial
attached to the articular margins and are thin and loose. Each has a Inferior longitudinal
joint
posteromedial accessory ligament attached below to the axial body near band of cruciform
the base of its dens, and above to the lateral atlantal mass near the ligament Axis
transverse ligament. The fibrous capsule for the median joint is also
C
relatively weak and loose, especially superiorly.
Occipital bone Alar ligaments
LigamentsAnteriorly, the vertebral bodies are connected by the ante-
rior longitudinal ligament (see Figs 43.64, 43.66): here, a strong, thick-
Apical ligament
ened band attaches above to the lower border of the anterior tubercle of dens
of the anterior arch of the atlas and below to the front of the axial body.
Posteriorly, the vertebral arches are joined by the ligamenta flava (see
Figs 43.65–43.66), which are attached to the lower border of the atlan-
tal arch above and to the upper borders of the axial laminae. At this
level, these ligaments form a thin membrane, pierced laterally by the Articular capsules
second cervical nerves.
Dens
Transverse atlantal and cruciform ligaments The transverse atlantal Axis, body
ligament (Fig. 43.67; see Fig. 43.33) is a broad, strong band that arches
across the atlantal ring behind the dens; its length varies about a mean
of 20 mm. It is attached laterally to a small but prominent tubercle on
the medial side of each atlantal lateral mass, and broadens medially
where it is covered anteriorly by a thin layer of articular cartilage. It
consists almost entirely of collagen fibres, which, in the central part of Fig .43 .67 The posterior aspect of the atlanto-occipital and atlanto-axial
the ligament, cross one another at an angle to form an interlacing mesh. joints . The posterior part of the occipital bone and the laminae of the


From its upper margin a strong median longitudinal band arises that cervical vertebrae have been removed and the atlanto-occipital joint
inserts into the basilar part of the occipital bone between the apical cavities opened . (Adapted with permission from Waschke J, Paulsen F
ligament of the dens and membrana tectoria, and from its inferior (eds), Sobotta Atlas of Human Anatomy, 15th ed, Elsevier, Urban &
surface a weaker and less consistent longitudinal band passes to the Fischer . Copyright 2013 .)
posterior surface of the axis. These transverse and longitudinal compo-
nents together constitute the cruciform ligament. The transverse liga-
ment divides the ring of the atlas into unequal parts (see Figs the cranial dura mater. The deep lamina consists of a strong median
43.32–43.33). The posterior two-thirds surrounds the spinal cord and band that ascends to the foramen magnum, and two lateral bands that
meninges, and the anterior third contains the dens, which the transverse pass to, and blend with, the capsules of the atlanto-occipital joints as
ligament retains in position even when all other ligaments are divided. they reach the foramen magnum. The membrane is separated from the
cruciform ligament of the atlas by a thin layer of loose areolar tissue,
Ligaments connecting axis and occipital bone Ligaments connecting and sometimes by a bursa.
the axis and the occipital bone consist of the membrana tectoria, the
paired alar ligaments, the median apical ligament, and the longitudinal Alar ligaments The alar ligaments are thick cords, about 11 mm long,
components of the cruciform ligament (see Figs 43.66–43.67). which pass horizontally and laterally from the longitudinally ovoid
flattenings on the posterolateral aspect of the apex of the dens to the
Membrana tectoria Inside the vertebral canal, the membrana tectoria roughened areas on the medial side of the occipital condyles. In most
is a broad strong band representing the upward continuation of the individuals there is also an anteroinferior band, approximately 3 mm
posterior longitudinal ligament. Its superficial and deep laminae are long, which inserts into the lateral mass of the atlas in front of the


both attached to the posterior surface of the axial body. The superficial transverse ligament. Fibres occasionally pass from the dens to the ante-
lamina expands as it ascends to the upper surface of the basilar occipital rior arch of the atlas. In addition, in some 10% of cases a continuous
bone, and attaches above the foramen magnum, where it blends with transverse band of fibres, the transverse occipital ligament, passes


BACk
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5
NOITCES
between the occipital condyles immediately above the transverse liga-
ment. The ligaments consist mainly of collagen fibres arranged in paral-
Iliolumbar
lel. The main function of the alar ligaments is now considered to be
ligament
limitation of atlanto-axial rotation, the left becoming taut on rotation
to the right and vice versa. The slightly downward movement of the
atlas during rotation helps permit a wider range of movement by reduc-
ing tension in the alar ligaments, and in the capsules and accessory
ligaments of the lateral atlanto-occipital joint.
Apical ligament of the dens The apical ligament of the dens fans out
from the apex of the dens into the anterior margin of the foramen Short posterior
sacroiliac
magnum between the alar ligaments, and represents the cranial con-
ligaments
tinuation of the notochord and its sheath. It is separated for most of
its extent from the anterior atlanto-occipital membrane and cruciform
Greater sciatic
ligament by pads of fatty tissue, though it blends with their attachments foramen Sacrotuberous
at the foramen magnum, and with the alar ligaments at the apex of the ligament
dens.
The ligamentum nuchae and the anterior longitudinal ligament also Sacrospinous Long posterior
connect cervical vertebrae with the cranium. ligament sacroiliac
ligament
SynovialmembraneThe synovial membranes of the lateral joints
Lesser sciatic
have no special features. The median joint has two synovial cavities that foramen Superficial fibres
sometimes communicate. The synovial cavity of the posterior compo- of posterior
nent of the median joint complex is larger, lying between the horizon- Sacrotuberous sacrococcygeal
tally orientated ovoid facet, on the posterior surface of the dens and the ligament ligament
cartilaginous anterior surface of the transverse ligament; communica- Sacrotuberous
tion often exists with one or both of the atlanto-occipital joint ligament,
cavities. helical margin
Falciform
VascularsupplyThe arterial supply of this region is derived from process


