Musculoskeletal: Anatomy - Overview of the thoracic wall

Question 1

Orientation of fibres external vs internal intercostals

Answer 1

External intercostals: fibres run infero-anteriorly
Internal intercostals: fibres run infero-posteriorly

Question 2

Attachments, innervations and actions of external intercostals

Answer 2

Attachments: from inferior rib border to superior border of rib below (from tubercle posteriorly to costochondral junctions anteriorly), continuous with external oblique muscles inferiorly
Innervation: intercostal nerves
Actions: elevate ribs in bucket-handle motion, increases anterior-posterior and lateral dimensions of the thorax to aid inspiration

Question 3

Attachments, innervations and actions of internal intercostals

Answer 3

Attachments: from inferior rib border to superior border of rib below, continuous with internal oblique muscles inferiorly
Innervation: intercostal nerves
Actions: depresses (interosseous) and elevates (interchondral) ribs to aid active expiration

Question 4

Between which muscles does the neurovascular bundle run?

Answer 4

Internal and innermost intercostals

Question 5

Describe the orientation of the components of the neurovascular bundle from superior to inferior

Answer 5

From superior to inferior: VAN (vein, artery, nerve)
Runs in inferior aspect of rib in costal groove (on internal surface)

Question 6

Four branches of the intercostal nerves

Answer 6

1. Rami communicantes: communicating branches between sympathetic trunk and intercostal nerves
2. Collateral nerves and vessels: extend inferiorly to help supply intercostal muscles
3. Lateral and anterior cutaneous branches: supply skin
4. Muscular branches: supply thoracic wall muscles

(Posterior rami of thoracic vertebra supply skin of posterior thorax/back)

Question 7

What is the origin of the intercostal nerves?

Answer 7

Arise from anterior rami of thoracic vertebra (except T12 which gives rise to subcostal nerve)

Question 8

Where are the intercostal spaces the widest? How are they widened further?

Answer 8

Anterolaterally
Widened further with inspiration, and with extension and lateral flexion of trunk to contralateral side

Question 9

What landmarks are used for posterior thoracotomy?

Answer 9

Posterolateral 5th to 7th intercostal spaces

Question 10

What landmarks are used for chest drain insertion?

Answer 10

“Triangle of safety”:
- Anterior to mid axillary line
- Posterior to pectoral groove
- Above 5th intercostal space (approx level of the nipple in males which is T4)

Question 11

Describe the course of the intercostal arteries

Answer 11

One large posterior intercostal: arises from supreme intercostal arteries for 1st and 2nd spaces, and from thoracic aorta for remainder
Two anterior intercostals: arise from internal thoracic (branch of subclavian) for 1st to 6th spaces, and musculophrenic for 7th to 9th

Question 12

Describe the drainage of the intercostal veins

Answer 12

Posterior and anterior intercostals anastamose, drain into azygous/hemi-azygous system then into SVC
Exception to this is the L superior intercostal vein which drains into the L brachiocephalic vein

Question 13

What is the vertebral level of the sternal angle?

Answer 13

T4/5

Question 14

Describe the transverse thoracic plane. What is its significance anatomically?

Answer 14

Extends from manubriosternal joint anteriorly to inferior endplate of T4 posteriorly
Divides thorax into superior and inferior mediastinum

Question 15

What structures are transected by the thoracic plane?

Answer 15

CLAPTRAP:
Cardiac plexus
Ligamentum arteriosum and L recurrent laryngeal
Aortic arch (inner concavity)
Pulmonary bifurcation
Tracheal bifurcation (carina)
Right-to-left movement of thoracic duct
Azygous vein drains to SVC -> SVC enters RA
Prevertebral and pretracheal fascia terminate

Question 16

What are the atypical intercostal nerves and what are their features?

Answer 16

1st and 2nd: on internal surface of rib rather than inferiorly in costal groove
1st: has no anterior cutaneous and often no lateral cutaneous branches
2nd +/- 3rd: large lateral branch called intercostobrachial nerve (supplies floor of axilla, posteromedial surface of arm)
7-11th: after giving off lateral cutaneous branches, pierce rectus sheath and become thoraco-abdominal nerves

Question 17

8 muscles of the thoracic wall

Answer 17

1. Serratus posterior superior
2. Serratus posterior inferior
3. Levator costarum
4. External intercostals
5. Internal intercostals
6. Innermost intercostals
7. Subcostal
8. Transversus thoracis

Question 18

Attachments, innervations and actions of serratus posterior superior

Answer 18

Attachments: nuchal ligament and spinous processes C7-T3; superior borders of ribs 2-4
Innervation: 2nd to 5th intercostal nerves
Actions: proprioception

Question 19

Attachments, innervations and actions of serratus posterior inferior

Answer 19

Attachments: spinous processes T11-L2; inferior borders of ribs 8-12
Innervation: anterior rami T9-12
Actions: proprioception

Question 20

Attachments, innervations and actions of levator costarum

Answer 20

Attachments: transverse processes T7-11 to subjacent ribs
Innervations: posterior rami C8-T11
Actions: elevates ribs

Question 21

Attachments, innervations and actions of innermost intercostals

Answer 21

As for internal intercostals:
Attachments: from inferior rib border to superior border of rib below, continuous with internal oblique muscles inferiorly
Innervation: intercostal nerves
Actions: depresses (interosseous) and elevates (interchondral) ribs to aid active expiration

Question 22

Attachments, innervations and actions of subcostals

Answer 22

Attachments: internal lower ribs to superior border of 2nd or 3rd ribs below
Innervations: intercostal nerves
Actions: as for internal intercostals (interosseous part depress ribs and interchondral part elevates ribs in forced expiration)

Question 23

Attachments, innervations and actions of transversus thoracis

Answer 23

Attachments: posterior surface lower sternum to internal surface costal cartilages 2-6
Innervations: intercostal nerves
Actions: weakly depresses ribs, ? proprioception

Question 24

What are the three main arteries supplying in the thoracic wall and their important branches?

Answer 24

1. Thoracic aorta: gives off posterior intercostal and subcostal arteries
2. Subclavian artery: gives off internal thoracic and supreme intercostal arteries
3. Axillary arteries: gives off superior and lateral thoracic arteries

Question 25

Describe the pattern of venous drainage above and below the umbilicus

Answer 25

Above umbilicus: to lateral thoracic vein then axillary vein
Below umbilicus: to great saphenous vein