Muscles - Scalenes

Question 1

Where are the scalenes located?

Answer 1

Lateral aspect of the neck. They form part of the floor of the posterior triangle of the neck.

Question 2

What are the functions of the scalenes?

Answer 2

1) Accessory muscles of respiration
2) Flexion at the neck

Question 3

Anterior scalene

Answer 3

Deep to the sternocleidomastoid.

Origin - anterior tubercles of the transverse processes of C3-C6

Insertion - scalene tubercle on the inner border of the first rib.

Action - elevation of the first rib. Ipsilateral contraction causes ipsilateral neck flexion. Bilateral contraction causes anterior flexion of the neck.

Innervation - anterior rami of C5-C6

Question 4

Middle scalene

Answer 4

Largest and longest of the three. Consists of several long thin muscle bellies than converge as one belly that inserts on to the first rib.

Origin - posterior tubercles of the transverse processes of C2-C7

Insertion - scalene tubercle of the first rib.

Action - elevation of the first rib. Ipsilateral contraction causes ipsilateral neck flexion.

Innervation - anterior rami of C3-C8

Question 5

Posterior scalene

Answer 5

Smallest and deepest muscles of the scalenes. Unlike the others, it inserts into the second rib.

Origin - posterior tubercles of the transverse processes of C5-C7.

Insertion - 2nd rib

Action - elevation of the 2nd rib + ipsilateral flexion of the neck.

Innervation - anterior rami of C6-C8

Question 6

Anatomical relationships

What important structures run through this area?

Answer 6

Brachial plexus + subclavian artery - runs between the anterior and middle scalene muscles. Important anatomical landmark for interscalene block.

Sublavian vein + phrenic nerve - runs anteriorly to the anterior scalene.

Subclavian vein runs horizontally to it.

Phrenic nerve runs vertically down the muscle.

Question 7

Clinical relevance - interscalene block

Answer 7

Brachial plexus runs between the anterior and middle scalene muscles.

In upper limb surgery, the brachial plexus can be infiltrated with local anaesthetic to avoid the use of general anaesthetic - known as interscalene block.

Local anesthetic is injected between these muscles at the level of the cricoid cartilage.

Question 8

Clinical relevance - accessory muscles of respiration

Answer 8

Scalene muscles collectively act to elevate the muscles at the 1st and 2nd ribs. In doing so, they increase the intrathoracic volume.

In patients with respiratory distress, the scalenes may be used as ‘accessory muscles of respiration’ to aid with breathing.

By increasing intrathoracic volume, the patient can ventilate their lungs more effectively. However, they are not required in ventilation of a healthy person. This is an important clinical sign of ‘respiratory distress’.