an anastomosis between branches of the deep cervical, occipital and Fig .43 .68 Joints and ligaments on the posterior aspect of the left half of
vertebral arteries. the pelvis and the fifth lumbar vertebra .
InnervationThe joints are innervated by branches of the ventral
primary ramus of the second cervical spinal nerve.
FactorsmaintainingstabilityThe most important factors main- ArticulatingsurfacesThe reciprocally curved surfaces of the facet
taining stability are the ligaments, of which the transverse atlantal liga- joints show considerable individual variation in alignment and shape.
ment is the strongest (see Fig. 43.33). The alar ligaments are weaker. Asymmetry (facet tropism) is not unusual.
Other ligaments connecting the axis and the occipital bone, the fibrous
capsules, the ligamentum nuchae and the posterior neck muscles also LigamentsThe major ligament associated with the lumbosacral junc-
contribute to stability; the suboccipital muscles play an important pro- tion is the iliolumbar ligament (see Fig. 80.9A; Fig. 43.68).
prioceptive and postural role.
Iliolumbar ligament The iliolumbar ligament is attached to the tip
MusclesproducingmovementsMovement is simultaneous at and anteroinferior aspect of the fifth lumbar transverse process, and
all three joints and consists almost exclusively of rotation around the sometimes has a weak attachment to the fourth transverse process. It
axis. The shape of the articular surfaces is such that, when rotation radiates laterally and is attached to the pelvis by two main bands. A
occurs, the axis ascends slightly into the atlantal ring, limiting stretch lower band passes from the inferior aspect of the fifth lumbar transverse
on the lateral atlanto-axial joint capsules. Rotation is limited mainly by process and the body of the fifth lumbar vertebra across the anterior
the alar ligaments, with a minor contribution from the accessory sacroiliac ligament to reach the posterior margin of the iliac fossa. An
atlanto-axial ligament. The normal range of atlanto-axial rotation is upper band, part of the attachment of quadratus lumborum, passes to


about 40°. the iliac crest anterior to the sacroiliac joint, and is continuous above
The muscles that produce atlanto-axial rotation act on the cranium, with the anterior layer of the thoracolumbar fascia. The lower ligament
transverse processes of the atlas and spinous process of the axis. They has a more vertical component that reaches the posterior iliopectineal
are mainly obliquus capitis inferior, rectus capitis posterior major and line; this component is a lateral relation of the L5 ventral ramus. A
splenius capitis of one side, and the contralateral sternocleidomastoid. posterior component of the iliolumbar ligament passes behind quad-
ratus lumborum to attach to the ilium.
Relationsand‘atrisk’structuresThe most important ‘at risk’ In neonates and children, the iliolumbar ‘ligament’ is muscular; the
relation is the spinal cord, lying posterior to the median atlanto-axial muscle is gradually replaced by ligament up to the fifth decade of life.
joint. Anteriorly, the atlanto-axial articulations, capsules and ligaments
are separated from the buccopharyngeal fascia and superior constrictor VascularsupplyThe vascular supply of the lumbosacral junction is
by longus capitis and longus colli, the prevertebral fascia and the retro- derived mainly from the iliolumbar and superior lateral sacral
pharyngeal (potential) space. arteries.
Variantsofcraniovertebraljoints InnervationThe lumbosacral junction is innervated by branches
derived from the fourth and fifth lumbar spinal nerves.
Anomalies of the craniovertebral joints are sometimes seen. Many are Relationsand‘atrisk’structuresThe lumbosacral disc is related
minor segmentation anomalies and may be incidental radiological or
anteriorly to the common iliac veins, the median sacral vessels, and the
osteological findings. More severe anomalies may lead to craniocervical
superior hypogastric plexus of nerves. The sympathetic trunks cross it
instability (Piper and Traynelis 1998).
anterolaterally, while the obturator nerves and lumbosacral trunks pass


close laterally. The relations of the lumbosacral facet joints are similar
LUMBOSACRAL JUNCTION to those of the lumbar facet joints (see above).
Articulations between the fifth lumbar and first sacral vertebrae resem- SACROCOCCYGEAL JUNCTION
ble those between other vertebrae. The bodies are united by a symphysis
that includes a large intervertebral disc. The latter is deeper anteriorly The sacrococcygeal joint is usually a symphysis between the sacral apex
at the lumbosacral angle. The synovial facet joints are separated by a and coccygeal base, united by a thin fibrocartilaginous disc that is
wider interval than those above. somewhat thicker in front and behind than laterally. Its surfaces carry


Muscles
739
34
RETPAHC
hyaline cartilage that varies from thin veils to small islands. Occasion- Semispinalis capitis
ally, the coccyx is more mobile and the joint is synovial. Sternocleidomastoid Splenius capitis
LigamentsThe anterior sacrococcygeal ligament consists of irregular Rhomboid minor
fibres that descend on the pelvic surfaces of both sacrum and coccyx,
Rhomboid major
and is attached in the same way as the anterior longitudinal ligament.
The flat superior posterior sacrococcygeal ligament passes from the Trapezius Levator scapulae
margin of the sacral hiatus to the dorsal coccygeal surface, roofing the Supraspinatus
Deltoid
lower sacral canal (see Fig. 43.68). The deep posterior sacrococcygeal Infraspinatus
ligament passes from the back of the fifth sacral vertebral body to the
dorsum of the coccyx and corresponds to the posterior longitudinal
ligament. On each side, the lateral sacrococcygeal ligaments connect the
coccygeal transverse processes to the inferolateral sacral angles, com-
pleting foramina for the fifth sacral spinal nerves. Similarly, the inter-
cornual ligaments connect the sacral and coccygeal cornua, and a
fasciculus connects the sacral cornua to the coccygeal transverse
processes.
VascularsupplyThe arterial supply of the sacrococcygeal junction
is derived from the inferior lateral sacral and median sacral arteries.
InnervationThe innervation of the sacrococcygeal junction is derived Teres minor
Triangle of
from the lower two sacral and the coccygeal nerves. auscultation Teres major
Latissimus dorsi Serratus
INTERCOCCYGEAL JOINTS anterior
Thoracolumbar
fascia Serratus posterior
In the young the intercoccygeal joints are symphyses, with thin discs of inferior
fibrocartilage between coccygeal segments. Segments are also connected External oblique Erector spinae
by extensions of the anterior and posterior sacrococcygeal ligaments. In Internal oblique


