SCALENE MUSCLES

SCALENE MUSCLES

There are usually three scalene muscles , the scalenus anterior , the scalenus medius and the scalenus posterior .

The scalenus medius is the largest, and the scalenus posterior the smallest, of three. These muscles extend from the transverse processes of cervical vertebrae to the first two ribs. They can, therefore , either elevate these ribs or bend the cervical part of the vertebral column laterally.

ADDITIONAL FEATURES OF THE SCALENE MUSCLES

·         Sometimes a fourth, rudimentary scalene muscle, the scalenus minimus is present. It arises from the anterior border of the transverse process of vertebra C7 and is inserted into the inner border of the first rib behind the groove for the subclavian artery and into the dome of  the cervical pleura. The suprapleural membrane is regarded as the flattened tendon of this muscle. Contraction of the scalenus minimus pulls the dome of the cervical pleura.

·         Relations of scalenus anterior . the scalenus anterior is a ‘key’ muscle of the lower part of the neck because of its intimate relations to many important relations to many important structures in this region . it is a useful surgical landmark. Its relations are :

ANTERIOR

(1)    phrenic nerve is covered by :

(2)    prevertebral fascia;

(3)    transverse cervical,supracapsular  and ascending cervical arteries ;

(4)    lateral part of carotid sheath containing the internal jugular vein;

(5)    descendens cervicals

(6)    inferior belly of omohyoid;

(7)    anterior jugular vein;

(8)    subclavian vein;

(9)    sternocleidomastoid branches of superior thyroid and suprascapular arteries

(10) sternocleidomastoid

(11) Clavicle

POSTERIOR

1.       Brachial plexus

2.       Subclavian artery

3.       Scalenus medius

4.       Cervical pleura covered by the suprapleural membrane.

             MEDIAL BORDER OF THE MUSCLE IS RELATED:

1.       In its lower part to an inverted ‘V’ – shaped interval , formed  by the diverging borders of the scalenus anterior and the longus colli. This interval contains many important structures as follows.

a.       Vertebral vessels running vertically from the base to the apex of this space;

b.      Inferior thyroid artery arching medially at the level of the seventh cervical transverse process ;

c.       Sympathetic trunk

d.      The first part of the subclavian artery traverses the lower part of the gap.

e.      On the left side the thoracic duct arches laterally at the level of the seventh cervical transverse process;

f.        The carotid sheath covers all the structures mentioned above.

g.       The sternocleidomastoid covers the carotid sheath.

·         UPPER PART

    The scalenous anterior is separated from the longus capitis by the ascending cervical artery.

THE LATERAL BORDER

    The border of the muscle is related to the trunks of the brachial plexus and the subclavian artery which emerges at this border and enter the posterior triangle.