Page 160 - untitled

AAAC71 21/5/05 11:00 AM Page 159
There are 12 thoracic, five lumbar, five sacral and 3–5 coccygeal ver-
and back of the bodies (the posterior ligaments thus lie within the ver-
tebrae. They are held together by ligaments, intervertebral discs and
tebral canal).
synovial joints between the articular processes. The weight-bearing
• Supraspinous and interspinous ligaments.
portion of the vertebra is the body so that the size of the vertebral bodies • Anterior and posterior longitudinal ligaments joining the front
increases from above downwards and when one of the bodies is dis- • Intertransverse ligaments.
eased it will eventually collapse. The bodies contain red bone marrow • Ligamenta flava (which contain much elastic tissue and join the
so that the veins that drain them (basivertebral veins) produce large laminae).
foramina on the backs of the bodies. • Capsular ligaments of the synovial joints between the articular
• Cervical vertebrae (Fig. 71.1): small bodies, bifid spines, transverse processes.
processes with anterior and posterior tubercles and a foramen
transversarium for the passage of the vertebral artery. The body of the Curves of the spine
first vertebra (atlas) fuses with that of the second (axis) during develop- In the fetus, the whole developing spine is curved so that it is concave
ment to produce its dens (odontoid process) which is held in place by a forwards (primary curvature). A few months after birth the baby begins
transverse ligament (Fig. 71.2). to hold its head up and the cervical spine develops a forward convexity
• Thoracic vertebrae (Fig. 71.3): heart-shaped bodies, upper and (secondary curvature). Later in the first year the baby begins to stand
lower demifacets for the heads of the ribs, long downturned spine, long up and another forward convexity develops in the lumbar region (sec-
transverse processes with a facet for the tubercles of the rib. ondary curvature). The primary curves are mainly due to the shape of
• Lumbar vertebrae (Fig. 71.4): a massive body, large transverse the vertebral bodies but the secondary curves are due to the shape of the
processes, a triangular vertebral canal and large, backwardly project- intervertebral discs.
ing spines so that a needle may be inserted between them in the opera-
tion of lumbar puncture. The articular facets face mediolaterally so Movements of the spine
that they prevent rotation. • Cervical spine: movement is free in the cervical region of the spine:
• Sacral vertebrae (Fig. 23.3): fused together to form the sacrum. flexion and extension, side flexion (associated with rotation to the
opposite side) and rotation. In rotation of the head the atlas rotates
The intervertebral joints around the dens of the axis, and in flexion of the head the occipital
The upper and lower surfaces of the bodies are covered with hyaline condyles move on the articular facets of the atlas.
cartilage and are separated by the fibrocartilaginous intervertebral • Thoracic spine: movement is somewhat restricted by the thinner
discs. Each disc has a peripheral fibrous ring (annulus fibrosus) and a intervertebral discs and the presence of the ribs. Rotation, however, is
central more spongy nucleus pulposus which lies nearer to the back free.
than to the front of the disc. The nucleus pulposus is rich in gly- • Lumbar spine: flexion and extension are free but rotation is almost
cosaminoglycans so that it has a high water content, but this diminishes absent because of the direction of the articular facets. Side flexion also
with increasing age. The nucleus may then herniate through the annulus occurs.
fibrosus, passing backwards (compressing the spinal cord), posterolat-
erally (compressing a spinal nerve) or upwards (into a vertebral Spina bifida
bodyaa Schmorl’s node). The discs are thickest in the lumbar and cer- Each vertebra develops in three partsbthe body and the two halves of
vical regions, so that these are the regions of most movement. the neural arch. These ossify in cartilage and, at birth, the three parts
The vertebrae are also held together by ligaments that join each of are still separate but they soon fuse. Failure of such fusion gives rise to
the components of the vertebrae (Fig. 71.5) except for the pedicles (the the condition of spina bifida. This may be symptomless (spina bifida
spinal nerves have to pass between these in the intervertebral foram- occulta) although the site of the lesion may be marked by a tuft of hair.
ina). Thus there are: If the defect is large, the meninges or even the spinal cord may herniate
onto the surface (meningocoele) and this may produce neurological
symptoms.

The spine 159