adult males all segments unite comparatively early, but in females forming floor of Internal oblique
union is later. In advanced age the sacrococcygeal joint becomes obliter- lumbar triangle
ated. Occasionally, the joint between the first and second segments is Fascia covering
synovial. The apex of the terminal segment is connected to overlying gluteus medius
skin by white fibrous tissue.
Fascia covering
Gluteus
MUSCLES gluteus maximus maximus
The musculature of the back is arranged in a series of layers, of which
only the deeper are true, intrinsic, back muscles (Fig. 43.69). The true
back muscles are characterized by their position and by their innerva-
tion by branches of the posterior (dorsal) rami of the spinal nerves. The
true back muscles below the neck lie deep to the posterior layer of
Fig .43 .69 Superficial muscles of the back of the neck and trunk . On the
the thoracolumbar fascia. In the lumbar region, where the layers of the left only the skin, superficial and deep fasciae (other than gluteofemoral)
thoracolumbar fascia are well defined, they occupy the compartment have been removed; on the right, sternocleidomastoid, trapezius,
between its posterior and middle layers. latissimus dorsi, deltoid and external oblique have been dissected away .
Lying superficial to the true, intrinsic muscles are the extrinsic,
‘immigrant’ muscles (see Fig. 43.69). The most superficial of these run
between the upper limb and the axial skeleton, and consist of trapezius, able to argue that this view may also be applied to the cervical and
latissimus dorsi, levator scapulae and the rhomboid muscles. Beneath thoracic muscles, and so for uniformity in this section, all muscles have
this layer lie the serratus posterior group, superior and inferior, which been described in this way.
are variably developed but usually thin muscles whose function may
Ligamentum nuchae
be respiratory or possibly proprioceptive. All the extrinsic muscles are
innervated by ventral rami. The ligamentum nuchae is not a ligament of the neck, for it does not


Trapezius, levator scapulae, rhomboid major, rhomboid minor and connect adjacent bones and lacks the internal structure typical of a liga-
latissimus dorsi are described on pages 816, 818 and 821 respectively, ment. It is a unique arrangement of tendons and fascia between the
serratus posterior superior and inferior are described on pages 941, 942. posterior muscles of the neck. It consists of a dorsal raphe and a median
The muscles of the posterior abdominal wall are described on page septal portion. The dorsal raphe lies superficially along the posterior
1085. midline of the neck. It is attached to the external occipital protruberance
The intrinsic muscles are also arranged in layers. The more superficial superiorly, and the tip of the C7 spinous process inferiorly. In its supe-
layers contain the splenius muscles in the neck and upper thorax, and rior half it consists of the aggregated tendons of the most medial fibres
the erector spinae group in the trunk as a whole. The deeper layers in- of the cervical portion of trapezius. Because of their longitudinal
clude the spinotransverse group, which is itself layered into semispina- arrangement, these tendons have been described as forming the funicu-
lis, multifidus and the rotatores, and the suboccipital muscles. Deepest lar portion of the ligamentum nuchae (Mercer and Bogduk 2003). In
of all lie the interspinal and intertransverse muscles. The latter group its inferior half, the funicular portion is joined by the obliquely orien-
constitute a mixture of dorsal and ventral spinal muscles. The lumbar tated tendons of splenius capitis and rhomboid minor. Across the
intertransversarii mediales, thoracic intertransversarii and medial parts midline the tendons of splenius capitis are continuous with those of
of cervical posterior intertransversarii are innervated by dorsal rami, but rhomboid minor on the other side, and they interweave with the
the others are supplied by ventral rami (Commentary 5.1). tendons of the reciprocal sets of muscles to produce the raphenous
structure of the ligamentum nuchae. From the ventral surface of the
Muscle attachments and fibre direction


dorsal raphe, a median fascial septum extends deeply towards the ver-
Although developmentally the muscles of the back extend caudally as tebral column and separates semispinalis capitis from its opposite
the vertebral column elongates, drawing their nerve supply with them, partner. A lateral expansion of the septum extends laterally ventral to
they have traditionally been described as if their fibres ran caudocrani- semispinalis capitis, separating it from multifidus and semispinalis cer-
ally, so that the ‘origins’ of the muscles lay distal to their ‘insertions’. vicis. The median continuation of the septum reaches the tips of the
It has been shown that in the lumbar spine it is more appropriate cervical spinous processes, and extends into the cervical interspinous
morphologically and biomechanically to view the muscles in the spaces as far as the ligamentum flavum. At upper cervical levels, the
reverse direction – from above downwards (Bogduk 2005). It is reason- septum is attached to the external occipital crest and the posterior


BACk
740
5
NOITCES
Semispinalis capitis
Semispinalis
Sternocleidomastoid Longissimus capitis
(cut) capitis Longissimus
capitis
Splenius capitis
Longissimus
cervicis
Levator scapulae
Longissimus
Iliocostalis
cervicis
cervicis
Splenius cervicis
Iliocostalis Iliocostalis
thoracis
Iliocostalis
Longissimus
thoracis
Longissimus
Spinalis
thoracis
Spinalis
thoracis Spinalis
Fig .43 .70 Splenius cervicis and splenius capitis . thoracis
Longissimus
tubercle of the atlas, and it blends with the posterior atlanto-occipital thoracis
and posterior atlanto-axial membranes. Passing through these mem-
branes, it is attached to the posterior surface of the dura mater (Dean
and Mitchell 2002). Only the dorsal raphe affords attachment to
muscles; no muscles arise from the median septum.
Splenius capitis Iliocostalis
AttachmentsSplenius capitis arises from the mastoid process and Iliocostalis lumborum
lumborum
the rough surface on the occipital bone just below the lateral third of
the superior nuchal line. Its fibres pass downwards and medially to
reach the midline. The lower fibres insert into the tips of the spinous Erector spinae
processes of the seventh cervical and upper three or four thoracic ver- aponeurosis
tebrae and the intervening supraspinous ligaments. The tendons of the
upper fibres interlace in the midline with those of the opposite side in
the dorsal raphe of the ligamentum nuchae in the lower half of the
cervical region (Fig. 43.70).
RelationsSplenius capitis lies deep to trapezius and covers semispi-
nalis capitis and longissimus capitis. The upper part of the muscle lies
beneath sternocleidomastoid. Between sternocleidomastoid and trape-
zius it forms part of the floor of the posterior triangle of the neck, above
and behind levator scapulae.


