Overview
The vertebral column is the main part of the axial skeleton which forms
the central axis of the skeleton. Its
main function is for the protection of the spinal cord and for the transmission
of body weight from the head, trunk and upper limbs, through the pelvic girdle
to the lower limbs. It is made up of on average 33 vertebrae which are united
by intervertebral discs (cartilaginous joints) and ligaments. 24 of the
vertebrae are discrete bones while the last 9 are fused together in the sacrum
and coccyx. There are 5 groups of vertebrae which make up the column each with
variation that contributes to their function in the column; cervical (7),
thoracic (12), lumbar (5), sacral (5), coccygeal (4).
Gross Anatomy
· Development
The formation of the vertebral
column begins in the 4th week of foetal development. Mesenchymal
cells known as sclerotomes form condensations around the notochord to create a
neural tube and form the basis of vertebral body and two neural arches. These
mesenchymal masses chondrify and become cartilaginous vertebrae. This results
in three primary ossification sites, one in the body and one in each arch by
the end of the 8th week of development. At birth, there are 3
discrete bony parts united by hyaline cartilage which eventually begin fusing within
the 1st year of life, first in the lumbar region followed by the
thoracic and cervical region reaching completion in the 6th year of
life
.
Five secondary ossification
centres develop during puberty in a typical vertebra: one at the tip of the
spinous process, one at the tips of each transverse process, and one at the
superior and inferior edges of the vertebral body known as the anular
epiphyses. Ossification is complete around age 25. Exceptions to the typical
pattern of ossification include C1, C2 and the sacrum and coccyx.
During fetal development, the
column is curved in a gentle c shape, which makes the primary curves, the
thoracic and sacral curvatures, however the secondary curvatures develop after
birth, with the cervical lordosis forming as an infant begins to lift their
head and the lumbar lordosis as they begin to walk.
· Macro-anatomy (e.g. surfaces, ridges, named areas)
A “typical” vertebra consists of
two main parts, the vertebral body and the vertebral arches,
which surround the vertebral canal providing the protection for the spinal cord
Vertebral Body
The vertebral body bears the major part of the weight
transmitted through the column. It is short and cylindrical, articulating with
the body of the adjacent vertebral body via strong intervertebral discs. It is
made of a thin shell of cortical bone surrounded by a core of porous cancellous
bone. The horizontal and vertical trabeculae pattern in the vertebral resists
the compressive forces which act on the body of the vertebrae.
Neural Arch
Each arch consists of paired pedicles and lamina, a spinous
process, lateral transverse processes and two superior and two inferior
articular facets. Short, rounded pedicles
arise from the posterolateral aspect of the body on either side. These support
flat lamina that meets its opposite
posteriorly in the midline to form the spinous
process. The transverse processes
arise from near the junction of the pedicles and laminae along with paired
superior and inferior articular processes. The tips of the spinous processes of
each arch may be palpable posteriorly in the midline with C7 being the most
prominent.
· Articulations (joints the bone is part of)
o Intervertebral Joints - The vertebrae articulate with its adjacent neighbour via
both its vertebral body and arch. Each
body on its superior and inferior aspect has a flat surface covered by hyaline
cartilage and united by a thick fibrocartilaginous intervertebral disc.
o Facet Joints
or Zygapophysial joints - The neural arches articulate via the paired superior
and inferior articular processes as
synovial joints which allow a small degree of movement in the vertebral column.
Synovial joints with a thin joint
capsule which allow gliding movements between the articular processes. The
shape and disposition of the articular processes vary depending on the
vertebral column region allowing for different types of movement
The different regions of the vertebral column also
articulate with other parts of the axial skeleton, e.g. the skull in the
cervical region, the rib cage in the thoracic region, the pelvis in the sacral
region.
· Blood Supply
The vertebral column is supplied by periosteal and equatorial branches of the segmental spinal arteries and their spinal branches. There are 31
paired branches which provide blood supply to the vertebral column. These arise
from the subclavian and vertebral arteries in the cervical region, the aorta in
the thoracic and lumbar region, and internal iliac artery in the sacral region.
The vertebrae are encircled on three sides by the paired
segmental artery, with the equatorial branches supplying the vertebral body,
and the posterior branches supplying the vertebral arches and muscles of the
back and the spinal branches supplying the vertebral canal. The spinal branches
enter via the intervertebral foramina to supply the periosteum, ligaments, and
meninges of the epidural space, with the radicular medullar branches supplying
the nervous tissue
The venous drainage of the vertebrae is into the internal
and external vertebral venous plexuses which drain into the internal iliac,
lumbar, azygos and basivertebral veins.
· Nerve Supply
The vertebral column is mainly innervated by (recurrent) meningeal branches of the
spinal nerves. These arise from the mixed spinal nerve. The mixed spinal
nerve is present prior to the nerve exiting the spinal canal and splits into
the anterior and posterior rami. The
recurrent meningeal nerves are the first branches from the spinal nerves and
provide localising pain sensation particularly in acute intervertebral disc
herniation and fractures.
