SCALENE MUSCLE
INTRODUCTION:-
Scalene muscles are a group of three pairs of muscles in the lateral neck.
1. Scalenus Anterior
2. Scalenus Medius
3. Scalenus Posterior
Sometimes, a fourth rudimentary scalene muscle, the SCALENE MINIMUS is present.
These muscle extend from the transverse processes of cervical vertebrae of the first two ribs.
They can either elevate these ribs or bend the cervical part of the vertebral column laterally.
1. SCALENUS ANTERIOR:-
It is most superficial and lies deep to sternocleidomastoid muscle.
Origin:-
Anterior tubercles of transverse process of cervical vertebrae 3 to 6.
Insertion:-
Scalene tubercle and adjoining ridge on the superior surface of the first rib [between subclavian artery and vein]
Nerve supply:-
Ventral rani of nerves C4 - C6.
Actions:-
Anterolateral flexion of cervical spine.
Rotates cervical spine ti opposite site.
Elevates the first rib during inspiration.
Stabilize the neck along with other muscles.
2. SCALENUS MEDIUS:-
It is longest and largest of all the scalene muscles.
Origin:-
1. Posterior tubercle of transverse process of cervical vertebrae 3 to 7.
2. Transverse process of axis and sometimes also of the Atlas vertebrae.
Insertion:-
Superior surface of the first rib behind the groove for the subclavian artery.
Nerve supply:-
Ventral rani of nerves C3 - C8.
Actions:-
Lateral flexion of the cervical spine.
Elevation of first rib.
Stabilises neck along with other muscles.
3. SCALENUS POSTERIOR:-
It is smallest and most deeply situated.
Origin:-
Posterior tubercles of transverse process of cervical vertebrae 4 to 6.
Insertion:-
outer surface of the second rib behind the tubercle for the serratus anterior.
Nerve supply:-
Ventral rami of nerves C6 - C8.
Actions:-
Lateral flexion of cervical spine.
Elevation of second rib.
Stabilizes neck along with other muscles.
4. SCALENUS MINIMUS:-
Origin:-
Anterior border of the transverse process of vertebrae C7.
Insertion:-
Inner border of the first rib behind the groove for the subclavian artery and into the dome of the cervical pleura.
Actions:-
Contraction of the scalenus minimus pulls the dome of the cervical pleura.
RELATIONS:-
The scalenus anterior is a key muscle of the lower part of the neck. Because phrenic nerve passes superficial to it, subclavian artery deep to it and branchial plexus lies at its lateral border.
The relations of scalenus anterior muscle are very important. So, it is a useful surgical landmarks.
ANTERIOR RELATIONS:-
1. Phrenic nerve
2. Two arteries:-
- Transverse cervical artery
- Suprascapular artery
3. Two veins:-
- Anterior jugular vein
- Subclavian vein
4. Two muscles:-
- Inferior belly of omohyoid
- sternocleidomastoid muscle
5. Carotid sheath
6. Clavicle
POSTERIOR RELATIONS:-
1. Root of brachial plexus
2. Subclavian artery
3. Scalenus medius muscle
4. Cervical pleura
5. Suprapleural membrane
OTHER RELATIONS:-
The medial border of scalenus anterior forms the lateral boundary of the scalenovertebral triangle or triangle of the vertebral artery. The contents of this triangle from the medial relations of the scalenus anterior.
The lateral border of scalenus anterior is related to trunks of brachial plexus, which emerge underneath it.
The upper part of scalenus anterior is separated from longus capitis by the ascending cervical artery.
CLINICAL CORRELATION:-
SCALENE SYNDROME:-
It consists of group of signs and symptoms produced due to compression of lower trunk of brachial plexus (C8 and T1) and subclavian artery in the scalene triangle either due to raising of its base by the cervical rib, if present, or due to spasm of scalene muscles.
Clinically, this syndrome presents as:
(a) tingling sensation and numbness along the inner border of forearm and hand, i.e., along the distribution of C8 and T1 spinal nerves.
(b) progressive paresis and wasting of intrinsic muscles of the hand (most of them are supplied by C8 and T1 spinal nerves)
(c) ischemic pain and absence of radial pulse due to compression of subclavian artery.
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