VascularsupplySee below.
Fig .43 .71 The erector spinae muscle group .
InnervationSplenius capitis is innervated by lateral branches of the
second and third cervical dorsal rami.
VariationsThe splenii may be absent or vary in their vertebral attach-
ActionsActing unilaterally, and synergistically with the contralateral ments. Accessory slips also occur.
sternocleidomastoid, splenius capitis rotates the head to the same side.
Erector spinae
Acting bilaterally, splenius capitis extends the head.
Erector spinae (see Figs 43.6; Figs 43.71–43.72) is a large musculotendi-
Splenius cervicis
nous mass that differs in size and composition at different vertebral
AttachmentsSplenius cervicis is confluent with splenius capitis, but levels. It consists of fascicles that assume systematic attachments to
covers more caudal regions of the neck and thoracic region (see Fig. homologous parts of the skull, the cervical, thoracic and lumbar verte-
43.70). It arises from the transverse process of the atlas, the tip of the brae, the sacrum and the ilium. Individual muscles are defined by the
transverse process of the axis and the posterior tubercle of the third attachments of their fascicles and the regions that they span. There are
cervical vertebra. Its fibres pass downwards and medially, wrapping three muscles, each with three regional parts (Table 43.1).
around the other posterior intrinsic neck muscles, to insert into the
third to sixth thoracic spinous processes. SpinalisSpinalis thoracis is the most medial portion of erector spinae
in the thoracic region. It consists of fascicles that arise from the spinous
RelationsSplenius cervicis lies deep to serratus posterior superior, the processes of the upper thoracic vertebra and insert into the spinous
rhomboids and trapezius. It covers the upper parts of the erector spinae processes of the eleventh and twelfth thoracic and first two lumbar
and the lower semispinalis muscles. vertebrae. The number of fascicles and their segmental attachments
vary. The fascicles are arranged in an overlapping series of increasingly


VascularsupplySee below. longer, flat arcs. The shortest fascicles have the lowest origin and highest
insertion, and the longest fascicles have the highest origin and lowest
InnervationSplenius cervicis is innervated by lateral branches of the insertion. Laterally, the muscle blends intimately with longissimus tho-
lower cervical dorsal rami. racis and is considered by some to be a component of that muscle.
Spinalis is irregularly and poorly developed in other regions. When
ActionsActing unilaterally, splenius cervicis rotates the upper cervical present, spinalis cervicis consists of paramedian fibres that arise vari-
vertebra, in the same way that the splenius capitis rotates the head. ously from the spinous processes of the axis and the third and fourth
Acting bilaterally, splenius cervicis extends the upper cervical spine. cervical vertebrae, and insert into the lower part of the ligamentum


34
RETPAHC
Back
Psoas major
Erector spinae Thecal sac Left L4/5 Left L4
facet joint nerve root
Fig .43 .72 An axial MRI of the lumbar spine at the level of the L4/5
intervertebral disc .
740.e1


Muscles
741
34
RETPAHC
Table 43.1 Components of erector spinae and their regional parts cular aponeurosis, the lumbar fibres of longissimus, from L1 to L5,
complete the systematic progression of attachments exhibited by the
Spinalis Longissimus Iliocostalis
thoracic fibres.
Spinalis thoracis Longissimus capitis Iliocostalis cervicis
Spinalis cervicis Longissimus cervicis Iliocostalis thoracis IliocostalisIliocostalis is the most lateral component of the erector
Spinalis capitis Longissimus thoracis Iliocostalis lumborum spinae. Its fascicles are attached to sites that are homologous with the
ribs.
Iliocostalis cervicis consists of slender fascicles that arise by long
tendons from the posterior tubercles of the fourth, fifth and sixth cervi-
nuchae and the spine of the seventh cervical vertebra (sometimes also cal vertebrae. They descend over the posterior thorax to insert into the
to the first and second thoracic vertebrae). Spinalis capitis is represented third to sixth ribs at their angles.
by occasional fibres of semispinalis capitis that insert into the spines of Iliocostalis thoracis is a narrow, fusiform muscle. The fibres arise
the seventh cervical and first thoracic vertebrae instead of reaching the from the back of the transverse process of the seventh cervical vertebra
thoracic transverse processes. and the superior borders of the angles of the upper six ribs; they lie
lateral to iliocostalis cervicis, and insert into the upper borders of the
LongissimusLongissimus is the central component of erector spinae. angles of the lower six ribs.
It assumes a series of attachments at sites that are homologous to the Iliocostalis lumborum consists of lumbar and thoracic parts. The
junction of the transverse and costal elements of the segment. These lumbar part is formed by fleshy fascicles that arise from the tips of
sites are represented at thoracic levels by the tip of a transverse process the first four lumbar transverse processes and the posterior surface of
and the immediately adjacent posterior surface of the rib; at cervical the middle layer of thoracolumbar fascia lateral to these tips. These


levels by the transverse process and posterior tubercle; and at lumbar fascicles descend to the ilium in a laminated fashion, such that those
levels by the accessory process (the transverse element) and medial half from higher levels cover those from lower levels. They insert into the
of the transverse process (the costal element). medial end of the iliac crest and the dorsal segment of the iliac crest,
Longissimus capitis is a narrow flat band of muscle that arises from with the fascicle from L4 assuming the most ventral and lateral attach-
the posterior edge of the mastoid process, under cover of splenius ment, and the fascicle from L1 assuming the most dorsal and medial
capitis and sternocleidomastoid. It descends across the lateral surface attachment. The attachment to the ilium is largely by fleshy fibres but
of semispinalis capitis and inserts by a series of tendons into the trans- the more superficial fibres are aponeurotic. The thoracic part consists
verse processes of the lower three or four cervical and upper four or so of eight or nine small fascicles that respectively arise from the lower
thoracic vertebrae. eight or nine ribs at their angles, lateral to the iliocostalis thoracis. Each
Longissimus cervicis is a long thin muscle that arises by tendons fascicle arises from its rib by a ribbon-like tendon. The tendons are
from the posterior tubercles of the transverse processes of the second longer at high levels but become progressively shorter at lower levels.
to sixth cervical vertebra. It descends into the thoracic region, between The muscle bellies of the fascicles are uniform in length, and each gives
the tendons of longissimus capitis and longissimus thoracis, to insert rise to a caudal tendon. These tendons are aggregated to form a dorsal
by tendons into the transverse processes of the upper four or five tho- aponeurosis that covers the lumbar part of iliocostalis lumborum and
racic vertebrae. inserts in a linear fashion into the medial end of the iliac crest and its
Longissimus thoracis is the largest component of erector spinae. It dorsal segment. Along this line the fascicles are represented serially,
consists of many small fascicles that are aggregated in a particular such that the fascicle from the twelfth rib attaches most laterally and


