Human Anatomy Vol 1

Failure of fusion of the two halves of the neural

arch results in 'spina bifida'. Sometimes the body

ossifies from two primary centres, and if one

centre fails to develop, one half, right or left of

the body is missing. This results in a hemivertebra

and lateral bend in the vertebral column or

scoliosis.

In young adults, the discs are very strong.

However, after the second decade of life

degenerative changes set in resulting in weakness

of the annulus fibrosus. When such a disc is

subjected to strain, the annulus fibrosus may

rupture leading to prolapse of the nucleus

pulposus. This is commonly referred to as disc

prolapse.It may occur even after a minor strain. Lr

addition to prolapse of the nucleus pulposus,

internal derangements of the disc may also take

place.

o Disc prolapse is usually posterolateral. The

prolapsed nucleus pu$osus presses upon adjacent

nerve roots and gives rise to pain that radiates

along the distribution of the nerve. Such pain

along the course of the sciatic nerve is called

sciatica. Motor effects, with loss of power and

reflexes, may follow. Disc prolapse occurs most

frequently in the lower lumbar region (Fig. 13.23).

It is also common in the lower cervical region from

fifth to seventh cervical vertebrae.

THORAX

Upper surface of body

Flg. 13.22: Ossification of a thoracic vertebra

Prolapsed

intervertebral

disc

Spinal nerve

Fig. 13.23: Disc prolapse causing pressure on the spinal

nerye

Cosloverlebrol Joints

The head of a typical rib articulates with its own

vertebra, and also with the body of the next higher

vertebra, to form two plane synovial joints separated

by an intra-articular ligament (Fig. 13.5).

This ligament is attached to the ridge on the head of

the rib and to the intervertebral disc. Other ligaments

of the joint include a capsular ligament and a triradiate

ligament. The middle band of the triradiate ligament

forms the hypochordalbow (Fig. 13.5), uniting the joints

of the two sides.

Coslotronsverse Joints

The tubercle of a typical rib articulates with the

transverse process of the corresponding vertebra to

form a synovial joint.

The capsular ligament is strengthened by three

costotransverse ligaments. The superior costotransverse

ligament has two laminae which extend from the crest

on the neck of the rib to the transverse process of the

vertebra above. The inferior costotransverse ligament

passes from the posterior surface of the neck to the

transverse process of its own vertebra. The lateral costo-

transverse ligament connects the lateral non-articular

part of the tubercle to the tip of the transverse process

of its own vertebra.

The articular facets on the tubercles of the upper six

ribs are conve& and permit rotation of the neck of the

rib for pump-handle moaements (Fig. 8.2$. Rotation of

rib-neck backwards causes elevation of second to sixth

ribs withmovingforwards and upwards of the stemum.

This increases the anteroposterior diameter of the thorax

(Fig. 13.25).

Monubrioslernol Joint

Manubriosternal joint is a secondary cartilaginous joint.
It permits slight movements of the body of the stemum
on the manubrium during respiration.