Chest wall

Made up of 12 thoracic vertebrae, 12 pairs of ribs and costal cartilages and the sternum, along with associated soft tissues.

Surface anatomy

Jugular/supra-sternal notch
Angle of Louis
- Articulation of sternal angle and 2nd costal cartilage
- Defines upper third of thoracic cage
- Level of aortic arch and tracheal carina and T4-T5
Nipple
- Men - 4th ICS, just lateral to the mid-clavicular line
Vertebra prominens - C7 spinous process
Scapulae
- Medial edge lies from ribs two to seven
- Spine extends diagonally upwards from medial edge at T3, to the acromion
- Scapular plane lies on a plane passing through the inferior angle of the scapula
Lungs

Muscle layers:

Anterior thorax:
- Pectoralis major
  - Arise from clavicular and sternocostal fibres
  - Converge into a flat tendon inserting into the inter-tubercular sulcus of the humerus
  - Lower edge forms the anterior axillary fold
  - Supplied by medial and lateral pectoral nerves (brachial plexus)
  - Clavicular function: flex, adduct, inwardly rotate and elevate the arm
  - Sternocostal function: Contribute to downward and forward movement of the arm
- Pectoralis minor
  - Arise from upper borders and outer surfaces of ribs 2-5
  - Form a flat tendon inserting to coracoid process of the scapula
  - Depress and rotate the shoulders downward
  - Supplied by the medial and lateral pectoral nerves
- Serratus anterior
  - Lie along the anterolateral aspect of the thoracic wall
  - Originate from ribs 1-8
  - Insert along the anterior surface and medial border of the scapula
  - Supplied by long thoracic nerve (anterior rami of 5th, 6th and 7th cervical nerves) - in danger during thoracic incisions in axilla, although this probably produces little morbidity
  - Hold the scapula to the thoracic wall and participate in adduction and elevation of the arms above the horizontal position
Posterior thorax:
- Trapezius
  - Arise from superior nuchal line of occiput, the ligamentum nuchae of neck, the spine of C7, and spines and supraspinous ligaments of all thoracic vertebrae
  - Superior fibres to lateral third of clavicles; middle fibres to acromion of scapula and spine; inferior fibres converge near the scapula and end in an aponeurosis
  - Supplied by spinal accessory nerves and filaments from C3 and C4
  - Elevate, depress or abduct the scapula
  - Encountered in posterior or posterolateral thoracic incisions
- Latissimus dorsi
  - Arise by broad aponeurotic origins from spines of lower thoracic vertebrae, lumbodorsal fascia, iliac crests and some slips from the outer surfaces of the lower three or four ribs
  - Fibres converge frontward and spiral upward to insert on the intertubercular groove of the humerus
  - Form the posterior folds of the axillae
  - Supplied by thoracodorsal nerve (posterior cord of brachial plexus)
  - Allow arm adduction, extension and medial rotation
  - Accessory muscles of respiration
- Scapular muscles
  - Levator scapulae
    - Thin long muscle located laterally on each side of the neck
    - Fibres lie diagonally down to the superior angle of the scapula
  - Rhomboid minor
    - Originate from C7 and T1 spines
    - Runs down to base of scapular spine
  - Rhomboid major
    - Starts from T2-T5 spines
    - Extends downwards to medial border of the scapulae, inferiorly
    - Can be encountered in posterolateral incisions, depending whether the incision is taken high up between scapula and vertebral column
  - All supplied by dorsal scapular nerve
  - Subscapularis
    - Arises from the costal surface of the scapula and inserts into the lesser tuberosity of the humerus
    - Supplied by subscapular nerves
    - Steadies the head of the humerus against the glenoid cavity and assists in medial rotation of the humerus
  - Teres major
    - Arises near the inferior angle of the scapula and inserts to the bicipital groove of the humerus
Outer layer intercostals
- External intercostals
  - Fill the 11 intercostal spaces
  - Arises from lower border of a rib and inserts to the upper border of the rib below
  - Thicker than internal intercostals
  - Fibres directed obliquely downward and lateral on the back, and downward, forward and medial on the front
  - Conventionally considered to elevate the ribs
  - Incomplete anteriorly - replaced by anterior intercostal membrane in the region of the costal cartilages
- Serratus posterior superior
  - Elevates upper ribs in inspiration
- Serratus posterior inferior
  - Depresses lower ribs in expiration
Middle layer intercostals
- Internal intercostals
  - Begin ventrally at sternum and extend as far laterally as the angles of the ribs, where they condense into thin aponeuroses called internal intercostal membranes
  - Fibres directed inferiorly and posteriorly, opposite to external intercostals
  - Conventionally considered to lower the ribs
Inner layer intercostals
- Innermost intercostals
  - Incomplete and variable
  - Fibres pass in the same direction as internal intercostals
  - Deep to neurovascular bundle
- Transversus thoracis group
  - Arises from the deep surface of the lower half of the sternum and fans outwards and upwards to join the costal cartilages of the upper six or so ribs