manner to produce a very long, and in some places thick, muscle. It has that from the fourth or fifth rib attaches most medial and inferiorly.
lumbar and thoracic parts.
The lumbar part is formed by fleshy bundles that arise from the ErectorspinaeaponeurosisTogether, the dorsal aponeuroses of
accessory process and the medial half or so of the posterior surface of the thoracic fibres of longissimus and the thoracic fibres of iliocostalis
the transverse process of each of the five lumbar vertebrae. The fascicles lumborum form a wide sheet of parallel tendons known as the erector
pass inferiorly and slightly laterally. Those from the first four lumbar spinae aponeurosis. It is attached to the lumbar spinous processes and
vertebrae converge on to a common flat tendon that covers the lateral supraspinous ligaments, the median sacral crest, the third sacral
surface of the muscle and separates it from the lumbar fibres of iliocos- segment, the dorsal segment of the iliac crest and the medial end of the
talis, for which reason it is called the lumbar intermuscular aponeuro- iliac crest, and covers multifidus and the lumbar fibres of both longis-
sis. The aponeurosis commences in the mid-lumbar region, with a simus and iliocostalis. Significantly, the erector spinae aponeurosis is
broad irregular base, and inferiorly it tapers to a truncated point that formed exclusively by the tendons of the thoracic fibres of longissimus
inserts into the medial surface of the ilium just dorsal to the ala of the thoracis and iliocostalis lumborum; it does not give rise to the lumbar
sacrum. The fascicle from the first lumbar vertebra attaches rostrally and fibres of these muscles, which are attached independently to the ilium.
dorsally to the aponeurosis. Successive fascicles attach to it more ven- Some of the more superficial fibres of multifidus may insert into the
trally and caudally. The fascicle from the fifth lumbar vertebra inserts deep surface of the erector aponeurosis over the sacrum, but otherwise


separately, deep to the intermuscular aponeurosis, into the ventrome- the substantive insertion of multifidus is into the sacrum. A portion of
dial aspect of the ilium and the upper fibres of the dorsal sacroiliac liga- the uppermost fibres of gluteus maximus arise from the dorsal surface
ment. Medially, the lumbar fibres of longissimus are separated from the of the inferolateral corner of the erector spinae aponeurosis. The lumbar
multifidus by a wide cleavage plane filled with fat and veins. intermuscular aponeurosis is a ventral extension of the erector spinae
The thoracic part consists of fascicles with small, fusiform muscle aponeurosis, separating the lumbar fibres of longissimus from those of
bellies that have short rostral tendons and long caudal tendons. The iliocostalis.
muscle bellies are arranged in a tiered fashion across the length of the
posterior thoracic wall, with the highest lying medially and the lowest RelationsErector spinae is covered in the lumbar and thoracic regions
lying laterally. The upper four fascicles arise from the tips of the first by the thoracolumbar fascia, and by serratus posterior inferior below
four thoracic transverse processes. The succeeding fascicles have bifid and the rhomboids and splenii above. In the lumbar region, it lies in
tendons that arise from the transverse process and the adjacent rib at the compartment between the posterior and middle layers of the tho-
each of the lower eight thoracic segments. The long caudal tendons of racolumbar fascia.
the thoracic fascicles of longissimus are aggregated in parallel to form
a wide aponeurosis, which allows them to assume a variety of caudal VascularsupplySee below.
insertions. The tendons of the uppermost fascicles insert into the
lumbar spinous processes and their supraspinous ligament. Those from InnervationErector spinae is innervated by the lateral branches of the
the first thoracic segment reach the L1–2 level, and those from the sixth dorsal rami of the cervical, thoracic and lumbar spinal nerves. At lumbar


thoracic segment reach the L5 level. The fascicles from the seventh to levels, lateral branches innervate iliocostalis and intermediate branches
ninth thoracic segments reach the median sacral crest, and those from innervate longissimus.
the tenth and eleventh thoracic segments attach transversely across the
posterior surface of the third segment of the sacrum. The fascicle from ActionsThe thoracic and lumbar components of erector spinae are
the twelfth thoracic segment reaches the sacrum and dorsal segment of powerful extensors of the vertebral column. Acting concentrically and
the iliac crest just below where the intermuscular aponeurosis of the bilaterally they can extend the thoracic and lumbar spines whereas
lumbar fibres of longissimus inserts into the ilium. The aponeurosis acting unilaterally they can laterally flex the trunk. However, more com-
covers the multifidus and the lumbar fibres of longissimus; it extends monly, erectores spinae act eccentrically.
from the midline as far laterally as the dorsal edge of the lumbar inter- From the upright posture, the trunk can flex forwards under the
muscular aponeurosis, with which it fuses. Within the lumbar intermus- influence of gravity. This movement is initiated by flexor muscles, such


BACk
742
5
NOITCES
as rectus abdominis, in order to bring the centre of gravity of the trunk border and lateral surface of the lamina above to the upper, posterior
forwards. Thereafter, erectores spinae control the descent of the thorax part of the transverse process of the vertebra immediately below; a
under gravity. When the trunk is fully flexed, many parts of erector rotator longus connects the base of the spinous process above to the
spinae cease to contract and become electromyographically silent. In transverse process two levels below. Rotatores are not obviously present
this position, flexion is limited by passive tension in the back muscles, at lumbar and cervical levels, where they may be represented by some
and tension in the thoracolumbar fascia, the posterior spinal ligaments of the deeper fascicles of multifidus.
and the intervertebral discs. Similarly, lateral flexion under gravity is
controlled by the contralateral erector spinae, with input from the MultifidusAt cervical, thoracic and upper lumbar levels, multifidus
abdominal oblique muscles. lies lateral to the spinous processes and covers the laminae of the
The function of the cervical and capital components of erector underlying vertebrae, but at lumbosacral levels it expands to cover the
spinae has not been determined. These are small muscles with very little posterior surface of the sacrum (Fig. 43.74). At each segmental level,
force capacity, and are poorly orientated to exercise extension or to multifidus is formed by several fascicles that arise from the caudal edge
control flexion of the head or cervical spine. As putative extensors they of the lateral surface of the spinous process and from the caudal end
are dwarfed by semispinalis and splenius. Axial rotation of the head of its tip. They radiate caudally to insert into the transverse elements of
draws longissimus capitis around the perimeter of the cervical spine, vertebrae two, three, four and five levels below (Macintosh et al 1986).
orientating it perhaps so that it is able to restore the head to neutral These sites are represented at cervical levels by the superior articular
from the rotated position. processes, at thoracic levels by the posterior surface of each transverse