The facet (zygapophysial)
joints are supplied by the articular branches of the medial branches of
the posterior rami of the corresponding spinal nerve and the two adjacent
spinal roots.
The intervertebral
discs and related ligaments are supplied by a number of branches of the ventral
rami of the spinal nerve and sympathetic nervous system. Although the spinal
cord terminates at the level of the L1/L2 vertebral body, the spinal nerves for
each segment exit the vertebral canal at their corresponding level.
· Ligamentous attachments
The stability of the
vertebral column is dependent on the ligaments running along its length. The
vertebral bodies are united by the anterior
and posterior longitudinal ligaments.
The anterior
longitudinal ligament runs from the occiput to the sacrum on the anterior
aspect of the vertebral body while the posterior from the axis (C2) to the
sacrum on the posterior aspect of the bodies.
Additional support is
provided posteriorly by the ligamentum
flavum and the supraspinous,
interspinous and intertransverse ligaments.
The ligamentum flavum
contains a large amount of yellow elastic tissue and unites adjacent laminae.
It is strong and maintains the curvature of the vertebral column and provides
support when it is flexed.
The supraspinous, interspinsous and
intertransverse ligaments help unite adjacent vertebra by attaching to the
spinous processes (supraspinous and interspinous ligaments) and the transverse
processes (intertransverse ligaments).
Clinical Anatomy
Spina
Bifida
Spina Bifida is a congenital disorder which results
from the failure of the neural arch of the vertebral column to close
adequately. It commonly affects the lumbar region of the back and if severe
enough can cause the contents of the vertebral canal to protrude. If the protrusion is just though the defect
and skin is intact, it is a meningocele. If there is protrusion of the spinal
cord and meninges through the defect and skin, it is known as a
myelomeningocele and can be associated to severe disability. However if there
is no cord protrusion it is known as Spina bifida occulta. Upto 5% of the
population are thought to have occulta and can often be identified by a hairy
dimple in the affected area.
Kyphosis
Kyphosis is a form of spinal disease which results
in abnormal concave shaping of the vertebral column in the thoracic region.
This is also be known as hyperkyphosis and the resulting deformity is often
called “Kelso’s hunchback”. It occurs most commonly due to osteoporosis and
arthritis, although congenital conditions such as Scheuermann’s disease can
cause structural kyphosis.
Scoliosis
Scoliosis is lateral curvature of the spine and is
the most common spinal disease affecting upto 0.5% of the population. It is
most common in females and may result in unequal growth of the side of the
vertebra leading to lack of fusion. It can be congenital, idiopathic or
secondary to conditions such as cerebral palsy or spina bifida.
Lordosis
Lordosis is the excessive convex shape of the
vertebral column in the lumbar region, also known as lumbar hyperlordosis or
“swayback”. It can often be a cause of lower back pain, and has a range of
causes including tight lumbar muscles, pregnancy, vitamin D deficiency in
children.
Spondylolisthesis
Spondylolisthesis is the forward displacement of a
vertebra. It occurs most frequently at L5 . The most common cause if a fracture
or congenital defect of the pars interarticularis of the neural arch. Backward
displacement of a vertebra is known as retrolisthesis.
Compression
Fractures
The commonest type of vertebral fracture is flexion
compression fracture which typically occurs at T12 and / or L1. This can result
in “wedging” of the affected vertebral body and in the majority of patients,
the posterior longitudinal ligament remains intact meaning the fracture is
stable. However if there is also forcible rotation with severe flexion, the
ligamentum flavum and interspinous ligaments can be ruptured resulting in
spinal cord compression.
Compression fractures are common in the elderly
population particularly in those who have osteoporosis. This is because osteoporosis
reduces the bone density of cancellous bone leaving the defects in the
trabecula pattern of the vertebral body.
Quick Anatomy
Key Facts
Ligament |
Attachment |
Function |
Ligmentum Flavum |
Connect all lamina from C2 to sacrum on inner surface of
lamina |
Preserve vertebral column alignment – maintain upright
posture |
Supraspinous ligament |
Connects the tips of the spinous processes from C7 to
sacrum. |
Limit hyperflexion |
Interspinous Ligaments |
Connect the root of one spinous process to the apex of
each spinous process |
Limit flexion |
Intertransverse Ligaments |
Attach to length of transverse processes to the transverse
process below. |
Limit lateral flexion |
Anterior Longitudinal Ligament |
Down anterior surface of all vertebral bodies and
intervertebral discs. From
the occiput to the sacrum |
Prevent hyperextension |
Posterior Longitudinal Ligament |
Down posterior surface of all vertebral bodies and
intervertebral discs. From
the axis (C2) to the sacrum |
Prevent hyperflexion |