Neurovascular bundle

Posteriorly, lies about midway in the intercostal space, but from the costal angle onwards comes to lie in the subcostal groove of the rib above, where it is partially projected by the downward projection of the lower border of the rib
Runs between the innermost and internal intercostal layers.
Generally ordered vein, artery and nerve, from cephalad to caudad
Artery
- Posterior and anterior branches anastomosing in each intercostal space. Posterior arteries much larger.
- Posterior arteries in spaces 1-2 from highest/supreme intercostal branch of costocervical trunk
- Posterior arteries in spaces 3-11 from descending thoracic aorta
- Anterior arteries are branches of internal thoracic artery (spaces 1-6) and musculophrenic artery (7-10)
Vein
- Generally follow the arterial distribution, but the posterior intercostal veins drain into the azygos system on right, and hemiazygos on left
Nerve
- Intercostal nerves come from T3-T12
- Upper six nerves terminate as anterior cutaneous nerves near the sternum
- Lower five nerves and subcostal nerve terminate in abdomen
Lymphatics
- Sternal glands located at the anterior ends of the intercostal spaces
- ICS lymphatics receive lymph from posterolateral chest, including intercostal muscles and parietal pleura
- Lower 4-5 ICS glands unite to form a trunk which descends to open into the origin of thoracic duct
- Upper ICS glands drain directly into thoracic duct

Bony anatomy

Ribs

- 12 ribs (can be 13 with cervical or lumbar rib)
  - 1-5 are directly attached by costal cartilages
  - 6-10 coalesce into the costal arch
  - 11-12 are floating ribs - no sternal attachment for costal cartilages, ending in muscle of thoracic wall
- Cervical rib
  - Persistence of a separate costal element of C7
  - Occurs in 1%, and 10% of those will have compressive symptoms
- Progressively increase in length to 7th rib then decrease again
- Ribs 3-9 are termed 'typical ribs' - head, neck, body/shaft. Head interacts with vertebral column via inferior facet to adjacent vertebral body, and upper facet to body of vertebra above it. Also interacts with the transverse process of the same numbered vertebrae, with the costotransverse ligament.
  - The costotransverse ligament is thick and strong, and this is the landmark for maximum posterior extent of incision in thoracotomy.
- Cervical rib - cartilaginous or ossified rib borne by C7, which may be shorter or longer and attached to the first costal cartilage or to the manubrium. Can compress subclavian vessels and/or the brachial plexus.

Sternum

- 15-20cm long flat bone
- Three portions:
  - Manubrium - top part
  - Body
  - Xiphoid - ends in the rectus abdominis sheath

Thoracic vertebrae

Cutaneous innervation

Supra-clavicular nerves (terminal branches of spinal nerves C3 and C4) supply the skin above, over and below the clavicles
Remainder of anterior thoracic wall supplied by anterior and lateral cutaneous branches of thoracic spinal nerves
Dorsal rami of C4, C5, C8, T1 and T2 supply skin over the back by medial cutaneous branches
Skin over inferior back is supplied medial and lateral cutaneous branches of T3-T10

Other features

Thoracic inlet (superior)

- Uppermost extent of the thoracic cavity
- Formed by manubrium, 1st ribs, and T1
- Anterior border lies about 2cm below the posterior border

Thoracic outlet (inferior)

- Bordered by xiphoid process, fused costal cartilages of ribs 7-10, anterior portions of 11th ribs, arches of 12th ribs and T12
- Anterior margin at T10; posterior margin at T12; reaches lowest level laterally (L2)