process near its base, and at lumbar levels by the mammillary processes.
Spinotransverse group
Fascicles that extend beyond the fifth lumbar vertebra insert into the
The spinotransverse muscle group consists of muscles where the fasci- dorsal surface of the sacrum. The longest fascicles from the first and
cles span between a spinous process and the transverse elements of
vertebrae at various levels below. The muscles are grouped according to
the length of their fascicles and the region that they cover (Table 43.2).
Rotatores have the deepest and shortest fascicles, and span one and
two segments, whereas the fascicles of multifidus span two, three, four
or five segments, and those of semispinalis span about six segments.
RotatoresRotatores thoracis (Fig. 43.73) consist of eleven pairs of
small quadrilateral muscles. The first pair lies between the first and Rotator brevis
second thoracic vertebrae, and the last between the eleventh and twelfth
thoracic vertebrae. One or more may be absent from the upper or lower
ends of the series. In each segment, a rotator brevis connects the lower
Rotator longus
Table 43.2 Components of the spinotransverse group
Rotatores Multifidus Semispinalis
Rotatores thoracis Multifidus Semispinalis cervicis
Rotatores cervicis Semispinalis thoracis
Fig .43 .73 Rotatores (thoracic region) . (With permission from Benninghoff,
Rotatores capitis Semispinalis capitis
Anatomie, 15th edition © Urban and Schwarzenberg, 1994 .)
A B Fig .43 .74 Multifidus . A, Cervicothoracic parts .
B, Lumbosacral parts .
Multifidus Multifidus


Muscles
743
34
RETPAHC
are covered at cervical levels by splenius, at thoracic levels by spinalis
thoracis, and at lumbar levels by the erector spinae aponeurosis. In the
neck, semispinalis capitis lies mainly deep to splenius and trapezius,
but a small portion may be exposed to form the uppermost part of the
floor of the posterior triangle of the neck.
Semispinalis
capitis VascularsupplySee below.
InnervationRotatores, multifidus, semispinalis thoracis and semispi-
nalis cervicis are all innervated by the medial branches of the dorsal
rami of the appropriate spinal nerves. Semispinalis capitis is innervated
Semispinalis
cervicis by descending branches of the greater occipital nerve (C2) and the third
cervical nerve (C3).
ActionsAll the spinotransverse muscles are extensors. They extend the
vertebrae from which they arise, or the head in the case of semispinalis
capitis. The predominantly longitudinal orientation of their fascicles
Semispinalis precludes any substantive action as rotators. Although rotatores have
thoracis been presumed to rotate the thoracic vertebrae, this action has not been
validated. Axial rotation has been expressly refuted as an action of the
lumbar multifidus.
Interspinales
Interspinales are short, paired muscular fasciculi attached above and
below to the apices of the spines of contiguous vertebrae, one on either
side of the interspinous ligament. They are most distinct in the cervical
region, where they consist of six pairs, the first between the axis and
third vertebra, and the last between the seventh cervical and first tho-
racic vertebrae. In the thoracic region they occur between the first and
second vertebrae (sometimes between the second and third), and the
eleventh and twelfth vertebrae. In the lumbar region there are four pairs
between the five lumbar vertebrae. A pair is occasionally found between
the last thoracic and first lumbar vertebrae, and another between the
fifth lumbar vertebra and the sacrum. Sometimes cervical interspinales
span more than two vertebrae.
Intertransversarii


Fig .43 .75 The attachments of semispinalis .
Intertransversarii are small muscles between the transverse processes of
the vertebrae. They are best developed in the cervical region, where they
consist of posterior and anterior sets of muscles separated by the ventral
second lumbar vertebrae insert into the dorsal segment of the iliac crest. rami of spinal nerves. Posterior intertransverse muscles are divisible
From each spinous process the shortest fascicles pass inferiorly and into medial and lateral slips. Each medial slip, the intertransverse
laterally to their insertion; the longer fascicles assume a progressively muscle ‘proper’, is often further subdivided into medial and lateral
steeper course and are arranged progressively more medially. The fasci- parts by the passage through it of the dorsal ramus of a spinal nerve.
cles from a given segment are flanked and overlapped dorsolaterally by There are seven pairs of these muscles, the highest between the atlas
fascicles from successively higher segments, an arrangement that and axis, and the lowest between the seventh cervical vertebra and the
endows the intact muscle with a laminated structure. first thoracic vertebra; the anterior muscles between atlas and axis are
often absent. In the thoracic region, intertransversarii consist of single
SemispinalisThe semispinalis muscles are formed by the longest muscles that span between the transverse processes of the last three
fascicles of the spinotransverse group. Three divisions are defined essen- thoracic and the first lumbar vertebrae. In the lumbar region, they again
tially by their origins (Fig. 43.75). consist of two sets of muscles. One set, intertransversarii mediales, con-
Semispinalis cervicis arises from the spinous processes of the second nects the accessory process of one vertebra with the mammillary
to fifth cervical vertebrae. Its fascicles span about six segments and cover process of the next. The other set, intertransversarii laterales, can be
the cervical and thoracic multifidus. They insert by fleshy or tendinous divided into ventral and dorsal parts; the ventral parts connect the
fibres into the posterior surfaces of the upper five or six thoracic trans- transverse processes of the lumbar vertebrae, and the dorsal parts


verse processes. The fascicle from the axis is the largest and is composed connect the accessory processes to the transverse processes of succeed-
chiefly of muscle. ing vertebrae.
Semispinalis thoracis consists of thin, fleshy fascicles that have long Different parts of the intertransversarii in the cervical and lumbar
tendons at both ends. They arise from the lower two cervical and the regions are homologous with certain muscles found in the thoracic
upper four thoracic spinous processes, and insert into the transverse region. The homologies are determined according to whether the
processes of the sixth to tenth thoracic vertebrae. They cover the thoracic muscle attaches between consecutive transverse elements of the verte-
multifidus. brae, or between transverse and costal elements, or between consecutive
Semispinalis capitis covers semispinalis cervicis. It arises from the costal elements. They are reinforced by the nerve supply of the muscle,
medial part of the area between the superior and inferior nuchal lines and by the relationship between the muscles and certain nerves.
of the occipital bone and forms a thick muscle bundle in the suboc- The medial slips of the ‘proper’ posterior intertransverse muscles of
cipital region. Individual fascicles pass inferiorly, laterally and ventrally the neck connect consecutive transverse elements, as do the intertrans-
from the muscle, ending as flat tendons that insert successively into the versarii mediales of the lumbar region. These muscles are homologous
superior articular processes of the lower four cervical vertebrae and the with the thoracic intertransverse muscles and ligaments. All are sup-
tips of the transverse processes of the upper six or seven thoracic verte- plied by dorsal rami. The lateral slips of the ‘proper’ posterior inter-
brae. The medial part of the muscle in the cervical region is formed by transverse muscles connect a transverse element to a costal element, as
the thoracic fascicles, which are more or less distinct from the rest, and do the intertransversarii laterales dorsales. They are homologous with
has been called biventer cervicis because it is traversed by an incomplete levatores costarum and are supplied by the ventral rami of spinal nerves.
tendinous intersection. At each level, the medial branch of a dorsal ramus separates the true


Semispinalis is not formed in the lumbar region, but vestiges of its intertransverse muscle from levator costae or its equivalent. The anterior
caudal tendons are represented as the mammillo-accessory ligaments intertransverse muscles of the neck and lateral parts of the posterior
of the lumbar vertebrae. intertransversarii connect the costal processes of consecutive vertebrae,
as do the intertransversarii laterales ventrales of the lumbar region;
RelationsAt cervical, thoracic and lumbar levels, components of they are homologous with the intercostal muscles and are supplied by
erector spinae lie lateral to the spinotransverse group of muscles. They ventral rami.


BACk
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5
NOITCES
ActionsofinterspinalesandintertransversariiThe functions RectuscapitisposteriormajorRectus capitis posterior major is
of interspinales and intertransversarii have not been established. They attached by a pointed tendon to the spine of the axis, becomes broader
are very small muscles and are unlikely to be able to generate enough as it ascends, and is attached to the lateral part of the inferior nuchal
force to be prime movers of the vertebrae. However, they are richly line and the occipital bone immediately below it. As the muscles of the
endowed with muscle spindles; the density approaches that found in two sides pass upwards and laterally, they leave between them a trian-
the lumbricals of the hand and in the extraocular muscles. It therefore gular space in which parts of recti capitis posteriores minores are visible.
seems reasonable to assume that the short muscles of the back may
serve a proprioceptive function in controlling the position of the verte- RectuscapitisposteriorminorRectus capitis posterior minor is
bral column and its movements. attached by a narrow pointed tendon to the tubercle on the posterior
arch of the atlas. As it ascends, it broadens before attaching to the
Vascular supply of the true back muscles medial part of the inferior nuchal line and to the occipital bone between
the inferior nuchal line and the foramen magnum. Either muscle may
The true (intrinsic) muscles of the back receive their blood supply from:
be doubled longitudinally. There is usually a soft tissue attachment to
the vertebral artery; deep cervical artery; superficial and deep descend-
the posterior atlanto-occipital membrane, which itself is firmly attached
ing branches of the occipital artery; deep branch of the transverse cervi-
anteriorly to the spinal dura in the same area (Zumpano et al 2006).
cal artery (when present); superior intercostal artery, via dorsal branches
of the upper two posterior intercostal arteries; posterior intercostal ObliquuscapitisinferiorObliquus capitis inferior, the larger of the
arteries of the lower nine spaces via dorsal branches; dorsal branches


two oblique muscles, passes laterally and slightly upwards from the
of the subcostal arteries; dorsal branches of the lumbar arteries; dorsal
lateral surface of the spine and the adjacent upper part of the lamina
branch of arteria lumbalis ima; and dorsal branches of the lateral sacral
of the axis to the inferoposterior aspect of the transverse process of the
arteries.
atlas.
The detailed pattern of the arterial supply of the deep muscles of the
back has been described by Michel Salmon (1994). These muscles are ObliquuscapitissuperiorObliquus capitis superior is attached by
supplied by dorsal branches of the posterior intercostal and lumbar tendinous fibres to the upper surface of the transverse process of the
arteries. In the thoracic and upper lumbar regions, where the compo- atlas. It expands in width as it ascends dorsally, and is attached to the
nents of erector spinae run in well-defined longitudinal columns, arte- occipital bone between the superior and inferior nuchal lines, lateral to
rial trunks from these dorsal branches run in the sulci between the semispinalis capitis and overlapping the insertion of rectus capitis pos-
columns and between erector spinae and multifidus, giving off branches terior major.
to supply the muscles. This vascular pattern is less regular in the lumbar
region. RelationsofthesuboccipitaltriangleMedially, the suboccipital
triangle is covered by a layer of dense adipose tissue, deep to semispi-
nalis capitis. Laterally, it lies under longissimus capitis and sometimes
Suboccipital muscles
splenius capitis, both of which overlap obliquus capitis superior. The
The suboccipital muscles (Fig. 43.76) are four small muscles that ‘floor’ of the triangle is formed by the posterior atlanto-occipital mem-
connect the occipital bone, atlas and axis posteriorly. They lie inferior brane and the posterior arch of the atlas. The vertebral artery and the
to the anterior part of the occipital bone, where three of the muscles dorsal ramus of the first cervical nerve lie in a groove on the upper
form the boundaries of the suboccipital triangle: rectus capitis posterior surface of the posterior arch of the atlas.


major lies above and medially; obliquus capitis superior lies above and
laterally, and obliquus capitis inferior lies below and laterally. With the VascularsupplyThe suboccipital muscles receive their blood supply
head in the anatomical position, the suboccipital triangle lies almost from the vertebral artery and deep descending branches of the occipital
in the horizontal plane. artery.
Obliquus capitis superior
Greater occipital nerve
Occipital artery Rectus capitis posterior minor
Semispinalis capitis Rectus capitis posterior major
Splenius capitis
Transverse process of atlas
First cervical dorsal ramus
(suboccipital nerve)
Vertebral artery
Second cervical dorsal ramus Obliquus capitis inferior
Longissimus capitis
Third cervical dorsal ramus Spinous process of axis
Levator scapulae
Semispinalis capitis
Splenius capitis
Trapezius
Fig .43 .76 The suboccipital triangles, posterior view . (From Drake RL, Vogl AW, Mitchell A, et al (eds), Gray’s Atlas of Anatomy, Elsevier, Churchill
Livingstone . Copyright 2008 .)


Movements of the vertebral column
745
34
RETPAHC
InnervationAll the suboccipital muscles are supplied by the dorsal Axial rotation involves twisting of vertebrae relative to each other
ramus of the first cervical spinal nerve. with accompanying torsional deformation of intervening discs. About
50% of cervical rotation occurs at the atlanto-axial joint. Elsewhere in
ActionsofthesuboccipitalmusclesThe suboccipital muscles the column, although movement is slight between individual vertebrae,
are involved in extension of the head at the atlanto-occipital joints and the range summates to become considerable for the column as a whole.
rotation of the head and atlas on the axis. Obliquus capitis superior In the postcervical column, the effective range of rotation is greatest at
and the two recti are probably more important as postural muscles than the thoracolumbar junction. There is very little rotation in the remain-
as prime movers but this is difficult to confirm by direct observation. der of the lumbar region.
Rectus capitis posterior major extends the head and, acting with obliq- In the cervical region, the upward inclination of the superior articu-
uus capitis inferior, rotates the face towards the ipsilateral side. Rectus lar facets allows free flexion and extension. The latter is usually greater,
capitis posterior minor extends the head. Obliquus capitis superior and is checked above by locking of the posterior edges of the superior
extends the head and laterally flexes it to the ipsilateral side. facets of C1 in the occipital condylar fossae, and below by slipping of
the inferior processes of C7 into grooves inferoposterior to the first
thoracic superior articular processes. Flexion stops where the cervical
MOVEMENTS OF THE VERTEBRAL COLUMN
convexity is straightened, checked by apposition of the projecting lower
lips of vertebral bodies on subjacent bodies. Cervical lateral flexion and
Spinal movements between individual vertebrae cannot be measured rotation are always coupled, and the superomedial inclination of the
accurately by skin-surface techniques; only biplanar radiography is suf- superior articular facets imparts rotation during lateral flexion.


ficient for this purpose. Movements of the entire lumbar spine can be Cervical motion can be considered to involve the upper (i.e. the
measured using skin-surface techniques, but the results are of limited atlanto-occipital and atlanto-axial complexes) and the lower cervical
clinical use because there is high inter- and intra-observer variation spine (C3–7). Two physiological movements take place at the atlanto-
(Pearcy et al 1984, Pearcy and Tibrewal 1984). occipital joints: those of flexion–extension and lateral flexion. The
The intervertebral discs are the principal sites of vertebral column atlanto-axial joints allow flexion–extension and rotation. Some studies
movement. Conversely, at most levels, the extent to which the discs may have suggested that maximum flexion–extension occurs between the
be deformed is also the limiting factor for motion. Bony deformation occiput and C1; however, Frobin et al (2002) noted between 12.6° and
in the subchondral bone and articular cartilage may contribute to move- 14.5° at this level, which is less than at some of the other cervical levels.
ment. Regional variations in mobility of the spine depend on the geo- Global cervical flexion ranges from 45° to 58°, depending on the
metry, orientation and properties of the facet joints and related method of assessment, age and sex; older subjects and females exhibit
ligamentous complexes. Physiological intervertebral movements usually less motion (Ordway et al 1997, Trott et al 1996). At an intersegmental
combine tilting (bending) and gliding (shear), so the instantaneous level, motion increases from the second cervical level and peaks at the
centre of rotation moves continually during the movement. During mid-cervical level (14–17° recorded at C4/5), before reducing at the
flexion and extension of the lumbar vertebrae, the centre of rotation junction of the cervical and thoracic spine (9.8–11.5° noted at C6/7)
usually lies near the centre of the intervertebral disc when viewed (Frobin et al 2002). Global ranges of lateral flexion range from 32° to


in the transverse plane, close to the superior end-plate of the vertebra 47°, with a gradual reduction in range with age and sex, while rota-
below. tional movements range from 63° to 78°. Intersegmental ranges of
The oblique and ovoid articular surfaces of the facet joints ensure motion vary from 4.7° to 6° for lateral flexion between C2 and C7, and
that spinal movements in different planes are usually ‘coupled’ to a 2–12° for rotation (White and Panjabi 1990).
certain extent. For example, lateral flexion would cause impingement In the thoracic region, especially superiorly, all movements are
of the articular surfaces on that side, leading to a posteriorly directed limited, reducing interference with respiration. Lack of upward inclina-
force on the upper vertebra that would act to rotate it about its long tion of the superior articular facets prohibits much flexion, and exten-
axis. Physiologically, coupled movements are variable. Although move- sion is checked by contact of the inferior articular margins with the
ments between individual vertebrae are small, their summation gives a laminae and of adjacent spines. Thoracic rotation is freer, though
large total range to the vertebral column in flexion, extension, lateral limited by the ribs at upper levels. Its axis is in the vertebral bodies in
flexion and axial rotation. Each pair of vertebrae with its interposed the mid-thoracic region, and in front of them elsewhere, so that rotation
disc and ligaments is termed a motion segment or functional involves some lateral displacement. The direction of articular facets
spinal unit. would allow free lateral flexion but this is limited in the upper thoracic
In flexion, the anterior longitudinal ligament becomes relaxed as the region by the resistance of the ribs and sternum. Rotation is usually
anterior parts of the intervertebral discs are compressed. At its limit, the combined with slight lateral flexion to the same side.
posterior longitudinal ligament, ligamenta flava, interspinous and Movement in the thoracic spine is frequently regionalized to upper,
supraspinous ligaments, and the posterior fibres of the intervertebral mid- and lower thoracic. In the upper thoracic, flexion ranges from 7.8°


discs are all tensed, the interlaminar intervals widen, the inferior articu- to 9.5°, increasing to 10–11.4° in the mid-thoracic and 12.5°–12.8° in
lar processes glide on the superior processes of subjacent vertebrae, the lower thoracic (Willems et al 1996). Extension is more consistent,
and their capsules become taut. Tension of extensor muscles is also ranging from 7.1° to 9.7° throughout the thoracic spine. Lateral flexion
important in limiting flexion, e.g. when carrying a load on the shoul- is greater in the lower thoracic spine, ranging from 5.6° to 6.2° in the
ders. Flexion is effectively absent in the thoracic region. In forward upper thoracic, 7.9° to 8.1° in the mid-thoracic and 11.9° to 13.2° in
flexion of the lumbar spine, the muscles normally protect the osteoliga- the lower thoracic. However, rotation is greatest in the mid-thoracic
mentous spine from injury. However, the margin of safety can be com- region, being 11.8°–15.9° in the upper thoracic, 21.5°–25.3° in the
promised during repetitive or sustained bending by a failure of the mid-thoracic, and 8.3°–11.8° in the lower thoracic.
spinal reflexes. Once the muscle protection is lost, flexion injury affects Flexion movements are generally greater than extension or lateral
first the interspinous ligaments and then the capsules of the facet joints. flexion in the lumbar region. Axial rotation occurs about a centre of
The ligamentum flavum has such a high content of elastin that it is rotation in the posterior anulus, and is limited by bony contact in the
always under tension, and can be stretched by 80% without damage. facet joints after only 1–2° of movement. Functional transition between
This ligament probably functions to provide a constant smooth lining thoracic and lumbar regions is usually between the eleventh and twelfth
to the vertebral canal, which is never overstretched in flexion and which thoracic vertebrae, where the facet joints usually fit so tightly that slight